Category: 7. Science

A red supergiant in the Milky Way has thrown a curveball at astronomers. DFK 52, a member of the Stephenson 2 cluster, sits inside a vast bubble of gas and dust that is about 8.2 trillion miles across and roughly the mass of the Sun.

Researchers used the ALMA radio telescope in Chile to observe the red supergiant, which is similar to the well-known star Betelgeuse. The project was led by Mark Siebert at Chalmers University of Technology.

ALMA revealed that the bubble is expanding, suggesting a violent outburst about 4,000 years ago that somehow did not end the star’s life.

Star bubble shows huge mass outburst

The team describes a complex cloud that spreads outward in tangled arcs and clumps, not a tidy sphere, and reaches astonishing size for material tied to a single star.

The experts report that the detached shell holds roughly one solar mass and extends about 1.4 light years across.

The researchers link the expansion to a short, intense episode of mass loss that happened a few millennia ago. That timing is recent in astronomical terms and sets up a natural test case for how massive stars shed material before they explode.

“We got a big surprise when we saw what Alma was showing us. The star is more or less a twin of Betelgeuse, but it’s surrounded by a vast, messy bubble of material,” said Siebert.

What the radio telescope saw

The ALMA array measures faint radio light from molecules like carbon monoxide and silicon monoxide, letting astronomers map gas speeds with the Doppler effect. Those data reveal both slow and fast components moving in different patterns around the star.

A compact, slower wind surrounds the star today at about 6.2 miles per second. A faster structure, likely a disk or ring oriented edge on, expands at about 16.8 miles per second and appears to be the relic of the ancient outburst.

This two-part picture matches the brightness and shape of the carbon monoxide emission. The model points to an equatorial feature containing only a few hundredths of the Sun’s mass, along with a slower, continuous wind shedding material at a modest rate.

Why the star lost mass

Why did DFK 52 throw off so much mass without dying? The survival of the star after such a forceful ejection raises questions about what set off the event.

“To us, it’s a mystery as to how the star managed to expel so much material in such a short timeframe. Maybe, like Betelgeuse seems to, it has a companion star that’s still to be discovered,” said Siebert.

The idea of a hidden partner that stirred the atmosphere and helped peel off outer layers has gained traction. 

Another possibility is a brief, unstable phase within the star itself. Episodic mass loss has been seen or inferred in other massive stars approaching the end of life, though the precise triggers remain debated.

What this means for future supernovae

Dense gas and dust close to a star can change how a supernova looks in its first days. When fresh ejecta slam into nearby material, the interaction can brighten the event and imprint unique features on the early spectrum.

Evidence for this behavior already exists. A 2017 paper on SN 2013fs showed that the exploding star had a compact but dense circumstellar medium that was shed shortly before the blast.

DFK 52’s bubble sits farther out, yet it proves the star has a history of strong mass loss. If the star ramps up again before it dies, the environment could set the stage for a very conspicuous supernova.

Comparing the star to other supergiants

DFK 52 draws comparisons to red supergiant icons like Betelgeuse and Antares. These are massive, swollen, cool stars nearing the end of their lives and expected to finish as Type II supernovae.

Betelgeuse itself showed how messy these stars can be when it dimmed in late 2019 and early 2020. That event was traced to a dust cloud formed by material leaving the star.

DFK 52 appears less luminous than the most extreme red supergiants but carries a larger, colder envelope at great distance. This combination hints at an unusual history that standard wind models do not capture.

What happens next

The team plans follow up observations to hunt for a companion and to refine the 3D structure of the shell. Better constraints on the gas chemistry and dust properties will also help sort out how the outburst unfolded.

“If this is a typical red supergiant, it could explode sometime in the next million years,” said study co-author Elvire De Beck.

“We’re planning more observations to understand what’s happening, and to find out whether this might be the Milky Way’s next supernova.”

The study is published in Astronomy and Astrophysics.

Image Credit: ALMA (ESO/NAOJ/NRAO)/M. Siebert et al

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A SpaceX cargo ship is scheduled to arrive at the International Space Station (ISS) on Monday morning (Aug. 25), and you can watch the rendezvous live.

A robotic Dragon capsule is expected to dock with the station on Monday around 7:30 a.m. EDT (1130 GMT), ending a roughly 29-hour orbital chase.

You can watch the action live here at Space.com courtesy of NASA, or directly via the agency. Coverage will begin at 6 a.m. EDT (1000 GMT) on Monday.

This Dragon is flying SpaceX’s 33rd mission for NASA’s Commercial Resupply Services program. The flight, known as CRS-33, began with a launch atop a Falcon 9 rocket early Sunday morning (Aug. 24).

The study, published in Science, focused on a gene known as MUC19, which is involved in the production of proteins that form saliva and mucosal barriers in the respiratory and digestive tracts. The researchers show that a variant of that gene derived from Denisovans, an enigmatic species of archaic humans, is present in modern Latin Americans with Indigenous American ancestry, as well as in DNA collected from individuals excavated at archeological sites across North and South America.

The frequency at which the gene appears in modern human populations suggests the gene was under significant natural selection, meaning it provided a survival or reproductive advantage to those who carried it. It’s not clear exactly what that advantage might have been, but given the gene’s involvement in immune processes, it may have helped populations to fight off pathogens encountered as they migrated into the Americas thousands of years ago.

“From an evolutionary standpoint, this finding shows how ancient interbreeding can have effects that we still see today,” said study author Emilia Huerta-Sánchez, a professor of ecology, evolution and organismal biology at Brown University. “From a biological standpoint, we identify a gene that appears to be adaptive, but whose function hasn’t yet been characterized. We hope that leads to additional study of what this gene is actually doing.”

Huerta-Sanchez co-authored the study with Fernando Villanea, a former post-doctoral researcher at Brown who is now at University of Colorado, Boulder; David Peede, a graduate student at Brown; and an international team of collaborators.

Not much is known about the Denisovans, who lived in Asia between 300,000 and 30,000 years ago, aside from a few small fossils from Denisova cave in Siberia, two jaw bones found in Tibet and Taiwan, and a nearly complete skull from China found this year. The finger fossil from Siberia contained ancient DNA, which enables scientists to look for common genes between Denisovans and modern humans. Prior research led by Huerta-Sánchez found that a version of a gene called EPAS1 acquired from Denisovans may have helped Sherpas and other Tibetans to adapt to high altitudes.

For this study, the researchers compared Denisovan DNA with modern genomes collected through the 1,000 Genomes Project, a survey of worldwide genetic variation. The researchers found that the Denisovan-derived MUC19 gene is present in high frequencies in Latino populations who harbor Indigenous American genetic ancestry. The researchers also looked for the gene in the DNA of 23 individuals collected from archeological sites in Alaska, California, Mexico and elsewhere in the Americas. The Denisovan-derived variant was present at high frequency in these ancient individuals as well.

The team used several independent statistical tests to show that the Denisovan MUC19 gene variant rose to unusually high frequencies in ancient Indigenous American populations and present-day people of Indigenous descent, and that the gene sits on an unusually long stretch of archaic DNA — both signs that natural selection had boosted its prevalence. The research also revealed that the gene was likely passed through interbreeding from Denisovans to another archaic population, the Neanderthals, who then interbred with modern humans.

Huerta-Sánchez said the findings demonstrate the importance that interbreeding had in introducing new and potentially useful genetic variation in the human lineage.

“Typically, genetic novelty is generated through a very slow process,” Huerta- Sánchez said. “But these interbreeding events were a sudden way to introduce a lot of new variation.”

In this case, she said, that “new reservoir of genetic variation” appears to have helped modern humans as they migrated into the Americas, perhaps providing a boost to the immune system.

“Something about this gene was clearly useful for these populations — and maybe still is or will be in the future,” Huerta-Sánchez said.

She’s hopeful that the recognition of the gene’s importance will spur new research into its function to reveal novel biological mechanisms, especially since it involves coding genetic variants that alter the protein sequence.

The research was supported by The Leakey Foundation, the National Institutes of Health (1R35GM128946- 01, T32 GM128596, R35GM142978, R01NS122766), the Alfred P. Sloan Foundation, the Blavatnik Family Graduate Fellowship in Biology and Medicine, the Brown University Predoctoral Training Program in Biological Data Science (NIH T32 GM128596), the Burroughs Wellcome Fund and the Human Frontier Science Program.

Since the early 2000s, scientists have been puzzled by a gleaming turquoise spot in the middle of the Antarctic Ocean showing up in satellite images.

The patch is located just south of the great calcite belt, a region that’s rich in the mineral form of calcium carbonate, and teeming with coccolithophores, tiny marine organisms that grow reflective calcite shells out of the mineral.

The patch itself, however, has been considered far too frigid to support these tiny plankton, causing a longstanding marine mystery.

Now, as detailed in a paper published in the journal Global Biogeochemical Cycles, scientists say they’ve finally nailed down a possible reason for the existence of the otherworldly iridescence.

The team ventured into the rough ocean waters on board a research vessel, taking detailed measurements at various depths to collect data that satellite images can’t provide.

“Satellites only see the top several meters of the ocean, but we were able to drill down with multiple measurements at multiple depths,” said Bigelow Laboratory for Ocean Sciences senior research scientist Barney Balch in a statement about the research.

To their surprise, they found that coccolithophores did, in fact, live in the frigid waters where no one thought they could survive — albeit in much smaller concentrations than in the great calcite belt. In the process, they got an unprecedented peek at how the ocean’s carbon cycles function.

Coccolithophores are caught in a massive war with another type of plankton, called diatoms, which turn organic carbon into energy, a vital source of food for marine life.

The border between the great calcite belt and the mysterious turquoise region was previously seen as a kind of no man’s land between these two factions of plankton.

But the researchers’ findings suggest that “moderate concentrations of plated coccolithophores and detached coccoliths were observed south of the great calcite belt all the way to 60°S,” the paper reads.

However, the majority of the reflectiveness is the result of the shiny outer layers of diatom plankton scattering the light, the researchers posit.

The findings could have considerable implications for our planet. Coccolithophores are so widespread, they’re considered a critical sink for atmospheric carbon.

“We’re expanding our view of where coccolithophores live and finally beginning to understand the patterns we see in satellite images of this part of the ocean we rarely get to go to,” Balch explained in the statement.

“There’s nothing like measuring something multiple ways to tell a more complete story,” he added.

More on plankton: Scientists May Be Able to Fight Global Warming by Supercharging Plankton

High-mass stars form quickly and push back hard on their surroundings. Radiation and winds should strip away the very fuel they need to grow, yet these stars still bulk up fast.

A new study points to a simple answer: long, dense streams of gas that deliver material straight to the center of action, even where a classic disk is hard to find or very small.

ALMA finds streams

The study was led by Fernando A. Olguin of Kyoto University with collaborators in Japan, Taiwan, China, and the United States.

Using the Atacama Large Millimeter/submillimeter Array in Chile (ALMA), the team examined a young, massive source called G336.018-00.827 ALMA1.

They found two gas streams converging toward the protostar, one of which connects directly to the central region, with a clear change in velocity that signals rotation and infall.

The researchers expected a prominent accretion disk a few hundred astronomical units across.

Instead, they saw spiral arms reaching inward and either no large disk or an extremely compact one, likely smaller than 60 astronomical units, or about 5.6 billion miles.

“Our work seems to show that these structures are being fed by streamers, which are flows of gas that bring matter from scales larger than a thousand astronomical units, essentially acting as massive gas highways,” said Olguin.

Gas streamers help stars grow

Astronomers classify high-mass stars as those above roughly eight times the Sun’s mass. According to a 2002 study, that threshold marks a regime where radiation pressure and ionized winds become strong and can choke off simple spherical collapse.

In massive protostars, theory and observations indicate that non-spherical accretion is needed, helping radiation escape through polar regions while matter continues to arrive through denser paths near the midplane.

A recent preprint explains that streamers fit this bill because they channel gas along narrow tracks with high momentum.

The ALMA1 data show that the western, blueshifted streamer carries enough material inward to overwhelm local feedback near about 61 astronomical units, which is approximately 5.7 billion miles.

That supply helps maintain a dense inner region where growth can continue despite radiation pressure from the young star.

These flows do not need to end at the disk edge. In ALMA1, the observed streamers penetrate well inside the expected disk radius, potentially feeding a very small unresolved disk or even the protostar itself, which changes how we picture the last link in the inflow chain.

ALMA shows spiral gas

ALMA’s long-baseline setup delivered a sharp view, resolving features on scales of about 86 astronomical units, or roughly 8 billion miles.

The team mapped both dust emission and several molecular lines, including methanol and sulfur monoxide, to trace motion and temperature structure around the central source.

Those tracers reveal a velocity gradient along one streamer that bends at a characteristic radius near 500 astronomical units, or about 46.5 billion miles.

The change implies a shift from infall-dominated flow to rotation-dominated motion as the gas nears the center.

Gas streamers beat radiation

Kinematic modeling indicates that the outer segment of the blueshifted streamer behaves like a rotating, infalling envelope.

Inside roughly 500 astronomical units, the speeds line up best with near-Keplerian rotation, as expected when gas settles into a compact structure before reaching the protostar.

At the point where the flow turns, the team sees signs of shocks that heat and concentrate material.

Vibrationally excited sulfur monoxide is compact and peaks near that location, consistent with gas slamming into denser regions as it changes course toward the inner system.

Mass estimates for the inner streamers fall in the range of a few tenths of a solar mass, with inferred infall rates high enough to replenish the center on useful timescales.

The modeled momentum of the inflow exceeds the local radiation force by about two orders of magnitude near the inner radius, which explains how accretion continues.

Taken together, the picture is simple. A large-scale reservoir funnels material into extended spiral arms, the arms feed narrow streamers, and those streamers push gas right into the inner tens of astronomical units where star growth is decided.

Gas streamers replace big disks

Large, rotating disks around young massive stars do exist. ALMA has imaged a roughly 1,000 astronomical unit disk with a prominent spiral arm around the forming O-type star AFGL 4176 mm1, a clear case where a massive disk structures the flow.

Streamers have also been spotted feeding lower-mass protostars, where arc-like flows guide gas from envelopes into compact inner regions.

That broader record suggests that filamentary feeding is a common tool nature uses across stellar masses, not just an outlier in one cloud.

ALMA1 shows that a large, obvious disk is not required for a high-mass protostar to keep growing.

A very small disk can still be present, but the heavy lifting can be done by the streamers themselves if the reservoir and geometry cooperate.

That flexibility helps resolve a long-standing tension in massive star formation.

If radiation pressure gets strong early, steady supply lines must find a way to keep delivering mass to the center without being blown away, and focused streams are well suited for that job.

What comes next

“We found streamers feeding what at that time was thought to be a disk, but to our surprise, there is either no disk or it is extremely small,” said Olguin.

The team plans to apply the same methods to other regions to test how often streamers dominate the final stages of accretion.

They will also probe even closer to the center to confirm or rule out tiny disks that current data cannot fully resolve.

The study is published in Science Advances.

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For almost two decades, astronomers have been trying in vain to explain extremely bright flashes of radio bursts emanating from deep space.

Despite only lighting up for a tiny fraction of a second, these fast radio bursts (FRBs) have been known to release as much energy as the Sun puts out in an entire year.

Now, in what’s being called a “turning point,” an international team of researchers has traced back the location of the origin of one of the brightest FRBs ever detected, allowing them to glean invaluable insights into the baffling phenomenon.

As detailed in a pair of new papers, astronomers used the Canadian CHIME/FRB radio-telescope to home in on an FRB, officially called 20250316A — but unofficially referred to as “RBFLOAT” for Radio Brightest Flash Of All Time” — which was first observed in March of this year near the Big Dipper.

Thanks to an array of “outrigger” telescopes spread out across North America, the team was able to pinpoint the origin of the FRB to a precise region that measures just 45 light-years across, significantly smaller than the average star cluster, in a galaxy some 130 million light-years away.

While that may sound somewhat overwhelming, given the fact that 45 light-years is roughly 30 times the diameter of our entire solar system, it’s an impressive feat.

“The precision of this localization, tens of milliarcseconds, is like spotting a quarter from [62 miles] away,” said lead author of one of the papers and McGill University-based postdoctoral researcher Amanda Cook in a statement. “That level of detail is what let us identify the host galaxy, NGC 4141, and match the burst with a faint infrared signal captured by the James Webb Space Telescope.”

That kind of precision allowed teams to trace back the FRB’s origin to a faint infrared signal, which was previously captured by NASA’s James Webb Space Telescope.

“The high resolution of JWST allows us to resolve individual stars around an FRB for the first time,” said Harvard research associate Peter Blanchard, lead author of the second paper, in the statement. “This opens the door to identifying the kinds of stellar environments that could give rise to such powerful bursts, especially when rare FRBs are captured with this level of detail.”

“This was a unique opportunity to quickly turn JWST’s powerful infrared eye on the location of an FRB for the first time,” he added in a separate Harvard press release, calling the faint infrared source an “exciting result.”

“This could be the first object linked to an FRB that anyone has found in another galaxy,” Blanchard said.

Despite the exciting advancement, we’re still far from calling the mystery solved once and for all.

Researchers have previously suggested that magnetars, the extremely dense and highly magnetized remains of dead stars, or neutron stars, could be causing FRBs, sending powerful flashes of radio emissions at regular intervals like a lighthouse.

And that’s just one of many candidates that have been put forward over the years.

Complicating matters is the fact that the astronomers have yet to observe 20250316A repeating itself. Other FRBs have been known to repeat and pulse in complex and highly regular patterns, adding to the overall mystery.

“It seems different energetically than the repeaters we’ve studied,” explained McGill postdoc researcher and CHIME/FRB researcher Mawson Sammons. “We’re now re-examining some of the more explosive models that had fallen out of favor.”

The team posits that the object spotted in the JWST observations could be a red giant, a Sun-like star nearing the end of its life cycle. An accompanying neutron star could be pulling mass away from the red giant, a process that may have triggered the outburst of radio emissions.

“Dozens of different ideas have been proposed to explain FRBs, but until now we haven’t had the data to test most of them,” said coauthor and Harvard astronomy professor Edo Berger in the Harvard press release. “Being able to isolate individual stars around an FRB is a huge gain over previous searches, and it begins to tell us what sort of stellar systems could produce these powerful bursts.”

“Whether or not the association with the star is real, we’ve learned a lot about the burst’s origin,” Blanchard added. “If a double star system isn’t the answer, our work hints that an isolated magnetar caused the FRB.”

The team is already gearing up in the hopes of being in the right place at the right time to catch the next FRB in the act.

“We can’t predict when and where the next FRB will come from, so we have to be ready to quickly deploy JWST when the time comes,” Berger said.

More on FRBs: Scientists Propose Interesting Explanation for Mysterious Signals From Space

An automatic fan enhances interfacial motion

Rhagovelia water striders are unique among water striders because these millimeter-sized semiaquatic insects use specialized fan-like structures on their propulsion legs that enable rapid turns and bursts of speed.

“I was intrigued the first time I saw ripple bugs while working as a postdoc at Kennesaw State University during the pandemic.” said Victor Ortega-Jimenez an integrative biologist now at the University of California, Berkeley, a lead author of the study. Ortega-Jimenez had previously studied the jumping performance of large Gerridae water striders from unsteady waters, but Rhahovelia bugs were different. “These tiny insects were skimming and turning so rapidly across the surface of turbulent streams that they resembled flying insects. How do they do it? That question stayed with me and took more than five years of incredible collaborative work to answer it.”

Until now it was believed that these fans were powered solely by muscle action. However, a study published on August 21 in Science, reports that Rhagovelia’s flat, ribbon-shaped fans can instead passively morph using surface tension and elastic forces, without relying on muscle energy.

“Observing for the first time an isolated fan passively expanding almost instantaneously upon contact with a water droplet was entirely unexpected,” said Dr. Ortega-Jimenez.

This remarkable combination of collapsibility during leg recovery and rigidity during propulsion allows the bugs to execute sharp turns in just 50 milliseconds and move at speeds up to 120 body lengths per second, rivaling the rapid aerial maneuvers of flying flies.

Collaboration is key

When Dr. Ortega-Jimenez joined Georgia Tech in 2020 after leaving KSU, he presented the project and preliminary observations on Rhagovelia bugs to Dr. Saad Bhamla, who became fascinated and eager to explore it further. It was Dr. Bhamla who brought Dr. Je-Sung’s group into the collaboration, opening new possibilities to integrate biology, physics, and robotics into the project.

“I saw a real discovery hiding in plain sight. Often, we think science is a lone genius sport, but this couldn’t be farther from the truth. Modern science is all about interdisciplinary team of curious scientists working together, across borders and disciplines to study nature and engineer new bioinspired machines” Said Dr Bhamla

This interdisciplinary effort, integrating experimental biology, fluid physics, and engineering design, continued for more than five years.

Rhagobot is born: The next generation of water strider robots

Creating an insect-size robot inspired by ripple bugs was a major challenge, particularly because the microstructural design of the fan remained a mystery. The breakthrough came when Dr. Dongjin Kim and Professor Je-Sung from Ajou University captured high-resolution images of the fan using a scanning electron microscope, that they were able to uncover the solution to this puzzle.

“We initially designed various types of cylindrical-shaped fans, which we generally think what hair looks like. However, the functional duality of the fan — rigidity for thrust generation and flexible for collapsibility — could not be achieved with cylindrical structures. After numerous attempts, we overcame this challenge by designing a flat-ribbon shaped fan. We strongly suspected that biological fans might share a similar morphology, and eventually discovered that the Rhagovelia fan indeed possess a flat-ribbon micro architecture, which had not been previously reported. This discovery further validated the design principle behind our artificial flat-ribbon fan.” said Dr Dongjin Kim, a postdoctoral researcher at Ajou University and also a lead author of this study.

With these insights they were able to decode the structural basis and function of this natural propulsion system and recreate it in a robotic form. The result was the engineering of a one milligram elastocapillary fan that deploys itself, which was integrated into an insect-size robot. This microrobot is capable of enhanced thrust, braking, and maneuverability, validated through experiments involving both live insects and robotic prototypes.

“Our robotic fans self-morph using nothing but water surface forces and flexible geometry — just like their biological counterparts. It is a form of mechanical embedded intelligence refined by nature through millions of years of evolution. In small-scale robotics, these kinds of efficient and unique mechanisms would be a key enabling technology for overcoming limits in miniaturization of conventional robots.” said Professor Je-sung Koh, a senior author of the study.

The study not only establishes a direct link between fan microstructure and aquatic locomotion control, but also lays the foundation for future design of compact, semi-aquatic robots that can explore water surfaces in challenging, fast-flowing environments.

The ripple bug’s fan structure, which rapidly collapses and reopens as it enters and exits water, has revealed an unprecedented biomechanical duality — high flexibility for rapid deployment and high rigidity for thrust. This duality addresses longstanding limitations in small-scale aquatic robotics, such as inefficient stroke recovery and limited maneuvering capacity.

Sketching vortices and waves on water

It is well known that during propulsion, non-fanned water striders (e.g., those of the Gerridae family) generate characteristic dipolar vortices and capillary waves when stroking their superhydrophobic legs on the water. In contrast, fanned Rhagovelia bugs produce a distinct and complex vortical signature with each stroke, closely resembling the wake produced by flapping wings in air.

“It’s as if Rhagovelia have tiny wings attached to their legs, like the Greek god Hermes,” said Dr. Ortega-Jimenez. “Future research is needed to determine whether ripple bugs can similarly produce lift-based thrust with their fan-like structures, in addition to drag-based propulsion.”

This possibility is intriguing, because evidence suggests that whirligig beetles and cormorants generate hydrodynamic lift for swimming propulsion via their hairy legs and webbed feet, respectively.

In addition to these vortices, Rhagovelia bugs also produce symmetrical capillary waves during leg propulsion, which appear to aid in thrust generation, along with strong bow waves that form at the front of the body.

Standing against turbulent waters

Natural streams pose a real challenge, especially for tiny animals that live and move at the interface. Ripple bugs, roughly the size of a grain of rice, must navigate highly dynamic, wavy, and turbulent waters, while escaping predators, catching prey and finding mates. The relative levels of turbulence that these insects endure daily far exceed what we typically experience during airplane turbulence. Surprisingly, twenty-four-hour monitoring of these bugs in the lab revealed their remarkable endurance.

“They literally row day and night throughout their lifespan, only pausing to molt, mate, or feed,” said Ortega-Jimenez. These unsteady conditions found in streams represent also a significant difficulty for designing interfacial micro-robots capable of moving effectively across such unpredictable waters.

“When designing small-scale robots, it’s important to account for the specific environment in which they will operate — in this case, the water’s surface. By leveraging the unique properties of that environment, a robot’s performance and efficiency can be greatly enhanced. The Rhagobot, for instance, can travel quickly along a flowing stream thanks to its intelligent fan structure, which is powered by surface tension and the drag forces from the water surface.” said Jesung Koh.

Finally, these discoveries can have wide-ranging implications for bioinspired robotics, particularly in the development of environmental monitoring systems, search-and-rescue microrobots, and devices capable of navigating perturbed water-air interfaces with insect-like dexterity.

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It’s one of the deepest mysteries of the human mind: Do we all see the world the same way? In 1956, three social scientists set out to answer this question. From their offices at Northwestern University, Donald Campbell and Melville Herskovits teamed up with Marshall Segall, of Syracuse University, to coordinate an ambitious new investigation. They sent researchers on a mission to societies near and far, urban and rural: A gold mine in Johannesburg; a community of foragers in the Kalahari Desert; the Philippine island of Mindoro; and even their own college campus in Evanston, Illinois.

Tucked into each of their suitcases was a booklet of drawings, including 12 examples of a prominent figure called the Müller-Lyer illusion. You may have seen it before: When two identical horizontal lines are capped with arrowheads pointing either inward or outward, the line with inward-facing arrowheads looks longer, even though it’s not.

At least, that’s how the illusion works here in the United States. But what about elsewhere? When the study was completed in 1961, the results shocked the scientific community: Not everyone was susceptible to this seemingly obvious illusion. While students in Illinois tended to report the top line as longer, Zulu pastoralists in South Africa had a much weaker response, barely experiencing the illusory effects. And the San foragers of the Kalahari seemed not to see anything remarkable at all, just two lines of equal length, as if the illusion simply wasn’t an illusion for them. This wasn’t like finding different shapes in a complicated abstract drawing, or even having different interpretations of a novel. It was as though something about human vision was fundamentally different from culture to culture. How was this possible?

Before we unravel the mystery, let’s first explain why this matters to psychology researchers like us. Psychology aims to capture enduring truths about the human mind. But in the vast majority of cases, psychological studies explore narrow subject pools, such as college students taking introductory courses. The reason is mostly convenience; such test subjects are available in large numbers on college campuses (where most researchers are), and they are happy to give a little bit of their time in exchange for a bit of compensation, such as course credit. But there is good reason to worry about doing research this way. Who is to say that attitudes toward nationalism, or the prevalence of ADHD, or the best tricks for sticking to a new diet—or really, anything else psychologists study—generalize from one very specific group to the whole of humanity? Psychology has been around for a while, but it wasn’t until relatively recently that the field began to reckon with these concerns more seriously and systematically, under the banner of a clever acronym proclaiming most psychology research subjects are “WEIRD”: Western, Educated, Industrialized, Rich, and Democratic. The idea has gained steam over the past 15 years, and researchers are trying to do better.

But which psychological principles should we expect to vary across groups? Which findings are cultural creations limited to WEIRD research subjects, and which reflect our common humanity—true for us and everyone else? Here’s where the illusion study becomes so consequential. It’s one thing to suppose that political attitudes or dietary practices differ around the world; any tourist can attest to this. But perception itself? Could it really be that our very eyes tell us something different about the world depending on where we grew up?

Segall and colleagues thought so, and even went a step further. They proposed that Americans see the illusion only because of their overexposure to carpentry—straight lines and sharp angles that are present in urban environments and the Müller-Lyer figure, but are less prevalent in the Kalahari. Raise someone in an environment without boxy structures or rectangular windows and doors, the idea goes, and the illusion won’t exist for them. Contemporary anthropologists have further popularized this view, arguing that “the Müller-Lyer illusion is a kind of culturally evolved by-product.” Call it the Cultural Byproduct Hypothesis.

This result and the theoretical apparatus built around it are now essentially part of the psychological canon. They are often taught to Psych 101 students as both a fascinating discovery about visual processing and a cautionary tale about unwarranted assumptions of universality. We shouldn’t assume that others experience the world like we do—that much seems true and even uncontroversial. And what better piece of evidence for this lesson than discovering that we literally see the world differently depending on where we grow up.

We weren’t so sure about all this. In a new paper, we revisited over 100 years of research on perception and came to nearly the opposite conclusion: This particular visual illusion, and many other aspects of our perceptual system, arise from deep within us, are likely common to humans across the globe, and certainly aren’t mere cultural creations. As impressive as the cross-cultural studies seem (more on that in a moment), there are powerful clues suggesting that the Cultural Byproduct Hypothesis can’t really be true.

Why not? For one thing, lots of other animals see the Müller-Lyer illusion. If you train a guppy to swim toward longer lines (yes, a real thing that can be done!), and then you show it the Müller-Lyer figure, it will swim towards the top line—suggesting that the guppy sees that line as longer. This is true for a veritable zoo of nonhuman creatures, including horses, parakeets, monkeys, and lizards, who all see the illusion as well. Did the guppies’ culture create the illusion for them too? Seems unlikely.

Another clue: The illusion doesn’t even need to be made of straight lines in order to work. There are versions of the Müller-Lyer illusion composed entirely out of curves, or just groups of dots; there’s even a version that uses people’s faces. That observation calls into question the purported link with carpentry, since the whole idea was that the illusion relies on features such as straight lines present in precisely constructed environments.

Perhaps the strongest clue of all is also the most remarkable. A humanitarian and scientific project called Prakash recently offered free corrective surgery to children in North India who were born with congenital cataracts—cloudy lenses that prevent light from entering the eyes, blinding them since birth. With new, clear, artificial lenses, these children were now able to see for the first time in their lives. Astoundingly, when shown the Müller-Lyer illusion—mere hours after recovering from their operations—they reported the top line as longer than the bottom line. Not only had these children never seen carpentry, they had never seen anything.
And yet they still experienced the illusory effects of the figure.

All this and more suggests that the illusion really is a result of who we are, not the buildings we happen to grow up next to. Despite our differences, we really do see the world similarly, sharing something in common with humans across the globe and throughout history.

But wait: If the evidence against the Cultural Byproduct Hypothesis is so overwhelming, then why did those three social scientists find different results in their cross-cultural study, with some groups seeming not to see the illusion at all?

First, the cross-cultural studies were never all that consistent with one another. When we looked even deeper into the published record, it was surprisingly easy to find contradictory results: A study from the early 20^th century found that a jungle-dwelling population in India showed a stronger illusion than a pastoralist community in the same country, and another study from 1970 similarly found stronger effects in a rural population indigenous to South Africa than in a nearby urban community. Even Segall, Campbell, and Herskovits’ more famous study contained contradictions within itself. For example, one of the samples showing the weakest illusion of all was a group of mineworkers. Mines, of course, are highly constructed, carpentered environments—exactly the kind of environment that should produce a large illusion, according to the theory.

Second, studies of this sort are open to bias. For starters, you have to translate the task instructions into a local dialect, which is not always easy; many of these researchers even worried about this difficulty, writing that they “were not completely sure of exactly what was communicated to the respondents at all times.” There are also biases introduced by experimenters who know something about the research hypotheses and might—consciously or not—tilt the results accordingly. In another telling passage, one experimenter wrote that he “developed very strong expectations of what answer the respondents should give to a given item, and if a respondent gave the other answer, there was the impulse to correct the respondent to ask him to reconsider.” There is even evidence that some of the cross-cultural data were excluded if the reported illusion was too strong, and that this masked some findings that would have challenged the overall narrative. It may well be, then, that the illusion was present in these diverse populations, and the experimenters simply failed to fully capture it in their measurements.

What does that mean for us today? Expanding psychological research to capture the diversity of human experience is a tide that lifts all boats, and is a project we wholeheartedly support (and engage in ourselves). But some experiences may well be universal.

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