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  • richardmitnick 2:58 pm on March 13, 2019 Permalink | Reply
    Tags: "Astronomers discover 83 supermassive black holes in the early universe", , , , , Princeton University,   

    From Princeton University: “Astronomers discover 83 supermassive black holes in the early universe” 

    Princeton University
    From Princeton University

    March 13, 2019
    Liz Fuller-Wright

    Astronomers from Japan, Taiwan and Princeton University have discovered 83 quasars powered by supermassive black holes in the distant universe, from a time when the universe was less than 10 percent of its present age.

    “It is remarkable that such massive dense objects were able to form so soon after the Big Bang,” said Michael Strauss, a professor of astrophysical sciences at Princeton University who is one of the co-authors of the study. “Understanding how black holes can form in the early universe, and just how common they are, is a challenge for our cosmological models.”

    This finding increases the number of black holes known at that epoch considerably, and reveals, for the first time, how common they are early in the universe’s history. In addition, it provides new insight into the effect of black holes on the physical state of gas in the early universe in its first billion years. The research appears in a series of five papers published in The Astrophysical Journal and the Publications of the Astronomical Observatory of Japan.

    2
    Light from one of the most distant quasars known, powered by a supermassive black hole lying 13.05 billion light-years away from Earth. The image was obtained by the Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope. The other objects in the field are mostly stars in our Milky Way or galaxies along the line of sight. Image courtesy of the National Astronomical Observatory of Japan

    NAOJ Subaru Hyper Suprime-Cam


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    Supermassive black holes, found at the centers of galaxies, can be millions or even billions of times more massive than the sun. While they are prevalent today, it is unclear when they first formed, and how many existed in the distant early universe. A supermassive black hole becomes visible when gas accretes onto it, causing it to shine as a “quasar.” Previous studies have been sensitive only to the very rare, most luminous quasars, and thus the most massive black holes. The new discoveries probe the population of fainter quasars, powered by black holes with masses comparable to most black holes seen in the present-day universe.

    3
    An artist’s impression of a quasar. A supermassive black hole sits at the center, and the gravitational energy of material accreting onto it is released as light.
    Image courtesy of Yoshiki Matsuoka

    HSC has a gigantic field-of-view — 1.77 degrees across, or seven times the area of the full moon — mounted on one of the largest telescopes in the world. The HSC team is surveying the sky over the course of 300 nights of telescope time, spread over five years.

    The team selected distant quasar candidates from the sensitive HSC survey data. They then carried out an intensive observational campaign to obtain spectra of those candidates, using three telescopes: the Subaru Telescope [above]; the Gran Telescopio Canarias on the island of La Palma in the Canaries, Spain; and the Gemini South Telescope in Chile.


    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level


    Gemini/South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    The team selected distant quasar candidates from the sensitive HSC survey data. They then carried out an intensive observational campaign to obtain spectra of those candidates, using three telescopes: the Subaru Telescope; the Gran Telescopio Canarias on the island of La Palma in the Canaries, Spain; and the Gemini South Telescope in Chile. The survey has revealed 83 previously unknown very distant quasars. Together with 17 quasars already known in the survey region, the researchers found that there is roughly one supermassive black hole per cubic giga-light-year — in other words, if you chunked the universe into imaginary cubes that are a billion light-years on a side, each would hold one supermassive black hole.

    4
    The 100 quasars identified from the HSC data. The top seven rows show the 83 newly discovered quasars while the bottom two rows represent 17 previously known quasars in the survey area. They appear extremely red due to the cosmic expansion and absorption of light in intergalactic space. All the images were obtained by HSC.
    Image courtesy of the National Astronomical Observatory of Japan

    The sample of quasars in this study are about 13 billion light-years away from the Earth; in other words, we are seeing them as they existed 13 billion years ago. As the Big Bang took place 13.8 billion years ago, we are effectively looking back in time, seeing these quasars and supermassive black holes as they appeared only about 800 million years after the creation of the (known) universe.

    5
    If the history of the universe from the Big Bang to the present were laid out on a football field, Earth and our solar system would not appear until our own 33-yard line. Life appeared just inside the 28-yard line and dinosaurs went extinct halfway between the 1-yard line and the goal. All of human history, since hominids first climbed out of trees, takes place within an inch of the goal line. On this timeline, the supermassive black holes discovered by Princeton astrophysicist Michael Strauss and his international team of colleagues would appear back on the universe’s 6-yard line, very shortly after the Big Bang itself.
    Image by Kyle McKernan, Office of Communications

    The survey has revealed 83 previously unknown very distant quasars. Together with 17 quasars already known in the survey region, the researchers found that there is roughly one supermassive black hole per cubic giga-light-year — in other words, if you chunked the universe into imaginary cubes that are a billion light-years on a side, each would hold one supermassive black hole.

    It is widely accepted that the hydrogen in the universe was once neutral, but was “reionized” — split into its component protons and electrons — around the time when the first generation of stars, galaxies and supermassive black holes were born, in the first few hundred million years after the Big Bang. This is a milestone of cosmic history, but astronomers still don’t know what provided the incredible amount of energy required to cause the reionization. A compelling hypothesis suggests that there were many more quasars in the early universe than detected previously, and it is their integrated radiation that reionized the universe.

    “However, the number of quasars we observed shows that this is not the case,” explained Robert Lupton, a 1985 Princeton Ph.D. alumnus who is a senior research scientist in astrophysical sciences. “The number of quasars seen is significantly less than needed to explain the reionization.” Reionization was therefore caused by another energy source, most likely numerous galaxies that started to form in the young universe.

    The present study was made possible by the world-leading survey ability of Subaru and HSC. “The quasars we discovered will be an interesting subject for further follow-up observations with current and future facilities,” said Yoshiki Matsuoka, a former Princeton postdoctoral researcher now at Ehime University in Japan, who led the study. “We will also learn about the formation and early evolution of supermassive black holes, by comparing the measured number density and luminosity distribution with predictions from theoretical models.”

    Based on the results achieved so far, the team is looking forward to finding yet more distant black holes and discovering when the first supermassive black hole appeared in the universe.

    The HSC collaboration includes astronomers from Japan, Taiwan and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University.

    The results of the present study are published in the following five papers — the second paper in particular.

    [1] “Discovery of the First Low-luminosity Quasar at z > 7”, by Yoshiki Matsuoka1, Masafusa Onoue2, Nobunari Kashikawa3,4,5, Michael A Strauss6, Kazushi Iwasawa7, Chien-Hsiu Lee8, Masatoshi Imanishi4,5, Tohru Nagao and 40 co-authors, including Princeton astrophysicists James Bosch, James Gunn, Robert Lupton and Paul Price, appeared in the Feb. 6 issue of The Astrophysical Journal Letters, 872 (2019),

    [2] “Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6,” appeared in the Dec. 20 issue of The Astrophysical Journal, 869 (2018), 150

    [3] “Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 6.9,” was published July 3, 2018 in The Astrophysical Journal Supplement Series, 237 (2018), 5

    [4] “Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7 < z ≤ 6.8,” was published July 5, 2017 in Publications of the Astronomical Society of Japan, 70 (2018), S35

    [5] “Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). I. Discovery of 15 Quasars and Bright Galaxies at 5.7 < z < 6.9”, was published Aug. 25, 2016 in The Astrophysical Journal, 828 (2016), 26 .

    See the full article here .

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    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 11:52 am on December 19, 2018 Permalink | Reply
    Tags: AdS/CFT, Beyond Einstein: Physicists find surprising connections in the cosmos, , From tiny bits of string, , Our world when we get down to the level of particles is a quantum world, , Princeton University, Relatability between gravity and subatomic particles provides a sort of Rosetta stone for physics, The idea that fundamental particles are actually tiny bits of vibrating string was taking off and by the mid-1980s “string theory” had lassoed the imaginations of many leading physicists,   

    From Princeton University: “Beyond Einstein: Physicists find surprising connections in the cosmos” 

    Princeton University
    From Princeton University

    Dec. 17, 2018
    Catherine Zandonella

    1
    Gravity, the force that brings baseballs back to Earth and governs the growth of black holes, is mathematically relatable to the peculiar antics of the subatomic particles that make up all the matter around us. Illustration by J.F. Podevin

    Albert Einstein’s desk can still be found on the second floor of Princeton’s physics department. Positioned in front of a floor-to-ceiling blackboard covered with equations, the desk seems to embody the spirit of the frizzy-haired genius as he asks the department’s current occupants, “So, have you solved it yet?”

    Einstein never achieved his goal of a unified theory to explain the natural world in a single, coherent framework. Over the last century, researchers have pieced together links between three of the four known physical forces in a “standard model,” but the fourth force, gravity, has always stood alone.

    No longer. Thanks to insights made by Princeton faculty members and others who trained here, gravity is being brought in from the cold — although in a manner not remotely close to how Einstein had imagined it.

    Though not yet a “theory of everything,” this framework, laid down over 20 years ago and still being filled in, reveals surprising ways in which Einstein’s theory of gravity relates to other areas of physics, giving researchers new tools with which to tackle elusive questions.

    The key insight is that gravity, the force that brings baseballs back to Earth and governs the growth of black holes, is mathematically relatable to the peculiar antics of the subatomic particles that make up all the matter around us.

    This revelation allows scientists to use one branch of physics to understand other seemingly unrelated areas of physics. So far, this concept has been applied to topics ranging from why black holes run a temperature to how a butterfly’s beating wings can cause a storm on the other side of the world.

    This relatability between gravity and subatomic particles provides a sort of Rosetta stone for physics. Ask a question about gravity, and you’ll get an explanation couched in the terms of subatomic particles. And vice versa.

    “This has turned out to be an incredibly rich area,” said Igor Klebanov, Princeton’s Eugene Higgins Professor of Physics, who generated some of the initial inklings in this field in the 1990s. “It lies at the intersection of many fields of physics.”

    From tiny bits of string

    The seeds of this correspondence were sprinkled in the 1970s, when researchers were exploring tiny subatomic particles called quarks. These entities nest like Russian dolls inside protons, which in turn occupy the atoms that make up all matter. At the time, physicists found it odd that no matter how hard you smash two protons together, you cannot release the quarks — they stay confined inside the protons.

    One person working on quark confinement was Alexander Polyakov, Princeton’s Joseph Henry Professor of Physics. It turns out that quarks are “glued together” by other particles, called gluons. For a while, researchers thought gluons could assemble into strings that tie quarks to each other. Polyakov glimpsed a link between the theory of particles and the theory of strings, but the work was, in Polyakov’s words, “hand-wavy” and he didn’t have precise examples.

    Meanwhile, the idea that fundamental particles are actually tiny bits of vibrating string was taking off, and by the mid-1980s, “string theory” had lassoed the imaginations of many leading physicists. The idea is simple: just as a vibrating violin string gives rise to different notes, each string’s vibration foretells a particle’s mass and behavior. The mathematical beauty was irresistible and led to a swell of enthusiasm for string theory as a way to explain not only particles but the universe itself.

    One of Polyakov’s colleagues was Klebanov, who in 1996 was an associate professor at Princeton, having earned his Ph.D. at Princeton a decade earlier. That year, Klebanov, with graduate student Steven Gubser and postdoctoral research associate Amanda Peet, used string theory to make calculations about gluons, and then compared their findings to a string-theory approach to understanding a black hole. They were surprised to find that both approaches yielded a very similar answer. A year later, Klebanov studied absorption rates by black holes and found that this time they agreed exactly.

    That work was limited to the example of gluons and black holes. It took an insight by Juan Maldacena in 1997 to pull the pieces into a more general relationship. At that time, Maldacena, who had earned his Ph.D. at Princeton one year earlier, was an assistant professor at Harvard. He detected a correspondence between a special form of gravity and the theory that describes particles. Seeing the importance of Maldacena’s conjecture, a Princeton team consisting of Gubser, Klebanov and Polyakov followed up with a related paper formulating the idea in more precise terms.

    Another physicist who was immediately taken with the idea was Edward Witten of the Institute for Advanced Study (IAS), an independent research center located about a mile from the University campus. He wrote a paper that further formulated the idea, and the combination of the three papers in late 1997 and early 1998 opened the floodgates.

    “It was a fundamentally new kind of connection,” said Witten, a leader in the field of string theory who had earned his Ph.D. at Princeton in 1976 and is a visiting lecturer with the rank of professor in physics at Princeton. “Twenty years later, we haven’t fully come to grips with it.”

    2

    Two sides of the same coin

    This relationship means that gravity and subatomic particle interactions are like two sides of the same coin. On one side is an extended version of gravity derived from Einstein’s 1915 theory of general relativity. On the other side is the theory that roughly describes the behavior of subatomic particles and their interactions.

    The latter theory includes the catalogue of particles and forces in the “standard model” (see sidebar), a framework to explain matter and its interactions that has survived rigorous testing in numerous experiments, including at the Large Hadron Collider.

    In the standard model, quantum behaviors are baked in. Our world, when we get down to the level of particles, is a quantum world.

    Notably absent from the standard model is gravity. Yet quantum behavior is at the basis of the other three forces, so why should gravity be immune?

    The new framework brings gravity into the discussion. It is not exactly the gravity we know, but a slightly warped version that includes an extra dimension. The universe we know has four dimensions, the three that pinpoint an object in space — the height, width and depth of Einstein’s desk, for example — plus the fourth dimension of time. The gravitational description adds a fifth dimension that causes spacetime to curve into a universe that includes copies of familiar four-dimensional flat space rescaled according to where they are found in the fifth dimension. This strange, curved spacetime is called anti-de Sitter (AdS) space after Einstein’s collaborator, Dutch astronomer Willem de Sitter.

    The breakthrough in the late 1990s was that mathematical calculations of the edge, or boundary, of this anti-de Sitter space can be applied to problems involving quantum behaviors of subatomic particles described by a mathematical relationship called conformal field theory (CFT). This relationship provides the link, which Polyakov had glimpsed earlier, between the theory of particles in four space-time dimensions and string theory in five dimensions. The relationship now goes by several names that relate gravity to particles, but most researchers call it the AdS/CFT (pronounced A-D-S-C-F-T) correspondence.

    3

    Tackling the big questions

    This correspondence, it turns out, has many practical uses. Take black holes, for example. The late physicist Stephen Hawking startled the physics community by discovering that black holes have a temperature that arises because each particle that falls into a black hole has an entangled particle that can escape as heat.

    Using AdS/CFT, Tadashi Takayanagi and Shinsei Ryu, then at the University of California-Santa Barbara, discovered a new way to study
    entanglement in terms of geometry, extending Hawking’s insights in a fashion that experts consider quite remarkable.

    In another example, researchers are using AdS/CFT to pin down chaos theory, which says that a random and insignificant event such as the flapping of a butterfly’s wings could result in massive changes to a large-scale system such as a faraway hurricane. It is difficult to calculate chaos, but black holes — which are some of the most chaotic quantum systems possible — could help. Work by Stephen Shenker and Douglas Stanford at Stanford University, along with Maldacena, demonstrates how, through AdS/CFT, black holes can model quantum chaos.

    One open question Maldacena hopes the AdS/CFT correspondence will answer is the question of what it is like inside a black hole, where an infinitely dense region called a singularity resides. So far, the relationship gives us a picture of the black hole as seen from the outside, said Maldacena, who is now the Carl P. Feinberg Professor at IAS.

    “We hope to understand the singularity inside the black hole,” Maldacena said. “Understanding this would probably lead to interesting lessons for the Big Bang.”

    The relationship between gravity and strings has also shed new light on quark confinement, initially through work by Polyakov and Witten, and later by Klebanov and Matt Strassler, who was then at IAS.

    Those are just a few examples of how the relationship can be used. “It is a tremendously successful idea,” said Gubser, who today is a professor of physics at Princeton. “It compels one’s attention. It ropes you in, it ropes in other fields, and it gives you a vantage point on theoretical physics that is very compelling.”

    The relationship may even unlock the quantum nature of gravity. “It is among our best clues to understand gravity from a quantum perspective,” said Witten. “Since we don’t know what is still missing, I cannot tell you how big a piece of the picture it ultimately will be.”

    Still, the AdS/CFT correspondence, while powerful, relies on a simplified version of spacetime that is not exactly like the real universe. Researchers are working to find ways to make the theory more broadly applicable to the everyday world, including Gubser’s research on modeling the collisions of heavy ions, as well as high-temperature superconductors.

    Also on the to-do list is developing a proof of this correspondence that draws on underlying physical principles. It is unlikely that Einstein would be satisfied without a proof, said Herman Verlinde, Princeton’s Class of 1909 Professor of Physics, the chair of the Department of Physics and an expert in string theory, who shares office space with Einstein’s desk.

    “Sometimes I imagine he is still sitting there,” Verlinde said, “and I wonder what he would think of our progress.”

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 1:27 pm on October 24, 2018 Permalink | Reply
    Tags: Biermann battery effect, , , , Princeton University,   

    From COSMOS Magazine: “Supercomputer finds clues to violent magnetic events” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    24 October 2018
    Phil Dooley

    1
    An aurora over Iceland, the product of sudden magnetic reconnection. Credit Natthawat/Getty Images

    Researchers are a step closer to understanding the violent magnetic events that cause the storms on the sun’s surface and fling clouds of hot gas out into space, thanks to colossal computer simulations at Princeton University in the US.

    The disruptions in the magnetic field, known as magnetic reconnections, are common in the universe – the same process causes the aurora in high latitude skies – but existing models are unable to explain how they happen so quickly.

    A team led by Jackson Matteucci decided to investigate by building a full three-dimensional simulation of the ejected hot gas, something that required enormous computing power. The results are published in the journal Physical Review Letters.

    The researchers modelled more than 200 million particles using Titan, the biggest supercomputer [no longer true, the writer should have known that] in the US.

    ORNL Cray Titan XK7 Supercomputer, once the fastest in the world.

    They discovered that a three-dimensional interaction called the Biermann battery effect was at the heart of the sudden reconnection process.

    Discovered in the fifties by German astrophysicist Ludwig Biermann, the Biermann battery effect shows how magnetic fields can be generated in charged gases, known as plasma.

    In such plasmas, if a region develops in which there is a temperature gradient at right angles to a density gradient, a magnetic field is created that encircles it.

    Astrophysicists propose that this effect might take place in interstellar plasma clouds, such as nebulae, and generate the cosmic magnetic fields that we see throughout the universe.

    In contrast with the huge scale of cosmic plasma clouds, magnetic reconnection happens at a scale of microns when two magnetic fields collide, says Matteucci.

    He likens the process to collisions between two sizable handfuls of rubber bands. In stable circumstances the magnetic field lines are loops, like the bands. But sometimes turbulence in the plasma pushes these band analogues together so forcefully that they sever and reconnect to different ones, thus forming loops at different orientations.

    Some of the new loops are stretched taut and snap back, providing the energy that ejects material so violently, and causes magnetic storms or glowing auroras.

    The Princeton simulation showed that as the fields collide there is a sudden spike in the temperature in a very localised region, which sets off the Biermann battery effect, suddenly creating a new magnetic field in the midst of the collision. It’s this newly-appearing field that severs the lines and allows them to reconfigure.

    Although Matteucci’s simulations are for tiny plasma clouds generated by lasers hitting foil, he says they could help us understand large-scale processes in the atmosphere.

    “If you do a back of the envelope calculation, you find it could play an important role in reconnection in the magnetosphere, where the solar wind collides with the Earth’s magnetic field,” he says.

    See the full article here .


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    Please help promote STEM in your local schools.

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  • richardmitnick 3:05 pm on September 12, 2018 Permalink | Reply
    Tags: A novel quantum state of matter that can be manipulated at will with a weak magnetic field, , , , Princeton University, , Scanning tunneling spectromicroscope operating in conjunction with a rotatable vector magnetic field capability, This could indeed be evidence of a new quantum phase of matter   

    From Princeton University: “Princeton scientists discover a ‘tuneable’ novel quantum state of matter” 

    Princeton University
    From Princeton University

    Sept. 12, 2018
    Liz Fuller-Wright, Office of Communications

    Quantum particles can be difficult to characterize, and almost impossible to control if they strongly interact with each other — until now.

    1
    An international team of researchers led by Princeton physicist Zahid Hasan has discovered a novel quantum state of matter that can be manipulated at will with a weak magnetic field, which opens new possibilities for next-generation nano- or quantum technologies. Researchers in Hasan’s lab include (from left): Jia-Xin Yin, Zahid Hasan, Songtian Sonia Zhang, Daniel Multer, Maksim Litskevich and Guoqing Chang. Photo by Nick Barberio, Office of Communications.

    An international team of researchers led by Princeton physicist Zahid Hasan has discovered a quantum state of matter that can be “tuned” at will — and it’s 10 times more tuneable than existing theories can explain. This level of manipulability opens enormous possibilities for next-generation nanotechnologies and quantum computing.

    “We found a new control knob for the quantum topological world,” said Hasan, the Eugene Higgins Professor of Physics. “We expect this is tip of the iceberg. There will be a new subfield of materials or physics grown out of this. … This would be a fantastic playground for nanoscale engineering.”

    Hasan and his colleagues, whose research appears in the current issue of Nature, are calling their discovery a “novel” quantum state of matter because it is not explained by existing theories of material properties.

    Hasan’s interest in operating beyond the edges of known physics is what attracted Jia-Xin Yin, a postdoctoral research associate and one of three co-first-authors on the paper, to his lab. Other researchers had encouraged him to tackle one of the defined questions in modern physics, Yin said.

    “But when I talked to Professor Hasan, he told me something very interesting,” Yin said. “He’s searching for new phases of matter. The question is undefined. What we need to do is search for the question rather than the answer.”

    The classical phases of matter — solids, liquids and gases — arise from interactions between atoms or molecules. In a quantum phase of matter, the interactions take place between electrons, and are much more complex.

    “This could indeed be evidence of a new quantum phase of matter — and that’s, for me, exciting,” said David Hsieh, a professor of physics at the California Institute of Technology and a 2009 Ph.D. graduate of Princeton, who was not involved in this research. “They’ve given a few clues that something interesting may be going on, but a lot of follow-up work needs to be done, not to mention some theoretical backing to see what really is causing what they’re seeing.”

    Hasan has been working in the groundbreaking subfield of topological materials, an area of condensed matter physics, where his team discovered topological quantum magnets a few years ago. In the current research, he and his colleagues “found a strange quantum effect on the new type of topological magnet that we can control at the quantum level,” Hasan said.

    The key was looking not at individual particles but at the ways they interact with each other in the presence of a magnetic field. Some quantum particles, like humans, act differently alone than in a community, Hasan said. “You can study all the details of the fundamentals of the particles, but there’s no way to predict the culture, or the art, or the society, that will emerge when you put them together and they start to interact strongly with each other,” he said.

    To study this quantum “culture,” he and his colleagues arranged atoms on the surface of crystals in many different patterns and watched what happened. They used various materials prepared by collaborating groups in China, Taiwan and Princeton. One particular arrangement, a six-fold honeycomb shape called a “kagome lattice” for its resemblance to a Japanese basket-weaving pattern, led to something startling — but only when examined under a spectromicroscope in the presence of a strong magnetic field, equipment found in Hasan’s Laboratory for Topological Quantum Matter and Advanced Spectroscopy, located in the basement of Princeton’s Jadwin Hall.

    All the known theories of physics predicted that the electrons would adhere to the six-fold underlying pattern, but instead, the electrons hovering above their atoms decided to march to their own drummer — in a straight line, with two-fold symmetry.

    “The electrons decided to reorient themselves,” Hasan said. “They ignored the lattice symmetry. They decided that to hop this way and that way, in one line, is easier than sideways. So this is the new frontier. … Electrons can ignore the lattice and form their own society.”

    This is a very rare effect, noted Caltech’s Hsieh. “I can count on one hand” the number of quantum materials showing this behavior, he said.

    The researchers were shocked to discover this two-fold arrangement, said Songtian Sonia Zhang, a graduate student in Hasan’s lab and another co-first-author on the paper. “We had expected to find something six-fold, as in other topological materials, but we found something completely unexpected,” she said. “We kept investigating — Why is this happening? — and we found more unexpected things. It’s interesting because the theorists didn’t predict it at all. We just found something new.”

    2
    When the researchers turn an external magnetic field in different directions (indicated with arrows), they change the orientation of the linear electron flow above the kagome (six-fold) magnet, as seen in these electron wave interference patterns on the surface of a topological quantum kagome magnet. Each pattern is created by a particular direction of the external magnetic field applied on the sample.
    Image by M. Z. Hasan, Jia-Xin Yin, Songtian Sonia Zhang, Princeton University.

    The decoupling between the electrons and the arrangement of atoms was surprising enough, but then the researchers applied a magnetic field and discovered that they could turn that one line in any direction they chose. Without moving the crystal lattice, Zhang could rotate the line of electrons just by controlling the magnetic field around them.

    “Sonia noticed that when you apply the magnetic field, you can reorient their culture,” Hasan said. “With human beings, you cannot change their culture so easily, but here it looks like she can control how to reorient the electrons’ many-body culture.”

    The researchers can’t yet explain why.

    “It is rare that a magnetic field has such a dramatic effect on electronic properties of a material,” said Subir Sachdev, the Herchel Smith Professor of Physics at Harvard University and chair of the physics department, who was not involved in this study.

    Even more surprising than this decoupling — called anisotropy — is the scale of the effect, which is 100 times more than what theory predicts. Physicists characterize quantum-level magnetism with a term called the “g factor,” which has no units. The g factor of an electron in a vacuum has been precisely calculated as very slightly more than two, but in this novel material, the researchers found an effective g factor of 210, when the electrons strongly interact with each other.

    “Nobody predicted that in topological materials,” said Hasan.

    “There are many things we can calculate based on the existing theory of quantum materials, but this paper is exciting because it’s showing an effect that was not known,” he said. This has implications for nanotechnology research especially in developing sensors. At the scale of quantum technology, efforts to combine topology, magnetism and superconductivity have been stymied by the low effective g factors of the tiny materials.

    “The fact that we found a material with such a large effective g factor, meaning that a modest magnetic field can bring a significant effect in the system — this is highly desirable,” said Hasan. “This gigantic and tunable quantum effect opens up the possibilities for new types of quantum technologies and nanotechnologies.”

    The discovery was made using a two-story, multi-component instrument known as a scanning tunneling spectromicroscope, operating in conjunction with a rotatable vector magnetic field capability, in the sub-basement of Jadwin Hall. The spectromicroscope has a resolution less than half the size of an atom, allowing it to scan individual atoms and detect details of their electrons while measuring the electrons’ energy and spin distribution. The instrument is cooled to near absolute zero and decoupled from the floor and the ceiling to prevent even atom-sized vibrations.

    “We’re going down to 0.4 Kelvin. It’s colder than intergalactic space, which is 2.7 Kelvin,” said Hasan. “And not only that, the tube where the sample is — inside that tube we create a vacuum condition that’s more than a trillion times thinner than Earth’s upper atmosphere. It took about five years to achieve these finely tuned operating conditions of the multi-component instrument necessary for the current experiment,” he said.

    “All of us, when we do physics, we’re looking to find how exactly things are working,” said Zhang. “This discovery gives us more insight into that because it’s so unexpected.”

    By finding a new type of quantum organization, Zhang and her colleagues are making “a direct contribution to advancing the knowledge frontier — and in this case, without any theoretical prediction,” said Hasan. “Our experiments are advancing the knowledge frontier.”

    The team included numerous researchers from Princeton’s Department of Physics, including present and past graduate students Songtian Sonia Zhang, Ilya Belopolski, Tyler Cochran and Suyang Xu; and present and past postdoctoral research associates Jia-Xin Yin, Guoqing Chang, Hao Zheng, Guang Bian and Biao Lian. Other co-authors were Hang Li, Kun Jiang, Bingjing Zhang, Cheng Xiang, Kai Liu, Tay-Rong Chang, Hsin Lin, Zhongyi Lu, Ziqiang Wang, Shuang Jia and Wenhong Wang.

    See the full article here .

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    About Princeton: Overview

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    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 12:33 pm on July 26, 2018 Permalink | Reply
    Tags: , , , , , Galactic-wind whisperers, OLCF ORNL Cray Titan XK7 Supercomputer, Princeton University,   

    From ASCRDiscovery: “Galactic-wind whisperers” 

    From ASCRDiscovery
    ASCR – Advancing Science Through Computing

    UC Santa Cruz and Princeton University team simulates galactic winds on the DOE’s Titan supercomputer.

    ORNL Cray Titan XK7 Supercomputer

    1
    A high-resolution, 18-billion-cell simulation of galactic winds created by Cholla hydrodynamic code run on DOE’s Titan supercomputer at the Oak Ridge Leadership Computing Facility, an Office of Science user facility. Shown is a calculation of a disk-shaped galaxy (green) where supernova explosions near the center of the galaxy have driven outflowing galactic winds (red, pink, purple). The red to purple transition indicates areas of increasing wind velocity. Image courtesy of Schneider, Robertson and Thompson via arXiv:1803.01005.

    Winds made of gas particles swirl around galaxies at hundreds of kilometers per second. Astronomers suspect the gusts are stirred by nearby exploding stars that exude photons powerful enough to move the gas. Whipped fast enough, this wind can be ejected into intergalactic space.

    Astronomers have known for decades that these colossal gales exist, but they’re still parsing precisely what triggers and drives them. “Galactic winds set the properties of certain components of galaxies like the stars and the gas,” says Brant Robertson, an associate professor of astronomy and astrophysics at the University of California, Santa Cruz (UCSC). “Being able to model galactic winds has implications ranging from understanding how and why galaxies form to measuring things like dark energy and the acceleration of the universe.”

    But getting there has been extraordinarily difficult. Models must simultaneously resolve hydrodynamics, radiative cooling and other physics on the scale of a few parsecs in and around a galactic disk. Because the winds consist of hot and cold components pouring out at high velocities, capturing all the relevant processes with a reasonable spatial resolution requires tens of billions of computational cells that tile the disk’s entire volume.

    Most traditional models would perform the bulk of calculations using a computer’s central processing unit, with bits and pieces farmed out to its graphics processing units (GPUs). Robertson had a hunch, though, that thousands of GPUs operating in parallel could do the heavy lifting – a feat that hadn’t been tried for large-scale astronomy projects. Robertson’s experience running numerical simulations on supercomputers as a Harvard University graduate student helped him overcome challenges associated with getting the GPUs to efficiently communicate with each other.

    Once he’d decided on the GPU-based architecture, Robertson enlisted Evan Schneider, then a graduate student in his University of Arizona lab and now a Hubble Fellow at Princeton University, to work with him on a hydrodynamic code that suited the computational approach. They dubbed it Computational Hydrodynamics on II Architectures, or Cholla – also a cactus indigenous to the Southwest, and the two lowercase Ls represent those in the middle of the word “parallel.”

    “We knew that if we could design an effective GPU-centric code,” Schneider says, “we could really do something completely new and exciting.”

    With Cholla in hand, she and Robertson searched for a computer powerful enough to get the most out of it. They turned to Titan, a Cray XK7 supercomputer housed at the Oak Ridge Leadership Computing Facility (OLCF), a Department of Energy (DOE) Office of Science user facility at DOE’s Oak Ridge National Laboratory.

    Robertson notes that “simulating galactic winds requires exquisite resolution over a large volume to fully understand the system, much better resolution than other cosmological simulations used to model populations of galaxies. You really need a machine like Titan for this kind of project.”

    Cholla had found its match in Titan, a 27-petaflops system containing more than 18,000 GPUs. After testing the code on a smaller GPU cluster at the University of Arizona, Robertson and Schneider benchmarked it on Titan with the support of two small OLCF director’s discretionary awards. “We were definitely hoping that Titan would be the main workhorse for what we were doing,” Schneider says.

    Robertson and Schneider then unleashed Cholla to test a well-known theory for how galactic winds work. They simulated a hot, supernova-driven wind colliding with a cool gas cloud across 300 light years. With Cholla’s remarkable resolution, they zoomed in on various simulated regions to study phases and properties of galactic wind in isolation, letting the team rule out a theory that cold clouds close to the galaxy’s center could be pushed out by hot, fast-moving supernova wind. It turns out the hot wind shreds the cold clouds, turning them into ribbons that would be difficult to push on.

    With time on Titan allocated through DOE’s INCITE program (for Innovative and Novel Computational Impact on Theory and Experiment), Robertson and Schneider recently used Cholla to generate a simulation using nearly a trillion cells to model an entire galaxy spanning more than 30,000 light years – 10 to 20 times bigger than the largest galactic simulation produced so far. Robertson and Schneider expect the calculations will help test another potential explanation for how galactic winds work. They also may reveal additional details about these phenomena and the forces that regulate galaxies that are important for understanding low-mass varieties, dark matter and the universe’s evolution.

    Robertson and Schneider hope that additional DOE machines – including Summit, a 200-petaflops behemoth that ranks as the world’s fastest supercomputer – will soon support Cholla, which is now publicly available on GitHub.

    ORNL IBM AC922 SUMMIT supercomputer. Credit: Carlos Jones, Oak Ridge National Laboratory/U.S. Dept. of Energy

    To support the code’s dissemination, last year Schneider gave a brief how-to session at Los Alamos National Laboratory. More recently, she and Robertson ran a similar session at OLCF. “There are many applications and developments that could be added to Cholla that would be useful for people who are interested in any type of computational fluid dynamics, not just astrophysics,” Robertson says.

    Robertson also is exploring using GPUs for deep-learning approaches to astrophysics. His lab has been working to adapt a deep-learning model that biologists use to identify cancerous cells. Robertson thinks this method can automate galaxy identification, a crucial need for projects like the LSST, or Large Synoptic Survey Telescope.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    Its DOE-funded camera “will take an image of the whole southern sky every three days. There’s a huge amount of information,” says Robertson, who’s also co-chair of the LSST Galaxies Science Collaboration. “LSST is expected to find on the order of 30 billion galaxies, and it’s impossible to think that humans can look at all those and figure out what they are.”

    Normally, calculations have to be quite intensive to get substantial time on Titan, and Robertson believes the deep-learning project may not pass the bar. “However, because DOE has been supporting GPU-enabled systems, there is the possibility that, in a few years when the LSST data comes in, there may be an appropriate DOE system that could help with the analyses.”

    See the full article here.


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  • richardmitnick 5:56 pm on April 25, 2018 Permalink | Reply
    Tags: , Princeton University, , Ultrahigh-pressure laser experiments shed light on cores of ‘super-Earth’ exoplanets   

    From Princeton University: “Ultrahigh-pressure laser experiments shed light on cores of ‘super-Earth’ exoplanets” 

    Princeton University
    Princeton University

    April 25, 2018
    Liz Fuller-Wright

    Using high-powered laser beams, researchers have simulated conditions inside a planet three times as large as Earth.

    Scientists have identified more than 2,000 of these “super-Earths,” exoplanets that are larger than Earth but smaller than Neptune, the next-largest planet in our solar system. By studying how iron and silicon alloys respond to extraordinary pressures, scientists are gaining new insights into the nature of super-Earths and their cores.

    “We now have a technique that allows us to directly access the extreme pressures of the deep interiors of exoplanets and measure important properties,” said Thomas Duffy, a professor of geosciences at Princeton. “Previously, scientists were restricted to either theoretical calculations or long extrapolations of low-pressure data. The ability to perform direct experiments allows us to test theoretical results and provides a much higher degree of confidence in our models for how materials behave under these extreme conditions.”

    1
    Inside the target chamber at the University of Rochester’s Omega Facility, lasers compress iron-silicon samples to the ultrahigh pressures found in the cores of super-Earths.
    Photo courtesy of Laboratory for Laser Energetics

    U Rochester Laboratory for Laser Energetics

    The work, which resulted in the highest-pressure X-ray diffraction data ever recorded, was led by June Wicks when she was an associate research scholar at Princeton, working with Duffy and colleagues at Lawrence Livermore National Laboratory and the University of Rochester. Their results were published today in the journal Science Advances written by by June Wicks, Raymond Smith, Dayne Fratanduono, Federica Coppari, Richard Kraus, Matthew Newman, J. Ryan Rygg, Jon Eggert and Thomas Duffy.

    Because super-Earths have no direct analogues in our own solar system, scientists are eager to learn more about their possible structures and compositions, and thereby gain insights into the types of planetary architectures that may exist in our galaxy. But they face two key limitations: we have no direct measurements of our own planetary core from which to extrapolate, and interior pressures in super-Earths can reach more than 10 times the pressure at the center of the Earth, well beyond the range of conventional experimental techniques.

    The pressures achieved in this study, up to 1,314 gigapascals (GPa) are about three times higher than previous experiments, making them more directly useful for modeling the interior structure of large, rocky exoplanets, Duffy said.

    “Most high-pressure experiments use diamond anvil cells which rarely reach more than 300 GPa,” or 3 million times the pressure at the surface of the Earth, he said. Pressures in Earth’s core reach up to 360 GPa.

    “Our approach is newer, and many people in the community are not as familiar with it yet, but we have shown in this (and past) work that we can routinely reach pressures above 1,000 GPa or more (albeit only for a fraction of a second). Our ability to combine this very high pressure with X-ray diffraction to obtain structural information provides us with a very unique tool — there is no other facility in the world that can do this,” he said.

    The researchers compressed two samples for only a few billionths of a second, just long enough to probe the atomic structure using a pulse of bright X-rays. The resulting diffraction pattern provided information on the density and crystal structure of the iron-silicon alloys, revealing that the crystal structure changed with higher silicon content.

    “The method of simultaneous X-ray diffraction and shock experiments is still in its infancy, so it’s exciting to see a ‘real-world application’ for the Earth’s core and beyond,” said Kanani Lee, an associate professor of geology and geophysics at Yale University who was not involved in this research.

    This new technique constitutes a “very significant” contribution to the field of exoplanet research, said Diana Valencia, a pioneer in the field and an assistant professor of physics at the University of Toronto-Scarborough, who was not involved in this research. “This is a good study because we are not just extrapolating from low pressures and hoping for the best. This is actually giving us that ‘best,’ giving us that data, and it therefore constrains our models better.”

    Wicks and her colleagues directed a short but intense laser beam onto two iron samples: one alloyed with 7 weight-percent silicon, similar to the modeled composition of Earth’s core, and another with 15 weight-percent silicon, a composition that is possible in exoplanetary cores.

    A planet’s core exerts control over its magnetic field, thermal evolution and mass-radius relationship, Duffy said. “We know that the Earth’s core is iron alloyed with about 10 percent of a lighter element, and silicon is one of the best candidates for this light element both for Earth and extrasolar planets.”

    The researchers found that at ultrahigh pressures, the lower-silica alloy organized its crystal structure in a hexagonal close-packed structure, while the higher-silica alloy used body-centered cubic packing. That atomic difference has enormous implications, said Wicks, who is now an assistant professor at Johns Hopkins University.

    “Knowledge of the crystal structure is the most fundamental piece of information about the material making up the interior of a planet, as all other physical and chemical properties follow from the crystal structure,” she said.

    Wicks and her colleagues also measured the density of the iron-silicon alloys over a range of pressures. They found that at the highest pressures, the iron-silicon alloys reach 17 to 18 grams per cubic centimeter — about 2.5 times as dense as on the surface of Earth, and comparable to the density of gold or platinum at Earth’s surface. They also compared their results to similar studies done on pure iron and discovered that the silicon alloys are less dense than unalloyed iron, even under extreme pressures.

    “A pure iron core is not realistic,” said Duffy, “as the process of planetary formation will inevitably lead to the incorporation of significant amounts of lighter elements. Our study is the first to consider these more realistic core compositions.”

    The researchers calculated the density and pressure distribution inside super-Earths, taking into account the presence of silicon in the core for the first time. They found that incorporating silicon increases the modeled size of a planetary core but reduces its central pressure.

    Future research will investigate how other light elements, such as carbon or sulfur, affect the structure and density of iron at ultrahigh pressure conditions. The researchers also hope to measure other key physical properties of iron alloys, to further constrain models of exoplanets’ interiors.

    “For a geologist, the discovery of so many extrasolar planets has opened the door to a new field of exploration,” said Duffy. “We now realize that the varieties of planets that are out there go far beyond the limited examples in our own solar system, and there is a much broader field of pressure, temperature and composition space that must be explored. Understanding the interior structure and composition of these large, rocky bodies is necessary to probe fundamental questions such as the possible existence of plate tectonics, magnetic field generation, their thermal evolution and even whether they are potentially habitable.”

    The research was funded by the National Nuclear Security Administration through the National Laser Users’ Facility Program (contract nos. DE-NA0002154 and DE-NA0002720) and the Laboratory Directed Research and Development Program at Lawrence Livermore National Laboratory (project no. 15-ERD-012).

    See the full article here .

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    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 3:27 pm on February 14, 2018 Permalink | Reply
    Tags: , Better together: Silicon qubits plus light add up to new quantum computing capability, Princeton University   

    From Princeton- “Better together: Silicon qubits plus light add up to new quantum computing capability” 

    Princeton University
    Princeton University

    Feb. 14, 2018
    Catherine Zandonella

    A silicon-based quantum computing device could be closer than ever due to a new experimental device that demonstrates the potential to use light as a messenger to connect quantum bits of information — known as qubits — that are not immediately adjacent to each other. The feat is a step toward making quantum computing devices from silicon, the same material used in today’s smartphones and computers.

    1
    In a step forward for quantum computing in silicon — the same material used in today’s computers — researchers successfully coupled a single electron’s spin, represented by the dot on the left, to light, represented as a wave crossing over the double-welled silicon chamber, known as a quantum dot, where the electron is trapped. The goal is to use light as a messenger to convey the quantum information to other locations on a futuristic quantum computing chip.
    Image courtesy of Emily Edwards, University of Maryland.

    The research, published in the journal Nature, was led by researchers at Princeton University in collaboration with colleagues at the University of Konstanz in Germany and the Joint Quantum Institute, which is a partnership of the University of Maryland and the National Institute of Standards and Technology.

    The team created qubits from single electrons trapped in silicon chambers known as double quantum dots. By applying a magnetic field, they showed they could transfer quantum information, encoded in the electron property known as spin, to a particle of light, or photon, opening the possibility of transmitting the quantum information.

    “This is a breakout year for silicon spin qubits,” said Jason Petta, professor of physics at Princeton. “This work expands our efforts in a whole new direction, because it takes you out of living in a two-dimensional landscape, where you can only do nearest-neighbor coupling, and into a world of all-to-all connectivity,” he said. “That creates flexibility in how we make our devices.”

    Quantum devices offer computational possibilities that are not possible with today’s computers, such as factoring large numbers and simulating chemical reactions. Unlike conventional computers, the devices operate according to the quantum mechanical laws that govern very small structures such as single atoms and sub-atomic particles. Major technology firms are already building quantum computers based on superconducting qubits and other approaches.

    “This result provides a path to scaling up to more complex systems following the recipe of the semiconductor industry,” said Guido Burkard, professor of physics at the University of Konstanz, who provided guidance on theoretical aspects in collaboration with Mónica Benito, a postdoctoral researcher. “That is the vision, and this is a very important step.”

    acob Taylor, a member of the team and a fellow at the Joint Quantum Institute, likened the light to a wire that can connect spin qubits. “If you want to make a quantum computing device using these trapped electrons, how do you send information around on the chip? You need the quantum computing equivalent of a wire.”

    Silicon spin qubits are more resilient than competing qubit technologies to outside disturbances such as heat and vibrations, which disrupt inherently fragile quantum states. The simple act of reading out the results of a quantum calculation can destroy the quantum state, a phenomenon known as “quantum demolition.”

    2
    From left to right: A new study on silicon qubits and light led by researchers at Princeton University included, from the Department of Physics, Stefan Putz, postdoctoral researcher; David Zajac, graduate student; Xiao Mi, graduate student; and Jason Petta, professor of physics.

    The researchers theorize that the current approach may avoid this problem because it uses light to probe the state of the quantum system. Light is already used as a messenger to bring cable and internet signals into homes via fiber optic cables, and it is also being used to connect superconducting qubit systems, but this is one of the first applications in silicon spin qubits.

    In these qubits, information is represented by the electron’s spin, which can point up or down. For example, a spin pointing up could represent a 0 and a spin pointing down could represent a 1. Conventional computers, in contrast, use the electron’s charge to encode information.

    Connecting silicon-based qubits so that they can talk to each other without destroying their information has been a challenge for the field. Although the Princeton-led team successfully coupled two neighboring electron spins separated by only 100 nanometers (100 billionths of a meter), as published in Science in December 2017, coupling spin to light, which would enable long-distance spin-spin coupling, has remained a challenge until now.

    In the current study, the team solved the problem of long-distance communication by coupling the qubit’s information — that is, whether the spin points up or down — to a particle of light, or photon, which is trapped above the qubit in the chamber. The photon’s wave-like nature allows it to oscillate above the qubit like an undulating cloud.

    Graduate student Xiao Mi and colleagues figured out how to link the information about the spin’s direction to the photon, so that the light can pick up a message, such as “spin points up,” from the qubit. “The strong coupling of a single spin to a single photon is an extraordinarily difficult task akin to a perfectly choreographed dance,” Mi said. “The interaction between the participants — spin, charge and photon — needs to be precisely engineered and protected from environmental noise, which has not been possible until now.” The team at Princeton included postdoctoral fellow Stefan Putz and graduate student David Zajac.

    The advance was made possible by tapping into light’s electromagnetic wave properties. Light consists of oscillating electric and magnetic fields, and the researchers succeeded in coupling the light’s electric field to the electron’s spin state.

    The researchers did so by building on team’s finding published in December 2016 in the journal Science that demonstrated coupling between a single electron charge and a single particle of light.

    To coax the qubit to transmit its spin state to the photon, the researchers place the electron spin in a large magnetic field gradient such that the electron spin has a different orientation depending on which side of the quantum dot it occupies. The magnetic field gradient, combined with the charge coupling demonstrated by the group in 2016, couples the qubit’s spin direction to the photon’s electric field.

    Ideally, the photon will then deliver the message to another qubit located within the chamber. Another possibility is that the photon’s message could be carried through wires to a device that reads out the message. The researchers are working on these next steps in the process.

    Several steps are still needed before making a silicon-based quantum computer, Petta said. Everyday computers process billions of bits, and although qubits are more computationally powerful, most experts agree that 50 or more qubits are needed to achieve quantum supremacy, where quantum computers would start to outshine their classical counterparts.

    Daniel Loss, a professor of physics at the University of Basel in Switzerland who is familiar with the work but not directly involved, said: “The work by Professor Petta and collaborators is one of the most exciting breakthroughs in the field of spin qubits in recent years. I have been following Jason’s work for many years and I’m deeply impressed by the standards he has set for the field, and once again so with this latest experiment to appear in Nature. It is a big milestone in the quest of building a truly powerful quantum computer as it opens up a pathway for cramming hundreds of millions of qubits on a square-inch chip. These are very exciting developments for the field ­— and beyond.”

    The research was supported by the U.S. Department of Defense under contract H98230-15-C0453, Army Research Office grant W911NF-15-1-0149, and the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF4535. Devices were fabricated in the Princeton University Quantum Device Nanofabrication Laboratory.

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    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 5:59 pm on December 15, 2017 Permalink | Reply
    Tags: , , How the prefrontal cortex is contributing to social behavior, Humans spend the majority of our time on social interactions, , New avenues of treatment for disorders that have social behavior deficits from autism to schizophrenia or dementia, , PNI-Princeton Neuroscience Institute, Princeton University   

    From Princeton University: “Hope for autism: Optogenetics shines light on social interactions” 

    Princeton University
    Princeton University

    Dec. 14, 2017
    Liz Fuller-Wright

    1
    From left: HeeJae Jang, Malavika Murugan, Ilana Witten and their colleagues have identified a neural substrate for social learning in mice, with possible relevance to disorders like autism.
    Photo by Danielle Alio, Office of Communications.

    Ilana Witten didn’t set out to study spatial learning. She thought she was investigating how mice socialize — but she discovered that in mouse brains, the social and the spatial are inextricably linked.

    “The data had to be screaming at us for a while before we realized what was really going on,” said Witten, an assistant professor of psychology and the Princeton Neuroscience Institute (PNI). “I think it’s pretty exciting, because it’s a different way to think about how the prefrontal cortex is contributing to social behavior.” In addition, she said, the data suggest new avenues of treatment for disorders that have social behavior deficits, from autism to schizophrenia or dementia.

    “This research could help us understand autism better,” said Malavika Murugan, a PNI postdoctoral research fellow and the lead author on their Dec. 14 paper in the journal Cell.

    Most previous research on social behavior has focused on the brain’s circuits for hardwired behaviors, like aggression, sex, or mothering. Finding a neural substrate for social learning provides a different perspective into social behavior, with possible relevance to disorders such as autism, which are thought to involve abnormalities in the same brain circuitry studied in this work.

    In the future, the researchers are interested in examining how the neural substrates of social and spatial learning differ in mouse models of autism. This may shed light on the question of whether autism stems from physical causes or deficits in social learning.

    “It’s pretty exciting to see a mechanism that supports a simple form of learning about something as cool as social behavior,” Witten said. “Learning is a process of changing. Learning means that the circuit can change over time … that there could be more hope to find behavioral or other types of interventions.”

    2
    When mice socialize in non-aggressive, non-sexual situations, they often begin by sniffing each other, as seen here, before moving on to grooming behaviors. Photo by Danielle Alio, Office of Communications.

    Witten and her colleagues “are taking the best possible approach to this question by delving deep into the fundamentals of circuity that encodes and modulates social interaction,” said Karl Deisseroth, the D.H. Chen Professor of Bioengineering and of Psychiatry and Behavioral Sciences at Stanford University, who is also an investigator with the Howard Hughes Medical Institute. “New basic understanding of social circuitry is welcome, since our ability to treat disordered social/communication function (as seen in autism, for example) is severely limited.”

    In their experiments, Witten and her team gave two mice a chance to socialize in a cage that limited the mobility of one of the mice (the “social target”), so the test mouse could choose whether or not to go to the target for friendly behaviors like sniffing and grooming. Later, the test mouse was reintroduced to the test cage. When the researchers used optogenetics, a biological technique which involves the use of light to control neurons, to inhibit the key social-spatial pathway they had identified in the brain, the test mouse wandered freely through the space. When they didn’t inhibit that circuit, the test mouse preferred to spend time where it remembered socializing with the other mouse.

    In other words, the test mouse had learned where the fun hangout spot was, and chose to return. Humans engage in this sort of social-spatial association all the time, Witten noted, whether it’s visiting the hottest new club or returning to a mall, a coffee shop, a park, or another spot where we remember spending quality time with friends.

    When the “cool kids” turn an otherwise dull spot into an exciting social destination, that’s a real-life example of what Witten observed with her mice: “The social target can change the value of a location,” she said.

    Like mice, humans spend the majority of our time on social interactions, Witten said.

    “Social interactions are some of the most rewarding interactions that mammals have,” she said. “They drive all sorts of different forms of learning, the simplest being what we found here: spatial learning, contextual learning.”

    Witten and her research team performed optogenetic experiments with the mice to isolate precisely which circuits of the brain are involved in social-spatial learning. Previous research had identified that the prelimbic cortex, part of the prefrontal cortex, has three “downstream” channels into the nucleus accumbens, the amygdala, and the ventral tegmental area. Witten’s team determined that only the pathway between the prefrontal cortex and the nucleus accumbens is linked to the social-spatial learning they observed.

    Some key discoveries were made by the undergraduate researchers who make up four of the paper’s 13 co-authors, Witten said: Varun Bhave, Class of 2019; HeeJae Jang, Class of 2017; Michelle Park, Class of 2016; and Josh Taliaferro, Class of 2015.

    “Ilana really takes care and time to mentor undergraduates regardless of their academic background,” said Jang.

    Jang, who concentrated in physics, joined Witten’s lab in her junior year. “At that time, I had not taken a single neuroscience class, but Ilana very generously gave me an opportunity,” she said.

    Jang did her senior thesis with Witten, and after two years of nights and weekends in the lab, she chose to continue as a research specialist in Witten’s lab after graduation, while she prepares for medical school. “I highly recommend the Witten lab to undergrads and senior thesis writers,” Jang said.

    This work at Princeton was funded by Pew, McKnight and Sloan Foundation grants to Witten; the National Institute of Health (DP2 DA035149-01 and 5R01MH106689-02 to Witten and 1F32MH112320-01A1 to Julia Cox, a postdoctoral research fellow in PNI); a Simons Collaboration on the Global Brain Postdoctoral Fellowship to Murugan; a National Science Foundation Graduate Research Fellowship Program grant to Nathan Parker, a graduate student in PNI); and National Alliance for Research on Schizophrenia and Depression Young Investigator Awards from the Brain & Behavior Research Foundation to Witten and Alexander Nectow, a visiting associate research scholar in PNI. Witten is also a New York Stem Cell Foundation—Robertson Investigator.

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    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 2:00 pm on November 2, 2017 Permalink | Reply
    Tags: , , , , Princeton University, Room for growth: Princeton’s Vertical Farming Project harvests knowledge for a budding industry   

    From Princeton University- “Room for growth: Princeton’s Vertical Farming Project harvests knowledge for a budding industry” 

    Princeton University
    Princeton University

    Nov. 2, 2017
    Morgan Kelly, Princeton Environmental Institute

    1
    Princeton University’s Vertical Farming Project was established as a model vertical farm — which involves growing food crops indoors on stacked shelves — to generate accessible and up-to-date research for the field. For her senior thesis, Princeton senior Jesenia Haynes (above) is analyzing the environmental impacts of growing kale and lettuce in a vertical farm versus a conventional farm. Haynes is one of several student researchers engaged in the Vertical Farming Project, which is part of the Campus as Lab Initiative.
    Video still from Nick Donnoli, Office of Communications

    Princeton University’s Vertical Farming Project began at a conference in 2016 when the topic turned to increasing the crop yield of hydroponic systems — wherein plants are grown indoors without soil by using only water and nutrient solutions — by pressurizing water with extra oxygen in a tank before feeding it to the plants. The idea was on everyone’s lips.

    Paul Gauthier knew it was wrong. A plant physiologist, he realized that once the water leaves the tank, it will depressurize and release more oxygen, which reduces photosynthesis.

    “They wanted to provide more oxygen to the roots to increase the yield, but they were doing the opposite of that,” said Gauthier, an associate research scholar in geosciences and the Princeton Environmental Institute. “That’s when I decided to get into the game.”

    In April, Gauthier launched the Vertical Farming Project with support from a High Meadows Foundation Sustainability Fund grant obtained through the Office of Sustainability. The project includes a number of student researchers and is part of the Campus as Lab Initiative. Vertical farming involves growing food crops indoors on stacked shelves. Hydroponics is the most popular form of vertical farming, but the concept is always the same. Sheltered from pests, frost and the scorching sun, plants can grow rapidly, with harvests taking place several times a year. The Princeton farm can produce mature basil in one month, month after month.

    Located in a small windowless room in Moffett Laboratory, Princeton’s vertical farm is used to identify the optimal conditions for growing food indoors. The farm contains about 80 plants. (No tomatoes, for space considerations: “If you give them the right conditions, they’ll grow and grow and grow and never stop,” Gauthier said.) The most successful plants are herbs and leafy greens, which allow for the occasional feast. The project has partnered with an eating club, the Terrace F. Club, which has incorporated the project’s bounty into meals. An Oct. 24 event at Forbes College featured dishes made with lettuce and herbs from the vertical farm and the Princeton Garden Project served alongside produce from a commercial food distributor.

    Gauthier, who has been at the University since 2012 and focuses his research on plant resilience to environmental stress, envisions the Princeton project as an open-source model for vertical farming. Free from having to turn a profit, he and the students involved in the project can experiment with various crops, techniques, technologies and nutrient solutions. Their focus is getting the best harvest with the least amount of resource consumption, then making those data publicly available. They grow less common crops such as edible flowers and wheat. Wheat from the Princeton vertical farm is ready for harvest in 65 days. One of Gauthier’s side projects is to see how much and how economically he can produce flour from a single wheat harvest. He would like to eventually grow citrus and fruit shrubs.

    “We want to create new knowledge in the field,” Gauthier said. “We want to prove that this is sustainable. All the research strengths of Princeton can be combined into this project: sustainability, environmental science, biology and engineering. We hope Princeton will start leading the field by providing new technologies and training students for consulting in this new industry.”

    Paul Gauthier (left), a plant physiologist and an associate research scholar in geosciences and the Princeton Environmental Institute, launched the project in April to identify the optimal conditions for growing various crops with the least amount of water and energy, then make those data publicly available to potential growers. In this video, Gauthier, Haynes and sophomore Seth Lovelace (right) discuss the project’s aims and their individual research interests.
    Video by [not named].

    A field ripe for cultivation

    In recent years, vertical farming has gained traction as a method for producing food for a growing global population that is running short on arable land. Reducing the need for new — or even existing — farmland would go a long way toward preserving natural ecosystems and restoring the ones ravaged by agriculture, according to Dickson Despommier, the Columbia University microbiologist whose 2010 book, The Vertical Farm, helped popularize the topic. Vertical farms reportedly consume up to 95 percent less water than conventional farming by recycling water and they also eliminate the chemical-laden runoff that poisons waterbodies and aquifers.

    The technique also has potential for bringing locally sourced and readily available food to arid and urban areas, which would reduce shipping-related carbon emissions. Several vertical farms are now based in and around New York City, including the world’s largest vertical farm, Newark-based AeroFarms, which produces up to 2 million pounds of produce annually and is headquartered in an old steel mill.

    Gauthier discovered, however, that the industry overall suffers a lack of accessible and up-to-date research on everything from leaf physics to a breakdown of the market. He found very little or outdated peer-reviewed data on nutrient efficiency, automation or sustainable energy and water use. The hydroponic farmers Gauthier has met largely rely on trial-and-error and information from the 1980s. Commercial vertical farms are private businesses that keep their research results to themselves, he said.

    “In science, we know very well how to grow plants hydroponically,” Gauthier said. “The problem is that the public doesn’t know that.”

    Admittedly, vertical farming is not a booming research area, Gauthier said. For instance, there’s little data on growing herbs and leafy greens, which are high-demand crops, he said. Plant and agricultural scientists largely focus on optimizing traditional farming, particularly through the use of genetically modified crops.

    “There’s a difference between what science is doing and what vertical farmers need to know,” Gauthier said.

    3
    The Princeton vertical farm contains about 80 plants. The most successful are herbs and leafy greens, which have been distributed on campus. The Terrace F. Club eating club has incorporated the vertical farm’s harvests into meals. An Oct. 24 event at Forbes College (above) featured salads made with lettuce from the vertical farm (foreground) versus lettuce from a commercial food distributor. Photo by Nick Donnoli, Office of Communications

    Questions keep cropping up

    For her senior thesis, Princeton student Jesenia Haynes is analyzing the environmental impacts of growing kale and lettuce in a vertical farm versus a conventional farm. Her focus is on water and electricity use, the energy costs of producing fertilizer, and the resources that go into shipping and delivering produce to consumers.

    Haynes, who is majoring in ecology and evolutionary biology with a certificate in environmental studies, has been working with Gauthier nearly since the project began. She has gardened since childhood, but her interest in sustainable agricultural was piqued by lectures and classes at Princeton such as ENV 200: “The Environmental Nexus.” While she enjoys growing food, she also is now aware of the obstacles vertical farming poses.

    “The maintenance of the farm for me has been the most challenging part. The biggest problem if you want to reproduce this system on a local scale is having the people to maintain it,” Haynes said. “But with any new initiative, you need to keep improving it. It takes time and effort. We have to keep working to make the process better.”

    In August, Manolya Adan, a graduate student of Gauthier’s based at Imperial College London, visited vertical farms around the United States. Her goal is to build a carbon-footprint model of the entire vertical-farm supply chain. Vertical farms are expanding rapidly, she said — in the past five years, the number in Asia has increased from 23 to 130. (A driving force is the advancement of light-emitting diode, or LED, technology that can provide ample light more efficiently than incandescent lightbulbs. In particular, Gauthier explained, LEDs now incorporate green light, which is essential for secondary plant metabolism.)

    Vertical farms frequently tout the environmental benefits of their trade, but there’s no publicly available information with which anyone can objectively verify those claims, Adan said. “Vertical farming holds a lot of promise, but I want to see what the actual benefit is in terms of reducing our environmental impact,” Adan said. “We want the industry to do well and we need to be sustainable. It’s about helping companies see what they themselves are doing and what they could do better.”

    Operational costs are a significant obstacle facing vertical, Gauthier said — more than 85 percent of vertical farms fail within two years. LEDs, labor and space are expensive, but there is no hard data on what drives these operations to close. Senior Rozalie Czesana, a Woodrow Wilson School of Public and International Affairs major, is preparing to examine the costs associated with running a small vertical farm, together with the feasibility of scaling them up to the community level. Her focus will be on “food deserts,” or areas such as low-income urban neighborhoods that often lack sufficient access to fresh, healthy food.

    Czesana, who established the project’s partnership with the Terrace F. Club, previously conducted a comparative study that examined the speed of growth and average water use of herbs and lettuce in the vertical farm versus a greenhouse. She found that the vertical farm is much more resilient to New Jersey weather — the heat wave in May 2016 killed most of the greenhouse produce despite constant care. She also found that while basil, lettuce and kale do much better in the vertical farm under a certain nutrient concentration, cilantro preferred the greenhouse.

    Sophomore Seth Lovelace, a prospective mathematics major, works with Gauthier to analyze the level of individual nutrients in the solution they feed the plants using a technique called inductively coupled plasma mass spectrometry (ICP-MS). They can then adjust the amount of a certain nutrient based on what a plant uses most, as well as adjust the micronutrients that influence flavor, Lovelace said.

    “We’re really trying to bring metrics to the vertical-farming game. All of our team members are trying to get data so we can make the farm grow better, to help these plants thrive,” Lovelace said. “Interdisciplinary research, when applied to any project, really enhances how the project moves forward. I think the access to this kind of research as an undergrad is amazing.”

    Gauthier welcomes the student interest. “I want undergrads involved because they are the next generation and the big burden of saving the planet will be on them,” he said. “When they are familiar with this system and know it, they can start thinking outside of the box.

    “The industry is growing for sure and it will be part of our lives in the future,” he said. “That’s what this project is about — understanding this system well enough to expand it.”

    4
    The Oct. 24 “Meet What You Eat” event featured the harvests from Princeton Garden and Vertical Farming projects. From left to right: sophomore Anna Marsh, Garden Project leader; junior Emmy Bender, Garden Project leader; sophomore Laurie Zielinkski; sophomore Natalie Grayson, vertical farm manager; Violette Chamoun, Campus Dining operations manager; Alex Trimble, Campus Dining chef du cuisine; senior Rozalie Czesana, who is conducting an economic analysis for the Vertical Farming Project; Gauthier; and Patrick Caddeau, dean of Forbes College.
    Photo by
    Nick Donnoli, Office of Communications

    See the full article here .

    Please help promote STEM in your local schools.

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    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 6:05 am on October 24, 2017 Permalink | Reply
    Tags: , , , , , , Princeton University, Production of gamma rays from merging neutron stars   

    From Princeton: “Steven S. Gubser: Thunder and Lightning from Neutron Star mergers” 

    Princeton University
    Princeton University

    October 18, 2017
    Steven S. Gubser

    As of late 2015, we have a new way of probing the cosmos: gravitational radiation. Thanks to LIGO (the Laser Interferometer Gravitational-wave Observatory) and its new sibling Virgo (a similar interferometer in Italy), we can now “hear” the thumps and chirps of colliding massive objects in the universe.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Not for nothing has this soundtrack been described by LIGO scientists as “the music of the cosmos.” This music is at a frequency easily discerned by human hearing, from somewhat under a hundred hertz to several hundred hertz. Moreover, gravitational radiation, like sound, is wholly different from light. It is possible for heavy dark objects like black holes to produce mighty gravitational thumps without at the same time emitting any significant amount of light. Indeed, the first observations of gravitational waves came from black hole merger events whose total power briefly exceeded the light from all stars in the known universe. But we didn’t observe any light from these events at all, because almost all their power went into gravitational radiation.

    In August 2017, LIGO and Virgo observed a collision of neutron stars which did produce observable light, notably in the form of gamma rays. Think of it as cosmic thunder and lightning, where the thunder is the gravitational waves and the lightning is the gamma rays. When we see a flash of ordinary lightning, we can count a few seconds until we hear the thunder. Knowing that sound travels one mile in about five seconds, we can reckon how distant the event is. The reason this method works is that light travels much faster than sound, so we can think of the transmission of light as instantaneous for purposes of our estimate.

    Things are very different for the neutron star collision, in that the event took place about 130 million light years away, but the thunder and lightning arrived on earth pretty much simultaneously. To be precise, the thunder was first: LIGO and Virgo heard a basso rumble rising to a characteristic “whoop,” and just 1.7 seconds later, the Fermi and INTEGRAL experiments observed gamma ray bursts from a source whose location was consistent with the LIGO and Virgo observations.

    NASA/Fermi Telescope

    NASA/Fermi LAT

    ESA/Integral

    The production of gamma rays from merging neutron stars is not a simple process, so it’s not clear to me whether we can pin that 1.7 seconds down as a delay precisely due to the astrophysical production mechanisms; but at least we can say with some confidence that the propagation time of light and gravity waves are the same to within a few seconds over 130 million light years. From a certain point of view, that amounts to one of the most precise measurements in physics: the ratio of the speed of light to the speed of gravity equals 1, correct to about 14 decimal places or better.

    The whole story adds up much more easily when we remember that gravitational waves are not sound at all. In fact, they’re nothing like ordinary sound, which is a longitudinal wave in air, where individual air molecules are swept forward and backward just a little as the sound waves pass them by. Gravitational waves instead involve transverse disturbances of spacetime, where space is stretched in one direction and squeezed in another—but both of those stretch-squeeze directions are at right angles to the direction of the wave. Light has a similar transverse quality: It is made up of electric and magnetic fields, again in directions that are at right angles to the direction in which the light travels. It turns out that a deep principle underlying both Maxwell’s electromagnetism and Einstein’s general relativity forces light and gravitational waves to be transverse. This principle is called gauge symmetry, and it also guarantees that photons and gravitons are massless, which implies in turn that they travel at the same speed regardless of wavelength.

    It’s possible to have transverse sound waves: For instance, shearing waves in crystals are a form of sound. They typically travel at a different speed from longitudinal sound waves. No principle of gauge symmetry forbids longitudinal sound waves, and indeed they can be directly observed, along with their transverse cousins, in ordinary materials like metals. The gauge symmetries that forbid longitudinal light waves and longitudinal gravity waves are abstract, but a useful first cut at the idea is that there is extra information in electromagnetism and in gravity, kind of like an error-correcting code. A much more modest form of symmetry is enough to characterize the behavior of ordinary sound waves: It suffices to note that air (at macroscopic scales) is a uniform medium, so that nothing changes in a volume of air if we displace all of it by a constant distance.

    In short, Maxwell’s and Einstein’s theories have a feeling of being overbuilt to guarantee a constant speed of propagation. And they cannot coexist peacefully as theories unless these speeds are identical. As we continue Einstein’s hunt for a unified theory combining electromagnetism and gravity, this highly symmetrical, overbuilt quality is one of our biggest clues.

    The transverse nature of gravitational waves is immediately relevant to the latest LIGO / Virgo detection. It is responsible for the existence of blind spots in each of the three detectors (LIGO Hanford, LIGO Livingston, and Virgo). It seems like blind spots would be bad, but they actually turned out to be pretty convenient: The signal at Virgo was relatively weak, indicating that the direction of the source was close to one of its blind spots. This helped localize the event, and localizing the event helped astronomers home in on it with telescopes. Gamma rays were just the first non-gravitational signal observed: the subsequent light-show from the death throes of the merging neutron stars promises to challenge and improve our understanding of the complex astrophysical processes involved. And the combination of gravitational and electromagnetic observations will surely be a driver of new discoveries in years and decades to come.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Princeton University Campus

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
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