Thursday, February 11th, 2016

Time	Event
10:25a	Scientists make first direct detection of gravitational waves Almost 100 years ago today, Albert Einstein predicted the existence of gravitational waves — ripples in the fabric of space-time that are set off by extremely violent, cosmic cataclysms in the early universe. With his knowledge of the universe and the technology available in 1916, Einstein assumed that such ripples would be “vanishingly small” and nearly impossible to detect. The astronomical discoveries and technological advances over the past century have changed those prospects. Now for the first time, scientists in the LIGO Scientific Collaboration — with a prominent role played by researchers at MIT and Caltech — have directly observed the ripples of gravitational waves in an instrument on Earth. In so doing, they have again dramatically confirmed Einstein’s theory of general relativity and opened up a new way in which to view the universe. But there’s more: The scientists have also decoded the gravitational wave signal and determined its source. According to their calculations, the gravitational wave is the product of a collision between two massive black holes, 1.3 billion light years away — a remarkably extreme event that has not been observed until now. The researchers detected the signal with the Laser Interferometer Gravitational-wave Observatory (LIGO) — twin detectors carefully constructed to detect incredibly tiny vibrations from passing gravitational waves. Once the researchers obtained a gravitational signal, they converted it into audio waves and listened to the sound of two black holes spiraling together, then merging into a larger single black hole. “We’re actually hearing them go thump in the night,” says Matthew Evans, an assistant professor of physics at MIT. “We’re getting a signal which arrives at Earth, and we can put it on a speaker, and we can hear these black holes go, ‘Whoop.’ There’s a very visceral connection to this observation. You’re really listening to these things which before were somehow fantastic.” By further analyzing the gravitational signal, the team was able to trace the final milliseconds before the black holes collided. They determined that the black holes, 30 times as massive as our sun, circled each other at close to the speed of light before fusing in a collision and giving off an enormous amount of energy equivalent to about three solar masses — according to Einstein’s equation E=mc2 — in the form of gravitational waves. “Most of that energy is released in just a few tenths of a second,” says Peter Fritschel, LIGO’s chief detector scientist and a senior research scientist at MIT’s Kavli Institute for Astrophysics and Space Research. “For a very short amount of time, the actual power in gravitational waves was higher than all the light in the visible universe.” These waves then rippled through the universe, effectively warping the fabric of space-time, before passing through Earth more than a billion years later as faint traces of their former, violent origins. “It’s a spectacular signal,” says Rainer Weiss, a professor emeritus of physics at MIT. “It’s a signal many of us have wanted to observe since the time LIGO was proposed. It shows the dynamics of objects in the strongest gravitational fields imaginable, a domain where Newton’s gravity doesn’t work at all, and one needs the fully non-linear Einstein field equations to explain the phenomena. The triumph is that the waveform we measure is very well-represented by solutions of these equations. Einstein is right in a regime where his theory has never been tested before.” The new results are published today in the journal Physical Review Letters. “Magnificently in alignment” The first evidence for gravitational waves came in 1974, when physicists Russell Hulse and Joseph Taylor discovered a pair of neutron stars, 21,000 light years from Earth, that seemed to behave in a curious pattern. They deduced that the stars were orbiting each other in such a way that they must be losing energy in the form of gravitational waves — a detection that earned the researchers the Nobel Prize in physics in 1993. Now LIGO has made the first direct observation of gravitational waves with an instrument on Earth. The researchers detected the gravitational waves on September 14, 2015, at 5:51 a.m. EDT, using the twin LIGO interferometers, located in Livingston, Louisiana and Hanford, Washington. Each L-shaped interferometer spans 4 kilometers in length and uses laser light split into two beams that travel back and forth through each arm, bouncing between precisely configured mirrors. Each beam monitors the distance between these mirrors, which, according to Einstein’s theory, will change infinitesimally when a gravitational wave passes by the instrument.  “You can almost visualize it as if you dropped a rock on the surface of a pond, and the ripple goes out,” says Nergis Malvalvala, the Curtis and Kathleen Marble Professor of Astrophysics at MIT. “[It’s] something that distorts the space time around it, and that distortion propagates outward and reaches us on Earth, hundreds of millions of light years later.” Last March, researchers completed major upgrades to the interferometers, known as Advanced LIGO, increasing the instruments’ sensitivity and enabling them to detect a change in the length of each arm, smaller than one-ten-thousandth the diameter of a proton. By September, they were ready to start observing with them. “The effect we’re measuring on Earth is equivalent to measuring the distance to the closest star, Alpha Centauri, to within a few microns,” Evans says. “It’s a very tough measurement to make. Einstein expected this to never have been pulled off.” Nevertheless, a signal came through. Using Einstein’s equations, the team analyzed the signal and determined that it originated from a collision between two massive black holes. “We thought it was going to be a huge challenge to prove to ourselves and others that the first few signals that we saw were not just flukes and random noise,” says David Shoemaker, director of the MIT LIGO Laboratory. “But nature was just unbelievably kind in delivering to us a signal that’s very large, extremely easy to understand, and absolutely, magnificently in alignment with Einstein’s theory.” For LIGO’s hundreds of scientists, this new detection of gravitational waves marks not only a culmination of a decades-long search, but also the beginning of a new way to look at the universe. “This really opens up a whole new area for astrophysics,” Evans says. “We always look to the sky with telescopes and look for electromagnetic radiation like light, radio waves, or X-rays. Now gravitational waves are a completely new way in which we can get to know the universe around us.” Tiny detection, massive payoff LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of some 950 scientists at universities around the United States, including MIT, and in 15 other countries. The LIGO Observatories are operated by MIT and Caltech. The instruments were first explored as a means to detect gravitational waves in the 1970s by Weiss, who along with Kip Thorne and Ronald Drever from Caltech proposed LIGO in the 1980s. “This has been 20 years of work, and for some of us, even more,” Evans says. “It’s been a long time working on these detectors, without seeing anything. So it’s a real sea change and an interesting psychological change for the whole collaboration.” “The project represents a triumph for federally funded research,” says Maria Zuber, vice president for research and E. A. Griswold Professor of Geophysics at MIT. “LIGO is an example of a high-risk, high-return investment in discovery-driven science. In this case the investment was major and sustained over many years, with a successful outcome far from assured. But the scientific payoff is shaping up to be extraordinary. While the discoveries reported here are already magnificent, they represent the tip of the iceberg of what will be learned about fundamental physics and the nature of the universe.” The LIGO Observatories are due for more upgrades in the near future. Currently, the instruments are performing at one-third of their projected sensitivity. Once they are fully optimized, Shoemaker predicts that scientists will be able to detect gravitational waves emanating “from the edge of the universe.” “In a few years, when this is fully commissioned, we should be seeing events from a whole variety of objects: black holes, neutron stars, supernova, as well as things we haven’t imagined yet, on the frequency of once a day or once a week, depending on how many surprises are out there.” Shoemaker says. “That’s our dream, and so far we don’t have any reason to know that that’s not true.” As for this new gravitational signal, Weiss, who first came up with the rudimentary design for LIGO in the 1970s as part of an experimental exercise for one of his MIT courses, sees the tiny detection as a massive payoff. “This is the first real evidence that we’ve seen now of high-gravitational field strengths: monstrous things like stars, moving at the velocity of light, smashing into each other and making the geometry of space-time turn into some sort of washing machine,” Weiss says. “And this horrendously strong thing made a very tiny effect in our apparatus, a relative motion of 10 to the minus 18 meters between the mirrors in the interferometer arms. It’s sort of unbelievable to think about.” This research was funded by the National Science Foundation. (Comment on this)
10:25a	Q&A: Rainer Weiss on LIGO’s origins Scientists from MIT and Caltech, along with others around the world, have made the first direct detection of gravitational waves reaching the Earth, using an instrument known as LIGO (Laser Interferometer Gravitational-Wave Observatory). LIGO is a system of two identical detectors located 1,865 miles apart. Each detector consists of two 4-kilometer-long vacuum tubes, arranged in an L-shape, through which scientists send laser beams. As each beam reaches the end of a tube, it bounces off a mirror and heads back in the opposite direction. All things being equal, both laser beams should arrive back at their source at precisely the same time and, due to interference, cancel the light that would go to a photodetector. If, however, a gravitational wave passes through the detector, according to Albert Einstein’s predictions of 100 years ago the wave should stretch space in one tube while contracting the space in the other tube by an infinitesimal amount, thereby destroying the perfect cancellation and allowing light to reach the photodetector. On Sept. 14, 2015, the LIGO Scientific Collaboration detected a very slight disruption in both detectors. After careful analysis, the researchers have confirmed that the disruption is indeed a signal of gravitational waves, originating from the merging of two massive black holes 1.3 billion light years from Earth. Today, LIGO involves some 950 scientists at universities around the United States, including MIT, and in 15 other countries. But nearly four decades ago, the instrument was merely an MIT class exercise, conceived by Rainer Weiss, now a professor emeritus of physics. MIT News spoke with Weiss about the history of LIGO’s design and the 40-year effort to prove Einstein right. Q: Where does the story of LIGO begin? A: It started here in 1967. I was asked by the head of the teaching program in physics to give a course on general relativity. By the time 1967 had rolled around, general relativity had been relegated to mathematics departments. It was a theory of gravity, but it was mostly mathematics, and in most people’s minds it bore no relation to physics. And that was mostly because experiments to prove it were so hard to do — all these effects that Einstein’s theory had predicted were infinitesimally small. Einstein had looked at the numbers and dimensions that went into his equations for gravitational waves and said, essentially, “This is so tiny that it will never have any influence on anything, and nobody can measure it.” And when you think about the times and the technology in 1916, he was probably right. The big thing that’s happened in the last 100 years is, people discovered things in astronomy which were very different from what they knew in 1916 — tightly compact sources, enormously dense, like a neutron star, and black holes. And there was technology for doing precision measurements, because you had lasers, masers, electronics, computers, and a whole bunch of stuff people didn’t have in 1916. So the technology and knowledge of the universe made it possible by the time we got into this, to contemplate trying to look for gravitational waves. In the 1960s, Joseph Weber at the University of Maryland had the idea that maybe the technology had gotten to the point where you could look for gravitational waves, and he invented a method for doing that. He imagined a sort of xylophone made of a great big mass, called resonant bars. He expected a gravitational wave would come along and pull on one of the bars and squeeze it, and as the wave left, it would leave a pulse, and the thing would ring and you could hear it. It was the first idea that you should do something active to go look for gravitational waves. And he had claimed a discovery in the 1960s. When I taught my course, the students were very interested in finding out what this was. And I’ll be honest with you, I couldn’t for the life of me understand the thing he was doing. That was the problem. Because it completely countered every intuition I had now developed about general relativity. I couldn’t explain it to the students. That was my quandary at the time, and that’s when the invention was made. I said, “What’s the simplest thing I can think of to show these students that you could detect the influence of a gravitational wave?” The obvious thing to me was, let’s take freely floating masses in space and measure the time it takes light to travel between them. The presence of a gravitational wave would change that time. Using the time difference one could measure the amplitude of the wave. Equations for this process are simple to write and most of the students in the class could do it. Forget for a moment that this was a thought experiment requiring impossibly precise clocks. The principle was OK. I didn’t think much more of it until about a year later, when I began to realize something about Weber’s experiments — nobody was getting the answer he was getting. He had made a huge and powerful claim. And I began to realize, maybe this was wrong, and maybe even his idea of how it works was wrong. So I sat down one summer in a little room in Building 20, the “Plywood Palace” on Vassar Street, and worked the whole summer on the idea that I had talked with my students about. And knowing what you could do with lasers, I worked it out: Could you actually detect gravitational waves this way? And I came to the conclusion that yes, you could detect gravitational waves, at a strength that was much better than what Weber was looking for. Q: What did it take to bring this idea into physical form? A: We had been building a 1.5-meter prototype in RLE [the Research Laboratory of Electronics] using [military] funding, and were fairly well along. All at once funding was gone, due to the Mansfield amendment, which was a reaction to the Vietnam War. In the mind of the local RLE administrators, research in gravitation and cosmology was not in the military’s interest and support was given to solid-state physics, which was deemed more relevant. For the first time, I had to write proposals to other government and private agencies to continue our research. Nobody was seriously working on gravitational wave interferometry yet, although as I learned later, others had thought about it as well. A German group at the Max Planck Institute in Garching had just been through building a Weber bar. They had worked with the Italians and found that Weber was wrong. They had probably done the very best experiment of anybody to show this. That was the mid ’70s. They were asked to review my proposal to the National Science Foundation, just as they were thinking about the next thing to work on. They had been thinking, as many other groups in the world had at the time, to make even better Weber bars by cooling them to close to absolute zero. Instead they made a decision to try the interferometer idea. They called me to ask if there were any students that had been trained on the 1.5-meter prototype so that they could offer them a job. (At exactly the time they called there were none; a little later David Shoemaker, who had worked on the MIT prototype, did join the Garching group.) They then built a 3-meter prototype, got it working, and did a beautiful job. Next they built a 30-meter one. By the time I got funding from the NSF and got going again, the German group had really solved most of the technical problems of the idea, and shown that all the calculations I had done were right on the money, that it worked just as calculated. They also added some ideas of their own that made it better. A key step was in 1975: Because I was also doing studies in cosmic background radiation supported by NASA, I was asked by NASA to run a committee on uses of space research in the field of cosmology and relativity. What came out of that committee, for me, was that I met [Caltech physicist] Kip Thorne, whom I had asked to be a witness for the committee. I picked Kip up at the airport on a hot summer night when Washington, D.C., was filled with tourists. He did not have a hotel reservation so we shared a room for the night. Kip had developed one of the best theory groups in gravitation at Caltech and was thinking of bringing an experimental gravitation group there. We laid out on a big piece of paper all the different experiments one could build a new group around. I told him about this thing we were working on. He had never heard about it, and he got very interested. What came of it was that Kip and I eventually decided Caltech and MIT would do this [project that became LIGO] together. Q: This was an ambitious vision, with undoubtedly a long and complicated history. What were some key moments that drove the project forward? A: In the later 1970s, the MIT group, now including Peter Saulson and Paul Linsay, did a study with industry to determine the feasibility of building a large, kilometer-scale gravitational wave interferometer. The study looked at how to make large vacuum systems and considered how to develop scaling laws for costs, the possible sites where one could build 5- to 10-kilometer L-shaped structures with minimum earth-moving, and the availability of optics and light sources. We looked at the possible sources of gravitational waves and several competing interferometer concepts that had been prototyped in different labs in the world. The information was put in a report, called the Blue Book, and presented to the NSF in 1983. Scientists from Caltech and MIT together presented the ideas developed in the Blue Book, as well as the results of the prototype research. The proposal we presented was to make a detector system sensitive enough to actually detect gravitational waves from an astrophysical source (not just a new prototype). The proposal was to build two detectors. You couldn’t do science with one; you had to have two separate detectors, equally sensitive, and long enough. That was a real struggle later on. You wanted to maintain those ideas, and people later wanted to shave it down: Why not just build one long one? Why build it so long? All these arguments were made but we stuck it out. We had to, otherwise we would never have survived and we wouldn’t be here today. We got an endorsement from the committee: risky research with the possibility of a profound outcome well worth considering as a new project by the NSF. By the mid 1980s, NSF kept trying to figure out how to start this. Then in 1986, an interesting thing happened that finally broke the logjam. Richard Garwin, who had worked with Enrico Fermi [1938 Nobel laureate in Physics] and with the Department of Energy, and made all the calculations and did the actual development of the first hydrogen bomb, had become chief scientist of IBM. He had read about Weber’s experiments and decided with another IBM associate to build a little one, much smarter than what Weber had built — and he saw nothing. NSF was trying to sell this huge new program for gravitational waves. Garwin gets wind of it, and he thought he had slayed this dragon. He wrote a letter to the NSF saying, “If you’re going to persist with this, you’d better have a real study.” So we ran a study at the American Academy of Arts and Sciences on Beacon Street in Cambridge. It was a one-week meeting with an excellent committee of hard-nosed scientists. The recommendation the committee made was unbelievably good: The project is absolutely worth doing, don’t divide it up into one detector at a time, make it the full length, no more prototypes. It also recommended a change in the management of the project to have a single director rather than a steering group, which was the way we had managed the project. By 1989, we wrote another proposal under the direction of Rochus Vogt [a former Caltech provost], which took us almost six months to write — it was a masterpiece. The proposal was to build two sites with 4-kilometer-long interferometers. The interferometers were to be staged. The first detector was based on the research, now reasonably mature, from the prototypes with a sensitivity that offered a plausible chance for detection. The second detector was based on newer advanced concepts that had not yet been fully tested but that offered the capability of a good chance for detection. The proposal made it through the National Science Board, got accepted, and money started coming in significant amounts. By the 1990s, the rest of the history is easier. Now under the direction of Barry Barish [a Caltech physics professor] the sites were being built and developed, vacuum systems were made, and we started running the first detectors. By 2010, we had run and made vast improvements in their sensitivity but had seen nothing. It was a clean nothing; the detectors had run at design and we saw no anomalies that could be interpreted as gravitational waves. Based on the fact that we [had achieved our desired] design sensitivity and had carried out the science to determine some interesting upper limits on possible sources, we received funding to build Advanced LIGO. Q: How momentous for you is this discovery? A: As far as having fulfilled the ambitions of a lot of us who have worked on this project, it is momentous. It’s the signal that all of us have wanted to see, because we knew about it, we had never had real proof of it, and it’s the limit of Einstein equations never observed before — the dynamics of the geometry of space-time in the strong [gravitational] field and high velocity limit. To me, it’s a closure to something which has had a very complicated history. The field equations and the whole history of general relativity have been complicated. Here suddenly we have something we can grab onto and say, “Einstein was right. What  a marvelous insight and intuition he had.” I feel an enormous sense of relief and some joy, but mostly relief. There’s a monkey that’s been sitting on my shoulder for 40 years, and he’s been nattering in my ear and saying, “Ehhh, how do you know this is really going to work? You’ve gotten a whole bunch of people involved. Suppose it never works right?” And suddenly, he’s jumped off. It’s a huge relief. (Comment on this)
10:45a	Letter regarding the first direct detection of gravitational waves The following email was sent today to the MIT community by President L. Rafael Reif. To the members of the MIT community, At about 10:30 this morning in Washington, D.C., MIT, Caltech and the National Science Foundation (NSF) will make a historic announcement in physics: the first direct detection of gravitational waves, a disturbance of space-time that Albert Einstein predicted a century ago. You may want to watch the announcement live now. Following the NSF event, you can watch our on-campus announcement event. You can read an overview of the discovery here as well as an interview with MIT Professor Emeritus Rainer Weiss PhD '62, instigator and a leader of the Laser Interferometer Gravitational-Wave Observatory (LIGO) effort. The beauty and power of basic science I do not typically write to you to celebrate individual research achievements, no matter how impressive; our community produces important work all the time. But I urge you to reflect on today's announcement because it demonstrates, on a grand scale, why and how human beings pursue deep scientific questions – and why it matters. Today's news encompasses at least two compelling stories. First is the one the science tells: that with his theory of general relativity, Einstein correctly predicted the behavior of gravitational waves, space-time ripples that travel to us from places in the universe where gravity is immensely strong. Those rippling messages are imperceptibly faint; until now, they had defied direct observation. Because LIGO succeeded in detecting these faint messages – from two black holes that crashed together to form a still larger one – we have remarkable evidence that the system behaves exactly as Einstein foretold. With even the most advanced telescopes that rely on light, we could not have seen this spectacular collision, because we expect black holes to emit no light at all. With LIGO's instrumentation, however, we now have the "ears" to hear it. Equipped with this new sense, the LIGO team encountered and recorded a fundamental truth about nature that no one ever has before. And their explorations with this new tool have only just begun. This is why human beings do science! The second story is of human achievement. It begins with Einstein: an expansive human consciousness that could form a concept so far beyond the experimental capabilities of his day that inventing the tools to prove its validity took a hundred years. That story extends to the scientific creativity and perseverance of Rai Weiss and his collaborators. Working for decades at the edge of what was technologically possible, against the odds Rai led a global collaboration to turn a brilliant thought experiment into a triumph of scientific discovery. Important characters in that narrative include the dozens of outside scientists and NSF administrators who, also over decades, systematically assessed the merits of this ambitious project and determined the grand investment was worth it. The most recent chapter recounts the scrupulous care the LIGO team took in presenting these findings to the physics community. Through the sacred step-by-step process of careful analysis and peer-reviewed publication, they brought us the confidence to share this news – and they opened a frontier of exploration. At a place like MIT, where so many are engaged in solving real-world problems, we sometimes justify our nation's investment in basic science by its practical byproducts. In this case, that appears nearly irrelevant. Yet immediately useful "results" are here, too: LIGO has been a strenuous training ground for thousands of undergraduates and hundreds of PhDs – two of them now members of our faculty. What's more, the LIGO team's technological inventiveness and creative appropriation of tools from other fields produced instrumentation of unprecedented precision. As we know so well at MIT, human beings cannot resist the lure of a new tool. LIGO technology will surely be adapted and developed, "paying off" in ways no one can yet predict. It will be fun to see where this goes. *             *             * The discovery we celebrate today embodies the paradox of fundamental science: that it is painstaking, rigorous and slow – and electrifying, revolutionary and catalytic. Without basic science, our best guess never gets any better, and "innovation" is tinkering around the edges. With the advance of basic science, society advances, too. I am proud and grateful to belong to a community so well equipped to appreciate the beauty and meaning of this achievement – and primed to unlock its opportunities. In wonder and admiration, L. Rafael Reif (Comment on this)
12:00p	Pinpointing loneliness in the brain Humans, like all social animals, have a fundamental need for contact with others. This deeply ingrained instinct helps us to survive; it’s much easier to find food, shelter, and other necessities with a group than alone. Deprived of human contact, most people become lonely and emotionally distressed. In a study appearing in the Feb. 11 issue of Cell, MIT neuroscientists have identified a brain region that represents these feelings of loneliness. This cluster of cells, located near the back of the brain in an area called the dorsal raphe nucleus (DRN), is necessary for generating the increased sociability that normally occurs after a period of social isolation, the researchers found in a study of mice. “To our knowledge, this is the first time anyone has pinned down a loneliness-like state to a cellular substrate. Now we have a starting point for really starting to study this,” says Kay Tye, the Whitehead Career Development Assistant Professor of Brain and Cognitive Sciences, a member of MIT’s Picower Institute for Learning and Memory, and one of the senior authors of the study. While much research has been done on how the brain seeks out and responds to rewarding social interactions, very little is known about how isolation and loneliness also motivate social behavior. “There are many studies from human psychology describing how we have this need for social connection, which is particularly strong in people who feel lonely. But our understanding of the neural mechanisms underlying that state is pretty slim at the moment. It certainly seems like a useful, adaptive response, but we don’t really know how that’s brought about,” says Gillian Matthews, a postdoc at the Picower Institute and the paper’s lead author. Only the lonely Matthews first identified the loneliness neurons somewhat serendipitously, while studying a completely different topic. As a PhD student at Imperial College London, she was investigating how drugs affect the brain, particularly dopamine neurons. She originally planned to study how drug abuse influences the DRN, a brain region that had not been studied very much. As part of the experiment, each mouse was isolated for 24 hours, and Matthews noticed that in the control mice, which had not received any drugs, there was a strengthening of connections in the DRN following the isolation period. Further studies, both at Imperial College London and then in Tye’s lab at MIT, revealed that these neurons were responding to the state of isolation. When animals are housed together, DRN neurons are not very active. However, during a period of isolation, these neurons become sensitized to social contact and when the animals are reunited with other mice, DRN activity surges. At the same time, the mice become much more sociable than animals that had not been isolated. When the researchers suppressed DRN neurons using optogenetics, a technique that allows them to control brain activity with light, they found that isolated mice did not show the same rebound in sociability when they were re-introduced to other mice. “That suggested these neurons are important for the isolation-induced rebound in sociability,” Tye says. “When people are isolated for a long time and then they’re reunited with other people, they’re very excited, there’s a surge of social interaction. We think that this adaptive and evolutionarily conserved trait is what we are modeling in mice, and these neurons could play a role in that increased motivation to socialize.” Social dominance The researchers also found that animals with a higher rank in the social hierarchy were more responsive to changes in DRN activity, suggesting that they may be more susceptible to feelings of loneliness following isolation. “The social experience of every animal is not the same in a group,” Tye says. “If you’re the dominant mouse, maybe you love your social environment. And if you’re the subordinate mouse, and you’re being beat up every day, maybe it’s not so fun. Maybe you feel socially excluded already.” The findings represent “an amazing cornerstone for future studies of loneliness,” says Alcino Silva, a professor of neurobiology, psychiatry, and psychology at the David Geffen School of Medicine at UCLA who was not involved in the research. “There is something poetic and fascinating about the idea that modern neuroscience tools have allowed us to reach to the very depths of the human soul, and that in this search we have discovered that even the most human of emotions, loneliness, is shared in some recognizable form with even one of our distant mammalian relatives — the mouse,” Silva says. The researchers are now studying whether these neurons actually detect loneliness or are responsible for driving the response to loneliness, and whether they might be part of a larger brain network that responds to social isolation. Another area to be explored is whether differences in these neurons can explain why some people prefer more social contact than others, and whether those differences are innate or formed by experience. “There’s probably some part that could very well be determined by innate brain features, but I think probably an equal, if not greater, contribution would be from the environment in which individuals have developed,” Tye says. “These are completely open questions. We can only speculate about it at this point.” Mark Ungless, a senior lecturer at Imperial College London, is also a senior author of the study. MIT graduate students Edward Nieh and Caitlin Vander Weele are also lead authors. (Comment on this)

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