Cross two flashlight beams and they pass right through one another. That’s because particles of light, or photons, are mostly antisocial — they don’t interact with each other. But now scientists have spotted evidence of photons bouncing off other photons at the Large Hadron Collider at CERN, the European particle physics lab in Geneva.

“This is a very basic process. It’s never been observed before, and here it is finally emerging from the data,” says theoretical physicist John Ellis of King’s College London who was not involved with the study. Researchers with the ATLAS experiment at the LHC report the result August 14 in Nature Physics.
Because photons have no electric charge, they shouldn’t notice one another’s presence. But there’s an exception to that rule. According to quantum mechanics, photons can briefly transform into transient pairs of electrically charged particles and antiparticles — such as an electron and a positron — before reverting back to photons. Predictions made more than 80 years ago suggest that this phenomenon allows photons to interact and ricochet away from one another.

This light-by-light scattering is extremely rare, making it difficult to measure. But photons with more energy interact more often, providing additional chances to spot the scattering. To produce such energetic photons, scientists slammed beams of lead nuclei together in the LHC. Photons flit in and out of existence in the lead nuclei’s strong electromagnetic fields. When two nuclei got close enough that their electromagnetic fields overlapped, two photons could interact with one another and be scattered away.

To measure the interaction, ATLAS scientists sifted through their data to find collisions in which only two photons — the two that scattered away from the collision — appeared in the aftermath. “That’s the trickiest part of the whole thing,” says physicist Peter Steinberg of Brookhaven National Laboratory in Upton, N.Y., a member of the ATLAS collaboration. The scientists had to ensure that, in their enormous, highly sensitive particle detector, only two photons appeared, and convince themselves that no other particles had gone unaccounted for. The researchers found 13 such events over 19 days of data collection. Although other processes can mimic light-by-light scattering, the researchers predict that only a few such events were included in the sample.

The number of scattering events the researchers found agrees with the predictions of the standard model, physicists’ theory of particle physics. But a more precise measurement of the interaction might differ from expectations. If it does, that could hint at the existence of new, undiscovered particles.

Spacecraft have gone bite-sized. On June 23, Breakthrough Starshot, an initiative to send spacecraft to another star system, launched half a dozen probes called Sprites to test how their electronics fare in outer space. Each Sprite, built on a single circuit board, is a prototype of the tiny spacecraft that Starshot scientists intend to send to Alpha Centauri, the trio of stars closest to the sun. Those far-flung probes would be the smallest working spacecraft yet.

“We’re talking about launching things that are a thousand times lighter than any previous spacecraft,” says Avi Loeb, an astrophysicist at Harvard University who is part of the committee advising the initiative. A Sprite is only 3.5 centimeters square and weighs four grams, but packs a solar panel, radio, thermometer, magnetometer for compass capabilities and gyroscope for sensing rotation.

These spacecraft are designed to fly solo, but for this test, they hitched a ride into low Earth orbit on satellites named Max Valier and Venta-1. Each satellite has one Sprite permanently riding sidecar, and the Max Valier craft has another four it could fling out into space. Unfortunately, as of August 10, ground controllers haven’t yet been able to reach the Max Valier satellite to send a “Release the Sprites!” command. One of the permanently attached Sprites — probably the one on Venta-1 — is in radio contact.

Before sending next-gen Sprites off to Alpha Centauri, scientists plan to equip them with cameras, actuators for steering and other tools. “This was really just the first step in a long journey for Starshot,” Loeb says.

With its bright hue, this snake was bound to stand out sooner or later.

A newly discovered subspecies of sea snake, Hydrophis platurus xanthos, has a narrow geographic range and an unusual hunting trick. The canary-yellow reptile hunts at night in Golfo Dulce off Costa Rica’s Pacific coast. With its body coiled up at the sea surface, the snake points its head under the water, mouth open. That folded posture “creates a buoy” that stabilizes the snake so it can nab prey in choppy water, says study coauthor Brooke Bessesen, a conservation biologist at Osa Conservation, a biodiversity-focused nonprofit in Washington, D.C. In contrast, typical Hydrophis platurus, with a black back and yellow underbelly, hunts during the day, floating straight on calm seas.
The newly described venomous snake has been reported only in a small, 320-square-kilometer area of Golfo Dulce. After analyzing 154 living and preserved specimens, the researchers described the reptile’s characteristics July 24 in Zookeys. The scientists hope that the subspecies designation will enable the Costa Rican government to protect the sunny serpent, which they worry is already at risk from overzealous animal collectors.

Viking warriors have a historical reputation as tough guys, with an emphasis on testosterone. But scientists now say that DNA has unveiled a Viking warrior woman who was previously found in a roughly 1,000-year-old grave in Sweden. Until now, many researchers assumed that “she” was a “he” buried with a set of weapons and related paraphernalia worthy of a high-ranking military officer.

If the woman was in fact a warrior, a team led by archaeologist Charlotte Hedenstierna-Jonson of Uppsala University in Sweden has identified the first female Viking to have participated in what was long considered a male pursuit.
But the new report, published online September 8 in the American Journal of Physical Anthropology, has drawn criticism from some researchers. All that’s known for sure, they say, is that the skeleton assessed in the new report belonged to a woman who moved to the town where she was interred after spending her youth elsewhere.

“Have we found the Mulan of Sweden, or a woman buried with the rank-symbols of a husband who died abroad?” asks archaeologist Søren Sindbæk of Aarhus University in Denmark. There’s no way to know what meanings Vikings attached to weapons placed in the Swedish grave, Sindbæk says.

Although the new paper dubs the long-dead woman “a high-ranking female Viking warrior,” other interpretations of her identity are possible, Hedenstierna-Jonson acknowledges. But she notes that the Viking woman “was an exception in a sphere dominated by men, either if she was an active warrior or if she was ‘only’ buried in full warrior dress with a complete set of weapons.”

Excavations in the late 1800s at Birka, a Scandinavian trading center from the 700s to around 1000 (SN: 4/18/15, p. 8), uncovered the woman’s grave. Remains of Birka lie on the island of Björkö, about 30 kilometers west of present-day Stockholm. About 1,100 of more than 3,000 graves that encircle Birka have been unearthed.

Excavators noted that the body lay among a warrior’s gear. This equipment included an ax, a spear, arrows, a large knife, two shields and two horses. Playing pieces found in the grave, apparently for some type of board game, suggest the woman may have been a high-ranking officer with knowledge of military tactics and strategy, Hedenstierna-Jonson’s team speculates.
Researchers have typically assumed that Viking-era graves with weapons contain male warriors. Curiously, though, many skeletons in these graves, including that of the Birka woman, display no battle injuries.

Biological anthropologist Anna Kjellström of Stockholm University, a coauthor of the new study, reported at a meeting in 2013 that the Birka individual was a woman, based on pelvic shape and bone sizes. DNA from the Birka skeleton now confirms its female status and reveals many genetic similarities to present-day northern Europeans.

A comparison of two forms of radioactive strontium in teeth from the Birka woman, 15 other individuals excavated at Birka and pre-Viking age people from several parts of Sweden indicated that the woman moved to the trading center as a teenager or young woman. Humans absorb strontium from local rock formations through water and plant foods, leaving a chemical signature in teeth that approximately maps where these people grew up. The researchers estimate the woman was at least 30 years old when she died.

Findings in the new paper don’t demonstrate that the Birka woman was a Viking warrior, writes archaeologist Judith Jesch in a Sept. 9 post on her Norse and Viking Ramblings blog. Perhaps all alleged warriors in Viking-era warrior graves who lack serious wounds didn’t actually fight, contends Jesch, of the University of Nottingham in England. Hedenstierna-Jonson’s group provides no evidence that the Birka woman’s bones contain traces of strenuous physical activity expected from a warrior adept enough to avoid severe injuries, she writes.

“A certain amount of confusion” surrounds the original locations of bones excavated at Birka and then bagged for storage, including those of the proposed woman warrior, Jesch adds. Sloppy excavation practices at Birka more than 100 years ago sometimes accidentally lumped together bones from different graves, she says in her post.

Women could have been warriors during the Viking age, whether or not the Birka woman fought alongside men, says archaeologist Marianne Moen of the University of Oslo. Research over the past 30 years shows that Viking women were landowners, farmers, merchants, traders and participants in legal proceedings. Graves of two other Viking-era women, both in Norway, contain various weapons.

What’s important is not to hold women to a different standard than men when assessing comparable weapons placed in their graves, Moen asserts. The Birka find “was a warrior grave until it was sexed as female,” she says. “Now a lot of people would like to call it something else. That is where the danger lies here.”

A new species of hermit crab discovered in the shallow waters of southern Japan has been enjoying the perks of living like a peanut worm. Like the worms, the 7- to 8-millimeter-long hermit crab uses corals as a covering, researchers report September 20 in PLOS ONE.

Other kinds of hermit crabs live in coral reefs, but typically move in and out of a series of mollusk shells as the crabs grow. Diogenes heteropsammicola is the first hermit crab known to form a mutually beneficial relationship with two species of mobile corals called walking corals. Unlike more familiar coral species, these walking corals don’t grow in colonies and aren’t attached to the seafloor. Instead, each host coral grows with and around a crab, forming a cavity in the coral skeleton that provides a permanent home for the crustacean. In exchange, the crab helps the coral “walk.”
Walking corals are already known to be in a symbiotic relationship with a different sea creature — flexible, marine peanut worms called sipunculids. A symbiotic shift between such distantly related species as the worms and the crab is rare because organisms in a mutualistic relationship tend to be specialized and completely dependent on one other, says study coauthor Momoko Igawa, an ecologist at Kyoto University in Japan.
But similar to the worms, D. heteropsammicola appears to be well-adapted to live in the corals. Its extra slim body can slip inside the corals’ narrow cavity. And unlike other hermit crabs — whose tails curve to the right to fit into spiral shells — D.heteropsammicola’ s tail is symmetrical and can curl either way, just like the corals’ opening.
“Being able to walk around in something that is going to grow larger as you grow larger, that’s a big plus,” says Jan Pechenik, a biologist at Tufts University in Medford, Mass., who was not involved in the study. A typical hermit crab that can’t find a larger shell to move into “really is in trouble.”

D. heteropsammicola’s relationship with walking corals may begin in a similar way as it does with sipunculan worms, Igawa says. A walking coral larva latches onto a tiny mollusk shell containing a juvenile hermit crab and starts to grow. When the hermit crab outgrows the shell, the crustacean moves into the readily available host coral’s crevice, and the shell remains encapsulated in the coral.

By observing the hermit crab in an aquarium, Igawa and coauthor Makoto Kato, also an ecologist at Kyoto University, determined that the crab provides the corals with the same services as the worms: transportation and preventing the corals from being overturned by currents or buried in sediment.

Igawa hopes to search for this new hermit crab in Indonesia, a region where walking corals are normally found. Plus, because walking coral fossils are easy to come by in Japan, she also wants “to reveal the evolutionary history of the symbioses of walking corals [with] sipunculans and hermit crabs by observing these fossils.”

I recently wrote about the power that adults’ words can have on young children. Today, I’m writing about the power of adults’ actions. Parents know, of course, that their children keep a close eye on them. But a new study provides a particularly good example of a watch-and-learn moment: Toddlers who saw an adult struggle before succeeding were more likely to persevere themselves.

Toddlers are “very capable learners,” says study coauthor Julia Leonard, a cognitive developmental psychologist at MIT. Scientists have found that these youngsters pick up on abstract concepts and new words after just a few exposures. But it wasn’t clear whether watching adults’ actions would actually change the way toddlers tackle a problem.

To see whether toddlers could soak up an adult’s persistence, Leonard and her colleagues tested 262 13- to 18-month-olds (the average age was 15 months). Some of the children watched an experimenter try to retrieve a toy stuck inside a container. In some cases, the experimenter quickly got the toy out three times within 30 seconds — easy. Other times, the experimenter struggled for the entire 30 seconds before finally getting the toy out. The experimenter then repeated the process for a different problem, removing a carabiner toy from a keychain. Some kids didn’t see any experimenter demonstration.

Just after watching an adult struggle (or not), the toddlers were given a light-up cube. It had a big, useless button on one side. Another button — small and hidden — actually controlled the lights. The kids knew the toy could light up, but didn’t know how to turn the lights on.

Though the big button did nothing, that didn’t stop the children from poking it. But here’s the interesting part: Compared with toddlers who had just watched an adult succeed effortlessly, or not watched an adult do anything at all, the toddlers who had seen the adult struggle pushed the button more. These kids persisted, even though they never found success.

The sight of an adult persevering nudged the children toward trying harder themselves, the researchers conclude in the Sept. 22 Science. Leonard cautions that it’s hard to pull parenting advice from a single laboratory-based study, but still, “there may be some value in letting children see you work hard to achieve your goals,” she says.

Observing the adults wasn’t the only thing that determined the toddlers’ persistence, not by a long shot. Some kids might simply be more tenacious than others. In the experiments, some of the children who didn’t see an experimenter attempt a task, or who saw an experimenter quickly succeed, were “incredibly gritty,” Leonard says. And some of the kids who watched a persistent adult still gave up quickly themselves. That’s not to mention the fact that these toddlers were occasionally tired, hungry and cranky, all of which can affect whether they give up easily. Despite all of this variation, the copycat effect remained, so that kids were more likely to persist when they had just seen a persistent adult.

As Leonard says, this is just one study and it can’t explain the complex lives of toddlers. Still, one thing is clear, and it’s something that we would all do well to remember: “Infants are watching your behavior attentively and actively learning from what you do,” Leonard says.

In 1780, a powerful hurricane swept across the islands of the Caribbean, killing an estimated 22,000 people; 5,000 more died of starvation and disease in the aftermath. “Our planet is capable of unleashing extreme chaos,” begins the new NOVA documentary “Killer Hurricanes,” set to air November 1 on PBS.

To describe the human impact of such powerful tropical cyclones, the documentary primarily focuses on two storms: the Great Hurricane of 1780 and Hurricane Matthew, a Category 4 storm that slammed into Haiti and Cuba last October. Before the devastating 2017 Atlantic hurricane season (SN Online: 9/21/17), Matthew was considered the biggest Atlantic storm of the last decade.
Still, the film’s larger message remains timely: Studying the hurricanes of the past can offer insights into storms of the future — and, hopefully, help coastal and island communities prepare for such events.

The documentary describes the work of researchers as they examine both human and geologic records to track past cyclones. Because the Great Hurricane occurred during relatively recent history, researchers can use eyewitness accounts and ship records to estimate not only the size of the storm, but also to track its path and calculate the storm surge.
But geologists such as Jeff Donnelly of the Woods Hole Oceanographic Institution in Massachusetts and Amy Frappier of Skidmore College in Saratoga Springs, N.Y., are looking deeper into the past. Donnelly finds physical traces of prehistoric hurricanes buried in seafloor sediments, while Frappier detects chemical traces in stalagmites growing in caves across the Caribbean. These data reveal a troubling pattern: The frequency of strong hurricanes distinctly increases when ocean temperatures are warmer. What’s more, hurricanes’ paths have shifted northward over the last 450 years, moving closer to the contiguous United States.

As the film notes, ocean waters are now warming at a rapid rate. Meanwhile, sea levels are rising, and the water in the oceans expands as it warms. Both effects will augment the impact of storm surge from such cyclones.

“Killer Hurricanes” doesn’t break much new ground, and the film’s stark conclusion about the future paths and intensities of powerful cyclones is one that climate scientists have long been signaling. But coming on the heels of a deadly hurricane season, and with the United States’ future participation in the Paris climate accord in limbo (SN Online: 6/1/17), the film may serve as a powerful reminder of the human cost of climate change.

Light is a fan of the buddy system. Photons, or particles of light, have been spotted swapping energy with partners. This chummy behavior resembles how electrons pair up in materials that conduct current without resistance, known as superconductors, researchers report in a paper accepted in Physical Review Letters.

Although the photons exchange energy like electrons do, it’s unknown whether the particles are actually bound together as electrons are, and whether photons could produce an effect analogous to superconductivity. “This is a door that is opened,” says study coauthor Ado Jorio, a physicist at the Universidade Federal de Minas Gerais in Brazil. Now, he says, the questions that must be addressed are, “How far can we push this similarity? Can we find with photons incredible results like we find for electrons?”
In certain solid materials cooled to extremely low temperatures, electrons form partnerships called Cooper pairs (SN: 6/13/15, p. 8), which allow superconductivity to occur. Although the negatively charged particles typically repel one another, two electrons can bind together by exchanging phonons, or quantum packets of vibration, via the lattice of ions within these materials. This alliance coordinates the electrons’ movements and thereby eases their passage through the material, allowing them to flow without resistance. Superconductivity’s potential technological applications — which include energy-efficient power transmission, superstrong magnets and levitating trains — have attracted heaps of scientific interest in the phenomenon.

Now, Jorio and colleagues have shown photons behaving similarly to superconducting electrons. When the researchers shined a laser on water, pairs of photons that emerged from the liquid at the same time tended to have complementary energies. While one photon had lost a little energy, another had gained the same amount of energy, indicating that they were exchanging quantum vibrations. The effect appeared in a variety of transparent materials, says Jorio, and it was observed at room temperature, unlike electron pairing in superconductors.

The team also showed that the exchanged quantum vibrations were “virtual” — appearing only for fleeting moments — just like the vibrations exchanged by electrons. The theory that explains the interaction “is exactly the same as for the electrons,” Jorio says.

Scientists already knew that photons can lose or gain energy via vibrations, but the similarity with Cooper pairs is a new and interesting way of thinking about the effect, says physicist Ian Walmsley of Oxford University, who was not involved with the research. “It’s a field that has not yet been explored.”
It is still too early to know how far the analogy with superconducting electrons extends, says physicist Ben Sussman of the National Research Council of Canada in Ottawa, who was not involved with the research. But the connection seems worth investigating: “This is an interesting rabbit hole indeed.”

Halloween horror aside, vampires are really pretty spineless.

Most have no backbone at all. By one count, some 14,000 kinds of arthropods, including ticks and mosquitoes, are blood feeders. Yet very few vertebrates are clear-cut, all-blood specialists: just some fishes and three bats. Why hasn’t evolution produced more vertebrate vampires?

The question intrigues herpetologist Harry Greene of Cornell University, who “can’t think of a single example among amphibians and reptiles,” he says. (Some birds are opportunists, sneaks or outright meat eaters, but they don’t have the extreme specialization of bats.)
Kurt Schwenk of the University of Connecticut in Storrs, who studies feeding morphology, comes up empty, as well. As he muses over what animals might have precursor biology that could lead to blood feeding, “a leechlike or lamprey-like blood-sucking tadpole should be a real possibility,” he says. The idea gives him “the heebie-jeebies,” but some tadpole species have already evolved mouths that can cling, and plenty of tadpoles are carnivorous.
Looking at the question from a different point of view — asking what would favor, or not, the evolution of blood feeding—he comes up with a less disturbing answer. For carnivorous animals, eating meat is nutritionally better than sipping blood alone, he says. So vampirism might not offer much of an advantage. “If you don’t need to be light and you’re not a parasite,” he says, there’s “no point in limiting yourself to blood.” So maybe vampiric tadpoles aren’t part of some creepy future after all.
Some adult fishes have evolved blood feeding, even mainstream vertebrates with jaws and bones (unlike cartilage-only jawless lampreys). Among the clear-cut bony examples are some Vandellia canidru catfishes, which fasten onto a gill of a much larger fish and let the fish heart pump sustenance into them as they nestle inside the protected gill chamber. (This is different from the supposed, or maybe mythical, tendency of some canidru catfishes to misunderstand fluid streams and swim up the urethras of humans in the water.)

Among vertebrates, vampirism inside or outside of gills might have arisen from ancestors that hitchhiked on big fishes and nibbled off parasites, in the same way modern remoras (also known as suckerfish) do, suggests parasitologist Tommy Leung of the University of New England in Armidale, Australia. Biologists already know about parasite-picker species, such as some cleaner fish, that will cheat and nip mucus or scales if they can get them. Actual blood-sucking cheats could be mere geologic ages away from that evolutionary step. Vertebrates may have relatively few vampires, but a greater number of almost-vampires.

Full-scale vampirism “is a tough way to make a living,” says William Schutt of Long Island University in Brookville, NY, and author of a book on the topic, Dark Banquet. But also, he adds, one big reason why there are fewer vertebrate vampires than arthropod bloodsuckers may be in the numbers. There are just fewer vertebrates: an estimated 60,000 versus a whopping 10 million arthropods.

Artificial intelligence is getting some better perspective. Like a person who can read someone else’s penmanship without studying lots of handwriting samples, next-gen image recognition AI can more easily identify familiar sights in new situations.

Made from a new type of virtual building block called capsules, these programs may cut down the enormous amount of data needed to train current image-identifying AI. And that could boost such technology as machine-made medical diagnoses, where example images may be scarce, or the responsiveness of self-driving cars, where the view is constantly shifting. Researchers with Google will present this new version of an artificial neural network at the Neural Information Processing Systems conference in Long Beach, Calif., on December 5.
Neural networks are webs of individual virtual nerve cells, or neurons, that learn to pick out objects in pictures by studying labeled example images. These networks largely classify pictures based on whether they contain certain features. For instance, a program trained on a series of head shots might conclude that a face has two eyes, a nose and a mouth. Show that program a face in profile with only one eye visible, though, and it may not recognize the photo as a face, explains Roland Memisevic, a computer scientist at the University of Montreal who was not involved in the work.

To overcome that limitation, researchers can train a neural network on millions of photos from myriad angles, and the program memorizes all the different ways a face might look. Compared with the human brain, which doesn’t need anywhere near a million examples to know what a face looks like, this system is wildly inefficient. “It’s a disaster,” Memisevic says. “Capsules try to fix that.”

Instead of webs of individual artificial neurons, these new programs have webs of clusters of neurons, called capsules. These teams of neurons can provide more information than one neuron by itself. Each capsule is designed to track not only whether a certain feature is in an image, but also properties of that feature — say, a nose’s size, orientation and position. This spatial awareness helps the program better recognize objects in previously unseen scenarios.

A capsule-containing network trained on head shots could see a face in profile and deduce — based on the appearance of the visible eye, nose and mouth — that the other eye is simply obscured, and the picture depicts a face. Since capsule networks are better at applying what they know to new situations, these neural networks need less training data to achieve the same performance as their predecessors, says Sara Sabour, a computer scientist with Google Brain in Toronto.
Sabour and her colleagues trained one capsule network on images of handwritten numbers and tested it on pictures where each number was slightly distorted. The capsule network recognized the warped images with 79 percent accuracy; a typical neural network trained on the same amount of data only got 66 percent right.

In another experiment, Sabour and colleagues trained a similar capsule network on tens of thousands of photos of toys, and then asked it to recognize the toys from new viewpoints. In this challenge, reported in a paper submitted to the 2018 International Conference on Learning Representations in Vancouver, the capsule network was wrong only about 1.4 percent of the time. A conventional neural network made almost twice as many errors.