A growing band of digital characters that converse, read faces and track body language is helping humans to communicate better with one another. While virtual helpers that perform practical tasks, such as dealing with customer service issues, are becoming ubiquitous, computer scientist M. Ehsan Hoque is at the forefront of a more emotionally savvy movement. He and his team at the University of Rochester in New York create software for digital agents that recognize when a person is succeeding or failing in specific types of social interactions. Data from face-to-face conversations and feedback from professional counselors and interviewers with relevant expertise inform this breed of computer advisers.

One of Hoque’s digital helpers grooms people to be better public speakers. With words on a screen, this attentive app notes, for example, how many times in a practice talk a person says “um,” gestures inappropriately or awkwardly shifts vocal tone. With the help of Google Glass, the app even offers useful reminders during actual speeches. Another computerized helper, this one in the form of an avatar, helps people hone their job interviewing skills, flagging long-winded responses or inconsistent eye contact in practice interviews. In the works are computerized conversation coaches that can improve speech and communication skills among people with developmental conditions such as autism and mediate business meetings in ways that encourage everyone to participate in decision making.

“There has been some progress in artificial intelligence, but not much in developing emotional aspects of AI,” Hoque says. “We’re just cracking through the surface at this point.”
The U.S. Department of Defense and the U.S. Army have taken notice. With their financial support, Hoque is developing avatars that collaborate with humans to solve complex problems, and digital observers that monitor body language to detect when people are lying.
This is heady stuff for a 35-year-old who earned a doctoral degree just four years ago. Hoque, who was born in Bangladesh and immigrated to the United States as a teenager, did his graduate work with the MIT Media Lab’s Affective Computing research group. The group’s director, Rosalind Picard, helped launch the field of “affective computing” in the 1990s, which focuses on the study and development of computers and robots that recognize, interpret and simulate human emotions.

Hoque’s approach puts a service spin on affective computing. As a grad student, he developed software he dubbed MACH, short for My Automated Conversation coacH. This system simulates face-to-face conversations with a computer-generated, 3-D man or woman that sees, hears and makes decisions while conversing with a real-life partner. Digital analyses of a human partner’s speech and nonverbal behavior inform the avatar’s responses during a session. A simulated coach may, for instance, let a user know if smiles during an interview look forced or are mistimed. After a session, users see a video of the interaction accompanied by displays of how well or poorly they did on various interaction skills, such as keeping eye contact and nodding at appropriate times.

MACH got its start in trials that trained MIT undergraduates how to conduct themselves during interviews with career counselors. First, Hoque analyzed smiles and other behaviors that either helped or hurt the impressions job candidates left on experienced counselors in mock interviews. In a series of follow-up studies, his team developed an automated system that recognized impression-enhancing behaviors during simulated interviews. That pilot version of MACH was then put to the test. Women, but not men, who received MACH training and got feedback from their digital coach while watching videos of their initial interviews with a counselor displayed substantial improvement in follow-up interviews. MACH trainees who watched interview videos but got no feedback showed minimal improvement. Testing with larger groups of men and women is under way.
As he developed MACH, Hoque consulted MIT sociologist and clinical psychologist Sherry Turkle. That was a bold move, since Turkle has warned for 30 years that, despite its pluses, digital culture discourages person-to-person connections. Social robots, in particular, represent a way for people to escape the challenges of forging authentic relationships, Turkle contends.

But she came away impressed with Hoque, whose goals she calls refreshingly modest and transparent. “His avatars will be helpers and facilitators,” she says, “not companions, friends, therapists and pretend people.”

Hoque’s approach grew out of personal experience. He is the primary caregiver for his 16-year-old brother, Eshteher, who has Down syndrome and does not speak. Eshteher can make sounds to refer to certain things, such as food, and has limited use of sign language. “I’ve spent a lot of time with him and can read what he’s experiencing, like when he’s frustrated or repentant,” Hoque says.
So it’s not surprising that Hoque’s next-generation MACH, dubbed LISSA for Live Interactive Social Skill Assistance, is an avatar that conducts flexible, “getting acquainted” conversations while providing feedback on users’ eye contact, speaking volume, smiling and body movements via flashing icons.

LISSA has shown promise in preliminary tests aimed at improving the conversational chops of college students attending speed-dating sessions and individuals with autism spectrum disorders. Hoque plans to expand this technology for use with people suffering from social phobia and post-traumatic stress disorder. He’s also working on an avatar that trains doctors to communicate clearly and compassionately with patients being treated for life-threatening cancers.

Hoque’s work on emotionally perceptive avatars may eventually transform the young industry of digital assistants, currently limited to voices-in-a-box such as Apple’s Siri and Microsoft’s Cortana, says cognitive scientist Mary Czerwinski, a principal researcher at Microsoft Research Lab in Redmond, Wash. Avatar research “could lead to more natural, personable digital assistants,” Czerwinski predicts. Hoque agrees.

“In the future, we’ll all have digital, personalized assistants,” he says. If he gets his way, emotionally attuned helpers will make us more social and less isolated. That’s something to applaud — if we can manage to put down our smartphones.

One of the planet’s deadliest viruses makes an annual pass through the United States with little fanfare. It rarely generates flashy headlines or news footage of health workers in hazmat suits. There’s no sudden panic when a sick person shows up coughing and feverish in an emergency room. Yet before next spring, this season’s lethal germ will probably have infected millions of Americans, killing tens of thousands. Still, it’s often referred to as just the flu.

The influenza virus seems so normal to most Americans that only about half of us will heed those “time for your flu shot” banners that pop up at pharmacies and worksites every autumn. Those annual shots remain the best means of protection, but they must be manufactured months before flu season starts, based on a best educated guess of what strains of the virus will be circulating. That means even in a successful year, vaccine performance may not be impressive. During the 2015–2016 season, only about half of those immunized were protected, according to a study in the Aug. 10 New England Journal of Medicine. Some years’ vaccines are duds: For the 2014–2015 season, the vaccine protected only 19 percent of people who received it, based on U.S. Centers for Disease Control and Prevention data.
Scientists have long worked to develop a flu shot that works better and lasts longer. But, unlike the very stable measles virus, influenza is a moving target. While only a few strains of flu virus circulate worldwide in a typical year, dozens more may exist. Each one is highly likely to mutate from year to year, with just enough shape-shifting to be unrecognizable to the body’s defenses.

Now, after years of searching, scientists believe they have better strategies to attack the parts of the virus that stay the same from year to year, offering the hope of protection across multiple seasons. The vaccines being developed in laboratories around the world “offer more promise than we’ve ever had,” says Walter Orenstein, associate director of the Emory Vaccine Center in Atlanta. And there are new creative approaches: One research group is trying to make a kind of super shot by anticipating every possible mutation a circulating virus might undergo.

“I’m optimistic we are going to get to a vaccine,” says Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, or NIAID, in Bethesda, Md. Then, you may need to heed those “time for your flu shot” messages only once.
Researchers often describe the flu virus as looking like a ball with lollipops sticking out. Tucked inside the ball is RNA, which the virus needs to make copies of itself. The lollipops on the outside are proteins: hemagglutinin and neuraminidase. There are 18 different kinds of hemagglutinin and 11 kinds of neuraminidase. Each kind of flu virus is named for its particular combination of these proteins; the current forms circulating around the world are H1N1 and H3N2. Hemagglutinin attaches to human cells to launch an infection; neuraminidase is more important for spreading the virus once infection has occurred.

Flu viruses involved in human epidemics are divided into types A and B, and A viruses are sliced even further into group 1 and group 2. Influenza A, the most troublesome for vaccine scientists, travels the world among birds, pigs and humans. The bird and pig versions don’t easily infect people, but the virus is constantly mutating and even swapping genes with other influenza viruses it meets along the way. Sometimes these genetic changes create a version that allows a bird or pig flu to move directly into humans. In 2013, one called H7N9 moved into people in China (SN Online: 3/11/15). The virus has since infected more than 1,500 people. Mostly, though, the genetic changes are more subtle, with just enough alterations to evade the human immune system.
Like kids with a sweet tooth, the immune system gets most excited about the top part of the hemagglutinin lollipop, and makes antibodies against it. The top is, after all, the first thing the immune system notices once the virus slips inside the nose, mouth and lungs. Every year, genetic mutations in the virus slightly change the chemical flavor of the lollipop, making it more sweet or sour than last season’s — just different enough so the immune system doesn’t recognize it. That’s why most years there’s a new flu shot.

Sometimes, in the gene shuffling with viruses in birds and pigs, the changes are so great that the flavor changes completely. Those are pandemic years, when there is so little residual immunity that a large portion of the global population falls ill from the new virus. The devastating 1918 flu, which killed an estimated 50 million people globally, was caused by such a drastic genetic shift (SN Online: 4/29/14). The most recent pandemic occurred in 2009, with the appearance of the “swine flu,” so named because the virus was first found in pigs. By one analysis, it caused between 148,000 and 249,000 deaths around the world.

Attack the stem
The 2009 disaster helped provide a blueprint for some of the latest experimental vaccines. Researchers noticed that when people with swine flu developed antibodies to the virus, those antibodies did something odd: They favored the hemagglutinin stem — the stick of the lollipop. And, more important, they appeared to react broadly against two kinds of flu virus. Scientists had known that the hemagglutinin stem, or stalk, isn’t as apt to change as the lollipop top, which theoretically makes the stem a good target for a universal vaccine. But in a usual flu season, the human body isn’t inclined to make infection-fighting antibodies against the stem.

“Unfortunately, the immune system preferentially recognizes the head, and we don’t know why it does that,” says Adrian McDermott, an immunologist at NIAID. So after infection, the biggest share of antibodies flocks to the hemagglutinin head. (Neuraminidase, the bigger player in disease after infection, is a target for influenza treatments but not a major focus for vaccine development.)

But in a study reported in the Journal of Experimental Medicine in 2011, a team of scientists from Emory and elsewhere found that antibodies to the so-called swine flu behaved unexpectedly. “If you have a head that the immune system hasn’t seen, you potentially redirect to a stalk response,” McDermott says. “That was an aha! moment.”
Researchers investigated further. For one study in 2012 in Frontiers in Immunology, scientists from Canada injected these stem-recognizing antibodies into mice to see if the mice were shielded from a different strain of flu. Not only were the mice protected from lethal doses of flu virus, but the protection was also in large part due to the absence of familiar antibodies against the head, the researchers found. Without the distraction of a head it recognized, the immune system seemed to rally against the stem.

Then came the what ifs: What if a vaccine produced just antibodies to the stem? Would that be enough protection? For the last few years, McDermott and others have been trying to develop vaccines made of “headless stalks” — just the sticks of the lollipops. With no head in place to hoard the immune response, the vaccine might coax the body to make enough stem-focused antibodies to protect against flu, the researchers hoped, regardless of the seasonal mutations occurring at the top.

Several groups soon found that headless stalks are difficult to make. Without the top to stabilize it, the molecular assembly tended to break apart. Two teams working independently reported in 2015 their success in keeping the stalk in one piece. NIAID scientists and their partners held the stalks together by anchoring them to the protein ferritin, which can assemble itself into nanoparticles. In a study in Nature Medicine, the team reported that vaccinated mice and ferrets appeared to be protected from dying of the H5N1 bird flu after receiving the vaccine, even when they developed symptoms. Unvaccinated mice and ferrets died.

The second team, from the Janssen Center of Excellence for Immunoprophylaxis in Leiden, the Netherlands, and the Scripps Research Institute in La Jolla, Calif., glued the stalk together by creating a series of genetic mutations at its top. In Science, the researchers reported that the vaccine reduced the symptoms of flu in vaccinated monkeys.

“We realized that the stem has much less variability than the head, and then we developed the capability to use it for a possible vaccine,” says Fauci, commenting on both efforts. “These were two important things that came together.”

Despite progress, these stalk-focused vaccines haven’t yet been put to human tests that would show whether they could protect broadly against many mutations of flu circulating annually, which is the ultimate test. And some stalk-directed antibodies might be better than others. In July in Science Immunology, McDermott and colleagues reported that the stalk antibodies against group 2 of the A viruses appear to be more broadly effective than those against group 1 viruses.

Other researchers have stabilized the stalk by attaching a new hemagglutinin head — a lollipop flavor that the human immune system has never tasted. In this case, researchers from the Icahn School of Medicine at Mount Sinai in New York City took tops from two flu strains that circulate only in birds, and connected each one to a human hemagglutinin stalk. This experimental vaccine consists of two doses. The first dose prompts the immune system to make antibodies against the stalk with the first top, and a second dose produces a second round of antibodies against the stalk with the second top. The idea is that the abundance of stem-focused antibodies — amplified from the two shots of vaccine — will come to the rescue during a natural infection from a virus that possesses a third, totally different head.
“The human immune system will try to find something it has seen before,” says Peter Palese, chairman of microbiology at Mount Sinai. In theory, the only antibodies in play will be the ones responding to the parts of the stalk that the immune system recognizes, known as the “conserved domains.”

“The $64,000 question,” according to Palese: “Will the immune response to these conserved domains be enough to elicit a broad immune system reaction?”

In 2016, Palese and colleagues described a test of the vaccine in the Journal of Virology. Six ferrets given the two doses were housed with six ferrets infected with H1N1 flu. Within 10 days, the vaccinated animals had become infected but had no symptoms or signs of being able to easily spread virus to others. A report in June in the same journal described tests of the vaccine in mice against influenza B viruses; the animals were protected from normally lethal doses of flu.

What’s not known is whether the stem-focused antibodies are enough to protect people from all virus variants. The vaccine from the Mount Sinai researchers is entering the first human safety trials with drugmaker GlaxoSmithKline.

Unhide and seek
Another approach incorporates proteins that don’t tend to mutate like the hemagglutinin head but are hidden from the immune system under normal circumstances. When these proteins are made visible to types of white blood cells called T cells, the immune system wakes up. T cells don’t make antibodies, but certain T cells hold on to a memory of foreign molecules seen before. When these pre-programmed T cells recognize an infection, they destroy the invader.

This work began in the 1990s, when researchers at the Weizmann Institute of Science in Rehovot, Israel, set out to find parts of the virus that remain unchanged from year to year. The team identified stable regions in three proteins — hemagglutinin, plus one from the virus membrane and one from the virus core. In 2003, a company called BiondVax Pharmaceuticals formed to develop and test, in humans, an experimental vaccine that takes these proteins and packages them in a way that the immune system can recognize them.

So far, almost 700 volunteers have participated in six small trials, all of which showed signs of a lasting immune response among most volunteers. Writing in February in Vaccine, the researchers reported that the stored serum of elderly volunteers who received the vaccine in 2011 showed an immune response to new strains of flu that were circulating three years later. The company is starting larger trials to see if the vaccine can actually protect people from getting sick.
Out of many, one
Other experimental vaccines take a different approach. Rather than relying on precision to hit a narrow target, microbiologist Ted Ross and colleagues at the University of Georgia in Athens are attempting to cast a wide net. The researchers are taking hemagglutinin mutations from every flu strain that has ever circulated, dumping them into a kind of scientific blender and attaching them to particles that can form the basis of a vaccine.

“The question we asked is, how can we make a vaccine against a strain we don’t even know exists?” Ross says. The technique he uses is called COBRA for computationally optimized broadly reactive antigen. A computer compiles all seemingly possible genetic iterations of a particular flu type — in this case H1N1 — and then bundles them into one molecule. It’s kind of like taking every novel in your local library and combining them into one giant book.

Last year in the Journal of Virology, Ross and colleagues described a COBRA-derived vaccine that represented almost all forms of H1N1 that have been around for the last 100 years. The vaccine protected mice against infection from strains of H1N1 that the mice had never been exposed to. “We took a bunch of different hemagglutinins and mixed them into one hemagglutinin molecule,” Ross says. “It protected against any strain of H1N1 we could throw at it.”

The study caught the attention of vaccine maker Sanofi Pasteur, which plans to test the vaccine in clinical trials. Ross’ lab is now using the same strategy to develop a vaccine against H3N2 strains, the other dominant kind of flu circulating around the world. Same approach, different library.

Meanwhile, the virus isn’t waiting around. Based on the heavy flu season in the Southern Hemisphere, some experts are predicting this year’s epidemic could be severe. It’s still too early to know whether the current vaccine will provide good protection, but someday, a super shot may remove the guesswork altogether.

A gigantic emergency arresting gear system, capable of stopping the largest four-engined jet aircraft without discomfort to passengers, is being developed for the French Ministry of Transportation. The system consists of a nylon net … which engages the aircraft for the full width of its wingspan. Net and airplane are brought to a slow stop by energy absorbing devices located along the sides of the runway. — Science News, September 28, 1967
Catching commercial airliners in giant nets never took off. However, aircraft carriers have deployed nets since 1931 for emergency landings. In modern versions, nets are linked to energy-absorbers below deck to help bring a plane to a safe stop. Today’s net systems are a big improvement over the original barricade: Aviation pioneer Eugene Ely first landed an airplane on a ship, the USS Pennsylvania, in 1911. His landing relied on sandbag-secured ropes across the deck plus a canvas awning between the plane and the sea.
Editor’s note: This story was corrected on November 6, 2017. The nets used on the aircraft carriers to arrest airplanes were not made of nylon until after nylon became available in 1935.

Giardia has plagued people for a long time.

The parasite can bring about dysentery — a miserable (and occasionally deadly) mixture of diarrhea, cramps and fever. Scientists have now uncovered traces of the giardia parasite in the remains of two roughly 2,600-year-old toilets once used by the wealthy denizens of Jerusalem. The remains are the oldest known biological evidence of giardia anywhere in the world, researchers report May 25 in Parasitology.

The single-cell parasite Giardia duodenalis can be found today in human guts around the planet. This wasn’t always the case — but working out how pathogens made their debut and moved around is no easy feat (SN: 2/2/22). While some intestinal parasites can be preserved for centuries in the ground, others, like giardia, quickly disintegrate and can’t be spotted under a microscope.
In 1991 and 2019, archeologists working at two sites in Jerusalem came across stone toilet seats in the remains of mansionlike homes. These “were quite posh toilets” used by “swanky people,” says Piers Mitchel, a paleoparasitolgist at the University of Cambridge.

The original excavators of soil taken from beneath the seats of these toilets glimpsed traces of roundworm and other possible intestinal parasites in soil samples put under a microscope. Mitchel and his colleagues built on this analysis by using antibodies to search for the remains of giardia and two other fragile parasites in the millennia-old decomposed feces under both seats.

There was “plenty of doubt” that giardia was around in Jerusalem at the time because it’s so hard to reconstruct the movement of ancient disease, Mitchel says.

But the find hints that it was a regular presence in the region, says Mattieu le Bailly, a paleoparasitolgist at the University Bourgogne Franche-Comté in Besançon, France, who was not involved in the study.

The idea that a pathogen like giardia, which spreads via contaminated water and sometimes flies, existed and was possibly widespread in ancient Jerusalem makes a lot of sense, Mitchel says, given the hot, dry, insect-ridden climate around the Iron Age city.

Some ants have figured out how to keep from getting lost: Build taller anthills.

Desert ants that live in the hot, flat salt pans of Tunisia spend their days looking for food. Successful grocery runs can take the insects as far as 1.1 kilometers from their nests. So some of these ants build towering hills over their nests that serve as a landmark to guide the way home, researchers report in the July 10 Current Biology.
“I am surprised and fascinated that ants have visual acuity at the distances implied in this work,” says ecologist Judith Bronstein of the University of Arizona in Tucson who wasn’t involved in the new study. It “also implies that ants regularly assess the complexity of their local habitat and change their decisions based on what they conclude about it.”

Desert ants (Cataglyphis spp.) use a navigation system called path integration, relying on the sun’s position and counting their steps to keep track of where they are relative to their nest (SN: 1/19/17). But this system becomes increasingly unreliable as distance from the nest increases. Like other types of ants, desert ants also rely more generally on sight and smell. But the vast, almost featureless salt pans look nearly the same in every direction.

“We realized that, whenever the ants in salt pans came closer to their nest, they suddenly pinpointed the nest hill … from several meters distance,” says Markus Knaden, a neuroethologist at Max Planck Institute for Chemical Ecology in Jena, Germany. “This made us think that the hill functions as a nest-defining landmark.”

So Knaden and colleagues captured ants (C. fortis) from nests in the middle of salt pans and from along their shorelines. Only nests from the salt pan interiors had distinct hills, which can be up to 40 centimeters tall, whereas the hills on shoreline nests were lower or barely noticeable.
Next, the team removed any hills and placed the captured insects some distance away from their nests. Ants from the salt pans’ interiors struggled more than shore ants to find home. Since the shore ants were adept at using the shoreline for guidance, they weren’t as affected by the hill removal, the researchers conclude.

The team wanted to know if the ants were deliberately building a taller hill when their surroundings lacked any visible landmark. So, the researchers removed the hills of 16 salt pan nests and installed two 50-centimeter-tall black cylinders apiece near eight of them. The other eight nests were left without any artificial visual aid.
After three days, the researchers found that ants from seven of the unaided nests had rebuilt their hills. But ants from only two of the nests with cylinders had bothered to rebuild.

“These desert ants already told us about path integration and step counting for orientation…. But this business of building your own visual landmark, incredible,” says entomologist John Longino of the University of Utah in Salt Lake City who wasn’t involved in the research. “Are they sitting down to a council meeting to decide whether they need a bigger landmark? Is this somehow an evolved behavior in this one desert ant species?”

For now, it’s unclear how the ants decide to build, or not to build, a hill. Interestingly, nest building is usually performed by younger ants that are not foragers yet, Knaden says, and have not experienced the difficulty in finding a nest in the absence of a hill. That means there is an exchange of information between the veteran foraging ants and their novice nest mates, he says.

Bronstein also wonders about the risks of building the taller structures. Such risks “are implied by the fact that the ants don’t build such a structure where it isn’t needed,” she says. But, “for instance, isn’t it a clear cue to ant predators that food can be found there?”

Jellyfish have gotten a bad rap. In recent years, concerns about rising jellyfish populations in some parts of the world have mushroomed into headlines like “Meet your new jellyfish overlords.” These floating menaces are taking over the world’s oceans thanks to climate change and ocean acidification, the thinking goes, and soon waters will be filled with little more than the animals’ pulsating goo.

It’s a vivid and frightening image, but researchers aren’t at all certain that it’s true. In her new book, Spineless, former marine scientist Juli Berwald sets out to find the truth about the jellyfish take-over. In the process, she shares much more about these fascinating creatures than merely their numbers.
Among a few of the amazing jellyfish facts and tales throughout the book: Jellyfish have astoundingly complex vision for animals without a brain. They are also the most efficient swimmers ever studied, among the most ancient animals surviving on Earth today and some of the most toxic sea creatures (SN: 9/6/14, p. 16).

Rather than merely reciting these facts, Berwald takes readers on a personal journey, tracing how life pulled her away from science after she earned her Ph.D. — and how jellies brought her back. Through the tale of her experiments with a home jellyfish aquarium, she explains jelly biology, from the amazing shape-shifting properties of the mesoglea that forms a jellyfish’s bulk to why so many species are transparent. As she juggles family life with interviews with the world’s leading jellyfish researchers, Berwald also documents her travels to places around the globe where jellyfish and humans intersect, such as Israel’s coral reefs and Japan’s fisheries.
The answer to the question of whether jellyfish populations are on the rise ultimately lies at this intersection, Berwald finds. Marine scientists are split on whether populations are increasing globally. It depends on which data you include, and it’s possible that jellyfish numbers fluctuate naturally on a 20-year cycle. What is clear is that in coastal areas around the world, people have unwittingly created spawning grounds for huge numbers of jellyfish simply by building docks and other structures that quickly multiplying jellyfish polyps can attach to.

In the end, Berwald says, jellyfish became a “vehicle for me to explore the threats to the ocean’s future. They’re a way to start a conversation about things that can seem boring and abstract — acidification, warming, overfishing and coastal development — but that are changing our oceans in fundamental ways.” And that’s more interesting than an ocean full of goo.

A new eye on the variable sky just opened. The Zwicky Transient Facility, a robotic camera designed to rapidly scan the sky nightly for objects that move, flash or explode, took its first image on November 1.

The camera, mounted on a telescope at Caltech’s Palomar Observatory near San Diego, succeeds the Palomar Transient Factory. Between 2009 and 2017, the Palomar Transient Factory caught two separate supernovas hours after they exploded, one in 2011 (SN: 9/24/11, p. 5) and one earlier this year (SN: 2/13/17). It also found the longest-lasting supernova ever, from a star that seems to explode over and over (SN: 11/8/17).

The Zwicky survey will spot similar short-lived events and other cosmic blips, like stars being devoured by black holes (SN: 4/1/17, p. 5), as well as asteroids and comets. But Zwicky will work much faster than its predecessor: It will operate 10 times as fast, cover seven times as much of the sky in a single image and take 2.5 times as many exposures each night. Computers will search the images for any astronomical object that changes from one scan to the next.

The camera is named for Caltech astronomer Fritz Zwicky, who first used the term “supernova” in 1931 to describe the explosions that mark a star’s death (SN: 10/24/13).

If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.
Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

The accepted explanation for that accelerating expansion is an invisible pressure called dark energy. In the standard theory of the universe, dark energy makes up about 70 percent of the universe’s “stuff” — its matter and energy. Yet scientists still aren’t sure what dark energy is, and finding its source is one of the most vexing problems of cosmology.

Perhaps, the dark energy doubters suggest, the speeding up of the expansion has nothing to do with dark energy. Instead, the universe’s clumpiness may be mimicking the presence of such an ethereal phenomenon.
Most physicists, however, feel that proper accounting for the clumps won’t have such a drastic impact. Robert Wald of the University of Chicago, an expert in general relativity, says that lumpiness is “never going to contribute anything that looks like dark energy.” So far, observations of the universe have been remarkably consistent with predictions based on simulations that rely on approximations.
As observations become more detailed, though, even slight inaccuracies in simulations could become troublesome. Already, astronomers are charting wide swaths of the sky in great detail, and planning more extensive surveys. To translate telescope images of starry skies into estimates of properties such as the amount of matter in the universe, scientists need accurate simulations of the cosmos’s history. If the detailed physics of clumps is important, then simulations could go slightly astray, sending estimates off-kilter. Some scientists already suggest that the lumpiness is behind a puzzling mismatch of two estimates of how fast the universe is expanding.

Researchers are attempting to clear up the debate by conquering the complexities of general relativity and simulating the cosmos in its full, lumpy glory. “That is really the new frontier,” says cosmologist Sabino Matarrese of the University of Padua in Italy, “something that until a few years ago was considered to be science fiction.” In the past, he says, scientists didn’t have the tools to complete such simulations. Now researchers are sorting out the implications of the first published results of the new simulations. So far, dark energy hasn’t been explained away, but some simulations suggest that certain especially sensitive measurements of how light is bent by matter in the universe might be off by as much as 10 percent.

Soon, simulations may finally answer the question: How much do lumps matter? The idea that cosmologists might have been missing a simple answer to a central problem of cosmology incessantly nags some skeptics. For them, results of the improved simulations can’t come soon enough. “It haunts me. I can’t let it go,” says cosmologist Rocky Kolb of the University of Chicago.

Smooth universe
By observing light from different eras in the history of the cosmos, cosmologists can compute the properties of the universe, such as its age and expansion rate. But to do this, researchers need a model, or framework, that describes the universe’s contents and how those ingredients evolve over time. Using this framework, cosmologists can perform computer simulations of the universe to make predictions that can be compared with actual observations.
After Einstein introduced his theory in 1915, physicists set about figuring out how to use it to explain the universe. It wasn’t easy, thanks to general relativity’s unwieldy, difficult-to-solve suite of equations. Meanwhile, observations made in the 1920s indicated that the universe wasn’t static as previously expected; it was expanding. Eventually, researchers converged on a solution to Einstein’s equations known as the Friedmann-Lemaître-Robertson-Walker metric. Named after its discoverers, the FLRW metric describes a simplified universe that is homogeneous and isotropic, meaning that it appears identical at every point in the universe and in every direction. In this idealized cosmos, matter would be evenly distributed, no clumps. Such a smooth universe would expand or contract over time.
A smooth-universe approximation is sensible, because when we look at the big picture, averaging over the structures of galaxy clusters and voids, the universe is remarkably uniform. It’s similar to the way that a single spoonful of minestrone soup might be mostly broth or mostly beans, but from bowl to bowl, the overall bean-to-broth ratios match.

In 1998, cosmologists revealed that not only was the universe expanding, but its expansion was also accelerating (SN: 2/2/08, p. 74). Observations of distant exploding stars, or supernovas, indicated that the space between us and them was expanding at an increasing clip. But gravity should slow the expansion of a universe evenly filled with matter. To account for the observed acceleration, scientists needed another ingredient, one that would speed up the expansion. So they added dark energy to their smooth-universe framework.

Now, many cosmologists follow a basic recipe to simulate the universe — treating the cosmos as if it has been run through an imaginary blender to smooth out its lumps, adding dark energy and calculating the expansion via general relativity. On top of the expanding slurry, scientists add clumps and track their growth using approximations, such as Newtonian gravity, which simplifies the calculations.

In most situations, Newtonian gravity and general relativity are near-twins. Throw a ball while standing on the surface of the Earth, and it doesn’t matter whether you use general relativity or Newtonian mechanics to calculate where the ball will land — you’ll get the same answer. But there are subtle differences. In Newtonian gravity, matter directly attracts other matter. In general relativity, gravity is the result of matter and energy warping spacetime, creating curves that alter the motion of objects (SN: 10/17/15, p. 16). The two theories diverge in extreme gravitational environments. In general relativity, for example, hulking black holes produce inescapable pits that reel in light and matter (SN: 5/31/14, p. 16). The question, then, is whether the difference between the two theories has any impact in lumpy-universe simulations.

Most cosmologists are comfortable with the status quo simulations because observations of the heavens seem to fit neatly together like interlocking jigsaw puzzle pieces. Predictions based on the standard framework agree remarkably well with observations of the cosmic microwave background — ancient light released when the universe was just 380,000 years old (SN: 3/21/15, p. 7). And measurements of cosmological parameters — the fraction of dark energy and matter, for example — are generally consistent, whether they are made using the light from galaxies or the cosmic microwave background.

However, the reliance on Newton’s outdated theory irks some cosmologists, creating a lingering suspicion that the approximation is causing unrecognized problems. And some cosmological question marks remain. Physicists still puzzle over what makes up dark energy, along with another unexplained cosmic constituent, dark matter, an additional kind of mass that must exist to explain observations of how galaxies and galaxy clusters rotate. “Both dark energy and dark matter are a bit of an embarrassment to cosmologists, because they have no idea what they are,” says cosmologist Nick Kaiser of École Normale Supérieure in Paris.
Dethroning dark energy
Some cosmologists hope to explain the universe’s accelerating expansion by fully accounting for the universe’s lumpiness, with no need for the mysterious dark energy.

These researchers argue that clumps of matter can alter how the universe expands, when the clumps’ influence is tallied up over wide swaths of the cosmos. That’s because, in general relativity, the expansion of each local region of space depends on how much matter is within. Voids expand faster than average; dense regions expand more slowly. Because the universe is mostly made up of voids, this effect could produce an overall expansion and potentially an acceleration. Known as backreaction, this idea has lingered in obscure corners of physics departments for decades, despite many claims that backreaction’s effect is small or nonexistent.

Backreaction continues to appeal to some researchers because they don’t have to invent new laws of physics to explain the acceleration of the universe. “If there is an alternative which is based only upon traditional physics, why throw that away completely?” Matarrese asks.

Most cosmologists, however, think explaining away dark energy just based on the universe’s lumps is unlikely. Previous calculations have indicated any effect would be too small to account for dark energy, and would produce an acceleration that changes in time in a way that disagrees with observations.

“My personal view is that it’s a much smaller effect,” says astrophysicist Hayley Macpherson of Monash University in Melbourne, Australia. “That’s just basically a gut feeling.” Theories that include dark energy explain the universe extremely well, she points out. How could that be if the whole approach is flawed?

New simulations by Macpherson and others that model how lumps evolve in general relativity may be able to gauge the importance of backreaction once and for all. “Up until now, it’s just been too hard,” says cosmologist Tom Giblin of Kenyon College in Gambier, Ohio.

To perform the simulations, researchers needed to get their hands on supercomputers capable of grinding through the equations of general relativity as the simulated universe evolves over time. Because general relativity is so complex, such simulations are much more challenging than those that use approximations, such as Newtonian gravity. But, a seemingly distinct topic helped lay some of the groundwork: gravitational waves, or ripples in the fabric of spacetime.
The Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, searches for the tremors of cosmic dustups such as colliding black holes (SN: 10/28/17, p. 8). In preparation for this search, physicists honed their general relativity skills on simulations of the spacetime storm kicked up by black holes, predicting what LIGO might see and building up the computational machinery to solve the equations of general relativity. Now, cosmologists have adapted those techniques and unleashed them on entire, lumpy universes.

The first lumpy universe simulations to use full general relativity were unveiled in the June 2016 Physical Review Letters. Giblin and colleagues reported their results simultaneously with Eloisa Bentivegna of the University of Catania in Italy and Marco Bruni of the University of Portsmouth in England.

So far, the simulations have not been able to account for the universe’s acceleration. “Nearly everybody is convinced [the effect] is too small to explain away the need for dark energy,” says cosmologist Martin Kunz of the University of Geneva. Kunz and colleagues reached the same conclusion in their lumpy-universe simulations, which have one foot in general relativity and one in Newtonian gravity. They reported their first results in Nature Physics in March 2016.

Backreaction aficionados still aren’t dissuaded. “Before saying the effect is too small to be relevant, I would, frankly, wait a little bit more,” Matarrese says. And the new simulations have potential caveats. For example, some simulated universes behave like an old arcade game — if you walk to one edge of the universe, you cross back over to the other side, like Pac-Man exiting the right side of the screen and reappearing on the left. That geometry would suppress the effects of backreaction in the simulation, says Thomas Buchert of the University of Lyon in France. “This is a good beginning,” he says, but there is more work to do on the simulations. “We are in infancy.”

Different assumptions in a simulation can lead to disparate results, Bentivegna says. As a result, she doesn’t think that her lumpy, general-relativistic simulations have fully closed the door on efforts to dethrone dark energy. For example, tricks of light might be making it seem like the universe’s expansion is accelerating, when in fact it isn’t.

When astronomers observe far-away sources like supernovas, the light has to travel past all of the lumps of matter between the source and Earth. That journey could make it look like there’s an acceleration when none exists. “It’s an optical illusion,” Bentivegna says. She and colleagues see such an effect in a simulation reported in March in the Journal of Cosmology and Astroparticle Physics. But, she notes, this work simulated an unusual universe, in which matter sits on a grid — not a particularly realistic scenario.

For most other simulations, the effect of optical illusions remains small. That leaves many cosmologists, including Giblin, even more skeptical of the possibility of explaining away dark energy: “I feel a little like a downer,” he admits.
Surveying the skies
Subtle effects of lumps could still be important. In Hans Christian Andersen’s “The Princess and the Pea,” the princess felt a tiny pea beneath an impossibly tall stack of mattresses. Likewise, cosmologists’ surveys are now so sensitive that even if the universe’s lumps have a small impact, estimates could be thrown out of whack.

The Dark Energy Survey, for example, has charted 26 million galaxies using the Victor M. Blanco Telescope in Chile, measuring how the light from those galaxies is distorted by the intervening matter on the journey to Earth. In a set of papers posted online August 4 at arXiv.org, scientists with the Dark Energy Survey reported new measurements of the universe’s properties, including the amount of matter (both dark and normal) and how clumpy that matter is (SN: 9/2/17, p. 32). The results are consistent with those from the cosmic microwave background — light emitted billions of years earlier.

To make the comparison, cosmologists took the measurements from the cosmic microwave background, early in the universe, and used simulations to extrapolate to what galaxies should look like later in the universe’s history. It’s like taking a baby’s photograph, precisely computing the number and size of wrinkles that should emerge as the child ages and finding that your picture agrees with a snapshot taken decades later. The matching results so far confirm cosmologists’ standard picture of the universe — dark energy and all.

“So far, it has not yet been important for the measurements that we’ve made to actually include general relativity in those simulations,” says Risa Wechsler, a cosmologist at Stanford University and a founding member of the Dark Energy Survey. But, she says, for future measurements, “these effects could become more important.” Cosmologists are edging closer to Princess and the Pea territory.

Those future surveys include the Dark Energy Spectroscopic Instrument, DESI, set to kick off in 2019 at Kitt Peak National Observatory near Tucson; the European Space Agency’s Euclid satellite, launching in 2021; and the Large Synoptic Survey Telescope in Chile, which is set to begin collecting data in 2023.

If cosmologists keep relying on simulations that don’t use general relativity to account for lumps, certain kinds of measurements of weak lensing — the bending of light due to matter acting like a lens — could be off by up to 10 percent, Giblin and colleagues reported at arXiv.org in July. “There is something that we’ve been ignoring by making approximations,” he says.

That 10 percent could screw up all kinds of estimates, from how dark energy changes over the universe’s history to how fast the universe is currently expanding, to the calculations of the masses of ethereal particles known as neutrinos. “You have to be extremely certain that you don’t get some subtle effect that gets you the wrong answers,” Geneva’s Kunz says, “otherwise the particle physicists are going to be very angry with the cosmologists.”

Some estimates may already be showing problem signs, such as the conflicting estimates of the cosmic expansion rate (SN: 8/6/16, p. 10). Using the cosmic microwave background, cosmologists find a slower expansion rate than they do from measurements of supernovas. If this discrepancy is real, it could indicate that dark energy changes over time. But before jumping to that conclusion, there are other possible causes to rule out, including the universe’s lumps.

Until the issue of lumps is smoothed out, scientists won’t know how much lumpiness matters to the cosmos at large. “I think it’s rather likely that it will turn out to be an important effect,” Kolb says. Whether it explains away dark energy is less certain. “I want to know the answer so I can get on with my life.”

On astrophysicists’ charts of star stuff, there’s a substance that still merits the label “here be dragons.” That poorly understood material is found inside neutron stars — the collapsed remnants of once-mighty stars — and is now being mapped out, as scientists better characterize the weird matter.

The detection of two colliding neutron stars, announced in October (SN: 11/11/17, p. 6), has accelerated the pace of discovery. Since the event, which scientists spied with gravitational waves and various wavelengths of light, several studies have placed new limits on the sizes and masses possible for such stellar husks and on how squishy or stiff they are.
“The properties of neutron star matter are not very well known,” says physicist Andreas Bauswein of the Heidelberg Institute for Theoretical Studies in Germany. Part of the problem is that the matter inside a neutron star is so dense that a teaspoonful would weigh a billion tons, so the substance can’t be reproduced in any laboratory on Earth.

In the collision, the two neutron stars merged into a single behemoth. This remnant may have immediately collapsed into a black hole. Or it may have formed a bigger, spinning neutron star that, propped up by its own rapid rotation, existed for a few milliseconds — or potentially much longer — before collapsing. The speed of the object’s demise is helping scientists figure out whether neutron stars are made of material that is relatively soft, compressing when squeezed like a pillow, or whether the neutron star stuff is stiff, standing up to pressure. This property, known as the equation of state, determines the radius of a neutron star of a particular mass.

An immediate collapse seems unlikely, two teams of researchers say. Telescopes spotted a bright glow of light after the collision. That glow could only appear if there were a delay before the merged neutron star collapsed into a black hole, says physicist David Radice of Princeton University because when the remnant collapses, “all the material around falls inside of the black hole immediately.” Instead, the neutron star stuck around for at least several milliseconds, the scientists propose.

Simulations indicate that if neutron stars are soft, they will collapse more quickly because they will be smaller than stiff neutron stars of the same mass. So the inferred delay allows Radice and colleagues to rule out theories that predict neutron stars are extremely squishy, the researchers report in a paper published November 13 at arXiv.org.
Using similar logic, Bauswein and colleagues rule out some of the smallest sizes that neutron stars of a particular mass might be. For example, a neutron star 60 percent more massive than the sun can’t have a radius smaller than 10.7 kilometers, they determine. These results appear in a paper published November 29 in the Astrophysical Journal Letters.

Other researchers set a limit on the maximum mass a neutron star can have. Above a certain heft, neutron stars can no longer support their own weight and collapse into a black hole. If this maximum possible mass were particularly large, theories predict that the newly formed behemoth neutron star would have lasted hours or days before collapsing. But, in a third study, two physicists determined that the collapse came much more quickly than that, on the scale of milliseconds rather than hours. A long-lasting, spinning neutron star would dissipate its rotational energy into the material ejected from the collision, making the stream of glowing matter more energetic than what was seen, physicists Ben Margalit and Brian Metzger of Columbia University report. In a paper published November 21 in the Astrophysical Journal Letters, the pair concludes that the maximum possible mass is smaller than about 2.2 times that of the sun.

“We didn’t have many constraints on that prior to this discovery,” Metzger says. The result also rules out some of the stiffer equations of state because stiffer matter tends to support larger masses without collapsing.

Some theories predict that bizarre forms of matter are created deep inside neutron stars. Neutron stars might contain a sea of free-floating quarks — particles that are normally confined within larger particles like protons or neutrons. Other physicists suggest that neutron stars may contain hyperons, particles made with heavier quarks known as strange quarks, not found in normal matter. Such unusual matter would tend to make neutron stars softer, so pinning down the equation of state with additional neutron star crashes could eventually resolve whether these exotic beasts of physics indeed lurk in this unexplored territory.

Galileo’s most famous experiment has taken a trip to outer space. The result? Einstein was right yet again. The experiment confirms a tenet of Einstein’s theory of gravity with greater precision than ever before.

According to science lore, Galileo dropped two balls from the Leaning Tower of Pisa to show that they fell at the same rate no matter their composition. Although it seems unlikely that Galileo actually carried out this experiment, scientists have performed a similar, but much more sensitive experiment in a satellite orbiting Earth. Two hollow cylinders within the satellite fell at the same rate over 120 orbits, or about eight days’ worth of free-fall time, researchers with the MICROSCOPE experiment report December 4 in Physical Review Letters. The cylinders’ accelerations match within two-trillionths of a percent.

The result confirms a foundation of Einstein’s general theory of relativity known as the equivalence principle. That principle states that an object’s inertial mass, which sets the amount of force needed to accelerate it, is equal to its gravitational mass, which determines how the object responds to a gravitational field. As a result, items fall at the same rate — at least in a vacuum, where air resistance is eliminated — even if they have different masses or are made of different materials.

The result is “fantastic,” says physicist Stephan Schlamminger of OTH Regensburg in Germany who was not involved with the research. “It’s just great to have a more precise measurement of the equivalence principle because it’s one of the most fundamental tenets of gravity.”
In the satellite, which is still collecting additional data, a hollow cylinder, made of platinum alloy, is centered inside a hollow, titanium-alloy cylinder. According to standard physics, gravity should cause the cylinders to fall at the same rate, despite their different masses and materials. A violation of the equivalence principle, however, might make one fall slightly faster than the other.

As the two objects fall in their orbit around Earth, the satellite uses electrical forces to keep the pair aligned. If the equivalence principle didn’t hold, adjustments needed to keep the cylinders in line would vary with a regular frequency, tied to the rate at which the satellite orbits and rotates. “If we see any difference in the acceleration it would be a signature of violation” of the equivalence principle, says MICROSCOPE researcher Manuel Rodrigues of the French aerospace lab ONERA in Palaiseau. But no hint of such a signal was found.

With about 10 times the precision of previous tests, the result is “very impressive,” says physicist Jens Gundlach of the University of Washington in Seattle. But, he notes, “the results are still not as precise as what I think they can get out of a satellite measurement.”

Performing the experiment in space eliminates certain pitfalls of modern-day land-based equivalence principle tests, such as groundwater flow altering the mass of surrounding terrain. But temperature changes in the satellite limited how well the scientists could confirm the equivalence principle, as these variations can cause parts of the apparatus to expand or contract.

MICROSCOPE’s ultimate goal is to beat other measurements by a factor of 100, comparing the cylinders’ accelerations to see whether they match within a tenth of a trillionth of a percent. With additional data yet to be analyzed, the scientists may still reach that mark.

Confirmation of the equivalence principle doesn’t mean that all is hunky-dory in gravitational physics. Scientists still don’t know how to combine general relativity with quantum mechanics, the physics of the very small. “The two theories seems to be very different, and people would like to merge these two theories,” Rodrigues says. But some attempts to do that predict violations of the equivalence principle on a level that’s not yet detectable. That’s why scientists think the equivalence principle is worth testing to ever more precision — even if it means shipping their experiments off to space.