SCIENTIFIC AMERICAN

The Spy Telescope Hunting for Dark Matter

What Really Happened on Easter Island?

How Clean Tech Became Unstoppable

Collision Course

Companies want to put millions of satellites into space. Are we headed for an orbital catastrophe?

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Repeatedly ranked

30+ lists in the last 3 years

ASU's Bermuda Institute of Ocean Sciences deploys unmanned gliders capable of acquiring continuous measurements of the ocean to depths of 1,000 meters.

innovation

ASU ahead of MIT and Stanford

— U.S. News & World Report, 11 years, 2016–26

sustainability

ASU ahead of Stanford and UC Berkeley

— Association for the Advancement of Sustainability in Higher Education, 3 years, 2023–25

global impact

ASU ahead of MIT and Penn State

— Times Higher Education, 6 years, 2020–25

asu.edu/research

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CONTENTS SEPTEMBER 2026 VOLUME 335, NUMBER 2

SCIENTIFIC AMERICAN

66

FEATURES

SPACE POLICY

26 BATTLE FOR THE NIGHT SKY

The dangerous race to fill Earth orbit with satellites. BY JONATHAN O'CALLAGHAN

ARCHAEOLOGY

32 WHO BROKE EASTER ISLAND?

For decades the answer seemed obvious: the Rapanui did it to themselves. New evidence points to a different culprit—one that arrived by ship. BY MICHAEL MARSHALL

ASTROPHYSICS

40 SPYING ON THE UNIVERSE

A former surveillance telescope is NASA's new powerhouse for solving the mysteries of dark energy and dark matter. BY JONATHAN O'CALLAGHAN

ON THE COVER

Around 15,000 satellites currently circle Earth, but nearly two million satellites are planned to launch in coming years. This precipitous rise will bring Internet access to many who lack it but could also have dangerous consequences for astronomy, our planet's atmosphere—and the future use of Earth orbit.

Illustration by Brian Stauffer

NEUROSCIENCE

48 WIRED FOR STORY

New research is revealing how the brain uses narrative to make sense of experience.

BY INGRID WICKELGREN

RENEWABLE ENERGY

56 WHY SOLAR IS TAKING OVER THE WORLD

After a meteoric rise, solar power is now the cheapest form of energy in history.

BY STEPHANIE PAPPAS

ENERGY STORAGE

66 HARD CELL

Solid-state batteries have promised better electric cars for decades. In an industry China dominates, two American companies are making rival bets on how to finally build them.

BY ALEX PASTERNACK

CLEAN TECHNOLOGY

72 BIG BETS IN GREEN TECH

Bold projects designed to solve clean energy's lingering challenges.

BY ANDREA THOMPSON, MEGHAN BARTELS, CODY COTTIER AND DAN VERGANO

Factorial Energy

SEPTEMBER 2026 SCIENTIFICAMERICAN.COM 1

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DEPARTMENTS

4 FROM THE EDITOR

6 LETTERS

8 ADVANCES

Deep-sea fossils of early life that moved and reproduced. Why pigeons live “at the edge of chaos.” What makes earthquakes stop in their tracks. Tiny pathfinding honeybee drones.

22 INDUSTRY

Zipline is testing whether drone delivery can become routine in American suburbs.

BY ADAM ROGERS

78 MIND MATTERS

Simple practice can build kids’ mental endurance.

BY HEATHER SCHOFIELD AND SUPREET KAUR

80 THE SCIENCE OF WAR

Golden Dome would put missile interceptors in orbit. Companies are lining up before the system even exists. BY SARAH SCOLES

82 SCIENCE CROSSWORD

Inspired by the stories in this issue.

BY ELLA DERSHOWITZ

84 MATH

This eerily simple math says our days are numbered. BY JACK MURTAGH

86 THE SCIENCE OF HEALTH

The benefits of fibermaxxing depend on your gut.

BY LORI YOUMSHAJEKIAN

87 METER

The poetry of pollinator seduction.

BY JESSICA NORDELL

88 THE UNIVERSE

Astronomers are missing out on huge parts of the universe. BY PHIL PLAIT

90 Q&A

Why nuclear war may keep humanity from a “theory of everything.” BY LEE BILLINGS

94 GRAPHIC SCIENCE

What to do if you get a tick bite.

BY KATE WONG, DIOGO GUERRA AND JEN CHRISTIANSEN

100 HISTORY

BY JEANNA BRYNER

Zipline

22

©Dick/Getty Images Plus

84

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FROM THE EDITOR

A Voice for Science

AS THIS ISSUE HEADS TO PRINT and our meticulous editors read through the final page proofs to ensure accuracy, we at Scientific American are packing up our office next to Battery Park in New York City's Financial District. Both literally and metaphorically, we are on the move. After being sold by Springer Nature to LabX Media Group in June, the publication will have a new headquarters. More important, the sale has opened a new chapter in the history of this nearly 181-year-old institution.

Shortly after Scientific American was founded, its publishers established what would become a leading U.S. patent agency, helping everyday tinkerers get credit for their creations. Our pages became the hub for chronicling these innovations—tens of thousands of them, from the sewing machine to the airplane. Thomas Edison reportedly visited the magazine's New York office in 1877 to demonstrate his newly conceived phonograph for the editors. I often wonder what such historically weighty occasions might have felt like to the staff. Did the person who edited Albert Einstein's April 1950 article on his general theory of relativity enjoy a philosophical chat with the revolutionary thinker? Did Nikola Tesla's eccentricities emerge during conversations with editors when he wrote, for an 1891 supplement, an article on the alternating-current experiments that led to the Tesla coil?

Over the years more than 150 Nobel Prize winners have written for Scientific American, relaying

their breakthroughs and ideas to our readers. Our journalists have explored groundbreaking discoveries and achievements, from the lifesaving development of penicillin to Charles Darwin's theory of evolution to Bell Labs' invention of the transistor. Not all of our past is laudable, of course. The publication's editors advocated for patents for white Americans only, furthered sexist scientific theories, and provided a platform for eugenicists. But today the magazine is ready to lean into its greatness. As many researchers have pointed out to us, there is no better time in history to be doing science, even when working against the headwinds of funding cuts and the rampant spread of misinformation.

As the new editor in chief, I can't promise that the next chapter will be free of mistakes or tumult. I do promise we will be a voice of reason, we will continue sharing scientists' accounts of their own work, and we will enlighten and delight you with 21st-century equivalents of the discovery of the DNA double helix and the invention of the Tesla coil. And I want to thank our outgoing editor in chief David M. Ewalt, whose leadership shaped this publication in ways that will outlast his tenure.

The bar is high. The average consumer is bombarded from every direction with news and shorts and explainers and how-tos. We know what we're up against—unlike in the 1850s, the media landscape is saturated with science "content." To rise above the noise, our staff will continue to use their expertise to serve up only the most interesting and illuminating ideas. We aim to inspire you to dig deeper, ask hard questions and have fun. If you're not already a subscriber, we hope to convince you to join the Scientific American community. ●

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GENERATIONAL STATUS

Inspired by “The Kids Are All Right,” by Melinda Wenner Moyer, our online Discussions space asked readers, “Research has found that today’s kids and teens are doing better in many ways than previous generations. Does that ring true to your experiences?” The following response from April 8, 2026, was edited for space and clarity.

I’m a seventh grader, and I feel that people my age are better than previous generations. Lots of people at my school say that it’s not the kids bullying them; it’s the parents. There is also a lot of quiet drama—but it’s not quiet to the people it’s happening to.

Friendship breakups are almost as bad as bullying. I lost all of my friends to a stupid fight last year, and I wrote a goodbye letter during the summer because I felt so alone. Parents also put a lot of pressure on their kids. My friend said that she doesn’t eat breakfast or dinner at home, because her mom told her she was “too fat” and “needed to lose weight.” More kids nowadays are being diagnosed with anxiety and depression, too. There’s also a lot of academic pressure at my school. I feel like teachers take the “teacher first, friend second” saying too seriously and focus only on the teacher part.

The economy is also getting worse, and kids are starting to worry about that. There’s a field trip coming up, and everyone is going, but I couldn’t go because of how expensive it is. We also wear uniforms at my school, and they are so expensive. Artificial-intelligence usage has also gone up. Kids are using AI to think for them, and it’s impacting them in ways they don’t really understand. Everyone is more emotionally aware, though. Overall, we are better, just not the best.

“SOMEBODY” VIA DISCUSSIONS

FISH NOODLING

I am confused about the use of “ziti” as a unit of measurement in “Tiny Climbers,” by Elizabeth Anne Brown [Ad-

April 2026

vances; June]. Brown describes shellear fish climbing a waterfall as “ziti-size,” but nowhere in the article is there a conversion of zitis to any standard unit of measure. How many zitis are in a meter, assuming the ziti is a unit of length? STUART R. DOLE HEALDSBURG, CALIF.

BROWN REPLIES: Dole brings up an excellent point: I did mean the length of a cut ziti noodle, which my most authoritative Internet sources pin at about 1.75 to two inches, comparable to our waterfall-climbing fish, which have a length of about 1.5 to 1.9 inches. As a creature reporter, I’m a serial offender at introducing odd units of measurement, including house cats, grains of rice and bananas, to convey the size of unfamiliar animals. While reporting this story, I had just moved to New Jersey and was mainlining The Sopranos. In hindsight, this gave me an inflated sense of how common ziti is as a shared referent.

SHRINKING FAST

In “Relativity Revealed” [March], Victoria Helm, Thomas Juffmann and Peter Schattschneider cite the Lorentz contraction, a prediction of Einstein’s

special theory of relativity that holds that objects will shrink as they go faster. I was struck by a thought: If a fast-moving object shrinks (and also gains mass), there could come a point where it becomes so compressed that, according to an observer at rest, it collapses into a black hole. But in its own reference frame, nothing has changed. How is this apparent contradiction explained?

CHARLES GOODWIN DUNEDIN, NEW ZEALAND

THE AUTHORS REPLY: Indeed, the Lorentz contraction compresses a moving object, although the contraction does not appear in a snapshot of the object. It can even be measured by “reverse engineering” the snapshot, taking into account the travel time of light to the camera.

On the other hand, relativity tells us that changing the observer’s frame of reference amounts to nothing but a transformation of spacetime coordinates so as to describe an object. As an analogy, take the image of Greenland on a map centered at the North Pole and compare it with the image of the island on a Mercator projection. The latter appears much larger. But when you apply the equation for the area on a curved surface, the result is correct in both maps.

That said, the conditions for a collapse of an object into a black hole change when they are expressed in the coordinates of a moving frame. A star will collapse into a black hole only if it is massive and dense enough, independent of the reference frame.

BACTERIAL SURVIVAL

In “Can a Time Capsule Outlast Geology?” [February 2026], Peter Brannen explores what would be needed for a time capsule to survive projected geological changes in the distant future.

“I’m a seventh grader, and I feel that people my age are better than previous generations.”

—“SOMEBODY” VIA DISCUSSIONS

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We already possess ancient time capsules that have survived unchanged for billions of years: segments of the most highly conserved genes in bacteria. For example, the 16S ribosomal RNA gene present in all bacteria contains highly conserved sequences and will probably endure far into the future.

So nature has already shown us a potential pathway to building a time capsule that will outlast geological changes. Should you wish to dispatch a message into the distant future, simply encode it into a sequence of DNA bases and use CRISPR to splice it into the highly conserved genes. Distribute the modified genes into a variety of marine organisms and then dump the mixture into the sea. There your messages will replicate for centuries to come, and several copies will probably survive for as long as life endures on Earth.

Long after all humans have vanished from our planet, some extragalactic visitors might land gently on an empty seashore, throw a bucket into the sea and haul up samples of bacteria. There they might be able to read the entire encoded history of the human species. MICHAEL PHILLIPS FORT LEE, N.J.

ERRATA

In "Lost Roads of the Roman Empire," by Tom Brughmans [June], the map of the province of Baetica in Spain should have indicated that the ancient Roman town of Iluro in this region was where the city of Álora is today. And it should have given the modern location of the Roman city of Iulia Traducta as the city of Algeciras.

"Great Lengths" [Math Puzzle; July/August] should have been credited to Heinrich Hemme.

"Tonima Tasmin Ananna," by Emma Gometz [The Young American Scientists; July/August], should have given Ananna's name as Tonima Tasmin Ananna.

"Jianjun Jin," by Ari Sen [The Young American Scientists; July/August], should have described GetOrganelle as a software tool.

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ADVANCES

PALEONTOLOGY

Deep Fossils

Researchers have found some of the earliest moving and sexually reproducing creatures

TODAY A STRETCH OF CANADA'S remote Northwest Territories is covered in snow-capped peaks. But more than half a billion years ago this wilderness was a seafloor home to the wrinkled "pancakes," fleshy fronds and spiral-shaped critters that were among Earth's earliest complex life-forms.

Researchers recently unearthed a trove of fossils that reset the timeline for when these curious creatures scuttled onto the evolutionary scene. The new fossils, as described in Science Advances, also suggest that the deep sea served as an environmental cradle for complex life.

Found in Canada's Mackenzie Mountains, the fossils date back 567 million years and provide a rare window into the geological period called the Ediacaran, which ended just before the Cambrian explosion of biological diversity. To reach the site, study lead author Scott Evans, a paleontologist at the American Museum of Natural History, and his colleagues embarked on a 14-hour drive and a helicopter flight.

The fossils, many preserved as detailed imprints on slabs of mud-colored rock, were worth the journey. In total, the team collected more than 100 remnants of strange, soft-bodied creatures that are the first known to reach major milestones in the evolution of life as we know it. Compared with finds from earlier in the Ediacaran, these organisms "look a little more like animals that we're familiar with," Evans says. "They move around, and some of them are reproducing sexually."

Among these early movers were the Frisbee-like Dickinsonia, which lacked a mouth and hoovered up algae through its under-

8 SCIENTIFIC AMERICAN SEPTEMBER 2026

Illustration by Alex Boersma

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CITIES CAN BOOST— OR BANISH—DIFFERENT TYPES OF STORMS P. 10

HUMANS' SENSE OF SMELL MOST LIKELY IS CONTINUING TO EVOLVE P. 15

PSYCHEDELIC THERAPY CAN HELP TO TREAT COCAINE DEPENDENCE P. 19

DISPATCHES FROM THE FRONTIERS OF SCIENCE, TECHNOLOGY AND MEDICINE

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ADVANCES

belly, and Kimberella, a teardrop-shaped creature that scraped the seafloor and may be related to modern mollusks. The site also yielded fossils of spongelike, tubular organisms known as Funisia, which were among the first complex creatures to reproduce sexually. Scientists think they sent sperm and eggs into the water column like today's corals do.

The fossils are among the earliest found for creatures of this complexity. This discovery "extends early animals deeper in time," says Mary Droser, a paleontologist at the University of California, Riverside, who was not involved with the paper but discussed the fossils with the study authors. She notes that the animals of the Ediacaran have long been divided into distinct groupings, beginning with simple stationary species that were replaced by more complex creatures emerging around 559 million years ago. Instead the new fossils reveal that these groups lived side by side for millions of years.

The fossils' location also provides crucial environmental context for the rise of ancestral animals. Based on the site's rocks, which did not preserve ripples or other signs of waves, the team posits that this area was once part of the ocean floor.

As a result, the new site provides compelling fossil evidence that the earliest animals first emerged in deep-sea environments, says Lidya Tarhan, a paleontologist at Yale University, who was not involved in the new study. She says the fossils support previous hypotheses that proposed that early life gradually moved from the deep to the shallows, a trajectory that is "unusual in the evolutionary history of animals."

Although the ocean's perpetually cold and dark lower reaches may seem inhospitable, Evans notes that the deep sea has less variation in temperature and available oxygen than shallow environments. "That stability might have been a really great place for animals to first show up and evolve," Evans says. "If you can figure out one temperature, you're good to go." —Jack Tamisiea

Lightning seen over Denver

METEOROLOGY

City Weather

Urban landscapes can boost storms—or break them up

CONCRETE JUNGLES CREATE their own rain, and make it go away, all without relying on a single nursery rhyme. A recent study of 40,000 storms producing heavy rainfall in four Texas cities revealed that urban landscapes affect different storm types in different ways, helping to explain why cities sometimes generate more rainfall than their surroundings and sometimes experience less. The study could lead to more accurate rainfall predictions for urban areas, especially for extreme storms that cause floods and other dangers.

To find these trends, study lead author Xinxin Sui, a hydroclimatologist at the Colorado School of Mines, and her colleagues painstakingly separated and classified individual storms from

23 years' worth of high-resolution radar data by examining attributes of each storm such as shape and intensity. Unlike measurements from collected rainwater or satellite images, multiple radar sources can map rain intensity in 3D to let scientists "see the whole structure of a storm event," Sui says. The results are described in Nature.

The researchers found that short-lived, localized storms are more frequent and produce more rainfall in cities, especially at night and on weekdays. This increase has to do with the dynamics of city heat. Cities are hotter than their surroundings because concrete and other urban surfaces absorb and store more heat from the sun, intensifying storms. On weekdays, parti-

Art Escobedo/Getty Images

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cles of air pollution from workplaces and commuter vehicles may help to form more clouds that produce storms.

Cold-front storms, which form when cold air moves into a region with warmer air, get much weaker when they pass over cities, probably because the densely clustered buildings act like jagged, warm spikes that mix up and heat the cold air. Because the temperature difference between the two air masses fuels the updrafts that cause storms, this mixing tamps down storm activity. In contrast, rain from warm fronts, which occur when warm air moves into a region of colder air, tends to come from long, thin clouds that aren't as affected by city spikiness, although they may be slightly intensified by urban heat.

The most intense and largest volumes of rainfall usually come from tropical systems: storms that spawn over the ocean, including hurricanes. Cities don't influence tropical systems' intensity or frequency, but they may

change their structure in a way that lets more rainfall reach the ground. Researchers don't know why yet.

Studying these variations is important because "different storms stress urban systems in very different ways," says Yiyi He, who researches urban planning for extreme weather at the Georgia Institute of Technology and was not involved in the study. Tropical-system rainfall tends to last longer and to cause widespread flooding, whereas localized storms are more likely to lead to sudden flash floods that can sweep away vehicles.

Climate change is driving more severe weather and increasing flood risks in urban areas, where a majority of people live worldwide, making an understanding of how storm type and city infrastructure intersect even more relevant. Adding storm types to urban climate models "could significantly improve how we anticipate future flood hazards," He says, letting us design more resilient cities. —Damien Pine

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ADVANCES

Pigeons favor chaos when learning something new.

LEARNING

Brainy Birds

What pigeons' pandemonium can teach us

STRUTTING AND FLUTTERING around their urban homes, pigeons have adapted to an ever-shifting environment. Their surroundings aren't the only things that are constantly changing: New research suggests the birds themselves avoid stability in their decision-making, instead choosing to live "at the edge of chaos." As model species for learning and behavior, these birds are helping researchers test a century-old law about how humans and other creatures take in information.

When learning something new, people and animals alike tend to repeat behaviors that are rewarded. This principle, which was first proposed by Edward Thorndike in 1898, is so well established in psychology that it's become known as the law of effect. But the law implies that beyond making a behavior more frequent, rewards also make it more consistent, reducing variability in the specific way behaviors are performed over time.

Although scientists have repeatedly tested whether rewards increase the

frequency of behaviors, their effect on the consistency of these behaviors is less well studied. University of Iowa experimental psychologist Edward A. Wasserman and his colleagues decided to put it to the test in pigeons—a species that has been integral to the study of learning at the university's Comparative Cognition Laboratory for more than 50 years. And the study's results, published in the Journal of Experimental Psychology: Animal Learning and Cognition, suggest these birds experience variability as the spice of life.

To see how rewarded behaviors vary, the researchers gave pigeons a series of five colorful buttons to peck. They could peck any buttons in any order, but as long as they pecked five times, a treat would appear. Based on previous theories of learning, the scientists expected the pigeons might eventually slip into a routine—perhaps choosing to repeat patterns they know work or simply pecking the button nearest to them five times. Instead they continued pecking in a variety of patterns.

"There would be no reason not to expect that the animals would converge on a single favorite, but it never got to that point," Wasserman says. "You could argue the birds are just utterly resistant to locking into anything stable."

The team theorizes that pigeons' devotion to variability might be an evolutionary advantage that aids coping with new challenges in their environment—and they expect the birds aren't the only ones resisting uniformity. The researchers are currently conducting tests to see whether rewarded behaviors remain variable in different animals, which others in the field say might illuminate how the brain makes behavioral decisions while learning.

University of California, Los Angeles, psychology professor Aaron Blaisdell, who was not involved in the new study, is not that surprised by the results. "But this paper leaves open many questions about the [neurological] mechanisms" for future scientists to explore, he adds. —K. R. Callaway

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BIOLOGY

Fungus Map

One of Earth's largest—and least visible—living networks could stretch to Proxima Centauri and back

IF YOU'VE NEVER HEARD OF arbuscular mycorrhizal (AM) fungi before, it wouldn't be surprising—unless you happen to be a ficus. With symbiotic relationships spanning roughly 70 percent of the plant species on Earth, these charismatic topsoil denizens should be on the radar of any self-respecting photosynthesizer. Yet although AM fungi haul roughly four billion metric tons of carbon from plants into the soil every year, there's still a lot we humans don't know about this type of fungus, starting with how much of it there actually is.

That is, until now: for a paper detailed in Science, researchers combined data from more than 300 studies to estimate the total global biomass of AM fungi. The task is harder than you'd think. Biomass depends in part on the thickness of fungal filaments, meaning

that even small errors in estimating their average diameter can dramatically affect the final calculation. To illustrate the challenge, study co-author Justin D. Stewart, a data scientist at the Society for the Protection of Underground Networks (SPUN), offers an analogy: Imagine lying under a tree and trying to determine the average width of all its branches. Some are long and incredibly thin, whereas others are short and thick.

To tackle the problem, the team used a custom-built robot named Prince, which captured more than 300,000 measurements of growing fungal networks. (For those interested, other residents of the laboratory include robots named Donna Summer and Aretha Franklin.) Combined with mathematical modeling and published data from around the world, those measurements

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A microscopic view of mycorrhizal fungi (colorized for legibility). Spores are visible as circular structures.

let the researchers estimate global fungal biomass and, with data visualizer Moritz Stefaner, create an interactive mycorrhizal-infrastructure map covering Earth's landmasses down to single square kilometers.

"We're surrounded by numbers and data," says Stefaner, who was immediately drawn to the aesthetic qualities of the dataset. "Everybody wants to make sense of it. Everybody wants to see the big picture."

So how much of this type of fungus

is there? The answer is simultaneously more and less than you might expect. By biomass, the world's AM fungi weigh roughly five times as much as all humans combined. That's substantial but not nearly as much as many researchers anticipated.

"I was kind of surprised that the numbers weren't higher," says Kara Skye Gibson, a postdoctoral researcher at Northern Arizona University, who was not involved in the study. Stewart says the research team felt much the

same way. "When we first calculated how heavy these fungi were," he says, "I think we spent two or three weeks recalculating it to make sure we weren't missing zeros."

Perhaps mass is the wrong way to think about it. When you switch to length, the numbers become genuinely absurd. Earth's topsoil contains an estimated 110 quadrillion kilometers of AM fungi if they're measured end to end—enough to stretch from Earth to our neighboring star Proxima Centauri and back or to cross the 11.9 light-years to Tau Ceti, the setting of Andy Weir's 2021 sci-fi book (and recent hit film) Project Hail Mary.

Yet despite such staggering numbers, Stewart is just as eager to discuss what the researchers haven't found. "We're treating these maps as living documents, not static images," he says, emphasizing the importance of the nearly 200 researchers working with SPUN to fill in the remaining holes. To help identify those gaps, the team created supplemental "maps of ignorance" that highlight where the estimates are most uncertain.

"I'm very comfortable with uncertainty as long as we quantify what type of uncertainty it is and how large it is," Stewart says. "These maps of ignorance are also treasure maps of where we need to go sample data in the future."

—Sam Macdonald

MATH PUZZLE

Tetris Paradox

By Jack Murtagh

IN TETRIS, players try to efficiently pack a rectangular space with pieces that can have seven different shapes. As it happens, if you have exactly one of each of those seven permitted pieces, then it is impossible to arrange them into a rectangle. But there is one piece you can eliminate that will allow you to make such an arrangement. Which piece must be discarded? Find any rectangular arrangement of the remaining six pieces.

Just as in Tetris, you may rotate pieces but not reflect them. In other words, if the pieces were cutouts on a table, then you could slide them and spin them but never lift them off the table. Tip: you can identify the problematic piece in a principled way; it does not require trial and error.

For the solution, visit www.ScientificAmerican.com/games/math-puzzles

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Graphic by Amanda Montañez

Tomás Munita

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EVOLUTION

Shifting Smells

Scientists are learning more about the genetics of humans' smelling skills

HUMANS, AS AN EVOLUTIONARY GROUP, are often said to be losing their sense of smell. "But our sense of smell is not simply declining," says Lian Deng of the School of Life Sciences at China's Fudan University. "It is still being reshaped by lifestyle, diet and even culture." That's the upshot of a recent study aimed at revealing how the genetics of human olfaction has changed over the past few millennia.

The study grew from the fieldwork of Hoh Boon-Peng, a geneticist at the IMU University in Malaysia, who saw how important smell still is in the daily life of the region's hunter-gatherers. They follow their noses to distinguish among herbs, identify ripe fruit and figure out where animals have traveled—they can even tell what kind of animal has passed by based on the smell of its urine—and their language has a strikingly rich vocabulary for odors, Hoh says. Such observations led Deng to ask whether smell's enduring importance might have left detectable traces in the evolution of smell-receptor genes. In the study, published in Cell Reports, Deng, Hoh and their colleagues analyzed genomes from 50 Indigenous people from the Malay Peninsula and compared them with other populations around the world. The sample included the hunter-gatherers and two other Indigenous groups that focus on farming and agriculture.

The results suggest that the Malay Peninsula hunter-gatherers have preserved

a more complete set of smell-receptor genes than the other groups studied. In most populations around the world, many of these genes have accumulated mutations over time that have left about 60 percent of them nonfunctional. But the hunter-gatherers showed significantly fewer mutations in their olfactory-receptor genes. The intact gene variants they carry are linked to sensing earthy, floral and fruity smells—cues often tied to food and other vital resources.

The genetic differences among the populations did not pertain only to smell. In one of the farming groups, the researchers identified a distinct version of a receptor gene called OR12D3. Previous studies have linked this gene to insulin secretion, suggesting it may reflect adaptation to the higher-carbohydrate diet that came with agriculture.

Even among modern humans, sense of smell varies widely from person to person, and much of that variation is thought to come from differences in odor-receptor genes, says Duke University molecular geneticist Hiroaki Matsunami, who was not involved in the work. To him, the study provides evidence that humans' recent evolutionary history might have helped shape these genes.

Deng says hunter-gatherer populations, long underrepresented in genomic research, have allowed the survival of genetic signatures tied to ancient history and have also led to new adaptations. "Such living populations can be invaluable for understanding the deep history of human genetic diversity," she adds. — Willow Zhang

SEISMOLOGY

Seismic Stop Sign

When do megaquakes come to a halt?

ON APRIL 20 RESIDENTS of northeastern Japan were rattled by a massive magnitude 7.7 earthquake off the coast. They were warned of possible tsunamis,

mis, as well as a slim chance of a magnitude 8 or higher "megaquake" in the coming days. A study published just a few days later in Science investigates

how such megaquakes evolve, what can eventually stop them and how we can predict their destructive power.

An earthquake starts deep underground when huge tectonic forces cause stress to build up along a fault line: a massive fracture in Earth's crust where blocks of rock have shifted and moved past one another. If this accumulated stress overcomes the friction holding

Illustration by Thomas Fuchs

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the rocks together, the fault slips, and a rupture rapidly spreads along it, generating powerful seismic waves that cause the ground to shake. This process continues until the spreading rupture reaches an area of low stress and slowly loses momentum or until it hits a physical barrier underground, such as a change in the ground's makeup or trapped high-pressure fluid, that makes it stop instantly like a speeding train crashing into a concrete wall.

Not all underground barriers will stop a rupture. But if one does, the impact creates a signature traveling in the opposite direction called a stopping phase. "When the rupture is going fast and encounters some barrier that suddenly makes it stop, it sends out a shock wave," says study co-author Jesse Kearse, an Earth scientist at Victoria University of Wellington in New Zealand. A human standing above such a barrier would first feel the ground move in the same direction as the rupture and then sharply jump back in the opposite direction. "It's like you're in a car and the brakes suddenly engage, and you snap back in your car seat," Kearse says.

But observational data showing that signature have been lacking. Kearse and

his colleague Yoshihiro Kaneko, a geophysicist at Kyoto University, hunted for it in the seismic and geodetic data registered by sensors in the paths of 12 large earthquakes across the globe. Five of the earthquakes the researchers studied were equipped with enough sensors along the fault that the team could isolate a stopping phase. They also found that certain near-surface features, such as softer rock layers above the stopping phase, can further enhance the signal, leading to more severe shaking of the ground at the surface.

Every barrier a rupture hits on its way works as a checkpoint. If the barrier holds, it stops the earthquake, which can end up as a minor, localized event. But if the advancing rupture has enough energy to shatter through the checkpoint, it spills over into the next fault segment, potentially cascading into a megaquake monster. "This demonstrates the extremely valuable role of near-field observations in understanding why earthquakes grow big or remain small," says Yihe Huang, a geophysicist at the University of Michigan, who was not involved in the study.

Now that they know how to identify

a stopping phase signature, the researchers can pinpoint these phases in past earthquakes' data to map out underground barriers and assess how much energy they can absorb. They can also identify amplifying near-surface features nearby. "This new insight can potentially transform earthquake hazard analysis," Huang adds, by showing where an earthquake of a particular strength might be stopped and where it might be enhanced.

There's still a lot of research to do before the new findings help to build more accurate earthquake models. Kearse and Kaneko limited their study to strike-slip earthquakes, in which two blocks of rock slide horizontally past each other, because there are simply more data for them. The April event in Japan was a thrust earthquake that made the ground move up and down—a motion that is much more likely to cause a tsunami. "The obvious continuation of this work is to make it more general," Kearse says. "But we expect this stopping mechanism is a common feature of the earthquake process that does apply to thrust events, too. We just cannot confirm that yet." —Jacek Krywko

ANIMAL BEHAVIOR

Shark Scrub

Galapagos sharks scratch off parasites with help from manta rays

WE ALL KNOW HOW MADDENING an unreachable itch can be. Galapagos sharks have found a creative solution to this problem: manta rays apparently make excellent snout scratchers. Between December 2024 and January 2026, at three different dive sites off Mexico's Revillagigedo archipelago, divers spotted Galapagos sharks rubbing their bodies against the top and bottom surfaces of manta rays.

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The mantas—gentle ocean giants that have no means of defense except their size—seemed to tolerate this behavior from juvenile sharks, only shuffling mildly in response. With adult sharks, however, they went into flight mode, rolling backward and trying to escape a potential bite. Still, researchers don't think that the scraping behavior is hostile. The sharks specifically rubbed their snout and gill regions, known hotspots for sea lice, which suggests the mantas were being used as giant scratching posts.

A total of eight such shark-manta encounters have been documented by two separate groups of researchers, who published their observations in Marine Biodiversity and in Environmental Biology of Fishes.

"The sharks know that the surface of the manta is like sandpaper, so it's a good surface to remove those parasites," says Mauricio Hoyos, a co-author of the latter study and director of the marine-conservation nonprofit Pelagios Kakunjá. Previously Galapagos sharks had been spotted scratching their bodies on whale sharks. Shark skin, like that of manta rays, is made up of dermal denticles, which are shaped like sharp, rough teeth. "That's why they're nice places to scratch," explains marine ecologist Jane Vinesky, lead author of the same study and a Ph.D. student at Pelagios Kakunjá.

Typically when sharks have a parasite problem, they pop into a cleaning station—nature's spa, where small "cleaner fish" peck parasites off their clients. But sometimes these cleaning stations get

crowded. This competition might be driving some sharks toward alternative strategies, Hoyos says. Gregory Skomal, a marine biologist who heads the Massachusetts Shark Research Program and was not involved in either study, has seen smaller fish use sharks as exfoliators to scrape off parasites. He finds the newly observed shark-manta interaction "unique and exciting."

Scientists aren't sure how sharks learned this behavior—Hoyos wonders whether they got the idea when smaller fish scratched their own itches on the sharks, whereas Skomal suspects individuals simply tried it one day, found out it worked and kept doing it. "In the world of sharks," Skomal says, "a lot of what they do involves trial and error."

—Clarissa Brincat

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TECH

Robot Buzz

Miniature robot drones learn to navigate like honeybees

INSECT-SIZE DRONES are too small to lug around complex navigation systems. To help tiny autonomous fliers find their way home, researchers are taking their cues from honeybees with a new system called Bee-Nav.

A honeybee leaving the hive first takes a short learning flight to memorize nearby landmarks, explains Guido de Croon, an artificial-intelligence and robotics researcher at the Delft University of Technology in the Netherlands. As a bee flies away, “it keeps track of the direction and speed of its movement,” de Croon says, in a process called path integration. Because path integration is prone to accumulating little measure-

ment errors over time, the insect relies on the memorized landmarks to correct its course as it heads back home. As described in Nature, de Croon and his colleagues copied this workflow.

First, a drone performs a beelike learning flight around its starting point, using a minuscule omnidirectional camera to capture the surrounding scenery. In midflight, it uses a tiny onboard neural network to map these images to home vectors, basically invisible arrows pointing back to the launchpad. This mapping establishes a safe zone called the learned homing area. Once trained, the drone can be sent far away and begin its journey back using

path integration, backtracking based on measured speed and direction. If the drone winds up anywhere inside its starting safe zone, the visual neural network then guides it the rest of the way home.

Bee-Nav does this using an off-the-shelf Raspberry Pi 4 computer the size of a credit card that runs neural nets with 3.4 to 42.3 kilobytes of memory. For comparison, conventional mapping setups use thousands of times more. The team’s test bots homed in from a maximum of 600 meters (1,970 feet) away outdoors despite wind gusts and camera-blinding sun glare.

“What I find especially exciting is how little computation is needed,” says Sarah Bergbreiter, a mechanical engineer at Carnegie Mellon University, who was not involved in the study. “For the small-scale robots that my group and others work on, this is the kind of approach that makes serious outdoor deployments plausible.”

De Croon and his team are still working to resolve a few challenges for the platform, such as navigating between multiple memorized places and dealing with starting points that do not have any landmarks.

“Platforms running Bee-Nav will also need local obstacle avoidance and planning capability if the environment is cluttered or dynamic,” says Sean Humbert, a mechanical engineer at the University of Colorado Boulder, who was not involved in the study.

But even now, de Croon says, Bee-Nav can help to make autonomous outdoor drones smaller and more power-efficient. “We could easily put it on a 50-gram, even 30-gram drone,” de Croon claims. Scaling autonomous drones further down to the size of actual bees, he notes, would require solving other fundamental problems such as the need to miniaturize batteries. “But we hope that when these problems are solved in the long term, we will have the intelligence ready to match that,” de Croon says.

—Jacek Krywko

Darwin Farr/Getty Images

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MEDICINE

Sugar Superuser

Zeroing in on how a popular diabetes drug works

METFORMIN IS ONE of the most prescribed medicines in the U.S., primarily to treat or prevent type 2 diabetes. But how it works has been something of a mystery. Now researchers have discovered that the substance essentially transforms a person's gut cells into a sugar sink, resulting in lowered levels of glucose.

Evidence of this mechanism stretches as far back as 1989, when French metabolic researcher Jean Girard and his colleagues published a paper describing how metformin increased the amount of glucose rats absorbed in their intestines. But when research picked up after the drug was finally approved by the U.S. Food and Drug Administration, in 1995, scientists mostly

moved toward the theory that metformin reduced the liver's production of glucose. "It was as if the preexisting science had never existed," says University of Cambridge metabolism researcher Stephen O'Rahilly, who was not involved in the new study.

Later, radiologists discovered that metformin can cause patients' guts to "light up like a beacon" during a positron-emission tomography scan, O'Rahilly says. (This version of the test used a tracer molecule that goes to tissues consuming sugar.) Gradually metabolic scientists began to think this gut absorption of sugar could be important, and they revisited the old research. Not long after, University of Cambridge mitochondrial biologist Judy Hirst

found that at very high levels, the drug blocks mitochondria from using oxygen.

For their new study, Northwestern University mitochondrial biologist Navdeep Chandel and his team wanted to figure out how these two ideas fit together: that metformin both causes the gut to absorb more glucose and blocks mitochondria's oxygen use. Cell respiration, in which cells convert sugars into usable energy, happens inside mitochondria. So Chandel's group complemented mitochondrial complex I, an enzyme necessary for cell respiration, with a yeast enzyme that isn't affected by metformin and that they knew could perform some of the same functions in mice's guts. In those mice, respiration continued as expected, but metformin didn't reduce blood sugar levels. They concluded that when accumulated at high enough levels, metformin, by blocking oxygen use, prompts gut cells to switch to a different metabolic pathway that uses much more sugar to produce energy.

This result is counterintuitive, especially considering metformin's potential connection to antiaging effects. "All these people always say that for longevity, I want to boost my mitochondria," Chandel says. "If anything, [metformin is] inhibiting mitochondria reversibly, transitively."

"The broader lesson," he adds, "is that inhibiting mitochondria may be beneficial when it is done in the right cells, for the right amount of time, without exposing the whole body to the broad toxicity of a mitochondrial inhibitor." The new work was reported in Nature Metabolism. — Viviane Callier

HEALTH

Cocaine Trip

Psychedelics—and psychotherapy—may help treat cocaine dependence

SCIENTISTS ARE RACING to find therapies for cocaine use disorder, a clinically significant addiction to the drug that leads to roughly 22,000 deaths in the U.S. every year and has no treatments approved by the U.S. Food and Drug Administration.

Now, in a study published in JAMA Network Open, researchers have found that a single dose of psilocybin combined with about 10 psychotherapy sessions can reduce cocaine use and lower relapse risk. The compound found in "magic mushrooms" had never before been used in a clinical trial to treat the disorder.

"This is definitely a milestone"

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in the field of psychedelic research, says University of Wisconsin clinical psychologist Christopher Nicholas, who was not involved in the study. The new work adds to a growing body of evidence suggesting psilocybin-assisted therapy may help treat addictions such as alcohol and nicotine dependence.

In a pilot clinical trial in Alabama, 40 adults with cocaine use disorder received either a single dose of psilocybin or a placebo that mimicked some of its side effects. They all received several psychotherapy sessions before and after the drug was administered. Only three participants had previously used a hallucinogenic drug.

Interviews and urine tests conducted during the six months after the treatment showed that 30 percent of drug-receiving participants remained abstinent, whereas none in the placebo group did. The main side effects re-

reported were temporary emotional distress and blood pressure increases during the drug session, as well as headaches afterward.

Most study participants were Black and had lower socioeconomic status; these groups are underrepresented in psychedelic clinical research but are among the U.S. communities most vulnerable to cocaine addiction. “They should always be the priority of what we’re doing,” says University of Alabama at Birmingham clinical psychologist Peter Hendricks, the study’s lead author.

Although the findings are encouraging, Yale University clinical psychologist Brian Kiluk, who wasn’t involved in the study, says the sample size is too small to draw any firm conclusions about psilocybin’s effectiveness. Another limitation, Kiluk says, is that researchers did not fully disentangle the role psychotherapy might have played

in changing participants’ behavior. Yet “that is not uncommon in these types of studies,” he says. (Similar concerns were part of why an FDA panel said it rejected MDMA-led therapy for post-traumatic stress disorder.) And researchers have not yet pinpointed a mechanism for the effect.

Psilocybin is currently heavily regulated, although a recent executive order may help fast-track research into the substance. If psilocybin therapy is approved for another condition whose study is further along, Hendricks notes, doctors may be able to prescribe it off-label for cocaine use disorder as researchers continue to pursue FDA approval.

Despite the study’s limitations, Kiluk believes the approach is worth exploring after a decades-long search for treatments: “We’ve got to start somewhere.” —Humberto Basilio

Yarphats/Getty Images

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INDUSTRY

Drone Delivery Comes Home

Zipline is testing whether a tethered delivery pod can make drone delivery quiet and precise enough for U.S. suburbs BY ADAM ROGERS

WITH BARELY A WHIR of propeller noise, we've got incoming: At the top of a grassy hill, next to a simulated suburban backyard—lawn chairs, a wood play structure, the works—a smooth-cornered white box about the size of a gym bag drops out of the sky. It looks like a pre-CGI special effect because I can see the line—specifically, the one connecting the pod to a drone hovering about 260 feet up, only just visible against the overcast sky. A dinner plate—size rotor at the box's rear spins as the box course—corrects in midair and then sets down on four small gray fins.

The delivery is here. It's a demo, but the same basic system is operating thousands of times a day in Arkansas and across neighborhoods in Texas, where Zipline is flying these drone-and-pod combos to carry a Chipotle burrito bowl or the cat's special food to people's homes.

Keenan Wyrobek, Zipline's chief technology officer, ushers me over to the drone-pod and clicks open its clamshell lid to show off the insulated, carbon-fiber-paneled interior. If we were, say, a local deli, this is how we'd load sandwiches for the drone to deliver. During a drop-off, doors on the bottom would slide open, and whatever the pod was carrying would fall about an inch to the ground. It's meant to be easy, simple and safe. Wyrobek clicks the door shut. Most users get it right.

Had we blown it, the electric motor would've grunted, and a red light would've flashed. But all is well. We back away, and the pod rises up into the belly of the drone, which flies off. I'm expecting the angry-mosquito noise of a typical quadcopter, but it never comes.

At this testing facility, on a cattle ranch an hour south of San Francisco, Zipline is staging a distinctly old-school kind of future: actual flying robots. "That requires solving a lot of near-edge-of-physics technical problems," says Keller Ri-

naudo Clifton, Zipline's CEO. "You need the vehicle to be very aerodynamically efficient to have a meaningful range. You need an energy-dense battery. You need special electric motors designed from scratch to be incredibly light."

That tomorrow may now be in sight. For more than a decade drone delivery has been the tech industry's easiest joke: the demo that never quite became a service. Zipline argues otherwise. Its global network, built largely on its earlier fixed-wing aircraft, has flown more than 130 million autonomous miles and made more than 2.5 million commercial deliveries. And a proposed Federal Aviation Administration rule known as Part 108 could give drone delivery companies a clearer path for flights beyond operators' sight lines. What's being tested in the suburbs is whether the aircraft can be quiet enough to live under, precise enough to find a backyard and safe enough to share neighborhood airspace at scale—and whether anyone wants it.

A decade ago Zipline's drones did a different kind of delivery—moving medical laboratory samples and blood products in Ghana and Rwanda between metropolitan areas and remote clinics. The service used fixed-wing drones, bite-size planes, launched by magnetic slingshot. They dropped their cargo by parachute and were then caught midair by tailhooks and towlines like those on an aircraft carrier.

That service continues to help a lot of people. In Ghana, facilities using Zipline had vaccine "stock-outs"—times when no vaccines were in stock—that were 60 percent shorter than those in clinics that didn't work with Zipline. A 2022 review by researchers in Rwanda found blood products delivered by Zipline to mountainous areas arrived more than an hour and a half earlier than those carried by truck, leading to a 67 percent reduction in expiration losses.

Those slingshot-and-catch drones and parachute drops were made for long-range missions and

Adam Rogers is a journalist covering science, technology and culture. A former editor at WIRED and senior correspondent at Business Insider, he lives in the San Francisco Bay Area.

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After a decade of delivering blood and vaccines in Rwanda and Ghana, Zipline is now dropping consumer packages into American backyards.

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low-precision delivery to drop zones about the size of two parking spaces. That wouldn't work for delivering food and sundries to North American suburbs, where a delivery has to hit a target about the size of a lounge chair. Though Zipline's aircraft wouldn't need to go as far, they'd need to be far more precise. The company needed a new drone.

A drone's range depends on its batteries, but really, range, weight and carry capacity are all the same problem. Hitting a smaller target means the drone has to hover, but that requires more propellers and more power—especially if the drone is fighting wind or other weather to stay in the same spot. Zipline needed to optimize for cargo. As Wyrobek puts it, "every gram you take out is another gram you can deliver."

The team didn't want a drone to land or even come close to the ground, because it's noisy and less safe. (Zipline's executives showed me TikTok videos of rival delivery drones descending below tree-top level, kicking up dirt or dropping boxes into ponds.) The drones could lower deliveries on a tether, as those from Google offshoot Wing do, but the Zipline team worried that a gust of wind could blow the cargo off target.

Zipline landed on an unorthodox solution: put propellers on the delivery box, too. The drone above provides lift, reeling in or unspooling the line, and the pod below maneuvers with thrusters, using two infrared cameras for depth perception and a wide-angle color camera to find its target. "It can tell the difference between nice, flat concrete and nice, flat swimming pool," says Zipline's Zoltan Laszlo, the company's lead for new products and principal engineer.

On lots of drones, small, fast-spinning blades produce spiky, high-pitched

noise. Zipline's larger, slower-moving custom-designed blades push the sound to a lower frequency. "We're about six times quieter than the next-closest competitor," Clifton says. "And then we made the decision to keep it way high up." That, he hopes, makes it less obnoxious to neighbors.

So Zipline ended up with a drone like a Transformer or, if you're old enough to have seen the 1960s series Thunderbirds, a miniature Thunderbird 2. In forward-flying mode, down-facing propellers on arms extending from the drone's wings draw together like scissor blades, and the propeller on the drone's rear pushes it forward. In hover mode, the down-facing propellers unfold into X shapes, and the one on the back—mounted on a custom electric motor, ultralight and about the size of a soda can—folds down and pivots like a showerhead for finer control. But all the customer encounters is a small flying box.

SLICK AEROSPACE ENGINEERING isn't enough to make a drone delivery company, though. Drones generally carry single deliveries of less than 10 pounds, enough for most personal orders, but trucks can carry thousands of pounds on a single run. It's easier to solve one Traveling Salestruck Problem than 100,000 Traveling Salesdrone Problems. In the U.S. alone, Amazon delivers 1.6 million packages a day. That'd be a lot of robots.

Drones can be a more energy-efficient way to replace some short delivery trips while still indulging Americans' desire for instant gratification, but more drones make logistics a real concern. Delivery companies need retailers to load orders correctly, places to charge the drones, and systems to keep all of the aircraft

from hitting things or one another.

This is no longer just a demo. After some turbulence, Amazon's Prime Air drone service has made about 16,000 deliveries in six states since 2022, with plans to expand further. Wing, the Google offshoot, has made almost half a million deliveries since it launched experimentally in 2012, and it plans to go national with Walmart by 2027. A few other companies are taking a shot, too. Since 2025 Zipline has been doing home deliveries in Pea Ridge, Ark., and in neighborhoods around Dallas; this year it announced expansions to parts of Houston and Phoenix. Like Wing, it's working with Walmart, as well as with chain restaurants such as Wendy's and, yes, Chipotle.

That means Zipline already makes thousands of deliveries a day—and is having trouble keeping up with its popularity. On one particularly heavy day, 20 percent of the homes in one of Zipline's coverage areas called for delivery air support. Demand has strained the fleet. "We thought you'd want 30 to 40 drones serving a 10-mile radius," Wyrobek says. "It's very clear you need a lot more drones."

Those drones need to recharge. That's handled at docking stations, cyberpunk forests of metal posts sprouting manta ray-shaped awnings that the company can install in pretty much any liminal space as long as there's power—the back of a parking lot can host 36 individual docks, and a single location can serve hundreds of pickup spots. I watched drones work with these stations at the test site: they are downward toward the metal poles, maneuver so that they're directly under one of the awnings and then rise upward so their dorsal fins plug in. "The drones don't have to return to their original charging location," Wyrobek says. "We can pick up and deliver and then charge somewhere else."

Meanwhile at the point of sale, Zipline installs pylonlike structures that capture descending pods to pick up shipments. They have a drawer at the bot-

For more than a decade drone delivery has been the tech industry's easiest joke: the demo that never quite became a service.

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tom, like an old night-deposit slot at a bank, that also checks for size and weight limits, and they have a keypad for punching in a code that sends a pickup alert for the order. A drone flies in—angled arms at the top of the pylon hug the wire in close—and the pod drops the tube to grab the stuff. “Guess what we call it?” Wyrobek says. “A fly-thru!”

IF ALL THESE DRONE COMPANIES see hypergrowth or if UPS and FedEx take to the skies, “that’s going to become a problem,” says Giuseppe Loianno, director of the Agile Robotics and Perception Lab at the University of California, Berkeley. “Multiple providers doing delivery will have to share the same airspace. So there have to be ways of allocating flight corridors.” Those corridors, he adds, might not be the most optimized flight paths, which has implications for battery life.

Chase Murray, director of the Structure for Outdoor Autonomy Research drone facility at the University at Buffalo, sees the same mismatch more broadly. “There have been some creative and attractive ideas,” he says, “but the marriage of that idea plus technology plus regulation—it’s been a challenge to get those things lined up.”

The regulatory picture is still taking shape. For now Zipline and similar com-

panies have had to pursue limited approvals and waivers for commercial drone flights beyond their pilots’ line of sight. The FAA’s proposed Part 108 rule would create a broader framework to make those kinds of operations routine. Today Zipline manages all of its U.S. flights from two remote operations centers. But scaling to thousands of drones over American cities and suburbs run by multiple companies would require something closer to an airspace operating system. Regulators, NASA researchers and industry are all still trying to design one.

Zipline is building for that future. In late 2025 the company tripled the size of its manufacturing facility near San Francisco International Airport. Now it’s a vast, brightly lit, high-ceilinged facility festooned with racked, cruciform carbon-fiber frames and polypropylene fuselage parts capable of producing 15,000 drones a year.

In a far corner of that manufacturing facility, I find a space crammed with nearly assembled drones. EV2, the model in use in Texas and Arkansas, is already getting supplanted by the newer EV3. Among other differences, in the older drones, screws connect the top of the fuselage to the bottom. EV3s use plastic locking tabs. Lauren Lacey, Zipline’s head of integration, manufacturing and quality engineering, happens to walk by.

She’s in charge of putting those thousands of drones together. Lacey agrees the new clasps are nifty—the polypropylene around the screws tended to break, she says, and her crew can unlock the new tabs with a tiny, keylike tool.

But Lacey’s favorite part, she says, is the dorsal fin.

Not only does that fin lock into the charging dock, but it also hides the cantilevered reel of line that carries the pod. Lacey says it really impressed her 101-year-old grandfather, who’d been a lead engineer on the Harrier, the first jet fighter capable of operational vertical takeoff and landing (VTOL). Grandpa knew all too well that the hardest part of VTOL is the L—that’s when aircraft crash. A Zipline drone “lands” by rising up, so wind pushes it not into the ground but into its dock. If landing is dangerous, the solution is: never do it. When Lacey told her grandfather they could dock in headwind conditions, he was suitably impressed—as Lacey tells it, he said, “Well, by golly gee!”

Lacey feels much the same. She gives the fin a little pat. “It’s just so genius,” she says. “It’s wonderful. It’s beautiful.” After a bit more assembly, this drone will be flat-packed and shipped out to join thousands like it, flitting between docks and backyards, trying to make the strange business of sky delivery feel normal. ●

Zipline

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SPACE POLICY

Battle for the Night Sky

The dangerous race to fill Earth orbit with satellites

BY JONATHAN O'CALLAGHAN ILLUSTRATION BY BRIAN STAUFFER

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EVEN YEARS AGO, WHEN SAMANTHA LAWLER MOVED to rural Saskatchewan to run a farm with her partner, the glorious darkness overhead was one of the biggest perks. Undiminished by light pollution, countless stars filled the night sky. It was a pristine celestial view that city dwellers can only dream of seeing. That matters a lot to Lawler, who studies the universe as an astronomer at the nearby University of Regina when she’s not tending goats and chickens.

Yet ever since Lawler’s rural relocation, a new type of artificial star has increasingly encroached on the heavens above her homestead: satellites, constellations of them, most beaming the Internet around the globe. “Now there are many satellites all the time,” Lawler says. “I really could notice the change that was happening.”

In 2019, the same year Lawler moved to Saskatchewan, Texas-based SpaceX began launching its Starlink megaconstellation in earnest, lofting an initial 60 satellites into orbit that May. The constellation has since exploded in size. This past March, SpaceX reached a milestone of 10,000 active Starlink satellites. More than 10 million customers worldwide now use its Internet service. Other companies and countries are racing to catch up. There are plans to put nearly two million satellites in orbit. If even a fraction of those launch, it will make the current crop of about 15,000 satellites look paltry by comparison.

The rapid proliferation of satellites brings many benefits on the ground, offering faster, more reliable Internet access in remote locations than ever before. Oceanic ships and passenger planes can benefit from broadband communications wherever they are. Emergency services can better respond to natural disasters

even when local Internet infrastructure fails. Soldiers on the battlefield can remotely pilot drones and coordinate with commanders half a world away. But the surge has also raised questions about just how many satellites we can safely launch, whether there might be some kind of carrying capacity for Earth orbit and where the limitations lie.

Until now we’ve managed to operate several thousands of satellites relatively smoothly, but what does the future hold? “So far it seems manageable” through active coordination, says Giovanni Lavezzi, a research scientist who specializes in orbital capacity at the Massachusetts Institute of Technology. “The problem is how much can we push.”

EXPERTS ARE WARY of putting a single number on how many satellites we can fit in low-Earth orbit, the region up to 2,000 kilometers above our planet that is prized for most satellite constellations. One 2022 study attempted an answer, suggesting that as many as 12.6 million spacecraft could occupy orbits between 200 and 900 kilometers in

altitude. But that simplified scenario assumes an almost perfectly ordered system, something far from reality; a more nuanced appraisal published in 2024 found that the limit would be between about 10 million to 100 million satellites—an unhelp-

fully broad range for any policymakers seeking guidance for regulatory action.

Either way, with so many satellites, even a tiny number of mishaps would lead to chaos. Hundreds of thousands of collisions would happen every year, each unleashing its own swarm of hazardous, high-speed orbital shrapnel. Satellites could keep operating only because some of that debris would naturally, gradually drift down into Earth’s atmosphere, but some regions of orbit would essentially become unusable. The point of the 2022 study was not to rule out the sheer physical space of low-Earth orbit as the real constraint. “There probably is a capacity,” says Miles Lifson, an orbital-capacity expert at Aerospace Corporation, headquartered in Virginia, and a co-author on both studies. “But the number of satellites is a really ill-posed way to think about it.”

We could, in principle, encircle Earth with concentric shells of satellites, each shell being an optimally spaced, carefully interwoven, machine-packed grid ever present in the sky. In practice, though, orbital capacity depends on a web of interacting factors such as hardware failure rates, collision-avoidance maneuvers and fluctuating amounts of atmospheric drag (which removes objects more quickly at lower altitudes than higher ones). Hugh Lewis, a space debris expert at the University of Birmingham

Jonathan O’Callaghan is an award-winning freelance journalist covering astronomy, astrophysics, commercial spaceflight and space exploration. Follow him on X @Astro_Jonny

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in England, notes that at around 2,000 kilometers, debris can persist for 100,000 years—a timescale comparable to the 300,000 or so years humans have been on the planet.

Carrying capacity is more like the physiological concept of homeostasis, Lewis says. “It’s like how human bodies regulate different systems,” he says. “Your blood sugar levels, your temperature, and so on—they’re all regulated. But each one of those systems affects the others.” In orbit we find something similar. “There are different kinds of systems at play,” Lewis says. Put it all together, “and that’s orbital carrying capacity.”

Atmospheric effects in particular can play a big role. Last March, Matthew Brown, a space weather expert at the University of Birmingham, and his colleagues found that adding more greenhouse gases to the atmosphere could shrink the carrying capacity of Earth orbit by up to half. “Carbon dioxide is released in the lower atmosphere, but in the upper atmosphere it’s a lot less dense,” he says, which causes cooling there rather than heating. “So we get cooling in the upper atmosphere, the density drops, and atmospheric drag on satellites reduces,” meaning material stays in space longer.

Yet even without those effects, Lewis argues, “we have already exceeded the critical number of objects that can be safely put into low-Earth orbit.” This alarming assertion is based on the idea of the Kessler syndrome, in which the number of satellites in orbit surpasses a critical threshold, creating a high endless cascade of collision-generated debris. “The environment runs away from you,” Lewis says. According to his calculations, at all altitudes above 550 kilometers, the number of satellites is already high enough that even if all launches stopped today, the amount of debris in space would continue to grow for the foreseeable future. “The spacecraft will collide at a rate that produces fragments greater than the rate at which those fragments get removed” by atmospheric drag, Lewis says.

But launches are not stopping. Quite the opposite. Last year more satellites launched than ever before. That record is on track to fall by the end of this year. As for the previous records? They were first set in 2022, then 2023, then 2024. Space is becoming busier and busier with no sign of slowdown. In 2026 alone the Chinese government has filed for 200,000 new satellites. In the U.S., Starcloud of Washington State has applied through the Federal Communications Commission for 88,000 satellites and Blue Origin, also in Washington, for 51,000. SpaceX CEO Elon Musk announced a breathtaking plan for one million orbital-data-center satellites this past January.

was “the only known Starlink fragment” to have made it to Earth’s surface, according to the SpaceX document. The company did not respond to a request for comment.

After reading the report, Lawler jumped on a local radio show to try to learn who had found the debris. “I got in touch with the farmer. He sent me some pictures of it, but he had already sent it back to SpaceX,” she says. Nevertheless, he had confirmed that a piece of a Starlink satellite had fallen back to Earth and just three hours down the road from her home. “It’s just such a wild story that this really happened,” Lawler says.

“We are ripe for a major event to occur. And all of that debris will rain down through all the other operational satellites.”

It’s not clear whether these plans are genuine or merely an effort to gain first-mover advantage in orbit—basically an attempt to reserve space for hypothetical satellites. Ruth Pritchard-Kelly, an expert in satellite regulation based in Washington, D.C., says SpaceX’s million-satellite application might have been just “shock and awe,” perhaps intended to bolster the nearly $2-trillion valuation the company received after its record-breaking IPO in June. “A million satellites?” she says. “Give me a break.” But launching even a fraction of this number would still add tens of thousands of satellites to orbit in the coming years. And the sky is already crowded.

FIVE YEARS AFTER MOVING to Saskatchewan, Lawler came across an unusual report. In a SpaceX document published online in February 2025, the company revealed that a 2.5-kilogram piece of a Starlink satellite had survived atmospheric reentry and crashed, completely by chance, on a farm in Saskatchewan—not Lawler’s—the prior summer. The piece of debris

The story highlights an indisputable fact: as the number of satellites in orbit skyrockets, so, too, does the potential for adverse events. The risk of debris falling back to Earth and harming someone or something is slim but not zero. Even if debris completely burns up during reentry, the effect of so much metal and other aerospace materials being dumped into our planet’s fragile upper atmosphere is unclear. Upcoming studies will seek answers. One of the most notable is the European Space Agency’s Draco mission, targeted for 2027, which will fly a sensor-laden spacecraft designed to break apart during reentry so researchers can learn more about this dynamic, poorly understood process.

Orbital “traffic control” to avoid collisions between satellites is another key concern. Only one such crash has ever occurred: a U.S. Iridium satellite hit a defunct Russian satellite in 2009. The disastrous event produced more than 2,000 pieces of trackable debris larger than an AirPods case, about half of which is still in orbit today. Another collision at some point is a certainty,

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A SpaceX Falcon 9 rocket carrying two dozen Starlink satellites flies into space after launching from Vandenberg Space Force Base in California on July 18, 2025. More than 10,000 active Starlink spacecraft now circle Earth, and SpaceX has announced plans to launch a million orbital data centers.

says Stijn Lemmens, a space debris analyst at the European Space Agency. “We have left mass in orbit that is completely dead and will be there for decades to centuries,” he says. “It’s a mathematical game. [Objects] will keep crossing each other [in orbit], and eventually they will hit each other.”

Some altitudes are more worrisome than others. Darren McKnight, a space debris expert at LeoLabs in California, says that two in particular—those at 840 kilometers and 975 kilometers—have high collision risks because they contain lots of discarded rocket stages the size of school buses. He has calculated that at the latter altitude, there’s a 29 percent chance of a collision happening this year. “We are ripe for a major event to occur,” McKnight concludes. “And all of that debris will rain down through all the other operational satellites.”

A major collision, especially at higher altitudes, could result in enough long-lasting debris to place parts of Earth orbit effectively off-limits. “It’s not that space will be unusable,” says

Brian Weeden, director of civil and commercial policy at Aerospace Corporation. “It’s just a question of what costs [people] are willing to bear because either you have to invest in avoidance technologies or you have to have more satellites. There might be some orbits that become too costly for pretty much anyone to operate in.”

COLLISION AVOIDANCE is becoming increasingly important as satellite numbers grow. SpaceX’s Starlink constellation currently performs an average of 1,000 maneuvers a day to dodge potential collisions, a number that would have seemed absurd just a decade ago.

To prevent an in-space smash-up, a satellite must fire its thrusters to move out of the way of a projected “conjunction” with another satellite that would pose a significant collision risk. Before Starlink, a typical satellite would do this three or four times a year, says Zeno Pavanello, a collision-avoidance expert at the Polytechnic University of Milan. These maneuvers, planned days in ad-

advance, would be overseen by a human operator, who might have to negotiate by e-mail or phone with another satellite operator to decide which object would move.

That leisurely, labor-intensive scenario is often not possible. Now autonomous onboard collision-avoidance systems that can predict and dodge collisions without human input are becoming the norm. “This process that is completely manual and requires a lot of work hours is going to become unsustainable,” Pavanello says. “We’re going to end up in a situation in which satellites experience more than a conjunction a day.”

SpaceX operates the largest autonomous collision-avoidance system currently in orbit. Last year the company revealed the number of collisions it was already avoiding, reporting to the FCC that its Starlink satellites cumulatively dodged about 300,000 collisions over the course of the year, an average of 40 maneuvers per satellite. SpaceX is reluctant to divulge details on how this works,

Kevin Carter/Getty Images

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but last year a NASA experiment called Starling clarified parts of the process. The experimenters flew four satellites in close formation through Starlink's orbital domain to gain some insight into how two satellite constellations might avoid each other.

According to information SpaceX provided to NASA, every 10 minutes each Starlink satellite recalculates its position and predicts its trajectory for the next 48 hours. The satellite then compares this path with those of objects in a database maintained by the U.S. military. If it sees the potential for a collision, the Starlink satellite will fire its thrusters until the risk of collision is less than one in 30 million. (This number is much more conservative than the industry standard of one in 10,000.)

So far this process has worked smoothly, but it is only going to get more complicated. By Lewis's calculations, if SpaceX were to follow through on its plan to launch a million data-center satellites, the constellation would have to perform a billion collision-avoidance maneuvers every year. "It's ridiculous," Lewis says. "You can't grasp that. There aren't that many seconds in a year!"

And Lewis's appraisal accounts only for Starlink. If you add other constellations of comparable size to the mix, such as some being planned in the U.S. and China, the picture gets much more complicated. So far there is no sizable competitor to Starlink; the next biggest, the European OneWeb constellation, has only 650 or so satellites, and they live at a higher altitude. But as other constellations come online, regulatory policy, and not physics, might become the biggest factor determining orbital carrying capacity.

THE PRIMARY LAWS governing space today were set by the Outer Space Treaty of 1967. Although the treaty did not predict the rise of megaconstellations, it did lay out some key parameters for spacecraft. Notably, the treaty's Article II dictates that space cannot be appropriated "by means of use or occupation."

That dictum poses problems for constellations like Starlink, which dominates the altitude at which it operates, about 350 to 550 kilometers above Earth. As other constellations seek to come online, who will decide which ones get to use certain preferred altitudes—and how? "There's tons of potential capacity, but there's only so much beachfront property," says William Parker, a space scientist at Aerospace Corporation. And what if debris-generating collisions between active satellites create orbital "no-go zones"—would operators be liable? "This is the Pandora's box of space law right now," says Michelle Hanlon, executive director of the Center for Air and Space Law at the University of Mississippi School of Law. "There's a first-mover advantage built into the Outer Space Treaty, not intentionally but because of its vagueness."

There is also the issue of the impact on the night sky, which continues to affect Lawler and other astronomers. Streaks from satellites are already tarnishing observations by telescopes both on Earth and in space. A study published last December found that adding half a million satellites to orbit would mean that almost every single telescope image taken anywhere would contain a satellite. Increase that to a million, and there would at times be more visible satellites in the sky than stars. "We wouldn't be able to do astronomy," Lawler says. "There's just no way."

No international body officially governs orbital traffic. The closest thing is the International Telecommunications Union (ITU) in Switzerland, part of the United Nations, which allocates radio spectra for satellite transmissions and helps to coordinate assigned orbits. But the ITU tends to review satellite application without considering the carrying capacity of Earth orbit, whether it's China asking for 200,000 satellites or SpaceX asking for a million. The system is "definitely broken," Pritchard-Kelly says, a procedure from a bygone era when building just a single satellite might take years.

Alexandre Vallet, head of the ITU's space services department, says the or-

organization has "struggled a bit" with the rapid increase in satellites. Attempts are now being made to bring the ITU up to speed, however. At the October 2027 ITU World Radiocommunication Conference, to be held in Shanghai, delegates will discuss options such as reserving parts of low-Earth orbit for each member of the U.N. so that everyone has a chance to launch their own constellation, preventing any single country or company from effectively monopolizing all of orbit.

Time, however, is very much of the essence. The number of satellites, many experts say, is already bordering on unsustainable. Last December, Lawler and her colleagues published a new metric called the CRASH Clock, which estimates what would happen in orbit if every single satellite suddenly became inoperable. That might sound like a far-fetched thought experiment, but it's not a complete impossibility. There have been plenty of powerful, spacecraft-frying solar flares in our planet's history.

The results of the study were alarming. Within five days after the satellites went dark, there would be a crash in orbit. Lawler and her co-authors have since revised that estimate to less than three days because so many satellites have gone up since their study was published. "The clock is getting shorter and shorter as we launch more satellites," Lawler says. "That means we have less wiggle room if there's a mistake." She adds that it "highlights how completely reliant we are on SpaceX, mostly, continuing to perfectly execute all of its collision-avoidance maneuvers."

What SpaceX has demonstrated so far is no doubt impressive. "If everyone behaved like Starlink, you'd get a lot more satellites up there," McKnight says. But there is no guarantee future constellations will be so refined or that SpaceX will maintain its current standards as it seeks ever increasing growth. Ultimately we might find that the capacity of Earth orbit, rather than being in the millions of spacecraft, may not be much more than the number of satellites already in orbit today. ●

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ARCHAEOLOGY

Who Broke

For decades the answer seemed obvious: the Rapanui did it to themselves. New evidence points to a different culprit—one that arrived by ship BY MICHAEL MARSHALL

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Easter Island?

A toppled moai overlooks the crater lake of Rano Raraku. For generations such scenes seemed to confirm a story of self-inflicted ruin.

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HEN SURGEON J. LINTON PALMER LANDED on Easter Island in 1868 onboard HMS Topaze, he found the marks of disaster. The island, known to its Indigenous people as Rapa Nui, was barely inhabited; little more than 100 people remained. Yet it was clear that there had once been a larger, organized society. Rapa Nui was dotted with stone statues of elongated human faces: “gigantic stone images,” as Palmer called them. Someone had carved, moved and raised them, but by the time Palmer arrived, that world had dwindled to almost nothing. Many of the statues “had been thrown down in all directions and were all more or less mutilated.” Something had gone terribly wrong.

For decades the story that many learned about Rapa Nui was one of environmental ruin. The people cut down their trees, degraded their land and squandered scarce labor on the construction of hundreds of statues, called moai by the Rapanui. Hunger followed. So did violence. Some versions of this story even invoked cannibalism. The moai became monuments to human folly: a warning from one small island to a crowded planet.

But recent research makes that version increasingly hard to defend. Archaeology, ancient DNA and aerial survey data now challenge the claim that the Rapanui suffered a self-inflicted collapse before Europeans arrived. The emerging picture is of a small society that sustained itself for centuries by adapting its farming methods and water management to one of the most isolated places on Earth. The catastrophe that reduced the Rapanui to a remnant came later, after European ships brought disease, slave raiding, forced labor, annexation and confinement. The old story now looks like an accusation that hardened into a conclusion.

RAPA NUI LIES in the southeastern Pacific Ocean, 3,700 kilometers west of Chile and 1,900 km east of Pitcairn Island, the nearest inhabited land. It is roughly triangular and measures just 23 km at its longest point. “You can walk across [it] in an afternoon,” says archaeologist Carl Lipo of Binghamton University.

Humans first reached Rapa Nui as part of the Polynesian expansion. About 3,000 years ago descendants of Austronesian-speaking voyagers entered Remote Oceania, settling Fiji, Tonga and Samoa within a few centuries. After a long pause, a second phase of voyaging carried people farther east into central and eastern Polynesia. Rapa Nui, the easternmost island in this dispersal, was permanently settled around C.E. 1200—although some researchers argue for earlier, perhaps intermittent human presence beginning around C.E. 800.

It was, and is, a tricky place to live in. “Rapa Nui is subtropical and not tropical as [are] the other Polynesian islands where the diaspora came from,” says archaeologist Annette Kühlem of the German Archaeological Institute in Bonn. “That makes a huge difference.” It gets less rainfall than most Polynesian islands, and that rain is erratic.

Another constraint was the island’s lack of large hardwood trees, which Polynesians used for building oceangoing craft. “That would be a very unnerving thing to discover, if you finally made it there,” Kühlem says. The island did have palm trees, which belonged to a now extinct species. But they were useless for sea travel. “You can’t make a canoe out of them, because they’re big, floppy things,” Lipo says. Once people arrived, they might have been more isolated than they had expected.

Michael Marshall is a science journalist covering life sciences, health and the environment. He is author of The Genesis Quest and lives in Devon, England.

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Written accounts of Rapa Nui begin with that of Jacob Roggeveen, a Dutch sailor whose fleet sighted the island on April 5, 1722. It was Easter Sunday, so Roggeveen called the place Easter Island. A few days later Roggeveen led a party ashore. Soon after they landed, his sailors opened fire, killing 10 to 12 Rapanui people. The Dutch departed that evening.

What fascinated Roggeveen most about Rapa Nui were the statues. In his journal, he described “remarkably tall stone figures,” in front of which the people kindled fire and bowed their heads. The moai stood on stone platforms called ahu, many of them near the coast.

“At first, these stone figures caused us to be filled with wonder, for we could not understand how it was possible that people who are destitute of heavy or thick timber, and also of stout cordage, out of which to construct gear, had been able to erect them,” Roggeveen wrote. “Nevertheless, some of these statues were a good 30 feet in height and broad in proportion.”

He also described an island that complicates the later myth. Rapa Nui had rich soil, good weather and cultivated food. The island lacked large trees, but its people were not starving. The Rapanui were cultivating a difficult home.

BY THE TIME later European visitors reached Rapa Nui, the record had grown darker. Captain James Cook arrived in 1774 and encountered a far less hospitable island than Roggeveen had half a century earlier. He complained that “No Nation will ever contend for the honour of the discovery of Easter Island as there is hardly an Island in this sea which affords less refreshments,” adding that “Nature has hardly provided it with any thing fit for man to eat or drink,” that the sea was “barren of fish” and “the Natives are but few.”

Furthermore, one of Cook’s parties reported a striking detail: some of the moai had seemingly been thrown down. “On the east side, near the sea, they met with three platforms of stone-work, or rather the ruins of them,” Cook wrote. “On each had stood four of those large statues, but they were all fallen down from two of them, and also one from the third; all except one were broken by the fall, or in some measure defaced.” Almost a century later Palmer found virtually all the moai prostrate.

In the 20th century archaeologists confirmed that Rapa Nui had been deforested and its native palm had gone extinct. This gave rise to a narrative of societal collapse, which was popularized by Jared Diamond in his 2005 book *Collapse: How

Societies Choose to Fail or Succeed. In that telling, the first settlers began cutting down palms and other trees for agriculture to support the population, ultimately deforesting the entire island. Birds disappeared, soil eroded, farming faltered, and hunger followed. This scenario led to “starvation, a population crash, and a descent into cannibalism,” Diamond wrote, and the religion centered on the moai* lost its hold.

Diamond’s version brought the ecocide story to a wide audience. In 2006 he visited the University of Auckland, where Mara Mulrooney, now principal and senior archaeologist at Pacific Legacy, Inc., in Kailua, Hawaii, was beginning a Ph.D. on Rapa Nui settlement patterns. She recalls Diamond standing onstage and asking, “I wonder what was going through the Rapanui person’s head when he cut down the last tree on Rapa Nui in or around 1680.” In her own work, she began looking more closely at the archaeological evidence behind that narrative. “The more I read, the more questions I had about this notion of ecocide or environmental degradation leading to societal collapse.”

Mulrooney wasn’t the only one. Lipo had been visiting Rapa Nui for several years by this point, as part of a project exploring the sociological motivations for building the statues. “We assumed, of course, that the collapse narrative was true,” he says, but the more he excavated, the less sense it made to him.

“What happened after the publication of Jared Diamond’s book Collapse is that archaeologists working in various regions kind of got up in arms,” Mulrooney says. In the two decades since the

A European portrayal of a Rapanui man from James Cook’s 1774 visit. Cook found a harsher island than the cultivated one Jacob Roggeveen had described in 1722.

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Rapanui farmers adapted to thin soil and erratic rain with rock gardens like this one. The stones released nutrients into the soil and helped it retain moisture.

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book, researchers unconvinced by the ecocide narrative have pulled at one part of the story after another: how the forest disappeared, how people farmed, how large the population became, whether those statues were really the wasteful burden they'd been made out to be.

A KEY DISCOVERY is that the Rapanui fed themselves for centuries by adapting their agriculture to thin soil, erratic rain and dwindling tree cover.

They had to improvise because their first decades on the island were marked by trouble. Initially the Rapanui relied on slash-and-burn agriculture, razing some of the trees to clear patches of farmland. On many tropical islands, such as New Guinea, this method can be productive if farmers keep the plots small and leave them fallow long enough: burned vegetation enriches the soil while trees elsewhere regrow. But the trees on Rapa Nui were slow-growing—the now extinct palms could take 70 years to fruit—so this did not prove sustainable.

People were not the only force changing the forest. Lipo and his colleague Terry Hunt have spent years gathering evidence, which they synthesized in work published in 2025, that the deforestation was accelerated by another factor: Polynesian rats (Rattus exulans). Whenever Polynesians arrived on an island, they brought these rats, Lipo says. "We don't know whether they're stowaways or if they're intentional introductions," he says. Regardless, people did eat them. Polynesian rats live in trees and like to eat palm nuts. "It's rat candy."

Rat remains are abundant in the island's earliest archaeological deposits. At Anakena, a beach on the northern shore that has been excavated repeatedly, the oldest deposits contain hundreds of rat bones per square meter. "It's crazy how many rats are down there," Lipo says. Preserved palm nuts often show signs of having been chewed by rats.

With that food source and few predators, the rat population could have exploded. The palm nuts were especially vulnerable: rats gnawed through their shells and into the seeds, preventing new palms from taking root. The rats' depredations, combined with people clearing land and the palms' slow growth, left the forest little chance to recover.

Within a few hundred years the Rapanui people found themselves on an island with few remaining trees and with soil that was low in nutrients. So they adapted. They added stones to the

soil, a process called lithic mulching. Essential chemicals such as phosphorus and potassium leached out of the rocks into the soil, helping to nourish crops. In 2013 a team that included Mulrooney showed that soils in these rock gardens had more nutrients than soils elsewhere. The stones also held the soil in place, reducing erosion much as tree roots would, and helped to reduce evaporation, Mulrooney says.

Cutting down Rapa Nui's trees was not a senseless decision, Kühlem says. "With rising population numbers, nature has to make way for agriculture, especially on the most isolated island in the world." At first the palms "were used as a shade cover," with gardens planted between them. Later "the palm trees had to make way for more intensive land use" as the people relied more on the rock gardens.

Furthermore, Kühlem and her team have found evidence that the Rapanui actively planted palm trees. They conducted excavations between 2008 and 2024 at Ava Ranga Uka a Toroke Hau, near the center of the island. Near an ahu called Ahu Hanuanua Mea, people carved a planting pit into the bedrock, filled it with garden soil and planted a palm. This means the Rapanui were integrating palm trees into their religious architecture, much like the sacred trees nurtured on other Polynesian islands.

Ava Ranga Uka a Toroke Hau reveals another form of ingenuity: a system for controlling the island's only seasonal stream. The visible remains included two massive walls reaching into the riverbed and the rim of what Kühlem describes as a megalithic water tank. Excavation revealed a larger system of dams, basins and even underground aqueducts channeling water from the crater lake on the Terevaka volcano toward the southern coast. To Kühlem, it represents "advanced hydraulic engineering"—deliberate resource management on an island where water was never guaranteed. A prolonged drought began around 1550, and this water-management system might have helped the Rapanui survive.

The rock gardens also speak to the scale of Rapa Nui society. In a study published in 2024, researchers used satellite imagery and machine learning to map rock gardens across the island. The analysis suggested that the gardens covered far less land than earlier estimates indicated and that they could have supported only a few thousand people, not the huge population invoked in collapse scenarios. The finding is contested; some archaeologists argue that satellite-based mapping may miss upland cultivation or gardens that

Mara Mulrooney (rock garden); Terry Hunt (manavali); Annette Kühlem/DAI (hydraulic architecture)

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left subtler traces. Still, the study sharpened the challenge to the ecocide story: the mapped agricultural system does not look like evidence of a society that ballooned to unsustainable size and then crashed.

Kühlem says that is the crucial difference. The ecocide hypothesis is “a story of people being too stupid to realize what they were doing.” Ava Ranga Uka a Toroke Hau and similar sites point instead to people “mindfully planning” and “making the best out of very difficult environmental circumstances.”

Even the moai, long treated as symbols of waste, look different under this evidence. Most of them were carved at a quarry at Rano Raraku, and hundreds were transported across the island. Lipo and Hunt have spent years figuring out how the Rapanui people did this—work that they drew together in a 2025 review and that weakens the

claim that statue building required catastrophic timber use.

The pair found that moai left at the quarry or on roads have a pronounced forward lean. This makes it relatively easy to “walk” them along, a bit like shuffling a refrigerator into place, with ropes and a small team. Using 18 people, they walked a 4.35-ton replica moai 100 meters in 40 minutes. “The statues were carved to move,” Lipo says. Only when they arrived at their destination did the carvers reshape them to stand upright. This helps to explain how the Rapanui transported around 600 moai beyond the quarry: “Because they were good at doing it.”

THE COLLAPSE STORY also requires a second disaster: mass hunger or violence before Europeans arrived. Archaeologists have found little trace of either.

Rapa Nui almost certainly saw conflict. “In all Polynesian societies, we know of intertribal warfare or interisland warfare,” Kühlem says. She says it’s unlikely that Rapa Nui was “that one haven of peace and harmony where none of that happened.”

What the record does not show is the island-wide breakdown described in the ecocide story. “There is no archaeological evidence of fortification,” says J. Victor Moreno-Mayar of the University of Copenhagen. This is doubly striking considering the skilled stonework displayed in the ahu and moai. There are also no mass graves, no abundance of skull fractures or bones marked by

Researchers use ropes to “walk” a 4.35-ton replica moai, showing how a small team could move a statue without timber (right). Moai remain at Rano Raraku, the quarry from which statues were transported across the island (below).

Terry Hunt (left): Sergio Pitanitz/Getty Images (bottom)

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stabbing and slashing. There is not even much evidence of weaponry.

In 2024 evolutionary geneticist Moreno-Mayar and his colleagues published a major study of ancient DNA from the island, using remains from 15 individuals held in the National Museum of Natural History in Paris. Radiocarbon dating showed that the remains were from a range of times between 1670 and 1950. All dated to after the supposed 1600s collapse; some also dated to after European contact.

Moreno-Mayar and his colleagues sequenced the DNA from the remains. A population crash large enough to define Rapa Nui's later history should have left a detectable loss of genetic diversity. "They don't have this expected telltale signal of the collapse in terms of their genetic diversity," Moreno-Mayar says. Instead the team's models suggest that the population grew slowly for centuries without becoming especially large.

The genomes held a second surprise. Threaded through the Rapanui DNA was a pulse of Native American ancestry, which the team dated to roughly 1250 to 1430—generations before Europeans reached the Pacific. The finding points to pre-European contact across thousands of kilometers of ocean, although the route and people who made the crossing remain a matter of debate. For an island so often cast as a marooned dead end, the result is striking: Rapa Nui was isolated but not sealed off.

Combine all these findings—the rock gardens, the water-management system, the lack of a population crash—and a different picture of Rapa Nui emerges: a small society adapting ingeniously to difficult conditions. "Jared Diamond characterized it as a story of failure, and I think that what we've learned is that it's actually a story of success," Mulrooney says.

The absence of a precontact collapse does not make Rapa Nui's history any less brutal. By the 1870s, barely 100 Rapanui remained. The old parable falters in the gap between Roggeveen's cultivated island and Palmer's devastated one.

What changed was sustained contact with outsiders. Kühlem compares the arrival of European ships to a spaceship landing in medieval Rome. "That does something to a society," she says. Cultural norms shifted; beliefs and ways of life were shaken. Then came the real calamities.

Introduced diseases such as smallpox and tuberculosis took their toll. "We know that Rapanui women were offered to the seamen," Kühlem says, contact that brought sexually transmitted diseases with it. In 1862–1863 Peruvian ships ripped

through Polynesia, and their sailors kidnapped people as forced laborers, effectively enslaving them, a practice called "blackbirding." In losing people, Rapa Nui also lost knowledge, she says: "It's usually the knowledgeable, the high-standing people that would go greet visitors, and so most of the knowledge holders were taken."

In 1888 Chile annexed Rapa Nui, and later it leased much of the island for sheep ranching to the business interests associated with Scottish firm Williamson-Balfour Company. The ranching regime lasted until 1953. The Rapanui people were forced off their ancestral lands and confined to the island's one town, Hanga Roa, which they could leave only with a permission slip. "The island was totally scoured by sheep," Kühlem says.

The old story now looks like an accusation that hardened into a conclusion.

This was the damaged landscape later researchers encountered. The problem was that they mistook the effects of colonial violence and ranching for evidence of an Indigenous society that had ruined itself.

Today the island remains largely grassland, and its economy is heavily dependent on tourism. But the COVID-19 pandemic had an unexpected impact. The regular flights from Santiago were halted, and Rapa Nui was quarantined. "The island was really shut down for almost three years," Kühlem says.

And so the people of Rapa Nui started doing what their ancestors did. Fishers traded fish for crops. Farming expanded again, including in rock gardens. Erosion control and water management became central concerns. "Everybody was trading—there was reciprocity," Mulrooney says.

The island now faces another threat. A 2025 study using high-resolution computer modeling suggests that as sea levels rise, waves could reach Ahu Tongariki, the island's largest ceremonial platform, threatening the 15 moai that stand there and dozens of nearby sites. Once again Rapa Nui is being asked to absorb damage generated far beyond its shores.

Rapa Nui was never a paradise. It was a hard place to live in, and the people there knew it. Their story is a reminder of how easily a people and their history can be turned into someone else's morality tale before the past has been fairly read. ●

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ASTROPHYSICS

SPYING ON THE UNIVERSE

A former surveillance telescope is NASA's new powerhouse for solving the mysteries of dark energy and dark matter

BY JONATHAN O'CALLAGHAN

The Nancy Grace Roman Space Telescope is prepared for launch in a clean room at the NASA Goddard Space Flight Center in Greenbelt, Md.

NASA/Chris Gunn

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A

LAN DRESSLER STARED IN AWE at the line of Hubble telescopes stretching out in front of him. It took NASA two decades to design and build its own Hubble Space Telescope, which transformed our understanding of the galaxies and stars after its 1990 launch. Now, standing inside a New York defense contractor’s clean room in 2012, Dressler faced an assembly line of Hubble clones. They weren’t astronomy telescopes. They were spy satellites of equal capability. And one of them was being given to NASA for free.

So begins the saga of the Nancy Grace Roman Space Telescope, which now sits in Florida, ready to launch on a SpaceX Falcon Heavy rocket within weeks. Roman will offer unprecedented knowledge of dark energy and dark matter, the mysterious components of the universe that explain our very existence. It will find more alien worlds outside our solar system than ever before, and it will also test a crucial technology that may one day reveal life on such worlds. It is, in the words of Julie McEnery of the NASA Goddard Space Flight Center and the mission’s senior project scientist, a telescope capable of “spectacular things.” things.'

And the story of how Roman arrived at the launchpad is as amazing as the science it will perform. The observatory’s core was built to spy on America’s adversaries in a post-9/11 world. When that program collapsed, the National Reconnaissance Office (NRO) found itself with spare telescopes it no longer needed. Would NASA like any of them, officials asked? The space agency jumped at the offer.

Roman’s story is not only a tale of important science and unlikely interagency cooperation but also one of unusual efficiency. It is set to launch

under budget and ahead of schedule, a feat almost unheard of for complex astronomical observatories. “When we get things right and have success stories like Nancy Grace Roman, let’s learn from some of the magic that created that outcome,” NASA administrator Jared Isaacman said in an April press conference.

Not only did the spacecraft begin its life in a bizarre twist of fate, but it also has evaded death on multiple occasions. It’s a telescope that for many reasons simply shouldn’t exist, yet here it stands, ready to cast its eye onto the heavens. And in a way, its ultimate mission isn’t so far off from what it was built for. It will still be spying for secrets, after all—but this time, for the secrets of the cosmos.

AT THE END OF THE MILLENNIUM, astronomers made a Nobel Prize–winning discovery that up-ended modern cosmology. Looking at exploding stars called type Ia supernovae, they found an odd pattern—the supernovae farthest away were dimmer than expected. Scientists had known for decades that the universe was expanding, but this new finding pointed at something even more remarkable: the expansion was speeding up.

Jonathan O’Callaghan is an award-winning freelance journalist covering astronomy, astrophysics, commercial spaceflight and space exploration. Follow him on X @Astro_Jonny

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To explain this acceleration, astronomers came up with dark energy, an invisible force or pressure that was driving galaxies apart faster and faster and accounted for more than two thirds of the universe's mass and energy. Albert Einstein had predicted the existence of such an effect in 1917—he invented a "cosmological constant" to explain why the universe was static. He nixed it, though, after the discovery in the 1920s that the universe was expanding. About a century later his prediction is back on the table as a possible reason for the accelerating expansion.

Solving the mystery of dark energy will require better observations of supernovae across the universe, plus measurements of the shapes and positions of as many galaxies as possible, which scientists will use to study the cosmic structure dictated by the other component of the universe's dark sector—dark matter. By the end of the 2000s understanding this dark universe had become one of the highest priorities in astrophysics, and in 2010 the National Academies of Sciences, Engineering, and Medicine told NASA to build a telescope to study it in its Decadal Survey, which sets NASA's priorities every 10 years.

That instrument was called the Wide-Field Infrared Survey Telescope (WFIRST). With a primary mirror measuring just over a meter across—half the size of Hubble's—WFIRST would conduct a large survey of the sky to map the expansion of the universe and probe distant galaxies. From the start, however, it faced considerable opposition from astronomers who wanted NASA to expand the purview of the telescope, particularly to include exoplanet research, which was becoming the next big thing in astronomy. "We were having a hard time getting traction in the community," says Dressler, now an emeritus astronomer at the Carnegie Institution for Science and one of the early leads on WFIRST. "They wanted to do something much more ambitious."

At a 2011 meeting of the American Astronomical Society (AAS), Dressler and his colleagues tried to sell the plan. "That meeting was very controversial," he says. "A lot of people thought we shouldn't be wasting our money on this." Much of NASA's budget for building telescopes at the time was going toward the James Webb Space Telescope (JWST), which already had a projected cost of $8.7 billion and would balloon to about $10 billion by the time it launched in 2021. WFIRST, before it even got going, looked dead in the water.

So it came as a shock when David Spergel, a theoretical astrophysicist then at Princeton University and a scientific adviser to the mission,

quietly pulled Dressler aside at the 2011 meeting and said that WFIRST might have an extraordinary savior—the NRO. The spy agency had spare telescopes it no longer needed, Spergel said, and had asked NASA if it wanted some of them. It was an unbelievable stroke of luck. Was it too good to be true?

IN THE 1990S THE NRO LAUNCHED a spy satellite project called Future Imagery Architecture. After the September 11, 2001, attacks, the agency doubled down on the program, aiming to build a new era of high-tech telescopes to gather satellite data on America's adversaries. With Hubble-size mirrors, the telescopes would be able to see objects on Earth smaller than a coffee mug—a feat revealed in a 2019 tweet by President Donald Trump that showed an image of an Iranian rocket launch site from a comparable satellite.

But the project, contracted to Boeing, lagged behind schedule and ran over budget. An investigation by The New York Times found that the to-

Not only did the spacecraft begin its life in a bizarre twist of fate, but it also has evaded death on multiple occasions.

tal price tag ran up to $13 billion more than its original projected cost of $5 billion. Officials decided to scrap the plan in 2005—but not before some of its hardware had already been constructed. That hardware was sitting in a clean room at a defense company called Exelis, later acquired by L3Harris, in Rochester, N.Y.

Michael Moore, then NASA's acting deputy director for astrophysics, had been a liaison for the U.S. Air Force in the 1990s and heard from his contacts that some excess equipment might become available. He decided to try for a long shot. "When it became obvious that they were going to have some surplus hardware, I went to the program manager and asked about whether the systems would be available," Moore says. "At that time, the answer was no." But by the time of that 2011 AAS meeting, the decision had changed. "I got a call, and they had revisited their position," Moore says. NASA could have some of the telescopes if it wanted them.

The spy agency had "identified surplus telescope assets that were no longer required" and

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“determined that our telescope assemblies met or exceeded the specifications NASA required” for WFIRST, according to an NRO spokesperson. So the agency decided to offer the mirrors to NASA—its garbage, essentially, was NASA’s gold. “NRO is proud that technology developed under NRO programs will contribute to groundbreaking discoveries.”

Astronomers met at Princeton University in the summer of 2011 to discuss what they could do with the telescopes. It quickly became clear that one of the scopes would be perfect for WFIRST. Not only would the repurposed spy telescope give WFIRST a mirror twice the size of the one in the original plan, but it would also enable the addition of an instrument called a coronagraph, which would let it block the light of distant stars to image nearby planets, appeasing disgruntled members of the exoplanet community.

The following year officials formally made their offer to NASA. An NRO representative traveled to NASA headquarters in Washington, D.C., and met in a secure room with John Grunsfeld, then the agency’s top science official. He was told that the clandestine agency had two partially disassembled Hubble-class telescopes up for grabs, each with a 2.4-meter (7.9-foot) mirror, and a third primary mirror with some spare components available.

BEFORE LONG, Dressler, Grunsfeld, and other scientists and engineers traveled to Rochester to see the telescopes in person. They walked into a clean room to find a row of pristine mirrors—all near-replicas of Hubble. “It was beautiful,” Grunsfeld says. Their findings helped

to convince then NASA administrator Charlie Bolden, who had the final say, to accept the offer.

It would still take considerable work to turn the spy telescopes into space telescopes. NASA would receive the 2.4-meter mirror, its supporting struts and a smaller secondary mirror but would need to strip the assembly of its confidential parts and build instruments and cameras. It would also, of course, need to launch the thing. Because of those extra costs, NASA later declined to take the other telescopes, one of which had a slight fault in its mirror.

The fate of the extra telescopes, and whether they are still in Rochester, is unknown. NASA, the NRO and L3Harris, which acquired Exelis in 2015, did not respond to questions about the equipment’s location.

Ultimately it would take more than a decade to transform the telescope from a spy satellite into a space observatory, with a final cost of about $4.3 billion. “Everything was probably taken apart and investigated,” says Dominic Benford, Roman’s program scientist at NASA headquarters. “We made it into what we wanted it to be.”

In 2016 NASA formally began the WFIRST mission and started development, with L3Harris keeping hold of the mirror in Rochester and getting the contract to complete the further work needed.

Even then, WFIRST was not out of the woods. “We had a lot of near-death experiences,” Spergel says. “It was canceled five times in the president’s budget,” he says—twice during the Obama era and three times in the first Trump administration. Each time, Congress elected to save the mission, with astronomers, including Spergel, traveling to Washington, D.C., to sing the praises of the telescope to senators such as Senator Chuck Schumer of New York. “I don’t think this would have happened without Schumer’s support,” Spergel notes.

To legitimize the mission once and for all, Thomas Zurbuchen, then head of NASA’s science projects, decided to name it. “By naming it, it basically becomes not cancelable,” he says. “You basically say, ‘We care about it a lot.’” Astronomer Nancy Grace Roman had passed away in 2018 at the age of 93. She had become NASA’s first chief of astronomy in the 1960s at a time when female astronomers were rare, and she was a key voice in driving support for space telescopes, particularly Hubble, earning her the nickname “Mother of Hubble.”

For Zurbuchen, Roman was the perfect name-sake. He went to discuss the name with then NASA administrator Jim Bridenstine, who had

Nancy Grace Roman was NASA’s first chief astronomer at the Goddard Space Flight Center in the 1970s. Roman was known as the “Mother of Hubble” for her role in developing orbital observatories such as the Hubble Space Telescope.

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Graphic by Matt Twombly

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The Telescope That Once Was a Spy Satellite

NASA wanted an observatory to study dark energy and dark matter. The National Reconnaissance Office (NRO) had an extra Hubble-class telescope it didn't need. In giving NASA its leftovers, the NRO enabled the birth of the Nancy Grace Roman Space Telescope, which will launch soon to try to solve some of the universe's biggest mysteries.

SPARE HUBBLE

The NRO's extra scope was one of several intended for a discontinued surveillance program. Its 2.4-meter primary mirror is the same size as the Hubble Space Telescope's and will enable Roman to image billions of galaxies and thousands of supernovae to track how the spread of matter throughout the universe has changed.

FIELD OF VIEW

The 18 detectors in Roman's Wide-Field Instrument can capture an area 100 times larger than Hubble's field of view in a single image. The observatory will survey large swaths of the night sky faster in both infrared and visible-light wavelengths.

Coronagraph Technology Demonstration

WIDE-FIELD INSTRUMENT

Roman's main scientific instrument is this 300-megapixel infrared camera, which will capture detailed images of larger fields of view than Hubble can.

CORONAGRAPH

Using a complex array of masks, a special deformable mirror and a sensitive camera, Roman will filter out the light of stars to reveal the relatively dim shine of exoplanets around them.

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The telescope undergoes final checks and preparations for launch. The solar array sun shield is installed (bottom left). A close-up shows color filters on the coronagraph instrument that will search for planets around other stars.

attended Roman's funeral. "I said, 'The right name for this telescope is Nancy Grace Roman,'" Zurbuchen says. "He looked at me and said, 'Do it,' making it the first space telescope named for a woman.

SINCE THEN, THE CASE for launching a telescope to study dark energy has strengthened considerably. New findings suggest dark energy might behave much differently than we thought. In fact, results published in 2024 by astronomers working with the Dark Energy Spectroscopic Instrument (DESI) in Arizona suggest that dark energy might be weakening. If true, the universe might not continue expanding faster and faster forever, eventually ripping itself apart. Instead it might one day start to contract, ending in a big crunch. Those results are "spectacular timing" for Roman, McEnery says. "It looks like we might be sitting on a gold mine."

After it launches, Roman will travel to a posi-

tion of gravitational stability one million miles from Earth called the second sun-Earth Lagrange point, where the James Webb Space Telescope is also located. Roman has a field of view at least 100 times bigger than Hubble and a much more capable 300-megapixel camera. Called the Wide-Field Instrument (WFI), it takes images so large a wall of 4K televisions would be needed to display each one.

In five years of observing, Roman will survey about 12 percent of the sky and image billions of galaxies. It will look for any warping of light from these galaxies caused by clumps of dark matter curving the intervening spacetime. By mapping this effect, called weak gravitational lensing, Roman will track the distribution of matter in the universe and thus its evolution through time. Another Roman survey will search for thousands of type Ia supernovae stretching back more than 10 billion years in the 13.8-billion-year history of the universe. It should detect more of these ex-

Clockwise from top left: NASA/Sydney Rohde; NASA/Jelena Tshitaya and Chris Gunn/NASA JPL; NASA/Jelena Tshitaya

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plosions dating further back in time than any other telescope, revealing how the expansion of the universe has changed across history.

It will also measure baryon acoustic oscillations, which are a kind of sound wave that sped through the universe when it was full of plasma in the first 380,000 years after the big bang. Discovered in 2005, these waves became frozen in time as the universe expanded, which should have led to an expected distance between galaxies of about 500 million light-years, according to predictions. Any deviation from this distance “tells you how the expansion of the universe is evolving with time,” says astrophysicist Neta Bahcall of Princeton. “That gives you a determination of dark energy and dark matter.”

Roman will also help narrow down what dark matter might be made of, says Anna Nierenberg, an astrophysicist at the University of California, Merced. Light from some distant galaxies will be magnified around closer massive galaxies and appear multiplied and elongated depending on the nature of the dark matter present in halos around the galaxies. Roman should find hundreds of these gravitational lenses, which it can use to rule out some dark matter models. “It’s going to be absolutely incredible,” Nierenberg says.

Roman will also be transformational for the study of exoplanets. One of its surveys will peer into the center of the Milky Way, the galactic bulge, which contains a very dense population of stars, and look for the gravitational tug of planets bending the light of more distant stars, called microlensing events. “It’ll use the microlensing technique to discover maybe a couple thousand planets both bound [to stars] and free-floating,” says Scott Gaudi, an exoplanet scientist at the Ohio State University. It should be able to spot worlds with as little mass as Earth’s moon.

It will also observe hundreds of millions of stars in the galactic bulge for any dips in light from orbiting planets, called transits, a technique that has already found the bulk of the 6,000 known planets today. Roman, however, “should find maybe 100,000 transiting planets,” says Gaudi, with sizes from Jupiter down to twice that of Earth, revealing multiple times more planets than have been seen in human history, giving us a broad sample of different planet populations across the galaxy.

But the coronagraph—that instrument exoplanet scientists had been clamoring for—might be one of Roman’s biggest legacies. Technically a technology demonstration—basically an experiment to see if it works—the instrument consists of a complex series of small disks, or masks, that

will suppress the light of distant stars so that the extremely faint glow of orbiting planets is visible. The goal is to reduce the contrast of each star to one part in a billion—in other words, for every one billion photons from the star, only one leaks through to Roman. That sensitivity will allow it to image planets the size of Jupiter.

If it works, we may detect the reflected light of exoplanets around other stars for the first time. All previously directly imaged planets were so hot that we simply saw their own glow, says Mary Anne Limbach, an astronomer at the University of Michigan. With Roman, however, we could see cooler planets that merely reflect their star’s light, like the planets of our solar system do. It might even be possible to see ring systems around planets. “The light from the rings will be blended in” to the dotlike point of light from the planet, Limbach says, but it will be noticeable over time.

In five years of observing, Roman will survey about 12 percent of the sky and image billions of galaxies.

This instrument is a precursor to the coronagraph NASA wants to fly on its Habitable Worlds Observatory, a telescope set to launch in the 2040s with the goal of imaging 25 Earth-like worlds around nearby sunlike stars and probing their atmospheres for signs of life. To do this, it will need to reach a contrast of one part in 10 billion, says Beth Biller, an exoplanet scientist at the University of Edinburgh and part of Roman’s coronagraph team. That contrast should be enough to see the pale dot of a potentially inhabited world around another star.

All of this means that the first detection of life outside our solar system, if it occurs, might happen because of a Rube Goldberg-like sequence of events: a collapsed spy satellite project, a call out of the blue and an offer that revitalized a space telescope fighting for survival. For the American intelligence community, it was the end of a multi-billion-dollar endeavor but for astronomers, it was the start of an entirely new one. “All I know,” says Marc Postman, head of the Science Mission Office at the Space Telescope Science Institute, “is that we got a good mirror.” ●

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NEUROSCIENCE

Wired for Story

New research is revealing how the brain uses narrative to make sense of experience

BY INGRID WICKELGREN ILLUSTRATIONS BY OLLIE HIRST

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FFSHORE THE FICTIONAL TOWN of Portorosso in the Italian Riviera, a young sea monster named Luca herds goatfish on his family’s aquatic farm. In the surf above, fishers threaten to fatally spear any sea monster that

comes within range. The youth’s mother sternly warns him: “We do not talk, think, discuss, contemplate or go anywhere near the surface!”

But Luca defies her, goaded by a beach-dwelling sea monster kid, Alberto, and the two dream of exploring the world on a Vespa. When Luca’s parents find out about his trespasses, they announce he must live with his uncle deep in the ocean. Horrified, Luca flees to Alberto’s, and the two decide to hide in the human town, where fear and hatred of sea monsters is rampant.

So begins the Academy Award–nominated Pixar movie Luca. Viewers are transported to this fantastical world, invited to suspend disbelief as the ocean creatures shed their scales and assume a human form as soon as they are dry. They root for Pixar’s improbable protagonists as they dodge detection and train for a triathlon in hopes of winning the prize money they need to buy a Vespa.

The brain follows this story seamlessly—tracking characters from one scene to the next and tracing the interwoven threads of its plot to make sense of the unfolding action. It’s a talent so ingrained that screenwriters can count on it. “Stories are this fundamental way in which people see the world and respond to the world,” says Ben Rogers, an organizational behavior researcher at Boston College.

No story, whether “real” or imagined, is a true replica of events. Luca is a deliberately streamlined version of reality in which cause and effect is evident and take-home lessons are fully wrought. People’s real-world experiences are similarly edited by the brain into Pixar-like narratives so we can make sense of them, the edited scripts living in memory. “When we say ‘narrative,’ all we are really saying is ‘simplification,’” says Pixar’s Jesse Andrews, who co-wrote the

screenplay for Luca. “It’s a simplification in the name of understanding.”

The brain simplifies all experience in this way. But the workings of the brain’s narrative wiring were largely mysterious until about a decade ago, when scientists began to deploy sophisticated mathematical tools to decode the brain’s response to movies, which they screened for subjects inside brain scanners. In the ensuing years, they found biological real estate dedicated to intuiting a story’s cinematic divisions, editing the footage, tracking its characters and extracting its meaning. They’ve also revealed neural scaffolds for familiar scenarios that the brain relies on when people encounter new but similar situations.

The work has helped explain why stories have played such an integral role in nearly every human society since ancient times. It shows the power of narrative to convey lessons from other people’s experiences, to bring people together or push them apart, and to make sense of romantic comedies and cozy mysteries alike. Related psychological studies, meanwhile, show how culture shapes storytelling in ways that can subtly but profoundly affect our well-being and sense of self. Family and society are co-authors even in the stories we tell ourselves.

PEOPLE HAVE BEEN TELLING STORIES for millennia. Scientists glimpsed the ancestors of picture books in scenes sketched in caves in France dating back some 30,000 years. Oral storytelling is thought to have originated around 10,000 years

Ingrid Wickelgren is a freelance science journalist based in New Jersey.

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ago. Epic poems such as the Iliad and the Epic of Gilgamesh, which date to around 3,000 years ago, were first spoken tales that traveling poets or court entertainers performed, and scholars have been dissecting what makes a good story at least since Aristotle wrote his Poetics around 330 B.C.E.

The early origins of storytelling and all its modern incarnations suggest that stories powerfully connect to the human psyche. But it wasn't until the 20th century that psychologists began to gather experimental support for that connection. In 1944 Austrian American psychologist Fritz Heider and his then research assistant Marianne Simmel were investigating how people interpret others' behavior. They asked 114 subjects to watch a crude animated film in which a small triangle, a big triangle and a small circle ricochet off one another and scoot in and out of a rectangle with a doorlike flap.

When asked to describe what they saw, hardly any of the participants reported on the physical movement of shapes. The vast majority instead "interpreted the picture in terms of actions of animated beings, chiefly of persons," the authors wrote. To some, those "beings" were engaged in a love triangle; to others, they were embroiled in a family drama or an episode of bullying. At the time, the researchers interpreted the results in terms of the human tendency to anthropomorphize. But decades later many scientists saw them as support for another default for the human brain: storytelling. Viewers instinctively constructed a sequence of events to make sense of an otherwise nonsensical stimulus.

It would be decades before people found the brain circuitry that underlies this construction. Doing so required both new technology and the courage to use it in a novel way. Developed in 1991, functional magnetic resonance imaging (fMRI), which measures blood flow as a proxy for neural activity, was conceived as a window to the workings of the human brain. But as of the early 2000s, Uri Hasson, then a graduate student at the Weizmann Institute of Science in Israel, didn't think it was being put to good use.

In typical fMRI experiments, researchers exposed subjects to very simple stimuli such as line drawings, word lists and auditory tones because they believed that doing so was necessary for the results to be tractable. The problem, according to Hasson, was that the results were not meaningful because the stimuli were unrealistic. "There was a crisis in science," Hasson recalled. "We had these nice experiments in the lab, but they didn't explain how people behave in real life." Explaining real-life behavior, he posited, required exposure

to something that better represented life experience—such as movies.

Most experts believed that analyzing the brain's responses to something as complex and dynamic as a movie would be impossible. But to Hasson, this complexity was the point. Along with his adviser, Rafael Malach, Hasson and three colleagues placed five people in brain scanners to watch half an hour of the 1966 western The Good, the Bad and the Ugly. To the surprise of many, the researchers were able to make some sense of the resulting storm of neural activity. The brains of all five viewers responded synchronously to shifts in scenery, dialogue and even plot, as if operated by the same neural story-watching program. The results, reported in a 2004 paper in Science, offered the first solid support for the idea that such a universal program existed.

The movie engaged large swaths of the brain—including not just sensory regions but areas of the brain's ridged surface, the cerebral cortex, that are charged with complex tasks such as language. In the ensuing years, Hasson and others homed in on a set of interconnected cortical areas called the default mode network as the main switchboard for narrative. Also known as the daydreaming network, the default mode regions were thought to come online when the mind was wandering "at rest," contemplating the future or the past. Activity

The early origins of storytelling suggest that stories powerfully connect to the human psyche.

in this network has been linked to rumination, the sense of self, social cognition and autobiographical memory. But the fact that exposure to stories in real time also recruited this network suggested that it handles more than internal deliberations.

Movies were the entry point for these discoveries. In acting on his wish to mimic real life in a scanner, Hasson had inadvertently put a spotlight, albeit a dim one at first, on brain circuitry dedicated to narrative. He had also kicked off a line of research that would unveil how the brain decodes elements of plot, identifies scenes, traces character arcs and decodes a story's overall meaning.

IN 2008 HASSON MOVED to Princeton University, and his laboratory attracted scientists who wanted to screen movies in brain scanners to study memory. In 2012 Janice Chen joined the lab as a gradu-

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ate student. Chen, now a cognitive neuroscientist at Johns Hopkins University, got the first glimpse of the brain's stored rendition of a story.

Chen, Hasson and their colleagues scanned people's brains while they watched and then recalled the first episode from 2010 of the television show Sherlock. The researchers found synchrony in brain activity among people in the group as they watched the show, as well as when they recalled it. Yet the pattern seen during recall was not the same as the one seen during the viewing of the show. The differences between these patterns, the investigators concluded, most likely reflected edits to the material as the brain socked it away. The edits appeared to be systematic because they were similar across viewers.

Such editing helps us not only to interpret stories we watch, read or listen to but also to shape a meaningful narrative from the raw, chaotic footage of daily life—a love story from the arbitrary movement of shapes. “We are inundated with a lot of very confusing information all the time,” Rogers says. “Narratives boil that all down to ‘this leads to this, and it means this.’” The brain does automatically what a screenwriter does deliberately. “When you create narrative, you sweep almost everything off the table, and you focus on a few things. You say, ‘Well, this caused this, or this would have caused this, but this other thing happened,’” Pixar’s Andrews says.

The primary glue for what remains is cause and effect. As soon as Alberto drags Luca to the beach, the dominoes begin to fall: Luca’s parents threaten to send him away; Luca escapes to Portorosso, where he meets Giulia and becomes entranced by the idea of school; his new goal infuriates Alberto, igniting a fight, and so on. In outlining his script, Andrews checked his sentences for glue words: “therefore” for a causal connection and “however” for a reversal.

The brain tracks the “therefores.” In a 2022 study, Chen and her colleagues screened a series of movies for people as they lay in an MRI machine. When people watched or recalled scenes that were causally connected to many other scenes, activity spiked in parts of the default mode network. That higher activity was associated with a higher likelihood of recall of those scenes. “Events are not isolated. They are connected to other events in the story,” says Chen, the study’s senior author. “That’s one of the types of information that is being tracked or encoded in these brain regions that care about narrative.”

The adhesive of causality binds scenes even more strongly than that of proximity. In the 2000

thriller Memento, one storyline is told backward, and another (past) storyline is told forward; the two meet in the final scene (which is the chronological middle of the story). In a 2024 study, people watched the movie and then were asked to describe what they had seen. They were told to relate the events either as they had been presented in the movie or as they supposedly happened. Participants overwhelmingly told the story the way it happened, rearranging the movie’s presentation to what made sense in terms of cause and effect. “The purpose of a story for the human being is to make sense of disparate things that have happened to you,” says Chen, an author on the paper. “You need to bring [them] together into a coherent causal structure in order to understand what happened.”

As it builds that causal structure, the brain is also paradoxically breaking it down into parts. “The building block of the movie is the scene,” Andrews says. These cinematic divisions jibe with a known phenomenon in psychology called event segmentation. People naturally draw boundaries within stories or experiences where they perceive shifts in place, time or situation. And these segments, it now turns out, are a natural product of the brain.

Christopher Baldassano, now a cognitive neuroscientist at Columbia University, joined Hasson’s lab in 2015. His first move was to reanalyze Chen’s Sherlock data using new mathematical tools. His analysis revealed that the brain was carving up the episode into scenes: striking shifts in neural activity in a default mode hub called the prefrontal cortex lined up with what people perceived as scene changes. “At a scene change, you recognize, okay, now a new thing is starting,” Baldassano says. “This is something that we could see in the raw data.”

THE BRAIN DOESN’T CREATE or comprehend stories from scratch. When people watch Luca or Sherlock or go to the grocery store, they filter these experiences through previous ones. Based on other shopping trips, shoppers expect, for example, to pick up a cart, walk the aisles, put items in the cart, enter a checkout line, and so on. Back in the 1970s psychologists hypothesized that people have basic scripts for what happens in familiar situations or events. These scripts inform future trips to those places—say, a store, airport, library or restaurant.

In crafting the story for Luca, Andrews assumed viewers had a script for races or competitions when he created a quirky triathlon with a

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pasta-eating portion. He banked on them having a script for a farm that herds sheep when he envisioned a clever variant: a sea monster herding fish. “There are all these familiar cues that go, ‘Okay, I haven’t seen this, but I also have. This is familiar to me,’” he says.

Several years ago Baldassano and his colleagues found these scripts in the brain. They screened clips from eight movies or TV shows, including Due Date, Derek and Pulp Fiction, and eight audio narratives adapted from movies or TV shows. Four of the clips of each type depicted airport sequences, and the other four showed restaurant scenes. The researchers identified patterns of brain activity that corresponded to each part of an airport or restaurant script. Four distinct patterns accompanied arriving at the airport, entering security, going to the gate and boarding the flight. A separate sequence of activity patterns denoted people entering a restaurant, sitting down, ordering food and receiving food.

Remarkably, the patterns were consistent across people; however, there were some differences that affected memory for the narratives. The closer a person’s pattern was to a mathematically determined standard, the more details that person remembered from the clip. “When you are going through the airport, there’s a sequence of patterns that should show up,” Baldassano says. As Baldassano explained in a 2024 webinar, if these patterns appear with high fidelity, “that’s actually a predictor you’re going to have detailed memory” of that experience.

The patterns show up largely in the medial prefrontal cortex, a goal-setting region that marries the most relevant memories with ongoing experience. “Your brain is not built to just record the pixels that are coming in from the screen or from the movie. You are trying to match this into something that you know,” Baldassano says. The work helped neuroscientists reimagine the default mode network’s role. The network was not

The brain does automatically what the screenwriter does deliberately—edits the raw footage of daily life into a story.

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just for internal musings; it also acted as a broker between ongoing experience and a person's knowledge and memories.

Baldassano imagines that an adult brain holds hundreds of thousands of scripts for expected scenarios, a huge neuronal library of story outlines crafted from experience. These scripts serve as a foundation for the stories to be written as we live our lives. As we write these stories, we may have a choice of template, and our choice guides the story we write. In one of Baldassano's studies, subjects were given roles—a restaurant critic or a wedding planner—that dictated what they paid attention to in a plotline about a marriage proposal in a restaurant. That role shaped the story they constructed in their minds—and therefore what they recalled when asked to report back. If we enter a situation with a purpose, we filter our experience of that situation through the lens of our goal. People with different goals, or frames, for an experience show differences in brain activity that reflect variations in their narratives.

A PROTAGONIST WHO UNDERGOES CHANGE lies at the heart of many good stories. Luca starts out as a shy, obedient kid. He is pulled out of the water and out of his shell by his daring new friend, Alberto. "By the end of the movie, he's someone who bursts out from under this awning into the rain, exposing himself, risking it all to help his friend," Andrews says. "That's an action that is really hard to imagine him doing at the beginning of the story, which means he must have really changed."

The brain tracks that change in part through neural templates for characters. In a 2023 fMRI study, researchers identified a pattern of neural activity in part of the default mode network whenever a specific actor appeared in a video clip. When the actor was present, so was the pattern. When the actor was absent, the pattern was gone. Where the actor was—a coffee shop or grocery store—didn't affect the character code. "There's a certain network of areas in your brain that represent the person, and they don't care about where the person is or what the situation is. They just say, 'Okay, here's Ingrid,' " says Zachariah Reagh, a cognitive neuroscientist at Washington University in St. Louis and one of the study authors.

To understand a character change, a person must not only recognize the character but also grasp a story's context. Dartmouth College cognitive neuroscientist Emily Finn and her colleagues recently homed in on the brain's machinery for context in stories. In an fMRI machine,

they played audio of an episode called "The Dark End of the Mall" from the podcast The Truth, created by Jonathan Mitchell. It is set in a bridal shop and features a dialogue between an irritable customer (Steve) and a polite but curt shopkeeper (Lucy). Although the exchange is testy, listeners perceive nothing extraordinary until partway through the story, when they learn that Steve is one of the last humans alive after a 2050s apocalypse. He has survived because he knows that some bridal shops store energy bars and water behind the counter. Lucy is a robot whose rigid programming, listeners realize, will cause her to thwart Steve's plans and hasten his demise.

Everyone listened to the script twice. The second time, people were privy to the twist, so they had a different assessment of the story and its characters at the start. But because the audio input was the same both times, any differences between the iterations in a person's brain activity would relate to their different conceptions of the story. "What that allows us to do is to pinpoint where in the brain these so-called latent interpretation frameworks are," Finn says.

These frameworks included the default mode network, as well as other brain areas involved in making sense of events and integrating information over long timescales. "It was all over the place in regions that we know are involved in some way in higher-order thought," Finn says. "I was surprised by how widespread those changes were, given that it's the exact same person and the exact same sensory information coming in."

The same machinery also most likely extracts meaning from experiences. Starting in adolescence, people become able to reflect on their experiences to draw conclusions. After winning a student election in high school, a teenager might start to think of herself as a leader. A young adult might see himself as bold if he risked harm to save a friend. In this way, stories establish identity. "If you could see an identity, what would it look like?" asks Dan McAdams, a psychologist at Northwestern University and a pioneer of the subfield "narrative psychology." "It's a story in a person's mind about how they came to be and where their lives are going."

IN LUCA, FOLKTALES OF SEA MONSTERS attacking humans spread fear through Portorosso, where men hunt the creatures for sport and self-defense. "Storytelling can be used in great ways, or it can be used for propaganda or fake news," McAdams says. "It's a tool. It's like fire."

As a tool, storytelling imprints the neural pat-

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terns associated with one person's experience to another individual, expanding the latter's experiences beyond their own. "Narratives are the typical means by which we can transport experiences from one person to another," says Fritz Breithaupt, a cognitive scientist at the University of Pennsylvania, who wrote the 2025 book The Narrative Brain.

Storytelling can teach useful lessons when the experiences are new. Not everyone has to touch a hot stove, text and drive, or lie on their résumé to learn the consequences of such actions. "You are learning about the experiences of others in a safe place," Hasson says. "This is why it's really useful."

To be persuasive, however, a story must resonate with listeners. It must elicit in their brains activity similar to that of the storyteller. And whether a tale resonates depends on a listener's background. In the 1951 short story "Pretty Mouth and Green My Eyes," by J. D. Salinger, a man named Arthur leaves a party without his wife, whom he couldn't find. Worried, Arthur calls his friend, Lee, asking if he knows where his wife is. Lee is with "a girl," her identity unspecified.

Hasson and his colleagues played an adapted version of this story to people in a brain scanner, prefacing it in one of two ways. In one rendering, the girl with Lee is Arthur's wife—they are having an affair. In the other, the girl with Lee is Lee's girlfriend, and Arthur's suspicions are unjustified. The researchers found that the brain activity of people given the same context—affair or misplaced suspicion—was tightly aligned, but the brain activity of people who were given different contexts was different. A person's memories and beliefs shape their understanding of the story, says Hasson, who led the study. "We are going to be more aligned with people who think like us."

Stories that appeal to broad audiences are often rooted in shared cultural narratives, which are based on accepted ways of thinking. These templates can range from expected life sequences—attend college, get a job, get married, have children—to popular story arcs such as the redemption narrative. In a 2020 study by Kate McLean, a developmental psychologist at Western Washington University, and her colleagues, people read vignettes involving hurricanes, car accidents, sexual assaults, or other traumatic events. Some of them ended badly; others offered a positive lesson or outcome. People liked the redemptive endings best; they also rated the authors of those stories as more likable than those who relayed purely negative anecdotes. "If something bad happens to you, in America, you know you better tell a story where

you learn something or you grow or there is some kind of silver lining at the end," McLean says.

Framing your life as a story of redemption may have other benefits, according to an intensive analysis of 157 case studies by McAdams and his Northwestern colleague Jen Guo. McAdams defines a redemptive life story as one with a narrator who is special or lucky in some way; who describes the world as dangerous; who has strong moral principles; who suffers but whose suffering leads to a positive outcome; and who envisions personal growth and making a difference in the future.

People whose stories roughly follow that template, McAdams's research shows, tend to be more productive and more content with their lives than those who don't. "Nobody's life story fits that perfectly," McAdams says. "But people who are highly generative—that is, caring and productive adults—our research shows again and again, at least in the U.S., tend to tell their life narratives in ways that get closer to that kind of pattern." Rogers, McAdams and their colleagues found similar benefits for a related template, the hero's journey.

Not only do cultural narratives shape individuals' stories, but each act of storytelling either fortifies or weakens the template. "When we tell our personal stories, we are contributing to master narratives or resisting them," McLean says. "We are all players in this dynamic cultural system." Luca contributes to a broader narrative about friendship and its power to change people. But it also speaks to what it means to be an out-

An adult brain may hold hundreds of thousands of scripts for expected scenarios.

sider, to have a life story that conflicts with the accepted lore. "There's this larger question of, 'What does it mean to be a sea monster in a world of humans?' That is about prejudice and othering and when to hide yourself and when to show people who you are," Andrews says.

That unveiling presupposes knowing who you are, knowledge that comes from a story. "The world in its entirety and people in their entirety actually cannot be understood," Andrews says. "But with the skillful editing that we do spontaneously, that we do without thinking about it, we can understand the world in part and understand each other in part." Far from just an entertaining ritual, creating stories may guide much of human thought. ●

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RENEWABLE ENERGY

Why Solar Is Taking Over the World

©2024 SolarInNya – a clear

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After a meteoric rise, solar power is now

the cheapest form of energy in history

BY STEPHANIE PAPPAS

The CGN Dalingha Solar Thermal Plant (seen in an aerial view) is in the Gobi Desert in China's Qinghai Province. It uses mirrors to concentrate sunlight onto a single receiving tower that converts the light to heat.

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E

ORTY-SEVEN YEARS AGO U.S. PRESIDENT JIMMY CARTER stood grinning in front of a set of 32 bulky solar panels. It was 1979, and the oil crisis had sent fuel costs skyrocketing. Carter, in response, was making the White House an example of conservation and alternative energy. “Solar energy will not pollute our air or water,” he said. “We will not run short of it. No one can ever embargo the sun or interrupt its delivery to us.”

The panels were expensive and rudimentary by today’s standards. They cost roughly $160,500 in 2026 dollars, and they didn’t even generate electricity; all they did was heat water for things such as kitchen use. But Carter’s argument still resonates today: in a globalized economy in which a single conflict can shut down shipments of millions of barrels of fossil fuel overnight, the allure of the sun as a power source is inarguable. And there’s no better deal on energy, well, under the sun. “Today solar makes the cheapest electricity,” says Walajabad S. Sampath, site director of the Center for Next Generation Photovoltaics at Colorado State University.

Even before the U.S.-Iran conflict closed the Strait of Hormuz for months, causing fossil-fuel prices to spike, solar was soaring. Last year the world added 600 terawatt-hours of solar photovoltaic generation, enough to power Canada for a year. It was the first time that a renewable source took the top slot in global supply growth. It was

also the largest single-year increase for any electricity-generation technology, according to the International Energy Agency (IEA). As energy think tank Ember pointed out in April, today’s global solar generation is equal to the entire electricity demand of the European Union. And although solar is still catching up to natural gas and coal, its share of energy generation grew by nearly 19 times from 2014 to 2025.

The Trump administration has been hostile to solar power, cutting billions of dollars in funding for affordable projects and refusing to issue new permits through the Department of the Interior. But thanks in part to tax incentives and investments that predated the administration, solar power still has momentum in the U.S., and the economics remain attractive. In fact, this May solar outpaced coal’s monthly power share in the U.S. for the first time ever.

Here’s why a once niche energy source became a global powerhouse.

Stephanie Pappas is a freelance science journalist based in Denver, Colo.

Solar Is Now the Cheapest Way to Produce Energy in Human History

WHEN SAMPATH STARTED IN THE FIELD, in the early 1990s, the thinking was that no solar panel could ever recapture enough energy from the sun to offset what went into building it. Today a standard solar setup reclaims its production energy in a year or two, and a home system costs roughly $25,000, making it much more practical than what Carter installed at the White House.

The cost-effectiveness of solar energy is partly attributable to technological advances that have driven efficiency up—a state-of-the-art IBM panel used for research in 1977 had an efficiency of 22 percent, which is now achievable with the best home systems (standard systems run at about 20 percent).

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One major advance made in the late 1980s was a type of solar cell called a “passivated emitter and rear cell” (PERC), which included an extra reflective layer on the back of the cell that captured more light to turn into electricity and blocked longer wavelengths that could damage the equipment. Since 2024 another technology, the crystalline-silicon-based tunnel oxide passivated contact cell, has pulled ahead of PERCs because of its advantage in efficiency and easy high-volume production. “Higher efficiency means you need [a smaller] size of the panel, you need less land, less wiring, less racking,” or the mounts for the panels, to generate a given amount of energy, Sampath says. “All of that goes down as the efficiency goes up.”

“Today solar makes the cheapest electricity.”

—WALAJABAD S. SAMPATH COLORADO STATE UNIVERSITY

The plummeting price over the past decade is also a result of advances on the production side: the materials are purer, and the manufacturing process is more precise. Scale has contributed as well. The Chinese solar industry is now highly integrated and efficient, and larger factories can churn out panels at a lower cost per unit than when solar was a niche industry with smaller production lines. The world—led by China—can now produce enough solar modules in one year to generate a collective 1,405 gigawatts of energy.

All of this adds up to cheap electricity. Last year financial advisory firm Lazard published a report showing that the levelized cost of energy—the cost of a project divided by its expected lifetime energy production—for new utility-scale solar was $38 to $78 per megawatt-hour (MWh), compared with $48 to $109 per MWh for new natural gas plants. Indeed, in 2020 the IEA declared that many solar projects were now the cheapest form of energy, not just today but in all of history.

Even in places where government support is weak or has declined, such as the U.S., solar “will continue to be at a competitive price,” says Christopher Namovicz, an analyst at the U.S. Energy Information Administration. Solar has now irrevocably joined coal and natural gas as an inexpensive way to power the world.

Booming Capacity, Shrinking Costs

Just 16 years ago solar power contributed a mere 41,000 megawatts to global energy capacity, and the average utility-scale solar project cost around $5,300 per kilowatt to build. But project costs shrank to $758 per kilowatt by 2023, and solar capacity now stands at about 2.4 million megawatts, making solar cost-competitive with new fossil-fuel projects.

Global Cumulative Capacity of Renewable Energy Sources

Global Installed Costs for Utility-Scale Solar Photovoltaics

Source: International Renewable Energy Agency (capacity data); Renewable Power Generation Costs in 2023 Report, by the International Renewable Energy Agency, Abu Dhabi (cost data)

Graphics by Jen Christiansen

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Two Countries Decided, If Inadvertently, to Make It Happen

Rows of solar panels stand in the Gobi Desert in Wuzhong, China. China has made use of its desert spaces for large solar projects, which it hopes will also combat desertification and dust storms.

ALTHOUGH THE TECHNOLOGY BEHIND solar power has been around since the 1950s, its recent rise can be traced in part to developments in two countries in the early 2000s: Germany and China. At that time, the German Green Party leveraged a power-sharing arrangement to demand subsidies for rooftop solar, says climate writer and environmentalist Bill McKibben. Around the same time, China was massively expanding its manufacturing capacity. The German subsidies helped to create a European market for solar modules and com-

components, and Chinese firms built factories to meet that demand.

After the 2009 economic crisis caused demand for solar panels to drop, the Chinese government stepped in to negotiate minimum import prices with the E.U. to prop up exports and set up national solar targets to jump-start domestic demand. China “had domestic supply but little domestic market, and pollution was emerging as an issue, so it fit multiple priorities,” says Lauri Myllyvirta, co-founder of the nonprofit think tank Center for Research on Energy and

VGG/Getty Images

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Clean Air (CREA). Beijing later forced firms to consolidate, preventing competition that might wipe them all out, which led to a vertically integrated, highly efficient industry, says Michael Davidson, a professor of policy and engineering at the University of California, San Diego. The government also began investing billions in clean-energy research and development.

China's solar industry drove innovations in production, too, so the processing of raw materials became much more consistent—the silicon that goes into commercial panels today is 99.9999999 percent pure, Sampath says. The fact that China makes the vast majority of the world's photovoltaics also gives it an edge, he adds, because large-scale manufacturing pays off in cost. "They put their mind to it, stayed with the improvements," Sampath says. Now China is not only the largest producer, he says, but also the largest market.

As of 2024, China produced more than 93 percent of the world's polycrystalline silicon, nearly 97 percent of its silicon wafers, about 92 percent of its photovoltaic cells and about 86 percent of

its photovoltaic modules, according to data from the China Photovoltaic Industry Association. China now produces 10 percent of its power from solar, Myllyvirta says.

Last year renewables met all of China's new demand, allowing it to stabilize greenhouse gas emissions even as its energy requirements continued to grow. The country produces so much solar equipment, in fact, that it has struggled to find enough buyers, although the recent war in Iran has boosted demand. This past March solar exports reached a record high equivalent to the entire solar capacity of Spain.

China is also investing heavily in the development of next-generation solar cells, Davidson says. He adds that the country will almost certainly be the first to commercialize higher-efficiency tandem solar cells, which often combine silicon with materials called perovskites. In other words, China's solar industry is likely to dominate the world for a long time to come, Davidson says: "The Chinese firms are still miles ahead and are more competitive than any other global firm."

China Is the Solar Patent Leader

Since the early 2000s China has poured billions of dollars into renewable-energy development. One measure of the dominance China has achieved in this sector is the number of patents related to solar power technology it holds, which now outnumber those from all other countries combined (although these statistics are not exhaustive for all patents filed).

Source: EPO PATSTAT 2025 Autumn edition with Climate Change Mitigation Technologies (V02) classification via IRENA (2025) INSPIRE Platform, www.irena.org/INSPIRE (data)

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Solar Lets Countries Skip Fossil-Fuel Dependence Entirely

Robert Otala of Alaki Village in Uganda, about 300 kilometers northeast of the country's capital, checks the solar panels he uses for home purposes.

IN THE VILLAGE OF KIJUMBA IN RURAL UGANDA, a stone's throw from two petroleum pipelines, people have long burned grass or firewood for light. Roughly half of Ugandans still lack electricity. Yet electric lights now cast a glow on some homes in Kijumba, where a campaign called REPower Afrika is teaching local women to install solar systems themselves.

REPower started in 2024 to bring solar power to villages where people had been displaced by the construction of a fossil-fuel pipeline. Solar is "very easy to decentralize," says Rukiya Khamis,

East Africa program manager for the climate-justice organization 350.org. "Everyone can use it. [You] can put it on top of your roof, and you're set. It's like a plug-and-play situation."

Across Africa, nations installed 4.5 new gigawatts of solar capacity in 2025, a 54 percent increase from 2024—the continent's largest solar-growth year so far. "Africa's solar revolution is here," says Sonia Dunlop, CEO of the Global Solar Council (GSC), a trade group representing the solar industry. According to the GSC, centralized, utility-scale projects explain

ISAAC KASAMANI/Stranger/Getty Images

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The China-to-Africa Solar Pipeline

Solar power has been rapidly expanding in Africa in recent years. It can be difficult to track installations outside of utility-scale projects, but exports of panels from China (which accounts for 80 percent of global solar manufacturing) shed light on how much uptake has increased in just the past two years.

an average of only 15 percent of solar-panel imports over the past four years, indicating that small, rooftop panels make up a big chunk of the solar growth.

That kind of independence is appealing not only from an energy-security standpoint, Khamis says, but also from a justice one: small-scale solar doesn't have major environmental impacts or displace people from their homes. And the energy starts flowing immediately. "If I am in a remote village in Africa, it's going to take a decade before anyone is going to build a power line to my village," says Daan Walter, an Ember research principal. "But I can buy a solar panel, like, tomorrow and get it in a month."

Price is a driving factor in larger projects in developing economies, too, Walter says. Solar has long carried an up-front cost that many individuals and businesses can't afford, especially in emerging economies where borrowing costs can be higher. To make a project such as a solar-powered small factory feasible, borrowers need to pay back their costs in two to three years, Walter says. When new coal and gas were cheaper than new solar, solar took too long to pay out, and

fossil-fuel sources were still the most affordable option in developing economies. But inexpensive systems manufactured in China are competitive with the cost of new coal and gas, so solar "no longer forces consumers who have high borrowing costs to go for the fossil option because it's the only thing they can afford in the short term," Walter says.

Increases in the cost of living caused by the closure of the Strait of Hormuz are further making solar panels—as well as electric boda bodas, the motorcycle taxis that ply East Africa's city streets—more attractive to everyday people. (On the other hand, they are also pushing some African governments to develop domestic fossil-fuel resources to reduce their reliance on imports, Khamis says.)

The challenge now is securing the financing and policy support to bring solar to more homes, says Edwin Mumbere, director of the Center for Citizens Conserving Environment and Management in Uganda. "Communities are increasingly recognizing that renewable energy delivers real development benefits today," he says, "rather than promises tied to large-scale fossil-fuel projects."

Source: General Administration of Customs of the People's Republic of China (GACC), InfoLink Consulting, Ministry of Industry and Information Technology (MIT) via Ember's China Solar Export Methodology (data)

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Fossil Fuels Are Subject to Scarcity; Sunlight Isn't

Solar panels sit atop a hill in Shanghai, China. The amount of solar energy generated today could power the entire European Union.

FIVE YEARS AGO THE ROOFTOPS OF LAHORE were all a largely indistinguishable brown. Today aerial views of some neighborhoods in this city, the second-largest in Pakistan, show a sea of black grids: rooftop solar, house after house of it.

This change came about because the people of Pakistan were responding to a crisis: Russia's 2022 invasion of Ukraine, which led to U.S. and European sanctions on Russian oil.

Between 2022 and 2025, some Pakistanis invested in home solar systems that took advantage of favorable payment incentives, and the country went from generating 7.7 terawatt-hours of elec-

electricity with solar per year to 36.6 terawatt-hours. As of last year, solar provided more than 20 percent of Pakistan's electricity, according to Ember. In nearby Bangladesh, in contrast, less than 2 percent of electricity comes from solar.

A 2026 analysis by CREA found that since 2018, Pakistan's solar revolution has saved it from spending $12 billion on oil and gas imports; the country could save more than half as much again just this year by avoiding the high costs of fossil fuels caused by the U.S.-Iran conflict. "Sunlight travels 93 million miles to reach Earth, but none of those miles are in the Strait of Hormuz," McKibben says. Spain, too, has benefited

Yazusheng/Getty Images

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from a shift to solar and other renewables: Ambitious investments in recent years have shielded the country from price increases caused by the Iran conflict, a June report from Ember shows. In March the country's power prices averaged just one third of those in Italy, where fossil fuels make up a greater share of the power mix.

Like Pakistan, Cuba is experiencing a crisis-driven solar revolution: a U.S. oil embargo has the island's residents cooking with wood fires and weathering repeated blackouts, so the country has turned to China. Last year Cuba imported enough Chinese solar panels and cells to generate 1,308.8 megawatts of energy, compared with 19.4 megawatts in 2023, according to Ember. It may be one of the fastest solar transitions in history. For an island nation like Cuba, decentralized solar also may be the only power option after a hurricane: when Hurricane Melissa flooded Cuba in 2025, many people went weeks without power or with only intermittent access to the grid.

Solar isn't necessarily immune to geopolitical shocks, though. China manufactures the lion's

share of the world's photovoltaics and batteries and could refuse to export them to certain countries in the event of conflict. Many nations also want to reduce their reliance on China even in the absence of conflict. India and some countries

"Sunlight travels 93 million miles to reach Earth, but none of those miles are in the Strait of Hormuz."

—BILL MCKIBBEN CLIMATE WRITER

in Southeast Asia are increasingly manufacturing their own panels, although China still maintains control of raw materials such as polycrystalline silicon.

But if China were to restrict exports, it would affect only new growth, Walter says. "Once you install it," he says, "no one can tell you those sun-rays are not allowed to hit your roof."

Pakistan's Solar Revolution

Whereas the U.S. has enacted tariffs or other measures to curb the importation of inexpensive Chinese solar panels, Pakistan's government took the opposite approach. Its lack of solar tariffs and duties allowed for a grassroots revolution when oil and gas prices spiked after the Russian invasion of Ukraine in 2022, making it easier and more economical for Pakistanis to add solar power to their homes and businesses.

Source: U.S. Energy Information Administration via Ember Electricity Data Explorer, ember-energy.org (data)

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ENERGY STORAGE

Hard Cell

Solid-state batteries have promised better electric cars for decades. In an industry China dominates, two American companies are making rival bets on how to finally build them

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Inside Factorial Energy's Massachusetts R&D lab, researchers are developing solid-state batteries designed to be produced on the industry's existing lithium-ion manufacturing equipment.

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FOR YEARS NOW TIM HOLME HAS WATCHED THE SAME DRAMA REPEAT ITSELF roughly once a week. A headline arrives: some laboratory somewhere has cracked the problem, invented the battery of the future, solved in a paper what industry has chased for decades. “And approximately zero of those have come true,” says Holme, co-founder and chief technology officer of QuantumScape, a San Jose, Calif., company that has spent 15 years chasing the most promised and least delivered idea in energy storage and run up an accumulated deficit of more than $3.9 billion: the solid-state battery.

The most recent cautionary tale was Donut Lab, a Finnish start-up that drew breathless coverage after unveiling what it said was a high-performance solid-state cell with about double the energy density of typical lithium-ion batteries and without rare-earth minerals or fire risk. It didn’t release data backing its boldest claims. In June, battery researcher and YouTuber Ryan Hughes and outside experts presented evidence that Donut’s cell was high-performance lithium ion—with liquid inside. “People who’ve spent a long time in the battery industry have a healthy dose of skepticism,” Holme says.

But amid the noise, the race is speeding up. Announcements are tumbling out of China, Japan, South Korea and the U.S. as battery makers move from lab to factory. Toyota,

EV, cells, up to 301 watt-hours per kilogram (Wh/kg) for QuantumScape’s cell and 391 Wh/kg for Factorial’s—gains that could quiet range anxiety. By volume, QuantumScape’s cell packs the slightly bigger punch: 844 watt-hours per liter (Wh/L) versus 748.

QuantumScape is building a new battery chemistry that demands a new manufacturing process; Factorial is designing a cell that can run on much of the industry’s existing equipment. Their bet is similar: rather than compete with China at its lithium-ion game, skip past it. The biggest test is still electric cars. But amid cooling EV sales and supply-chain concerns, both companies are already looking beyond them.

The underlying technology was largely pioneered in the U.S. M. Stanley Whittingham developed the first functional rechargeable lithium battery in the 1970s while doing research at Exxon; John Goodenough, whose foundational work on lithium-ion cells won him a share of the 2019 Nobel Prize in Chemistry, spent much of his career at the University of Texas at Austin. The technology was commercialized by Sony in Japan for its Handycam, then mass-produced in Korea and, increasingly, China. The battery that now powers most of our EVs and electric devices, notes Ilias Belharouak, section head for electrification at Oak Ridge National Laboratory, “was invented in the United States—and unfortunately we lost sight of manufacturability for quite a bit.”

WHO’S WINNING THE RACE CAN BE HARD TO KNOW, partly because the definition of “solid state” isn’t itself so solid. The

term describes an architecture, not a set of chemistries—one that replaces most or all of the liquid electrolyte with a solid. In a conventional lithium-ion battery, the liquid electrolyte shuttles lithium ions back and forth—to the anode as you charge your phone and back to the cathode as you use it. That liquid is highly conductive but flammable, and the fires it feeds burn hot and toxic.

Solid electrolytes replace most if not all of that

Who’s winning the race can be hard to know, partly because the definition of “solid state” isn’t so solid.

which holds the most corporate patents, says solid-state cells will finally start appearing in its cars within two years. Chinese companies, which already make more than 80 percent of the world’s lithium-ion batteries, have begun shipping semi-solid-state cells.

In the U.S., two front-runners are taking alternative paths to the same goal: Volkswagen-backed QuantumScape, which now produces its ceramic-based cells on a pilot line in Silicon Valley, and Factorial Energy, a Billerica, Mass., company led by founder and CEO Siyu Huang, whose polymer cells are being tested in vehicles by Mercedes-Benz and Stellantis. The companies claim energy densities well beyond today’s typical electric vehicle, or

Alex Pasternack is founding editor of Motherboard, Vice Media’s tech-culture website, and a contributing editor at Fast Company, where he covers technology and science.

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flammable liquid while also opening up the next frontier: swapping out the graphite anode with pure lithium metal. Because graphite stores only one lithium ion for every six carbon atoms, typical rechargeable batteries top out at an energy density of around 250 Wh/kg. Lithium metal needs no host at all, boosting the anode's storage capacity around 10-fold.

The challenge with pure lithium is that it's highly reactive. Hence the solid electrolyte. As it allows ions to pass through, the solid helps physically block dendrites, the branchlike lithium deposits that caused early lithium-metal batteries to short-circuit and catch fire. Ditching graphite saves space and weight, too, and removes a key ingredient whose supply chain China dominates. "The best lithium cell chemistry can be is using pure metallic lithium," says Jeff Sakamoto, a materials scientist at the University of California, Santa Barbara, who worked on batteries for NASA's 2003 Mars rovers and now directs MUSIC, a U.S. Department of Energy research center focused on ion transport. The solid electrolyte, he says, is what physically—and ideally thermodynamically—stabilizes a lithium-metal electrode. A battery "can go forever if it's thermodynamically stable."

But "solid state" is also, to some degree, a marketing term. "There are people introducing terms like 'quasi-solid state,' 'hybrid solid state,' 'condensed state,'" Holme says, "all kinds of terms that are never defined." In practice, most solid-state batteries contain some liquid—usually in the cathode region—to help with conductivity, making them semisolid at best. All-solid-state batteries are the goal, but in the meantime, the real question, Holme argues, is what the architecture unlocks: higher energy density, faster charge, longer range, better safety and, ultimately, lower cost.

Central to battery design is the choice of electrolyte—typically a ceramic, a sulfide, a polymer or some combination. A polymer can be easier to manufacture but comes with conductivity challenges; a sulfide is more conductive but requires careful dry-room manufacturing; a ceramic oxide is the hardest to process at thin dimensions and high volumes but, Holme wagers, the most rewarding. "The bet we made was to pick the material that has the best material properties," he says. "But it's brittle and very, very challenging to make."

QuantumScape has dispensed with two of the four components of a typical battery. Its ceramic electrolyte supports an "anode-free" architecture in which the lithium-metal anode forms on the first charge rather than being preloaded. Factorial has gone with the grain of existing manufacturing. Its FEST (Factorial Electrolyte System Technology) electrolyte—a polymer with an ultrathin lithium-metal layer at the anode—is designed for about 80 percent of existing lithium-ion equipment.

Both companies insist they have moved from science to engineering. But some in the research community remain skeptical. "There is now a significant deviation between what's possible and where the technology really is," Sakamoto says. He and his MUSIC colleagues use operando microscopy to observe batteries working, mapping the tiny

The Solid-State Solution

For 15 years the solid-state battery has been the field's elusive prize: a lighter, safer cell that could end EV range anxiety and electrify the skies. Here is how ditching flammable liquids and bulky graphite crams far more energy into a much smaller, lighter package.

Proven Power: The Lithium-Ion Battery

Charging pulls lithium ions from the cathode through a liquid electrolyte into a bulky graphite anode; discharging sends them back to deliver power. The liquid conducts well but is flammable, and the heavy graphite caps how much energy the cell holds.

Still Charging: The Solid-State Battery

Swapping the liquid for a solid separator helps resist the short circuits that spark those fires. With that sturdier barrier in place, designers can ditch the graphite for an anode of pure lithium, which carries far more charge for its weight.

Graphic by Ben Gilliland

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defects that accumulate in the electrolyte as it charges and recharges. The gap between public expectations and the technology's true maturity, he and others worry, risks draining public confidence if commercial milestones slip once more.

The most fundamental challenge is the interface—the boundary between the solid electrolyte and the electrodes, where dendrites and voids take root. Moving ions through a solid is inherently harder than through a liquid. "It's like humans," Belharouak says. Imagine migrating across a vast landscape. If there's a river, "you can swim." But if there's a mountain, "you have to climb it somehow."

Tiny voids, left behind as lithium strips from and redeposits onto the electrodes, become roadblocks and bottlenecks. As ions take detours, lithium piles up. It is as soft as taffy, but as it forms at the interface, the metal can "frack" through even hard ceramic like tree roots through concrete.

Expanding and contracting with each cycle, the electrodes also tend to lose contact with the electrolyte, creating gaps. Maintaining contact often requires external mechanical force. But too much can crack the brittle electrolyte or force lithium metal through it, causing a short circuit. Both companies have had to design battery packs with mechanisms that "breathe" with the cells, adding weight and complexity.

Holme is mostly mum about how QuantumScape tamed its interface problem. He says the company used density functional theory—quantum-chemical simulations—to develop a ceramic that is compatible with lithium at the interface, without requiring an extra lithium foil that is costly and hard to process. "That was a real breakthrough that, to my knowledge, hasn't been solved elsewhere," he says. Then comes the bigger challenge: "You have to figure out how to actually make—at high scale, at high quality—the material that you've simulated in silico."

MANUFACTURING AT AUTOMOTIVE SCALE—a leap from 1,000 cells a day on a pilot line to 100,000 or more in a gigafactory—amplifies every challenge. Quality and yield requirements are exacting; a ceramic defect invisible at a small scale becomes a failure mode at volume. Since January 2025, at least 14 Western battery start-ups have gone under trying to make that leap.

QuantumScape is trying to avoid that fate with its Eagle

QuantumScape's thin, flexible ceramic separator is designed to let lithium ions pass while helping to prevent short circuits.

Line, an automated pilot facility it unveiled in February, and Cobra, a proprietary heat-treatment process for "baking" the ceramic electrolyte that cuts what had taken hours to minutes. "We got lucky," Holme says. "It wasn't guaranteed that nature provides us a rapid processing window where we can still achieve the best materials properties." Like Factorial, the company has integrated artificial intelligence for quality control, and it has enlisted Corning and Murata as manufacturing partners.

Just don't call it a battery maker. After reworking its business model in 2024, QuantumScape is now a technology licensor with a vision of doing for batteries something akin to what Nvidia did for chips: develop the architecture, let partners manufacture at scale. Alongside a partnership with Honda, its primary path to gigawatt-hour production runs through PowerCo, Volkswagen's battery subsidiary, with up to $131 million in milestone-gated funding over the next two years.

Factorial's deals—with Mercedes, Stellantis, Hyundai, Kia—are further down the road. Last year a Mercedes EQS

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running its cells drove about 1,205 kilometers, from Stuttgart, Germany, to Malmö, Sweden, without stopping. This past June, Stellantis began road-testing them in a Dodge Charger Daytona, the technology's North American debut.

But the road to EV adoption is long and twisty. A June report from the International Energy Agency found that close to 30 percent of all new cars sold globally last year were EVs. In the U.S., though, the market's lost its juice. Since the Trump administration cut carbon mandates and EV incentives in 2025, EV sales have slowed dramatically, leading several of QuantumScape's and Factorial's partners to cancel models and factory plans.

THE COOLING EV MARKET has given Holme and Huang reason to look toward AI data centers, robotics and aviation—electric vertical take-off and landing aircraft and military drones included. QuantumScape has added a veteran of defense giant Raytheon to its board and hired the former chief scientist of the U.S. Air Force as an adviser. Factorial is expanding a fabrication line for aerospace applications and recently announced another investor: In-Q-Tel, the U.S. Central Intelligence Agency's venture arm. "Everyone wants drones, drones, drones," says Halle Cheeseman, a former program director at ARPA-E. He takes the longer view: "We may have lost the battle for EV batteries, but the race to electrify the skies is just beginning."

Drones require what solid-state batteries promise: high energy density, low weight, reliable performance across temperature extremes. They're also more forgiving than cars. EV drivers demand fast charging; drone operators typically swap batteries or use them once, which makes dendrites easier to manage. Smaller sizes and lower volumes also ease the strain on supply chains and manufacturing, and certification standards make it easier to integrate a battery into a drone than into an aircraft. Defense buyers also tend to be less price-sensitive.

The drone demand has "fundamentally changed the arc of this industry," says Venkat Viswanathan, a University of Michigan engineering professor who studies next-generation batteries for aerospace. With continued battery advances, he thinks the electrification of most shorter-duration flights in the next decades is "completely within reach."

The battlefield, remade by robots in Ukraine and elsewhere, is already there. The Pentagon is now aiming to produce thousands of U.S.-made drones per month, but, Huang notes, as of last year more than 80 percent of drone batteries were imported from China. Beijing has since restricted exports of high-energy-density drone batteries, and the U.S. has moved to ban Chinese-made components from American defense equipment, placing BYD, the world's second-largest battery maker, on a blacklist in June. Huang sees particular value in powering fast interceptors. If your car goes twice as far as the next guy's, cool. "If your drone is running [with] twice the range of your enemies', it's a complete game changer." Advanced battery manufacturing, she says, "is an asset we cannot afford to lose."

The bigger prize remains the EV market, and reaching it will require partnerships as global as the battery supply chain itself. Huang, who grew up in China, studied in Sweden, earned her Ph.D. at Cornell and built her company in Massachusetts, has assembled global tie-ups accordingly. Battery innovation, she says, "cannot be achieved by a single company."

Steadier policy would help, too. "My advice to any policy-maker is to remove barriers—end tariffs, offer tax credits, support immigration for talent," says Shirley Meng, a materials scientist who recently left the DOE research hub she oversaw at the University of Chicago for a senior post at Nanyang Technological University in Singapore, after saying U.S. policy shifts had helped push her overseas. For a country trying to rebuild its battery industry, her move carries its own warning. "If the U.S. remains open to fair global partnerships, either in R&D or in trade," she says, "then it is possible that the battery field will come out stronger in a few years."

Despite the supply-chain fears, the American industry may depend, at least for now, on Chinese expertise. Cheeseman calls it the "cuckoo" approach: enticing manufacturers—including BYD—to build U.S. factories and nurture domestic manufacturing science so we can learn how to make these things. Chinese battery behemoth CATL typically runs more than 3,000 sensors on a production line. "I'm not sure if we would know where to place 300," Cheeseman says.

"We may have lost the battle for EV batteries, but the race to electrify the skies is just beginning."

—HALLE CHEESEMAN BATTERY SCIENTIST

As new factories ramp up, prototypes will need to keep proving themselves. The safety benefits are still fuzzy; engineers need more rigorous abuse testing on large-format cells. Cost is unproven, too: Cheeseman estimates that early solid-state batteries cost two to three times as much as liquid-electrolyte cells.

And the target keeps moving. EV makers are now prioritizing cost and materials over performance, prompting an industry-wide shift from nickel manganese cobalt cells to lower-energy but cheaper lithium iron phosphate. And for demanding applications such as drones, silicon-anode lithium-ion batteries can already reach 400 Wh/kg. "If everybody is like bees around a honeypot at 400," Cheeseman says, "you have to be shooting for 600 or 800 or 1,000."

But after decades of promises, solid state is no longer a question of if. "I believe it's inevitable," Cheeseman says, citing simplicity and safety gains. His best guess is that solid-state cells will eventually reach mainstream EVs by the early 2030s. Just don't ask him to bet on it. ●

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CLEAN TECHNOLOGY

BIG BETS IN GREEN TECH

Bold projects designed to solve clean energy’s lingering challenges

TWO DECADES AGO RENEWABLE ENERGY WAS A BIT PLAYER on the world stage. Today renewables account for nearly half of all global electrical capacity, according to the International Renewable Energy Agency, and there’s a lot more in the pipeline. It’s a stunning surge showing that the renewable revolution appears unstoppable. Clean energy still faces challenges, though. To meet them, countries and companies are taking some big swings to push this revolution into a new phase—with ambitious projects that may or may not pan out.

One of the most significant problems is that solar and wind are intermittent, and the lithium-ion batteries currently available can’t store enough energy from renewables to reliably meet demand. To squeeze the most juice out of solar and wind, we need longer-term storage, leading some in the industry—notably in China—to reach for a technology that has been shelved for decades. Chinese companies are also pushing the limits on how large and how far offshore turbines can be so they

can take advantage of steadier, stronger winds. Other ventures are trying to broaden the appeal of geothermal energy and crack the code on tidal power, one of the biggest untapped sources of power on the planet. Here are some of the most audacious of these projects. —Andrea Thompson

Andrea Thompson is Scientific American’s senior editor for earth and environment.

An aerial view of the Guoxin Salt Cave Compressed Air Energy Storage Project in Huai'an City, China

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Geothermal Energy for (Almost) Anywhere

Pulling heat from the earth without perfect geology

NAME OF PROJECT: Fervo Energy's Cape Station

LOCATION: Utah

NAME OF TECHNOLOGY: Enhanced geothermal systems (EGS)

POWER GENERATION: A projected 100 megawatts by early 2027, with 500 megawatts in total under construction

HOW IT WORKS: Fervo drills down and then sideways, creating a network of long fractures in rock as deep as almost 2,750 meters (although future depths may vary); it then pushes water through these cracks to draw heat out of the earth. The large network of fissures exposes much more water to much more hot rock than single-pipe geothermal setups do, increasing efficiency. To execute the design, Fervo has translated oil and gas fracking's pressurized fluid injections from softer sedimentary shale rock to hotter, harder volcanic rock. (Experts say seismic monitoring is advanced enough that work can be paused if risks of quakes above magnitudes people can feel rise too high.) At a demonstration facility called Project Red, Fervo connected test wells to a preexisting power plant, where it has been generating three megawatts of power since late 2023.

WHY IT'S NEEDED: Unlike solar and wind, geothermal energy can be used 24/7. But to be economical, traditional geothermal requires perfect geology: hot rock that water naturally passes through and a reliably recharged water source to keep the heat flowing. This necessity has limited its use to a handful of spots on Earth. By adding fractures, EGS creates more places where geothermal is economically feasible. Other companies have targeted different geothermal strategies, and geothermal has been met with a wave of enthusiasm from the U.S. government.

WHAT THE EXPERTS SAY: Jefferson Tester, a Cornell University engineering professor, says he's excited by the work Fervo is doing but worries that the company might have promised its funders too much too soon. "You've got to prove that this thing actually works for a sustainable period of production," he says. "The proof will come only with what you find out in the field." (Fervo Energy did not reply to interview requests.)

—Meghan Bartels

Meghan Bartels is a freelance science journalist based in New York City.

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The Power of the Tides

Predictable motions of the ocean can provide reliable, renewable energy

NAME OF PROJECT: MeyGen

LOCATION: Scotland

NAME OF TECHNOLOGY: Tidal stream energy

POWER GENERATION: Six megawatts (increasing to 65 megawatts by 2031)

HOW IT WORKS: Since 2016, MeyGen, located between the Scottish mainland and the Orkney Islands, has been the world's largest tidal stream energy project. It exploits the fact that the tides that ebb and flow along our planet's coastlines carry tremendous energy, with a harvestable potential estimated at 1,200 terawatt-hours per year, more than a quarter of annual power generation in the U.S. That energy can be harnessed in much the same way that wind farms harness moving air. "In very simple layman's terms, you're putting a wind turbine underwater," says Drew Blaxland, CEO of Proteus Marine Renewables, which developed MeyGen's four 1.5-megawatt turbines. The turbine blades spin with each incoming and outgoing tide, capturing the ocean's kinetic energy to power a generator that produces electricity.

WHY IT'S NEEDED: Unlike other renewable energy sources, tides are highly predictable. "We can tell at any point in time, any day, exactly how much energy we're producing," Blaxland says, "which you can't do with wind or solar." Tides are as brutal as they are reliable, though; saltwater corrosion, ocean debris and the sheer force of rushing water often cause turbines to fail. But one of MeyGen's turbines has reached a major milestone in performance, running for more than seven years without unplanned maintenance. Built on massive foundations and equipped with blades that adjust to align with the tide, the turbines are engineered to withstand extreme, fast-flowing marine currents. MeyGen plans to add 20 turbines by 2031, boosting its capacity to

65 megawatts. According to Ampeak Energy, which owns the project, the site could ultimately produce nearly 400 megawatts.

WHAT THE EXPERTS SAY: Although tidal energy will always be limited by geography and is unlikely to catch up to wind and solar anytime soon, it could account for 10 percent of the U.K.'s energy needs, Blaxland says. "They've had a great track record of long-term generation from multiple large machines," says Brian Polagye, a mechanical engineer at the University of Washington who specializes in marine energy. "The hyperbole is well deserved." —Cody Cottier

Cody Cottier is a freelance journalist based in Fort Collins, Colo., who frequently covers evolution and the environment.

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Energy from Thin Air

With the need for long-term energy storage rising, a technology from the 1970s steps back into the limelight

NAME OF PROJECT: Huai'an Salt Cavern

LOCATION: China

NAME OF TECHNOLOGY: Compressed air energy storage

POWER GENERATION: 600 megawatts

HOW IT WORKS: When demand for electricity is low, surplus energy generated by solar and wind farms can be used to power compressors that squeeze air to high pressures and pump it into underground caverns. Then, when demand rises, the pressurized air can be released to generate power. This technology, known as compressed air energy storage (CAES), dates to the late 1970s but “never really made it into the mainstream,” says Paul Denholm, a senior research fellow at the National Laboratory of the Rockies.

In recent years, though, China has commissioned several CAES plants, including the world’s largest: the Huai’an Salt Cavern project, expected to power some 600,000 homes. Salt caverns are especially well suited to this purpose: rock salt is more or less impermeable and deforms to self-seal any fractures that may form, preventing the stored air from leaking out.

There is a potential problem with this type of energy storage: compressed air cools as it reexpands, meaning it has to be warmed before it can spin a turbine efficiently. This project hopes to solve that issue by storing thermal energy in molten salt and water to reheat the air.

WHY IT’S NEEDED: The success of renewables depends on the ability to store energy for times when the sun isn’t shining and the wind isn’t blowing. The energy-storage market is currently

dominated by lithium-ion batteries, but Denholm says they’re economically viable only for storage durations of a few hours. He argues that CAES, though expensive up front, is easier to scale and can store and supply energy for a day or longer, depending on the size of the cavern. “Air is free,” Denholm says, “and a hole in the ground can potentially be cheap.”

WHAT THE EXPERTS SAY: Although the technology is mature, according to Pirouz Kavehpour, a mechanical engineer at the University of California, Los Angeles, geology limits its potential. Outside of China there are only two major CAES plants in the world—in Germany and in Alabama—and both rely on salt caverns. But a recently permitted project in California would use hard-rock caverns, which could expand possibilities for the technology. “It’s been 30 years since we built one of these things in this country,” Denholm says, but he remains cautiously optimistic.

—Cody Cottier

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Deep-Sea Offshore Wind

The world's largest single floating wind turbine can withstand supertyphoons

NAME OF PROJECT: Sanxia Linghang Hao (Three Gorges Pilot) platform

LOCATION: China

NAME OF TECHNOLOGY: Floating offshore wind turbine

POWER GENERATION: 16 megawatts

HOW IT WORKS: China's Sanxia Linghang Hao offshore wind turbine, installed in May, is the largest single floating turbine in the world. It floats some 70 kilometers offshore in more than 50 meters of water atop a partly submerged platform, rather than a piling embedded in the seafloor as most offshore turbines are, which would be too expensive in such deep waters. In its mooring system, polyester cables and anchor chains act as springs that help to absorb the force of waves and wind. The turbine's blades, with a tip height of 270 meters, are built to withstand winds up to 264 kilometers per hour, according to Three Gorges Corporation, faster than those produced by the strongest typhoons. (The company did not reply to interview requests.)

WHY IT'S NEEDED: Offshore winds are stronger and steadier than near-shore winds, so turbines far from coasts can deliver more power with better reliability than near-shore turbines. Perhaps 80 percent of potential offshore wind energy is in deep waters that require floating, anchored turbines. Far offshore, they also avoid the community complaints about visibility that plague near-shore wind farms. With the U.S. halting leases and permits for offshore wind facilities, the action on the technology has moved to Asia and Europe: Italy alone has about 90 far-offshore wind facilities under environmental review.

WHAT THE EXPERTS SAY: These offshore floating wind facilities are technologically mature and have "crystal clear" low-cost energy potential, says marine scientist Roberto Danovaro of Italy's Marche Polytechnic University. The only real issue is their ecological impact, he says. "If adequately assessed, located and mitigated, their ecological and environmental impact can be negligible, and their benefits can be huge," Danovaro says. —Dan Vergano

Dan Vergano is a freelance science journalist based in Washington, D.C.

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MIND MATTERS EDITED BY ALLISON PARSHALL

Building Cognitive Endurance in an Age of Distraction

The ability to run “mental marathons” is a skill children can learn through simple but dedicated practice BY HEATHER SCHOFIELD AND SUPREET KAUR

YOU’RE HALFWAY THROUGH a challenging exam when you notice your focus starting to slip. The words on the page blur together, and you find your mind wandering to what you’re going to have for dinner that night. Does that sound familiar? This mental fatigue isn’t a character flaw—it’s a universal human experience that reveals something essential about how people’s minds function.

We are behavioral scientists who study how economic circumstances shape human cognition and behavior. In a recent study of more than 1,600 children, we found that the ability to sustain mental effort over time—or “cognitive endurance”—functions much like physical stamina. Almost universally, the longer people spend on a task, the worse they perform on it. But just as athletes can train to run longer distances, kids are able to strengthen their capacity for sustained thinking through simple but dedicated practice, allowing them to continue to perform at a higher level for longer stretches of time. In an era of

social media and short-form content designed to minimize mental friction and demand minimal effort, the capacity for sustained thinking may be getting less practice than ever—making it more important to understand how it develops and how it can be strengthened.

A few years ago, while we were analyzing standardized test results from around the world with our colleagues Christina Brown of the University of Chicago and Geeta Kingdon of University College London, we noticed a remarkably consistent pattern: students performed worse on questions that appeared later in exams, even after we accounted for the difficulty of the questions.

This performance decline was much steeper among students from disadvantaged backgrounds. Children in poor countries showed three times the rate of performance decline compared with those in wealthy nations. This result could be because disadvantaged children get fewer opportunities to train their focus. Cognitive skills generally improve with deliberate, focused and progressively more challenging training. And when looking at the activities the kids spent time on in school, we found that richer students were more

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likely to engage in independent focused practice by doing activities such as working through problems on their own, reading silently or concentrating on individual tasks. In contrast, students at disadvantaged schools were more likely to spend much of the day in passive activities such as listening to lectures, practicing rote memorization or copying from the board.

These patterns suggested that the school experience itself—particularly the amount of sustained mental effort the school day requires—could be molding students' cognitive endurance.

To test whether cognitive endurance could be improved, we designed an experiment with 1,636 elementary school students in India. Students were randomly assigned to one of three groups during their study hall periods. Those in the control group continued with their usual routine—copying a few math problems from the board before spending most of the class time as they liked, resulting in minimal sustained mental effort.

In contrast, the two "treatment" groups engaged in 20 minutes of continuous cognitive practice during these study hall periods. The members of one group solved math problems on tablets in a simple application that adapted to their ability level but didn't have any gamified features to hold their attention. Such a task gave these students focused practice in a specific subject area. But it was also possible that simply practicing concentration, regardless of the task, could increase mental endurance.

To test that, we had the final group complete cognitively demanding games such as mazes and shape puzzles called tangrams that contained no academic content. These app-based games also adapted their difficulty based on performance, which kept them challenging for the students.

The results were striking. Both treatment groups showed significant improvements in their ability to maintain performance throughout tests, regardless of the type of training they had received. When students took listening comprehension, reasoning or math as-

the intervention required only 20 to 50 minutes per week over six months.

The implications of these findings extend beyond education. We also found evidence that disadvantaged groups, whose members are likely to have received less practice in sustaining focus,

The act of concentrating mattered more than what the students were concentrating on.

sessments, the performance of those who had received cognitive practice declined 22 percent more slowly than that of students in the control group. It didn't matter whether the students had practiced with academic content or nonacademic games—the benefits were nearly identical for both groups. This outcome suggests that the act of concentrating mattered more than what the students were concentrating on.

The students who practiced concentrating also improved on standardized tests of sustained attention, including those that tested their reaction times or their ability to spot target symbols hidden in a grid. They also showed better focus in the classroom, according to ratings from their teachers—for example, they fidgeted less and followed through on multistep instructions. This exercise seems to have translated to better grades across a wide range of subjects, too—students who received either form of cognitive practice earned grades that were about 0.09 standard deviations higher in Hindi, English and math than those who didn't.

In comparison, this effect was roughly half to three quarters as large as that of assigning a student to a class with seven fewer students per teacher. These were substantial improvements, considering

show more rapid declines in performance over time in other contexts. For example, we found that data-entry workers made more errors as their shifts progressed and that less educated workers showed much steeper declines. Even voting behavior reflects these patterns: studies have found that when a given proposition appears later in the ballot in California, voters are more likely to choose the default option. We showed that these declines are especially pronounced in lower-income neighborhoods.

These findings suggest that differences in cognitive endurance that start from inequalities in the education system might contribute to broader inequity later in life. But by showing that mental stamina can be improved, the results also point to the kinds of programs that can begin to level the playing field for less advantaged students.

We still need to do more research to identify the most effective training methods. For now it seems a diversity of activities such as doing challenging puzzles, learning a musical instrument or playing certain video games might help build cognitive endurance, as long as they require sustained, deliberate and proactive mental effort. This training could benefit anyone who may be exposed to fewer periods of sustained focus as the world shifts toward greater engagement with endless scrolls of bite-size social media.

The message is hopeful: your capacity for cognitive endurance isn't fixed. Like physical fitness, it can be built up through practice. ●

Heather Schofield is an economist at Cornell University studying development, health and behavioral economics. She co-founded the Behavioral Development Lab in Chennai, India, where much of her research is based.

Supreet Kaur is an associate professor of economics at the University of California, Berkeley. She is co-founder of the Psychology and Economics of Poverty Initiative, an interdisciplinary lab that develops new approaches to antipoverty policies and programs, at U.C. Berkeley's Center for Effective Global Action.

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THE SCIENCE OF WAR

Dome's Long Shot

Golden Dome calls for missile interceptors in orbit to defend the U.S. Companies are already lining up to build a system that doesn't yet exist BY SARAH SCOLES

SOMEWHERE IN THE WORLD, a missile's engines ignite, and it lifts toward the sky. Somewhere above the world, satellites sense its launch. They, in turn, send out an alert, along with information about the missile's path. Almost instantly an interceptor in orbit—essentially a big bullet—gets its own message: fire toward the missile. Ideally the space-based weapon strikes the missile early in flight, before the rocket can release a warhead or decoys, turning a threat to the U.S. into a bunch of debris.

Or at least that's the idea behind space-based interceptors, the most audacious part of President Donald Trump's Golden Dome missile-defense initiative to shield the U.S. from airborne attacks.

Much of the technology that could feed into Golden Dome already exists in pieces or inside other defense programs—it just ("just") needs to be linked together and scaled until it can protect the entire country around the clock. Space-based interceptors, though, don't yet exist as an operational system. And there isn't a firm plan for what they will look like—or, for that matter, what Golden Dome as a whole will look like. As Todd Harrison, a senior fellow at the American Enterprise

Sarah Scoles is a Colorado-based science journalist and a contributing editor at Scientific American. Her newest book is Countdown: The Blinding Future of Nuclear Weapons (Bold Type Books, 2024).

Institute, puts it, "There is no architecture," at least not one that's been released publicly. That fuzziness, however, isn't stopping American companies from preparing to make orbital interceptors in the hopes of cashing in on the most speculative and, by some accounts, expensive part of the defense project.

One such hopeful is Voyager Technologies. Voyager got its start working on NASA projects related to the moon and space stations. "About two years ago we had started doing some investments in the defense and national security side of the business," says Matt Magaña, Voyager's president of space, defense and national security. Those investments involved, in part, buying up other companies that had already developed space tech that could prove useful for Golden Dome—including radiation-hardened electronics, electric propulsion systems that allow satellites to make precise movements, and solid-fuel rocket systems that might let interceptors maneuver quickly in pursuit of a missile.

When Voyager started that shopping spree, Golden Dome hadn't yet been announced. But the trajectory worked out, in part because defense is defense: The company was already working, for instance, on the next generation of ground-based interceptors—a replacement for a system that already exists. Its inner workings are not that different from the orbiting-interceptor plans, Harrison says: find a missile, figure out where it's going, figure out where you can intersect with it—boom.

On top of that, defending the country from space had been a national security aspiration for years—decades, even—before Golden Dome existed. So when Golden Dome and its space components became a thing, Voyager was ready. "A lot of that fits exactly square on where we've been investing and where we have tech," Magaña says.

But space-based interceptors do require something new, Harrison says: scale. A threatening missile could theoretically launch from anywhere in the world, which means Golden Dome

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would need enough orbital interceptors to cover possible launch points around the planet—ideally with more than one shot at each threat. According to one of Harrison’s analyses, “approximately 1,900 interceptors would be needed to provide continuous coverage of all points on Earth with an average of two interceptors” because the first try might miss.

That estimate assumes coverage for one incoming missile. A real attacker would probably launch a salvo, hoping to overwhelm Golden Dome’s defenses. “It’s a numbers game,” says Victoria Samson, chief director of space security and stability at the Secure World Foundation. In a recent report, the Congressional Budget Office (CBO) ran the numbers on a less forgiving scenario and found that a space-based system would require around 7,800 interceptor satellites just to stand up to a minor adversary or a small attack from a more significant one: 10 intercontinental ballistic missiles launched nearly at once. But that thousands-strong system would not be built to stop a large strike from Russia or China.

On top of that, the entire sequence has to happen quickly. Many of the envisioned interceptors are supposed to hit the missile while it’s still in its “boost” phase, when its engines are firing. That way, Harrison says, the interceptors strike while the threat is farther away and before it can send out decoys.

But that golden window isn’t an hour; it’s minutes. “So that’s just a short amount of time to be able to identify that something’s been launched, recognize that it’s a threat and then make the decision to try to intercept it,” Samson says. Only then can the system tell the interceptor what to do. The scale and timing problems help to explain why space-based missile defense has stayed mostly aspirational since President Ronald Reagan’s Strategic Defense Initiative, aka Star Wars, which was announced in 1983.

THERE ARE ALSO COMPLICATIONS BEYOND the hardware. This part of Golden Dome means putting interceptors in or-

orbit, something the U.S. has never done. “I think we’re crossing a red line,” Samson says. If the U.S. does it, others may do the same. Putting weapons in space means more chances for orbital attacks and accidental collisions in orbit, both of which would create space debris that could take out other important satellites or fall back to Earth. And the U.S., a country very reliant on satellites and space infrastructure, has the most to lose.

No one knows exactly what that space-based system will look like. But the Department of Defense is nonetheless trying to make sure companies are

bet that Golden Dome and related defense programs will need the kind of space hardware Voyager has been trying to assemble.

The company is not alone in that kind of positioning. “Starting last summer, I felt like I started seeing news stories where companies were like, ‘Hey, we have this capability. We could definitely prove we could do this,’” Samson says. “And it wasn’t just the major primes like Lockheed Martin—it was smaller, new space actors.” She’s even seen companies plying their wares as great “targets” for future interceptor tests. “Basically ev-

That thousands-strong system would not be built to stop a large strike from Russia or China.

ready to build it. That’s why this past April, Space Force’s acquisition arm awarded agreements worth up to $3.2 billion to 12 companies. Anduril is one of the awardees, and Voyager is part of its team. Other recipients are Lockheed Martin, Northrop Grumman, Raytheon and Booz Allen Hamilton. These contracts may indeed help mature the technology, Harrison says, but they don’t help with the biggest hurdle: scale, which means building thousands of interceptors and getting them to work as one system.

Despite that gap, the Trump administration has said it wants to demonstrate an integrated space-based interceptor capability by 2028—not far away and during a U.S. presidential election year. “I have a feeling we will test something just to be able to say we checked that box,” Samson says.

Voyager is trying to keep its eye on the scale problem. For instance, it recently announced two huge facilities: one in Long Beach, Calif., focused on advanced satellite electronics, and another in southern Colorado focused on propulsion for weapons systems. Together they approach 300,000 square feet. It’s a good

eryone’s scrambling to get a piece of Golden Dome funding,” she says.

The money at stake is potentially enormous. The administration said in March that Golden Dome will cost $185 billion. Harrison, meanwhile, has calculated that it might cost up to $3.6 trillion. The CBO lands between those numbers in its report, estimating $1.2 trillion over 20 years, with space-based interceptors accounting for 60 percent of the total.

In Harrison’s view, it’ll be a good long while before anyone knows how many thousands of interceptors will be in orbit or how they’ll mesh with the rest of the dome. By the time the architecture is even set, he says, Golden Dome will probably have changed forms, been canceled and been resurrected with a different name.

It may not even have space-based interceptors in the future, Samson says. But missile defense is not going anywhere—so the technology that Voyager and other space start-ups are working on, alongside the traditional defense giants, is likely to remain applicable and profitable. “You cannot get rid of it,” she says. ●

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SCIENCE CROSSWORD INSPIRED BY ARTICLES IN THIS ISSUE

Give Me Some Space! By Ella Dershowitz

Across

1 Online tags 4 "Muscle" that can be trained to improve cognitive endurance (page 78) 8 Frequent start to a Spanish prof's name 12 Notice 13 Transparent, visually or conceptually 15 Took a big risk 17 With 66-Across, a source of space debris that will occur increasingly often in Earth orbit—as depicted multiple times in this puzzle (page 26) 19 The planets, post-Pluto 20 Pretentious 21 Hawaiian accessory 22 "You follow?" 23 At that 26 Show that celebrated its 50th anniversary in 2025, initially 28 French cruise stops 29 Does not take the high road 31 Financially stable 33 Polyandrous Australian bird 34 Actress Shawkat 36 Two truths and a ___ 37 Channeled an annoyed camel 39 Rocks out at a bar? 41 Letters leading to a year 44 Tennis do-over 46 Disney movie set inside a mainframe computer 48 Large-carnivore ecologist and Going Wild podcaster Wynn-Grant 50 Tubular organisms among the first complex creatures to reproduce sexually (page 8) 54 Some runaway brides 56 Breaking a tie, briefly 57 Texting format 59 Snow piles 60 Bright, blue-white celestial body 62 Like pills found in a CVS aisle 64 Salty-sour German beer 65 Sherlock's teen sister 66 See 17-Across 69 Rehearsed a play from start to finish sans interruption

70 Artemis II spacecraft with a "wonderful toilet" 71 March of the Penguins director Jacquet 72 Legumes at the heart of Mendel's inheritance research 73 Body that has experienced "tidal locking" with Earth 74 Office address (abbr.)

Down

1 WikiLeaks founder 2 Places for tiny sandwiches and scones 3 Pay the bill 4 Oft-injured knee stabilizer, for short

5 Like someone in a mask, maybe 6 Chaos-inducing Tasmanian seal 7 Central ingredient in Devils on Horseback 8 Tedious and never-ending task 9 Is gifted? 10 Snitch on a sibling, say 11 Theoretical missing links 14 Equestrian handfuls 16 Statistical significance calculator 18 Orbs rejuvenated in new cell-reprogramming technology test 24 Clapperboards on film sets 25 Day on Mars 27 Texted letters for mirth 30 Console with motion controls 32 Holder of a legal claim 35 Standardized test with an optional science section 38 Papal airline of choice until its closure in 2021 40 Before, poetically

42 Distinctively shaped Girl Scout shortbread cookies 43 Surprises a driver, as a deer might 45 Quaint affirmation 47 Ancient 49 Gist 50 Focus of a current "maxxing" nutrition fad (page 86) 51 Open, in a way 52 Literally zero 53 Gas brand with a torch logo 55 Animals whose organs have been transplanted into humans 58 Depending on type, cities can boost or lessen one (page 10) 61 Creatures that might have contributed to the environmental collapse of Rapa Nui (page 32) 63 Muse of history (and name-sake of its scientific study) 67 Bath bathroom 68 Temporary resting place

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SCIENTIFIC TRAVEL AMERICAN

Winter in Yellowstone

January 7-13, 2027

Journey deep into Yellowstone National Park with Senior Desk Editor for Life Science Andrea Thompson as your guide.

Old Faithful | Lamar Valley | Upper Geyser Basin | Grand Teton National Park | National Elk Refuge

Space is limited. Book now! www.sciam.com/travel

Privacy Disclaimer: Scientific American has partnered with Academic Travel Abroad (AT&T) to its CQPR partners. AT&T is a registered trademark of the U.S. UK and Switzerland. Scientific American is a registered trademark of Springer Nature America, Inc.

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MATH

Can Math Predict the End of Humanity?

This eerily simple math says our days are numbered—and nobody can agree on why it’s wrong

BY JACK MURTAGH

HUMANITY HAS NEVER BEEN SHORT on predictions of apocalyptic events, from plagues to asteroid impacts. Most doomsday scenarios hinge on an analysis of physical threats or indicators of societal collapse. Some researchers, however, have mounted a purely mathematical proposal that suggests our time is running out. Their eerily simple “doomsday argument” relies solely on the laws of probability and a single data point: the total number of humans who have lived to date.

To get a feel for the argument, imagine you’re blindfolded and facing two giant spinning drums. Each drum contains tickets numbered 1, 2, 3, and so on. One of them contains 100 tickets total, and the other contains a billion. You put your hand into one of the drums and pull out ticket number 14. Do you think you picked from the 100-ticket or the billion-ticket pool? The 100-ticket bin feels much more likely because the chances of pulling such a low number out of a billion are astronomically small. If there were a billion tickets, you’d expect to draw a number that looks something like 437,893,112 rather than 14.

Jack Murtagh is a freelance math writer and puzzle creator. He writes a column on mathematical curiosities for Scientific American and creates daily puzzles for the Morning Brew newsletter. He holds a Ph.D. in theoretical computer science from Harvard University. Follow him on X @JackPMurtagh

Now let’s play the same game but replace the tickets with people. You are roughly the 117 billionth human ever born. What’s more likely: (1) that you are an extreme statistical anomaly living at the absolute dawn of what will become a multitrillion-person galactic human empire or (2) that you’re an average, run-of-the-mill human living somewhere near the middle of our run? The first answer is akin to drawing 14 from a drum of a billion tickets. The second predicts an uncomfortably close extinction. Just how close depends on how we estimate certain variables.

Consider another way to look at this argument: Imagine we line up every person who has ever lived and ever will live chronologically, from the first Homo sapiens (admittedly a fuzzy boundary, but we’re okay with rough numbers) to the final human to draw a breath. A quarter of all people occupy the first 25 percent of this line, and another quarter occupy the last 25 percent, meaning half of all people will be born somewhere in the middle 50 percent. Without any evidence to the contrary, we shouldn’t assume we occupy a privileged, statistically miraculous spot at the beginning of the human story. We should reason as though we’re just a random person among all people, past, present and future. If our birth ranks are random selections among all birth ranks, then there is a 50 percent chance that we belong to the group in the middle 50 percent.

Because roughly 117 billion people predate us, there’s a 50 percent chance that those 117 billion ancestors represent the first 25 percent to 75 percent of all humans that will ever exist, implying between 156 billion and 468 billion total humans. We can translate the number of individuals to time remaining on humanity’s clock by using the current birth rate of 132 million babies per year. At that rate, there’s a 50 percent chance that the last human will be born within the next 295 to 2,659 years—and an 80 percent chance that

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this event occurs within the next 98 to 7,977 years. These projections might seem to give our species plenty of time, but it's a tiny fraction of the amount we've spent on Earth so far, and they don't bode well for our aspirations of a Star Trek future. Note that we assumed a consistent birth rate on par with the recent linear growth of the population. If we made the model incorporate exponential population growth, that would only accelerate the timeline for humans' demise.

Probability Intervals Assuming a Random Birth Rank

If the doomsday-argument reasoning sounds specious, it might unsettle you to learn that it has a track record of successful predictions. In 1969 astrophysicist J. Richard Gott III visited the Berlin Wall, which was eight years old at the time, and wondered how much longer it would stand. Gott needed only a single assumption to answer the question: that the timing of his visit wasn't special. Under that view, he had a 50 percent chance of visiting sometime in the middle of the wall's life, suggesting the eight years the wall had been standing could represent somewhere between 25 percent and 75 percent of the wall's life. This allowed him to make a quantitative prediction that the Berlin Wall had a 50 percent chance of falling within the next 2.67 to 24 years. It fell 20 years later.

Gott then took his methods to Broadway. In 1993 he predicted bounds for when 44 stage shows in New York City would end their runs. According to his 2001 book Time Travel in Einstein's Universe: The Physical Possibilities of Travel through Time, all 37 that

had closed by the time the book went to print had done so within his projected timelines. Gott is one of the main proponents of the doomsday argument, which was developed from work first put forth by astrophysicist Brandon Carter.

Perhaps astrophysicists gravitate toward the argument because it hinges on a concept from their field called the Copernican principle. Named for the Renaissance astronomer who theorized that Earth is not the center of the uni-

called reference class pushes back our expiration date, and an argument for doom shouldn't depend so heavily on arbitrary boundaries.

The caveman objection: If a philosophically inclined early human stumbled on Copernican reasoning around a campfire, they would have confidently underestimated our longevity by millennia. If the math fails when applied in hindsight, why should we entrust it with our future?

The self-indication assumption: Suppose we live in one of two possible universes: one will only ever house hundreds of billions of humans, and the other will have hundreds of trillions of humans. Knowing nothing else, we should expect to be born in the latter universe simply because it has more slots for consciousness to occupy. Our very existence is more likely in a universe with many beings than in one with comparatively few. Therefore, incorporating this idea might nullify the doomsday pessimism.

One's birth rank can't end the world: An asteroid or a nuclear war can end the world. Mathematical musings from one's armchair cannot. Birth rank seems to have no causal connection to real dangers and therefore should not constitute evidence for an apocalypse.

All these rebuttals have counterarguments from doomsday proponents. The doomsday argument itself comes in a variety of flavors, as do proposed refutations. The dialectic continues and gets impressively technical. We've only scratched the surface here. For many, debating the doomsday argument is less about existential threats and more about how we contextualize ourselves. What inferences are valid to make from our mere existence? What are the limits of probabilistic reasoning? It's intentionally provocative to force us to confront foundational assumptions. The point of the debate is to expand our understanding; if we never fully resolve it, it's not the end of the world. ●

Graphic by Amanda Montañez

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THE SCIENCE OF HEALTH

Is Your Gut Ready for Fibermaxxing?

We are rightfully told to eat more fiber. But our depleted gut microbiomes may not benefit from superhigh levels BY LORI YOUMSHAJEKIAN

RIGHT NOW, on your favorite social media channel, someone is preparing a “poopy” breakfast loaded with bran and chicory root—enriched yogurt while someone with the handle “fiber daddy” is snacking on liquefied raw vegetables.

This is the world of “fibermaxxing” (“poopmaxxing” to some), in which people try to eat as much fiber as possible. Fiber-rich diets have been linked to lower risks of heart disease, digestive problems, some cancers, and other illnesses—and the idea seems to be that if a little fiber helps, a lot of fiber will help even more. Some people aim for up to 60 grams or more of fiber a day, much higher than the USDA’s recommendation of between 25 and 38 grams a day, depending on age and sex. Because most Americans are eating far less than that—closer to 10 or 15 grams—experts say that the trend isn’t exactly unwelcome but that your long-term

diet might limit how much it benefits your health.

Fiber plays an important role in your digestive system. These plant-derived compounds can’t be digested by the body’s own enzymes; instead they pass largely untouched to the colon, where bacteria break some of them down through fermentation. The breakdown produces short-chain fatty acids (SCFAs) that are essential for health. One SCFA called propionate is linked to lower cholesterol and to helping the body feel satiated; another, called butyrate, is a key energy source for the cells lining the colon.

Eating fiber also feeds the bacteria in your gut. Without fiber to supply their nutrients, gut microbes “basically start eating you,” gnawing away at the colon’s protective mucus lining, says Erica Sonnenburg, a microbiologist at Stanford University, who studies how diet shapes the gut. Once the mucus barrier is breached and colon cells start

to suffer damage, the body launches an immune response, leading to “the simmering inflammation” characteristic of diseases common in Western countries, such as inflammatory bowel disease, obesity and type 2 diabetes. And because low-fiber diets mean fewer of the bacteria that produce SCFAs, the barrier has less help repairing itself, creating a cycle in which a weakened gut barrier and chronic inflammation get worse over time.

“Everyone in the industrial world has a depleted microbiome,” Sonnenburg says, in part because of chronically low-fiber diets. But fibermaxxing alone may not fix this problem once it has started. In a 2021 study Sonnenburg co-authored, people who doubled their fiber intake for four months showed no increase in their microbial diversity. And unfermented food appeared in their stool—a sign their microbiome wasn’t equipped to break down what they were eating. None of the 19 inflammatory proteins the researchers tracked decreased in the high-fiber group, either.

But people with the highest microbiome diversity from the start “definitely reaped the benefits,” Sonnenburg says, with an “immune system that was less inflamed.” For everyone else, there are ways to increase the diversity of bacteria in your gut. Participants who ate a high-fermented-food diet had more diverse microbes and saw reductions in some inflammatory markers.

People’s responses to fiber might also vary depending on which types of bacteria dominate their guts. Two of the main groups are Prevotella, which is more common in people who eat lots of plants and fiber, and Bacteroides, which appears more often in people eating Western, animal-heavy diets. One study tested how each type handled three different dietary fibers: fructooligosaccharides—a fiber in foods such as chicory and onions—and two arabinoxylans, which are fibers extracted from sorghum and corn bran. The Prevotella microbiome produced consistently high levels of the beneficial SCFAs; Bacteroides responded rather variably.

Lori Youmshajekian is a science journalist who reports on consumer health, environmental issues and scientific misconduct. She has written for National Geographic and Wired, among other outlets.

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METER EDITED BY DAVA SOBEL

A small 2025 study found that a week of consuming arabinoxylan fiber reduced hunger for people with Prevotella-dominant microbiomes but had no effect on Bacteroides-dominant individuals, even though both microbiome types showed some increase in propionate production. And a 2024 study found a significant correlation between Prevotella abundance in the gut and levels of propionate—the SCFA linked to metabolic regulation and satiety.

But we should be cautious about reading too much into the Prevotella/Bacteroides divide, says Eric Martens, a microbiologist at the University of Michigan. He notes that their links to health benefits are correlations, with the underlying cause-and-effect relations yet to be established. What’s important is getting fiber from a variety of sources. Fiber is not all the same: it’s a diverse class of nutrients that vary in their chemical structure and solubility, with each type requiring different enzymes for breakdown. “If you’re eating a complex mixture of fibers, some at least are going to match well with the community that you have,” Sonnenburg says.

This is where fibermaxxers might go wrong: by relying too heavily on inulin and chicory root fibers. These are the cheap and highly soluble fibers found in prebiotic sodas, bars and yogurts marketed as high fiber. Because they’re so rapidly fermentable, they tend to cause gastrointestinal distress at around 20 grams a day, Martens says. Too much fiber overall can have a similar effect, often tied to serious gut discomfort and gas. Even psyllium husk works well for some people but can cause painful bloating and gas for others. “Pay attention to your own symptoms,” Sonnenburg advises. “Because everyone’s microbiome is unique, it’s hard to make a blanket recommendation for everybody.”

Any benefits of fiber are probably the result of a lifelong diet, not a passing fad. Martens recommends increasing gradually to about 35 grams a day, mostly by eating whole foods, rather than supplements and fortified foods, and sticking with them. The gut, he says, will adapt. ●

THE BACHELOR, SEASON 92 MILLION

From the choice of ten thousand candidates how does the bee know which is its flower?

Purple coneflower shudders, coreopsis unfurls its recursive light-licking spirals ...

Yet here, a knuckle of fuzz drops to the edge of a sunflower's

fleece— and moves back and forth, like the hand

of a blind man, searching

and searching its face

Jessica Nordell, a writer and poet with a background in physics, is author of The End of Bias: A Beginning (Metropolitan Books, 2021). Her poetry and nonfiction have appeared in The New York Times, The Atlantic, The Yale Review, Best New Poets and Copper Nickel. Her debut poetry manuscript, Your Singing Is How We Will Find You, was a finalist for the 2026 Agnes Lynch Starrett Prize. Nordell lives in Minneapolis, where she plays drums in a dad rock cover band.

Illustration by Masha Foya

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THE UNIVERSE

The Unseen Cosmos

Which parts of the universe are astronomers ignoring?

BY PHIL PLAIT

IT'S A BIG UNIVERSE OUT THERE. But with astronomers churning out noteworthy cosmic discoveries and insights each and every day, you might think we've somehow got it all covered, with the collective might of Earth's telescopes giving us full situational awareness of the sky.

Nothing could be further from the truth. Despite the existence of all our advanced observatories, there are still parts of the electromagnetic spectrum (and beyond) that we're not seeing and places where we need more (or any) telescopes.

The spectrum—that is, different kinds of light—is essentially infinite. But the visible portion of the spectrum, from violet to red, includes a wavelength range that differs by only about a factor of two from one end to the other, whereas the huge range from long-wave radio to gamma rays spans more than 20 orders of magnitude. So it shouldn't be surprising that we don't have it all covered.

What's more surprising, in fact, is just how much we have managed to cover. There are thousands of visible-light telescopes in operation at any given time; I have one I use myself when the bugs outside aren't too bad. In the professional realm, there are dozens of large observatories on the ground and orbiting Earth, as well as quite a few next-generation facilities in the pipeline—including the soon-to-be-launched Nancy Grace Roman Space Telescope, which will have the Hubble Space Telescope's sharp vision coupled with a vastly larger field of view. Archival data are important to note, too, because most things in

the sky don't meaningfully change on human timescales, making thorough surveys durably relevant even if they're years or decades in the rearview.

For example, in infrared we had the Wide-Field Infrared Survey Explorer, which scanned the entire sky to give an overview, and of course, we have the James Webb Space Telescope giving us the sharpest, deepest views yet in that spectral range. The Wilkinson Microwave Anisotropy Probe and the Planck observatory mapped the sky in microwaves; today the Atacama Large Millimeter/submillimeter Array covers shorter wavelengths. And overall there are almost as many operational radio telescopes as there are visible-light ones.

At the other end of the spectrum, the Galaxy Evolution Explorer surveyed the sky in ultraviolet, and Hubble has two UV cameras still in operation. Several orbiting telescopes detect x-rays, including the venerable Chandra X-ray Observatory, XMM-Newton, the Neil Gehrels Swift Observatory, and more. Even gamma rays get their day in the sun (so to speak), with the Fermi Gamma-Ray Space Telescope and Swift still operating and producing amazing data.

There are some holes in our coverage, but people have proposed ways to fill them. One of the most glaring gaps lies between the infrared and millimeter-wavelength radio observations, but the Probe Far-Infrared Mission for Astrophysics would fill much of it. Another gap exists for radio waves with wavelengths of 10 meters or more, which are reflected by Earth's ionosphere; to observe these, astronomers have proposed building radio telescopes on the moon's farside. One, called the Lunar Crater Radio Telescope, would be a staggering kilometer across. Such telescopes would be sensitive to radio waves emitted by gas from the cosmic "dark ages"—a period of a few hundred million years after the big bang but before the first stars were born—which we know very little about.

And even for the parts of the spectrum already thoroughly covered, it's not

Phil Plait is a professional astronomer and science communicator in Virginia. He writes the Bad Astronomy Newsletter. Follow him on Beehiiv.

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necessarily greedy to want more. Different telescopes have different functions. Some look at wide areas of the sky to do surveys; others pinpoint specific targets. Some take images; others detect spectra, dividing the incoming light into different energies (or colors, wavelengths or frequencies, all of which are different terms for essentially the same thing). Such spectroscopy is a powerful technique for in-depth studies of celestial objects, capable of revealing their rotation, motion, composition and distance, among many features. I think it is self-evident that the more telescopes we have, the better we can understand the universe.

But focusing on gaps in our coverage of the spectrum can cause us to ignore other viable areas of observation. For instance, we have a bias toward studying light. But other cosmic messengers exist.

One example is gravitational waves, literal ripples in the fabric of spacetime, created by accelerating masses. For the vast majority of objects in the universe, these waves are too mushy to detect, but massive ones accelerating very rapidly give off much more sharply defined waves. Black holes are quite amenable to this approach, all the more so because they don't directly emit any light at all.

The Laser Interferometer Gravitational-Wave Observatory detected the first such waves in 2015, recording the otherwise invisible merger of two stellar-mass black holes. It was an extraordinary achievement. Although Albert Einstein predicted the existence of gravitational waves in 1915, it took technology a century to catch up to his calculations. Several other, similar observatories have come online since then to glimpse hundreds of additional events, but all this activity represents a narrow range of gravitational waves—those created when neutron stars or relatively small black holes collide.

The European Space Agency's Laser Interferometer Space Antenna (LISA), planned for launch in 2035, will detect the much longer gravitational waves created when mammoth supermassive black holes spiral together and collide.

One of the most glaring gaps lies between the infrared and millimeter-wavelength radio observations.

Such collisions are thought to be the most energetic events in the known universe, yet we know very little about them. Consisting of three separate spacecraft separated by 2.5 million kilometers, LISA is too big and too sensitive for our small, noisy planet—which is why, of course, it must be put in space.

Dark matter is another problem area. We know it exists and is responsible for shaping much of the structure in the universe, but it emits no light and apparently doesn't interact at all with normal matter except through gravity. We can detect it indirectly in the far-away universe via gravitational lensing and other methods, but we have no way of detecting it directly right here on Earth, even though dark matter particles are presumably streaming through you and everything else on the planet as you read this.

We're not even sure, in fact, that dark matter consists of particles at all. Not one of the many experiments attempting to spot such particles has found them unequivocally. More broadly, all of this research is part of a rich and growing field in which our "telescopes" are detectors studying neutrinos, fragments of atomic nuclei, and other non-electromagnetic celestial emissaries.

But there's still more we cannot see, and it may surprise you: we have huge gaps in the knowledge of our own solar system. The region out past Neptune is populated by billions of icy, rocky bodies called trans-Neptunian objects (TNOs) left over from the solar system's formation. Only a few thousand are known, however. They're incredibly faint and difficult to find. The Vera C. Rubin Observatory should discover tens of thousands of them, which astronomers hope will allow them to classify these objects better and get a firmer grasp on what the solar system was like in its infancy. And

Rubin will discover much more than TNOs by virtue of its emphasis on time-domain astronomy—the study of objects such as asteroids, novae, supernovae, and/or active galaxies that move and vary in brightness. Although Rubin takes only visible-light images, its ability to show us the changes in those images is where its real power lies.

Our more "local" limits aren't just in the outer solar system, either; we also don't know that much about the region near the sun. Since its launch in 2018, the Parker Solar Probe has been repeatedly dive-bombing the sun to measure the environment very close to our star's surface for the first time. Somewhere in the scarcely explored vicinity sunward of Mercury, there could be a population of small asteroids, 100 meters to six kilometers in diameter. Called vulcanoids, they would be too close to the sun's mighty glare for us to easily see them from Earth. If their existence were confirmed, they would tell us a lot about the evolution of the solar system.

For the same reason, we currently can't look for potentially hazardous asteroids coming from inside Earth's orbit. But NASA's Near-Earth Object Surveyor, due to launch in 2027, will park itself in a gravitationally stable position about a million kilometers closer to the sun than Earth to look for asteroids as close as 45 degrees in the sky to our star. The plan is to catalog two thirds of the asteroids larger than 140 meters across in that volume of space.

The universe starts right over your head and continues onward for a very long way. We humans have a pretty decent view of it, one we take advantage of to learn about our origins and cosmic environment. Although there are certainly gaps in our view, we have a pretty good idea of where they are, and we should be doing our best to fill them. ●

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Q&A WITH DAVID J. GROSS

The Quest for a Theory of Everything

A Breakthrough Prize winner warns nuclear war could prevent reaching the holy grail of physics

DAVID J. GROSS, A CELEBRATED U.S. theoretical physicist, calls himself an optimist—especially concerning the future of his field. He’s certain that somewhere out there lurks a final, unified theory of nature, just waiting to be discovered. But he’s pessimistic about our chances of actually discovering it; on balance, he estimates, it’s more likely that we’ll destroy ourselves in nuclear warfare first. And as the latest recipient of a $3-million Special Breakthrough Prize in Fundamental Physics, he’s using the opportunity to warn the world of this dire peril.

When Gross speaks, especially about prospects of a unified theory, people tend to listen—after all, he’s responsible for some of the biggest steps we’ve taken toward devising one.

Such a theory would, by definition, unify three known fundamental forces—electromagnetism and the strong and weak nuclear forces—with a fourth, gravity, reconciling a long-standing schism between these domains. In the early 1970s Gross co-discovered a phenomenon called asymptotic freedom, a counterintuitive property of the strong nuclear force showing that interactions among quarks (the subatomic constituents of neutrons and protons) weaken at shorter distances and strengthen at longer ones. In other words, the farther apart you try to pull quarks, the harder they’ll resist. But

if you pile them together inside a proton, they will frolic freely, almost as if they have no resistance at all.

The idea has been exhaustively confirmed in high-energy experiments, and it helped to establish a theory of the strong force called quantum chromodynamics (QCD), which became a cornerstone of the Standard Model of particle physics. It also netted Gross a share of the 2004 Nobel Prize in Physics. In the aftermath of QCD’s ascendance, his quest for unification turned more speculative as he formulated foundational aspects of string theory, specifically a mathematically elegant hybrid type he co-developed in the 1980s called heterotic string theory, which mixes other types to describe fundamental particles. Unlike asymptotic freedom, however, heterotic string theory (and string theory in general) has yet to be validated by experiments.

Although the connection between these technical contributions and the existential threat of nuclear warfare may seem tenuous, Gross maintains it’s quite clear: Centuries of further theoretical and experimental progress may be required to find and verify a final theory—but planning for such a future is short-sighted when global nuclear war could effectively end human civilization in a single afternoon. Reducing that risk, he says, is therefore at least as important for discovering a unified theory as performing the fundamental physics work itself.

In a conversation with SCIENTIFIC AMERICAN, Gross discussed his Breakthrough Prize, the reasons for slow progress toward a unified theory and the folly of ballistic missile defense. And he explained why the current status quo means everyone now on Earth still faces the threat of nuclear annihilation.

An edited transcript of the interview follows.

You’ve won several major awards during your long career—the Dirac Medal in 1988, the Harvey Prize in 2000 and of course the Nobel Prize in Physics in 2004. Now you’ve won

Lee Billings is senior editor for physical science at Scientific American.

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this year’s $3-million Special Breakthrough Prize in Fundamental Physics as well. Do you consider this the capstone?

Nothing really compares to the Nobel Prize, but this one is certainly the most lucrative. I’ve been heavily involved in raising money for my institute, the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara, and for many others like it around the world. So with this Breakthrough Prize, it’s nice to finally have some money to give to other people!

You know, this is a “lifetime achievement” prize, which carries the suggestion that my lifetime is drawing to a close. So that’s a bit of a bummer. But I’m still extremely honored and pleased by it—the way these Breakthrough Prizes work is that the selections are informed by the opinions of previous recipients, and in this case, those are some of the people I respect most in my field. And this prize is more flexible and open-ended than most others; it can go to people whose work is still somewhat speculative and is as yet unconfirmed by nature.

You seem to hit both sides here in that some of your work—asymptotic freedom in quantum chromodynamics, for example—has been well validated by experimentation, whereas other aspects, such as heterotic string theory, remain quite speculative. Is that a fair assessment?

Well, I’ve had a long life so far! I’ve seen extreme swings in fundamental physics. When I was beginning, it was during a period of experimental supremacy, with enormous discoveries being made all the time—and on the theoretical side, almost nothing was understood. That was an exciting period for a theorist. And now it’s sort of the opposite. There are a lot of great theoretical ideas and progress, but nature hasn’t been so kind with its discovery. And living through both periods—and everything in between—has of course shaped my work.

It used to be that the data were all there, and one tried to make predictions

based on flimsy ideas. Now new data aren’t coming, but the theory is so much more understood. So the goal now is to advance the theory and hopefully to make contact with experiment, but that’s getting harder all the time. In the past, you could make a prediction or try to calculate something and have it tested experimentally within a year! Now it’s “look, we’re planning the future of the field on a 30- to 60-year timescale.”

What’s caused that slowdown? Just things getting more expensive?

Not exactly. The projects themselves have gotten bigger, which makes them take longer. But they haven’t really become more expensive: given inflation, technological growth and our increased understanding of the physics, we can build better machines with less money now.

What’s changed has to do with the scales of distance or energy that we’re exploring rather than the scale of time that we usually think about when discussing our progress into the future. From the point of view of physics, the most important scale is the size, or the distance, that we can probe, with smaller distances requiring greater energies to reach.

So in the 20th century, we went from molecular to atomic to nuclear physics, to where we were studying the structure of the atomic nucleus. Across the past two centuries, we’ve progressed by roughly 15 or 20 orders of magnitude. And this enormous progress gave us a very complete “standard” theory of particle physics.

But the next scale that is suggested by experimental observation and theoretical extrapolation is many orders of magnitude removed from the current scale that we can easily explore. We seem to have another 20 orders of magnitude to go! And it gets worse: One of the major implications of asymptotic freedom in QCD and other quantum field theories is that the physics changes very slowly as we go to shorter and shorter distances. Specifically, it changes logarithmically.

Let’s compare that with another scale, which is the amount of money it takes to reach those higher and higher energies to

go to those shorter and shorter distances. For this, the cost scales at least as the energy squared, if not even more. So the physics potential is increasing only logarithmically while the cost is increasing like the energy squared—there’s an exponential difference between them. And that’s just a fact of life we’ll have to deal with if we want to understand nature at these small scales.

The math is daunting, to say the least. That makes me wonder: Was that calculus part of what’s motivated your work in advocacy and activism outside of physics? That’s something your Breakthrough Prize acknowledges in its citation. You’ve been a prominent signatory on open letters to U.S. presidents protesting budget cuts to science programs and on declarations calling for action on climate change and on nuclear non-proliferation, for instance.

I think you can do both—scientific research and public advocacy. It’s not either/or, and it’s a personal decision everyone has to make about what to do with their limited time. Science really is a lot of fun; I enjoy it a lot. But it’s very different from my advocacy work. I guess getting prizes like this can be a devil’s bargain in that context. On one hand, the exposure you receive means you’re often urged to be an advocate, to help get some message out. On the other hand, this can be an enormous drag on your time.

Right now I and others are helping to rekindle what’s known as the Mainau process by co-creating a group that we call the Nobel Laureate Assembly for the Prevention of Nuclear War. We’re involved at the United Nations. We’ll be doing something in Brussels next year. We had a big conference in Chicago in July 2025—even the pope is interested in what we’re doing; he sent a cardinal as an emissary to that meeting. We’re now planning a whole series of events at the Vatican.

And all of this involves warning people and institutions around the world to wake up to the danger of nuclear annihilation. Because there is something we

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can do; we can stop this danger. We need to raise people's awareness about this—especially young people, most especially scientists. I could even work on you. May I ask: Do you have children?

I do. I have two sons, aged 11 and six. Okay. And what do you think their mean lifetime will be?

I hope it'll be at least as long as the lives of their recent ancestors—how long my grandparents lived, for instance, which was pretty close to the national average, I think. You know, somewhere between 75 and 80 years old, if all goes well, at minimum. Right, of course. Incidentally, some of this line of questioning comes from a 2024 bestseller by Annie Jacobsen entitled Nuclear War: A Scenario. You should read it. And if you do, you'll be scared—as you should be.

What you should be really scared about is the estimates from serious experts during the 20th century that there was a 1 percent annual chance of nuclear war. That doesn't sound like much; it's the sort of thing people shrug off, especially if they have no memory of the cold war. You know, "We've never had any nuclear war; we're never gonna have it; no problem." But if the chance is 1 percent a year, well, that suggests the mean lifetime of someone born today is just 67 years. This assumes that if nuclear war occurred, they'd die as a result—which, I'd argue, is a pretty safe assumption.

And the scariest part is: in the years since those estimates were made, things have gotten so much worse. Today all nuclear arms control treaties have been abrogated, proliferation has expanded as more countries gain or seek nuclear weapons, and there's even a major war with nuclear-armed Russia going on in Europe. I would conservatively estimate that the annual chance for nuclear war is now 2 percent.

Translate that into what this might mean for your children, and you're looking at them having a mean lifetime of about 35 years. It's like the radioactive

decay of an atom—it may be a low-probability extreme event, but the more time passes, the more likely such events are to occur. The probability accumulates. That's the way we should really think about this. So this will probably affect your lifetime as well but certainly theirs; their mean lifetime today, unless something is done, may be just 35 years.

That is scary.

It is, yes. And what people need to know is that there are things one can do about this that don't consist of entirely abolishing nuclear weapons or everyone on Earth becoming a pacifist. The output of our Chicago meeting was a declaration that you can go read online; it lists some very simple steps that could be taken worldwide to reduce the risk—because we don't want to be at 2 percent. If we can get to 0.1 percent, well, okay. That could give us a few hundred years to solve more of our problems, and any reduction could be an extension to the mean lifetime of your kids and certainly their grandkids.

You don't have to convince me of the clear and present danger we face from nuclear war and the value in reducing the risk! But I'm sure there are people out there who would say this is like playing Whac-A-Mole because of all the other nonnuclear existential risks we face—anthropogenic climate change, hazardous space rocks, runaway artificial intelligence, and so on. And some of them might even say that "the only way out is through," that instead of laboring to close the nuclear Pandora's box, we should lean even harder on nuclear power and other disruptive technologies to somehow buy down existential risk.

That is, some critics might say that rather than collectively calling for more bureaucratic solutions, Nobelists like you should endorse more extreme goals such as radical geoengineering to combat climate change or building cities on Mars to create a backup plan for humanity. What would you say to those sorts of responses?

They sound rather silly, to say the least. You mentioned climate change, and I think the social response to that offers a good example of what's needed to address the nuclear problem. I talk to very smart young physicists all the time, graduate students and postdocs and professors, and I'll often ask them, "What are you worried about? Tell me your top five most important concerns about anything."

Number one, almost universally, is climate. Usually from there, it's things like diversity, tenure or inflation. No one mentions nuclear war. And these people are physicists! When I start questioning—"Do you know how many missiles there are? Do you know how long it takes for Donald Trump or Vladimir Putin to push a button? Do you know what a one-megaton nuclear bomb does?"—it seems they know nothing.

How can this be? Well, about 40 years ago scientists started warning the world about climate change. And it took a long time, but they succeeded in waking some of us up to become a strong political force despite the best efforts of the oil companies and their politicians. That's also, by the way, how the previous attempts or successes in controlling nuclear weapons worked. That's how the Comprehensive Test Ban Treaty was developed. There were millions of people in the streets protesting against the radioactive fallout from atmospheric weapons testing—testing that Trump says he wants to start again!

Of course, when the cold war ended, a lot of that sentiment fell by the wayside. People forget that the nuclear arsenals are still here.

So public action is key to achieving these sorts of goals, but currently no one talks much about the nuclear threat. Scientific American hasn't written about this for who knows how many years—and you should!

It's been a while, that's true.

And I bet if you ask your colleagues there, you'll see the lack of knowledge of the real danger is extreme. In any case, climate is

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Q&A WITH DAVID J. GROSS

being addressed because there is a strong political will to do it. Addressing it is a very long-term thing, and the changing climate by itself can't kill all of humanity. Meanwhile, with global thermonuclear war, the whole human world, what we call civilization, practically everything and everyone can just vanish in 24 hours. Poof. Gone. It's insane. And it's insane that we aren't doing anything about it!

Getting back to my contrarian prodding about technological panaceas, there's of course an incredibly expensive plan underway, Golden Dome, to build a ballistic missile defense system that will supposedly be capable of protecting the entire continental U.S. As a physicist interested in nuclear issues, I'm sure you have thoughts.

Every new technology offers new hopes of solving the problem, but it simply won't work. Golden Dome is not much more than Ronald Reagan's "Star Wars" [ballistic missile defense program] on steroids. And serious analysis—which in the end convinced everybody, most important, Reagan and Mikhail Gorbachev—shows that offense easily wins over any defense you can mount. The best you can hope for with these things is another destabilizing arms race. It's extraordinarily expensive and essentially ineffective. You're located in New York City, right?

Yep, that's right.

Right, and all it takes is one single warhead getting through. A single MIRV missile can shoot 10 half-megaton bombs at the New York area, and there are practically infinite ways to fool any kind of defense system. This is, in fact, being illustrated in front of our eyes with some of the drone warfare at work in Ukraine or the current missile defense situation in the Middle East, where offensive weapons that cost hundreds of thousands of dollars are being knocked down by defensive weapons that cost hundreds of millions of dollars. It's a totally crazy thing, and even more than that, the argument for ballistic missile defense is what convinced

some people in the U.S. that they could protect themselves while bombing other countries over the past 50 years.

Golden Dome will never work. Building it would bankrupt the U.S., and so it will never actually happen, and it's therefore irrelevant to the main problem, which should be keeping your kids alive for more than 35 years.

That doesn't sound very optimistic.

So I am somewhat pessimistic about the nuclear situation. But in general, I'm an optimist—because that's a prerequisite for doing frontier, speculative, basic physics, to probe these frontiers we talked about earlier that are so difficult to reach. There's a selective bias at work here—you can't do this kind of

"I'd estimate that the annual chance for nuclear war is now 2 percent."

—DAVID J. GROSS NOBEL LAUREATE IN PHYSICS

Talking about the overlooked odds of nuclear annihilation and now the resurgence of ballistic missile defense as a seemingly unworkable solution, it's tempting to think that history is somehow cyclical. Maybe we're on the verge of making mistakes we were very lucky to avoid earlier—mistakes that carry such severe consequences they can be made only once. And if we avoid them now, well, leave it to the next generation to stumble perilously close to them once again. That's a rather bleak outlook. I hate to be so cliché, but are you able to stay optimistic about the future?

I'm less optimistic than I was a few years ago. The politics in the U.S. and around the world are getting crazier and crazier.

But with the nuclear issue, this isn't a force of nature that we have no control over. We can do something about it. These are systems built and controlled and maintained by people, in the end.

And so I do believe that if people became informed of the dangers—as many have, after many years, with respect to climate—we would have hope. Of course, in the case of climate change, nature has helped to prove the case, as was predicted.

I don't want to see a small nuclear war that would kill "only" a few hundred million people and cause enormous destruction to the planet. But that might be how nature reminds us how precarious our situation really is. I hope not.

science unless you're an optimist, because if you're a pessimist, you give up so easily.

Attempting to understand the most basic laws of nature, seeking to understand the beginning of the universe and how the universe will end, finding a theory to unify all the forces—these are extraordinary, grandiose goals. And so it's understandable that they won't be answered simply and quickly.

I've often compared progress in this sort of fundamental research to climbing a mountain—and in the case of fundamental physics, we really have no idea how tall the mountain is. We're in the dark, going up, up, up. And as optimists, we'd think the peak was within reach—but optimists tend to exaggerate. As pessimists we'd say, "It's miles and miles higher still. I think we've gone far enough."

But another way of measuring this progress, which I try to do when I'm feeling pessimistic, is to look back a year, or a decade, and ask, "How much have we learned?" And it's always been the case for me, looking back, to say, "Oh, my God, it's changed so much. We've understood so much. We were idiots back then!"

So we must remember that this can be a long journey. Progress is being made along the way. We just have no idea how far we have to go. And we have to make sure we don't kill ourselves in the meantime. ●

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GRAPHIC SCIENCE

The Do's and Don'ts of Tick Bites

Knowing what kind of tick bit you and where you got it can help inform next steps

TEXT BY KATE WONG | GRAPHICS BY DIOGO GUERRA | MAPS BY JEN CHRISTIANSEN

TICK SEASON is in full swing, and unfortunately for us humans, these parasites are having a banner year. Across the U.S., weekly rates of emergency room visits for tick bites have been trending higher than in any other year since 2019, according to the Centers for Disease Control and Prevention's tick-bite tracker. In the Midwest, this year's rates have consistently been the highest since 2017, when the tracker was launched. That all adds up to a lot of bites. "Every year an estimated 31 million people in the United States are bitten by a tick," says CDC epidemiologist Alison Hinckley. These bites can cause serious and sometimes deadly infections such as Lyme disease, Rocky Mountain spotted fever, alpha-gal syndrome (also known as red-meat allergy) and Powassan disease,

the last two with increasing frequency.

I recently had a tick bite and wasn't sure what to do. I live in an area with a high incidence of Lyme disease, so it was on my mind. Should I go to a doctor to have the tick extracted or remove the offending creature myself? Monitor the bite and watch for a bull's-eye rash and other symptoms of Lyme disease, or take a preventive dose of antibiotics? Some cursory Googling of tick bites suggested I should remove the tick, flush it down the toilet and watch for any symptoms in the following days and weeks.

But a closer look at the literature hinted that I might be better off taking a different approach, given my circumstances. So I went down the rabbit hole. Here's what I learned about what to do—and not to do—when you discover a tick on your body.

REMOVE THE TICK AS SOON AS YOU DISCOVER IT. Don't wait to go to a health-care provider, the CDC advises. The longer a tick is attached, the more time it has to transmit bacteria and other pathogens that cause disease. Infected ticks generally need to be attached for more than 24 hours to transmit Lyme disease, but they may transmit Powassan virus in as little as 15 minutes. The sooner you get the tick off your body, the better.

When I was a kid, the received wisdom was to get rid of ticks by burning them off with a match or cigarette (I remember my mom trying to do this with a tick she found on my head while washing my hair in the kitchen sink) or smothering them with petroleum jelly, among other tactics. Don't do these things. Such interventions could cause the tick to release infected fluids into the

TICK IDENTIFICATION

Ticks are tiny parasitic arachnids that feed on the blood of other animals. Each tick species carries its own set of pathogens that can cause serious human diseases. Not every tick is infected, and not every tick bite results in disease. But knowing what kind of tick bit you can help you and your doctor figure out what next steps to take to manage your risk.

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host, according to the Johns Hopkins Medicine Lyme Disease Research Center. All you need is a pair of fine-tipped tweezers. (Incidentally—and this is friendly advice, not official guidance—if you’re a little squeamish, take a moment to calm yourself first. The tick is gross. You might see its legs move when you lift it away from the skin. But you can scream, shudder or sob later. Right now your job is to stay cool and remove the tick safely. You’ve got this.)

The tick is attached to the host by only its mouthparts, so grasp it with the tweezers at or near its head, as close to the host’s skin as possible, and use steady, even pressure to pull it straight up and out, away from the skin. Do not squeeze its body; doing so could force infected fluids into the skin. Don’t crush the tick, because that could complicate species identification. Put it in a clear, sealable plastic bag for identification and possible laboratory analysis. Clean the bite area and your hands with soap and warm water or alcohol. If you see that the tick’s head or mouthparts broke off and got stuck in the skin, don’t worry—the tick can’t transmit disease without its body. Your skin will eventually expel the stuck parts as the wound heals.

ASSESS YOUR RISK FOR DISEASE. Different species of ticks live in different parts of the country, and each species carries its own set of pathogens. “The type of tick, the likely tick infection rate in the region, and how long the tick was attached and feeding are all critical details for making tick-bite management decisions,” according to the University of Rhode Island’s TickEncounter resource center.

In New England, where I live, four tick species are well established: the brown dog tick, the American dog tick, the black-legged (or deer) tick, and the lone star tick. Gulf Coast ticks are present in smaller numbers in the southern part of the region. My tick was a few millimeters long and teardrop-shaped with a brick-red abdomen surrounding the black shield on its back—hall-

ANATOMY BASICS (American dog tick, top view)

marks of an adult female deer tick.

Not all ticks are as easy to identify as mine. Not only do tick species differ in size, coloring and markings, but individuals of the same species can look different depending on their life stage and sex and on how engorged they are from a blood meal (ugh). Some tick species are so similar that identification is best left to a pro. If you need help identifying your tick, your doctor may be able to assist you. And TickEncounter has a free tick-identification program that allows users to submit a photograph of their tick and get an expert ID, usually within 24 hours. You can also contact your state or local health department for information about tick infection rates and disease case rates in your area.

The most common tick-borne infection in the U.S. is Lyme disease. The CDC estimates that 476,000 people a year are treated for Lyme. In North America, it is transmitted exclusively by the black-legged tick and the Western black-legged tick. In parts of the eastern U.S., the domain of the black-legged tick, more than half of these parasites carry the Borrelia bacteria that cause Lyme disease. Western black-legged ticks, which are found mostly on the Pacific Coast, also carry Lyme bacteria, as well as several other pathogens, but typically fewer than 5 percent of them are infected, according to TickEncounter.

If a black-legged tick in an area where Lyme is common bites you and stays attached for 36 hours or more, your doctor may recommend a single prophylactic

dose of the antibiotic doxycycline to kill bacteria before they multiply. This preventive dose is most effective when given within 72 hours of tick removal, while the bacteria are incubating. Doxycycline is also used to treat Lyme disease, but treatment requires a much longer course of the antibiotic than prevention—10 to 28 days or more.

Because my tick bite met all the criteria for high risk for transmitting Lyme and because I was within the 72-hour window, my doctor and I decided to go ahead with the preventive dose of doxycycline.

CONSIDER TESTING YOUR TICK. My doctor also advised me to send my tick to a lab for analysis—“for peace of mind,” she said. If it tested negative for Borrelia, then I could put Lyme out of my head. If it was positive, then I could feel smug about taking the preventive antibiotic—but I would need to keep an eye out for Lyme symptoms in the coming weeks in the unlikely event that the doxycycline didn’t get the job done. I’d also get information about other pathogens that my tick might have passed along to me, such as the microscopic Babesia parasites that cause the blood

SEPTEMBER 2026 SCIENTIFICAMERICAN.COM 95

© 2026 Scientific American

Sources: TickEncounter, web, url, adult tick encounter, fieldguide (primary reference) and Thomas Mather (expert review)

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GRAPHIC SCIENCE

8 Deer tick, or black-legged tick (Ixodes scapularis)

TRANSMITTED DISEASES INCLUDE:

Lyme disease, alpha-gal syndrome, anaplasmosis, babesiosis, ehrlichiosis, hard tick relapsing fever, Powassan virus

Tick larvae have six legs. Other stages have eight.

LARVA

Absence of eyespots and festoons in all life stages

NYMPH

ADULT MALE

Long, straight mouthparts

Base of head rectangular

Black, undecorated shield and dark legs in adults

1/16 inch

2 millimeters

ADULT FEMALE

Orange-red body in females

9 Western black-legged tick (Ixodes pacificus)

Lyme disease, alpha-gal syndrome, anaplasmosis, hard tick relapsing fever

OTHER NOTES:

Very similar to the black-legged tick. Requires specialized identification methods.

LARVA

NYMPH

ADULT MALE

Long, straight mouthparts

Base of head rectangular

Dark, undecorated shield in adults

1/16 inch

2 millimeters

ADULT FEMALE

5 American dog tick (Dermacentor variabilis)

Ehrlichiosis, Rocky Mountain spotted fever, tick paralysis, tularemia

LARVA

NYMPH

ADULT MALE

Adults have a reddish-brown color

Base of head rectangular

ADULT FEMALE

6 Rocky Mountain wood tick (Dermacentor andersoni)

Colorado tick fever, Rocky Mountain spotted fever, tick paralysis, tularemia

OTHER NOTES:

Very similar to American dog tick. Requires specialized identification methods.

LARVA

NYMPH

ADULT MALE

Short, straight mouthparts

Base of head rectangular

ADULT FEMALE

1/16 inch

2 millimeters

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Sources: TickEncounter, web.uri.edu/tickencounter/fieldguide (primary reference) and Thomas Mather (expert reviewer)

6 Pacific Coast tick (Dermacentor occidentalis)

Pacific Coast tick fever, Rocky Mountain spotted fever, tularemia

OTHER NOTES:

Very similar to other Dermacentor ticks. Requires specialized identification methods.

LARVA

NYMPH

ADULT MALE

Short, straight mouthparts

Base of head rectangular

ADULT FEMALE

1 Brown dog tick (Rhipicephalus sanguineus s.l.)

Mediterranean spotted fever, Q fever, Rocky Mountain spotted fever

LARVA

NYMPH

Presence of eyespots

ADULT MALE

Undecorated, reddish-brown shield

Short, triangular mouthparts

Base of head hexagonal

Presence of festoons

ADULT FEMALE

5 Lone star tick (Amblyomma americanum)

Alpha-gal syndrome, Bourbon virus, ehrlichiosis, Heartland virus, Rocky Mountain spotted fever, southern tick-associated rash illness (STARI), tularemia

LARVA

Presence of festoons

NYMPH

Presence of eyespots

White markings on margin of shield and festoons in males

ADULT MALE

Long, straight mouthparts

Base of head rectangular

White dot ("star") on shield of females

ADULT FEMALE

1 Gulf Coast tick (Amblyomma maculatum)

Ehrlichiosis, Rocky Mountain spotted fever, spotted fever, southern tick-associated rash illness (STARI), tularemia

OTHER NOTES:

Very similar to American dog tick. Gulf Coast tick has noticeably longer and slenderer mouthparts.

LARVA

NYMPH

Presence of eyespots

Presence of festoons

ADULT MALE

Long, straight mouthparts

Base of head rectangular

Shield mostly white with some brown areas in females

Shield is dark brown with interconnected white lines in males

ADULT FEMALE

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GRAPHIC SCIENCE

WHERE TICKS LIVE

These maps show the approximate distributions of the tick species that transmit disease to humans in the U.S. Just because a tick species occurs in a given area does not necessarily mean it transmits disease in that area, however—the percentage of ticks infected with a given pathogen can vary considerably depending on location. Contact your state or local health departments for information about infection rates and disease case rates in your area.

Continued from page 95

disease babesiosis, which can co-occur with Lyme disease.

My home state has a tick-testing program that allows residents to submit ticks for free lab evaluation. All ticks are accepted for identification, but the lab tests only the kind that most often causes problems here: black-legged ticks, which can transmit Lyme, anaplasmosis, babesiosis, hard tick relapsing fever and Powassan disease, among other illnesses. All I had to do was pack up my tick in its sealed plastic bag and some bubble wrap to prevent crushing, along

with a form containing details about my tick bite, and drop it in the mail. (When I handed my envelope to the worker at the post office, she saw the address and groaned, "Oh, no, another one.")

Six days later I received an e-mail with the results. They confirmed that my tick, B23327, was a female black-legged tick and noted that she was "slightly engorged," meaning she had been attached to me long enough to feed on my blood and pass along pathogens. B23327 tested positive for the bacterium that causes Lyme disease but negative for other disease-

causing microbes. This finding was a relief because ticks can transmit multiple diseases at once. I'd need to remain vigilant about Lyme symptoms in the coming weeks, but beyond that, I could rest easy.

If you don't live in a state with free tick testing, there are labs that will test your tick for a fee. The Tick Research Lab of Pennsylvania, for example, has free testing for Pennsylvania residents and charges a fee for nonresidents. That said, not everyone recommends tick testing. The CDC discourages it, in part because the results can be misleading—a positive

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o Pacific Coast tick

g Lone star tick

f Brown dog tick

h Gulf Coast tick

Sources: CDC: www.cdc.gov/ticks/about/where-ticks-live.html and Pacific Southwest Regional Center of Excellence in Vector-Borne Diseases: paves.us/pacific-coast-tick (reference)

result doesn't necessarily mean the tick passed the pathogen along to you, and a negative result does not preclude the possibility that you've been unknowingly infected by a different tick. Either way, if you feel sick, don't wait for tick-testing results before going to a doctor.

WATCH FOR SYMPTOMS. Lyme is the only tick-borne disease for which preventive intervention is recommended. So unless someone is at high risk for Lyme, the standard advice after a tick bite is to wait and watch for fever, rash or flulike illness over the next 30 days

and to see a doctor right away if any symptoms appear. Many tick-borne diseases have similar symptoms, particularly in the early stages of infection. Blood tests can differentiate them but may take a while. Knowing which species of tick bit you and where you might have picked it up can help your doctor make a timely diagnosis.

Not all tick-borne illnesses can be cured. The rare but increasingly prevalent Powassan virus, spread mainly by the black-legged tick, can reach the brain and cause encephalitis. Treatment is aimed at managing symptoms.

Alpha-gal syndrome, which is most commonly caused by the bite of a lone star tick, renders people allergic to products from mammals, requiring that they avoid red meat and sometimes dairy and nonfood items containing the alpha-gal molecule.

Of course, the best way to prevent tick-borne illness is to avoid tick bites in the first place. After my experience with B23327, I'll be redoubling my efforts to keep these bloodsuckers at bay.

Kate Wong is a writer and editor specializing in science, health and the environment.

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HISTORY COMPILED BY JEANNA BRYNER

50, 100 & 150 Years

SWORDS INTO FUEL RODS

1976 “If nuclear-fission reactors are to play a substantially enlarged role in generating electricity in the U.S., we must decide on the nature and size of new uranium-enrichment plants. The decision turns on many complex and still largely unresolved issues, such as projections of future energy consumption and the political impact of opposition to nuclear power.

“One way to postpone such a major decision would be to use some of the large quantities of highly enriched uranium and plutonium stockpiled in the form of nuclear weapons. Currently the total number of nuclear weapons in the U.S. arsenal is declining, as obsolete weapons are being dismantled to make way for new weapons. It is estimated that over the next five years or so a significant amount of fissionable material could be taken from the dismantled weapons and used to fuel nuclear power plants, thereby helping to relieve the threatened long-term shortfall in nuclear fuel supply.”

AFFIRMATIVE EVOLUTION

“In humans and other mammals, the average female is smaller than the average male. This relation, however, is by no means universal. In the Quarterly Review of Biology, Katherine Ralls of the Smithsonian Institution reports that species in which females are of greater average size than males can be found in about 30 of the 122 families of living mammals.

“The phenomenon is characteristic of several taxa: the rabbits and hares, one family of bats, three

families of baleen whales, a subfamily of seals and two tribes of antelopes.”

A 25-FOOT “EYE”

1926 “Astronomers have planned a monster telescope, many times greater than the largest now in existence. The proposed reflecting telescope would have an aperture—the reflecting mirror—spanning 25 feet in diameter. If the proposed instrument was as long in proportion to its breadth, the tube would have to be 130 feet in length; but it would be desirable to give the mirror a deeper curvature, reducing the focal length to 1,000 inches, and making the skeleton tube of the instrument 86 feet long overall.

“Photographs taken with this arrangement would show images of the moon nearly two feet in diameter and of Jupiter more than a half-inch across. The 1,600-ton instrument would be a

marvel of precision. Its actual construction, however, awaits the necessary funds.”

A NOTABLE NEW BOOK

“Having completed a careful reading of the entire 976 pages of ‘The Splendour of the Heavens,’ the writer feels at a loss for adequate superlatives with which to characterize it. This book is called ‘a popular, authoritative astronomy.’ Each of these words appears to have been thoughtfully chosen. It is popular without being too popular. It is as authoritative as one has a right to expect when told that every one of its 19 co-authors is a member of the Royal Astronomical Society, and that the secretary of that famed old association of astronomers acted as one of its editors.

“The tome is an astronomy in that it covers practically

cally all the ground that a general astronomy should cover. It is not, however, a textbook but rather a book to be read, chapter by chapter, with keen interest.”

TWO PERSONALITIES IN ONE PERSON

1879 “Medical record books contain not a few reports of patients living double lives: cases in which there is a periodical loss of one phase of mental life and the assumption or resumption of another very different one, with an entirely different personality. Formerly such alterations of consciousness were explained by spiritual or demonic possession.

“In our more scientific days, the phenomena in question are much more satisfactorily explained by supposing that the patient’s mental life has been carried on by one side of his or her double brain, and that, when the action of that side is arrested by disease, the unused side takes up the intellectual function and continues until another paroxysm shifts the responsibility to the first used side. The reason that such lives are always double and never triple or manifold lies in the fact that we have only two independent brain lobes.”

BETTER STABLE DOORS

“Mr. Frank M. Dixon, of Jefferson City, Mo., has invented and patented a contrivance for hitching a horse and fastening a stable door in such a manner that the horse will be freed and the door opened in case of fire in the stable, and a contrivance for sounding an alarm at the same time.”

1876, Sweet Birds of Prey: “It must not be supposed that the food of honey buzzards is restricted to honey, which only forms its dessert; but they devote attention to small birds, insects, and reptiles, as well as rats, mice and small deer. They have also been known to purloin the eggs of other birds.”

100 SCIENTIFIC AMERICAN SEPTEMBER 2026

© 2026 Scientific American

Scientific American, Vol. 35, No. 13, September 1976

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Adventures in Astronomy: Approaching Infinity

Tuesdays, 7:30 PM - 9:00 PM, Eastern Time, over Zoom

September 29, 2026 thru January 12, 2027

Does the Universe have an edge?

How were atoms like carbon and oxygen created?

How did life on earth begin?

Is there intelligent life orbiting other stars?

The universe in 16 weeks

1. Geo-centrism, Kepler's laws, and the Kepler-Newton Law.
2. Eclipses, tides, solar system formation, planet tilts, and planet densities.
3. The rocky and giant planets, the Moon, escape velocity, and planet atmospheres.
4. The electromagnetic spectrum, acceleration from mass, solar system age, comets, asteroids, and measuring distances via parallax.
5. Measuring distances via Cepheid Variable stars, discovering other galaxies, the sun, fusion, and the Hertzsprung-Russell diagram.
6. Star birth, Wien's law, star temperatures, and star luminosities.
7. Stellar mass, stellar lifetimes, the creation of neutron stars and black holes, and the creation of elements from stellar explosions.
8. Pulsars, telescopes, adaptive optics, space telescopes, and telescope arrays.
9. Enjoying the night sky, galaxy classification, star clusters, active galactic nuclei, and synchrotron radiation.
10. The expanding universe, the Hubble-Lemaitre law, the Cosmological Principle, and dark matter.
11. Special and general relativity, gravitational red shift, black holes, and the cosmic microwave background.
12. Does the universe have an edge? How do we know there was a Big Bang? The age of the universe and its fate.
13. Inflation, the 4 forces of nature, string theory, the Anthropic Principle, and women astronomers.
14. Are there extraterrestrial civilizations in the universe? Habitable exoplanets, astrobiology, and the lifetimes of K-type stars.
15. Are there extraterrestrial civilizations on Earth? Have extraterrestrials created unidentified anomalous phenomena?
16. Are there extraterrestrial civilizations on Earth? Have humans observed extraterrestrials on Earth? The Copernican Principle.

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制度与权力批判深度研判：Scientific American (2026-09)

▌ 本日全报思想与文化深思雷达 (Intellectual & Cultural Significance Radar)

在系统通盘梳理本期《科学美国人》所涉及的机构变动与科学报道后，以下 2 个具体事件在制度结构、权力技术与知识生产层面最值得学者进一步深思：

1. 【学术媒体的资本重组与空间迁移】 [F5_10, F6_12]（版面：第5-6版/专业栏目）

   • 事件简述：拥有近 181 年历史的 $\textit{Scientific American}$ 在 2026 年 6 月被 Springer Nature 出售给 LabX Media Group，并同步将办公室搬迁至纽约市金融区电池公园旁。
   • 制度批判切入点：分析知识生产机构在资本逻辑驱动下的所有权变更，以及物理空间的迁移（从学术场域进入金融核心区）如何象征性地暗示其权力属性与连接网络的转变。

2. 【科学叙事的权力重构：深海与地质时间】 [F10_19, F11_21]（版面：第10-11版/专业栏目）

   • 事件简述：报道探讨了 5 亿年前加拿大西北地区作为海底世界的复杂生命形式，并引用埃文斯（Evans）的观点，认为深海环境的稳定性为动物的首次出现和进化提供了极佳场所。
   • 制度批判切入点：探讨科学话语如何通过对“稳定性”与“适应性”的定义，构建关于生命演化的必然性叙事，以及这种叙事如何影响我们对自然环境与生存条件的认知框架。

---

▌ 精选核心专题深度思想论证 (In-Depth Dialectical Monograph)

专题一：知识生产机构的“金融区化”：资本逻辑对学术权威的结构性捕获

本期报纸中一个极具象征意义的细节是 $\textit{Scientific American}$ 的所有权变更及其办公地点的迁移 [F5_10, F6_12]。这家拥有近 181 年历史的机构，在 2026 年 6 月被 Springer Nature 出售给 LabX Media Group 后，迅速将总部搬迁至纽约市金融区电池公园旁。这一物理空间的位移并非简单的行政搬迁，而是一次深刻的制度性转向。

从社会学场域理论视角来看，学术出版机构原本处于一种介于“专业权威”与“商业运作”之间的张力之中。然而，当其总部直接落户于金融核心区时，这种张力在空间维度上被重新定义。办公空间的地理位置决定了其权力网络的连接方式：它在物理上更接近于资本流动与媒体集团的聚集地。这种“金融区化”暗示了知识的筛选标准可能面临从“纯粹科学启发性”向“资本可变现性”或“市场可见度”偏移的风险。

进一步结合话语分析，$\textit{Scientific American}$ 在编辑寄语中将此次出售描述为“开启新篇章” [F5_10 🔍]，并强调其在校对最终页样以确保准确无误的专业精神。然而，这种修辞在掩盖所有权变更这一结构性剧变。当一个学术机构被纳入 LabX Media Group 这样的商业媒体矩阵时，其内部的编辑权力结构必然会被重塑。知识生产不再仅仅是为了记录创新，而是在一个被量化、被算法驱动的“内容”市场中竞争注意力。这种制度性的重组，标志着现代知识生产机构正被进一步纳入商业逻辑的框架，其学术权威在某种程度上被转化为一种可供交易的品牌资产。

专题二：环境决定论与演化叙事的认知框架

在关于“深海化石”的报道中，一个关键的认知逻辑浮现：深海环境因其在温度和可用氧气方面的波动比浅水环境更小，从而被定义为动物首次出现和进化的“极佳场所” [F11_21 🔍]。这种论述揭示了科学叙事中一种典型的“稳定性 $\rightarrow$ 适应性 $\rightarrow$ 进化”的因果链条。

这里存在一个深刻的认识论问题：当我们强调“如果你能适应一种温度，那就万事大吉了” [F11_21 🔍] 时，科学话语实际上在构建一种关于生存的“简化模型”。这种模型将复杂的生物演化过程归结为对特定物理参数（如温度稳定性）的响应。虽然这在生物学上具有解释力，但在知识生产的层面，它倾向于将环境因素设定为决定性的“容器”，而将生命形式设定为被动的“适应者”。

这种叙事方式在潜移默化中强化了某种“环境决定论”的认知框架。当我们将深海的稳定性视为进化的催化剂时，我们实际上是在用一种线性的、目的论的逻辑来解读地质时间。这种认知框架如果被泛化，可能会导致我们在看待当代环境危机时，过度依赖于对单一物理参数的控制，而忽略了生态系统内部复杂的、非线性的相互作用。因此，对深海化石的报道不仅是古生物学的记录，更是科学如何通过定义“理想环境”来构建生命历史叙事的典型案例。

---

▌ 面向学者的制度研究开放性追问 (Open Research Horizons)

1. 【关于知识生产的制度异化】：当顶尖学术媒体的物理空间与所有权结构全面向金融资本靠拢时，其内部的编辑筛选机制如何被隐蔽地重塑为“市场价值评估”机制？这种转向如何影响公众对科学真理的认知合法性？
2. 【关于科学叙事的认知边界】：在演化生物学的报道中，如何区分“必要的简化模型”与“误导性的决定论叙事”？科学传播在将复杂研究转化为大众可读的“稳定性叙事”时，丢失了哪些关键的认识论维度？
3. 【关于机构历史与资本逻辑的冲突】：一个拥有 181 年历史的学术品牌在面对资本兼并时，其“历史合法性”如何被新所有者工具化，以维持其在金融区环境中的学术权威假象？

理性与情感辩证深度研判：Scientific American (2026-09)

▌ 本日全报生活世界痛感与情感政治深思雷达 (Lifeworld & Affective Significance Radar)

在系统通盘梳理本期报纸所涉及的所有报道后，以下 3 个具体事件在个体生命体验、情感撕裂与生活世界崩解层面最值得学者进一步深思：

1. 【代际现状的认知撕裂】 [F7_14 🔍]（生活领域：家庭与教育）

   • 事件简述：针对“研究发现如今的孩子和青少年在许多方面都比前几代人做得更好”这一结论，杂志社向读者征集个人经历的回应。
   • 情感政治切入点：探讨量化研究的“整体向好”结论与个体在具体生活世界中体验到的真实感受之间可能存在的剧烈撕裂，揭示统计学理性如何可能掩盖微观生命中的情感真实。

2. 【相对论悖论中的认知焦虑】 [F8_16 🔍]（生活领域：科学认知与哲学）

   • 事件简述：读者在讨论洛伦兹收缩时提出，高速运动物体在静止观察者看来是否会坍缩成黑洞，而自身参考系却无感知，从而产生矛盾。
   • 情感政治切入点：分析人类在面对极端物理定律（Logos）时，由于直觉经验（Pathos）的失效而产生的认知失调与不安，探讨理性推演与感官真实之间的不可调和性。

3. 【深海进化之稳定性与生存本能】 [F10_20, F11_21]（生活领域：自然历史与生命哲学）

   • 事件简述：研究指出深海环境的温度和氧气波动极小，这种稳定性为地球最早复杂生命形式的出现提供了极佳场所。
   • 情感政治切入点：反思“稳定性”在生命演化中的情感意义——生存的底线并非在于对剧烈变化的适应，而在于一种极低熵状态下的持续存在，探讨“安稳”作为生命原初驱动力的哲学内涵。

---

▌ 精选核心专题理性与情感辩证论证 (The Dialectic of Logos and Pathos Monograph)

专题一：【统计学理性与微观生命体验的断裂：以“世代现状”讨论为例】

在《科学美国人》的“世代现状”栏目中，出现了一个典型的系统理性模型：基于大规模研究的结论认为，当代青少年在多个维度上优于前代人 [F7_14 🔍]。这种基于数据的 Logos 试图构建一个关于“进步”的线性叙事，将人类的成长与福祉量化为可比较的指标。

然而，杂志社通过征集读者回复的行为，实际上开启了一次生活世界的现象学还原。当读者被问及“这与你的经历相符吗？”时，讨论的重心从“统计数据的准确性”转移到了“个体生命体验的真实性”。这里发生了剧烈的Logos 与 Pathos 的辩证摩擦：统计学上的“整体向好”可能在个体层面被感知为一种“被否认的痛苦”。如果一个青少年在数据指标上（如教育程度、健康指标）处于高位，但在情感体验上（如孤独感、存在焦虑）处于低谷，那么系统理性不仅无法提供慰藉，反而可能通过“你应该比前人更好”的逻辑结论，对个体产生二次压抑。

这种话语温度差揭示了当代社会治理中的认知陷阱：当决策者过度依赖量化指标来定义“幸福”或“进步”时，微观生命中的情感真实被简化为数据噪声。通过批判情感理论视角来看，真正的社会关怀不应是对统计结论的重复，而应是对那些“不符合趋势”的个体痛感的接纳。

专题二：【物理定律的绝对理性与人类直觉经验的冲突：以洛伦兹收缩悖论为例】

在关于“快速收缩”的读者来信中，一个深刻的认知冲突被揭示：洛伦兹收缩作为狭义相对论的预测，认为物体在高速运动时会收缩 [F8_16 🔍]。读者提出的悖论——物体是否会因收缩而坍缩成黑洞，而自身参考系却毫无察觉——实际上是数学理性（Logos）与感官直觉（Pathos）的正面碰撞。

在这种冲突中，理性（相对论方程）是绝对的、非人格化的，它不依赖于观察者的感受而存在。但人类的认知结构是基于低速生活世界的，我们的“痛感”和“空间感”是基于欧几里得几何的直觉。当理性推演得出一个违背直觉的结论（如长度收缩、时间膨胀）时，个体产生的不是对真理的快感，而是一种深层的认知失调（Cognitive Dissonance）。

这种辩证摩擦体现为：科学理性要求我们放弃对“绝对空间”的情感依赖，而人类的意识则本能地试图通过构建“黑洞坍缩”等极端想象来弥合这种逻辑裂缝 [F8_16 🔍]。这证明了即使在最纯粹的物理学领域，人类也无法完全脱离其生物性的情感认知去理解宇宙。这种“无法理解的焦虑”恰恰是科学探索的动力所在——它将人类从舒适的直觉区推向冰冷的理性之巅，而在这个过程中，个体必须经历一次精神上的“脱壳”与重塑。

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▌ 面向学者的伦理与社会心理开放性研究追问 (Open Research Horizons)

1. 【关于量化幸福的伦理研究】：在社会科学研究中，如何建立一套机制，使得量化结论（如“代际向好”）在发布时能与微观个体的异质性体验共存，而非将其掩盖？
2. 【关于科学认知焦虑的心理学研究】：面对违背直觉的现代科学理论（如相对论、量子力学），人类在认知重构过程中产生的心理压力如何影响其对科学的信任度？
3. 【关于环境稳定性与生命韧性的哲学研究】：深海生物演化对稳定性的依赖 [F11_21 🔍] 是否可以为当代人类在剧烈变动的社会环境中寻找“心理避风港”提供一种生物学上的隐喻或启示？