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  • richardmitnick 10:00 am on April 23, 2022 Permalink | Reply
    Tags: "Information loss problem", , "Theoretical model offers a new perspective on black hole formation and evolution", , , In one of his seminal works Stephen Hawking showed that black holes radiate energy and that they slowly disappear., , Quantum Gravity   

    From phys.org: “Theoretical model offers a new perspective on black hole formation and evolution” 

    Fromphys.org

    April 22, 2022

    1
    Credit: Husain et al.

    Black holes are regions in space characterized by gravitational fields so intense that no matter or radiation can escape from them. They are solutions to Einstein’s field equations, with a point of unphysical infinite density at their center.

    Based on the classical theory of general relativity, all the matter that went into forming a black hole ultimately ends up at its center. This specific prediction is known as the “singularity problem.”

    In one of his seminal works Stephen Hawking showed that black holes radiate energy and that they slowly disappear. However, his work suggests that the radiation emitted by black holes does not contain all the information about the matter that went into its formation. In astrophysics, this is referred to as the “information loss problem.”

    Researchers at The University of New Brunswick (CA) have recently developed a theoretical model that would effectively address both the singularity problem and information loss problem, while also shedding more light on how matter collapses to form black holes. The model they devised, introduced in a paper published in Physical Review Letters, offers an alternate perspective on the formation and evolution of black holes than that proposed by classical theories.

    “The question of the fate of a black hole and what happens to the matter (or information) that formed it, has been an open problem for fifty years,” Viqar Husain Jarod George Kelly, Robert Santacruz and Edward Wilson-Ewing, the researchers who carried out the study, told Phys.org, via email. “It is widely believed that a theory of quantum gravity is required to solve this problem. We know a lot about how collapsing matter forms black holes in general relativity, but the question of how collapse occurs in quantum gravity is also an open problem.”

    The key objective of the recent work by Husain and his colleagues was to introduce a model that precisely addresses the singularity problem and gravitational collapse at the same time. To do this, they used a construct of loop quantum gravity to incorporate the fundamental discreteness of space in classical equations that describe gravitational collapse.

    “We studied the problem using simple dust matter that exerts no pressure because this is the simplest type of matter; its motion is described by a manageable equation that can be solved on a laptop,” Husain explained. “This equation is a modified version of the classical Einstein equations, which incorporates fundamental discreteness of space at the microscopic level.”

    The numerical method that the researchers used in their study was developed by Sergei K. Godunov, a renowned Russian scientist who was conducting theoretical research focusing on fluid flow problems. Notably, this method can handle shock wave formation, the physical phenomenon that occurs when an object moves at supersonic speeds and pushes on the surrounding air (e.g., when a jet breaks through the sound barrier).

    “We followed the evolution of a cloud of collapsing dust particles until it formed a black hole,” Husain, Kelly, Santacruz and Wilson-Ewing said. “The numerical method allowed us to follow the evolution of matter even inside the black hole region toward the point where the singularity would be in the classical solution.”

    The quantum gravity-corrected equation introduced by Husain and his colleagues solves the singularity problem more dynamically than classical models. More specifically, it suggests that matter falls into the center of the black hole, reaches a large but finite density, and then bounces back, forming a shock wave.

    “Quantum gravity effects are important at the shock wave and allow it to move outwards inside the black hole, which is not possible when using classical equations,” the researchers said. “At the same time, the curvature of spacetime gets large, but never diverges (as it does in classical theory).”

    Using the numerical tool introduced by Godunov, the researchers were also able to compute the lifetime of a black hole, from its formation to its disappearance, when a shock wave emerges from its horizon and the horizons starts to disappear. Interestingly, the black hole lifetime they computed is far shorter than the evaporation time predicted by Hawking. This suggests that their model could help to resolve the information loss problem, but more studies will need to be carried out to confirm this.

    In addition, the equation outlined by Husain and his colleagues introduces the production of shock waves in the development of black holes. In the future, it could thus prompt astronomers to evaluate the possibility of detecting the shock waves emanating from black holes.

    “If this turns out to be possible, our results may provide a ready explanation; but this too requires further careful exploration,” the researchers added. “In our next studies, we would like to try to establish whether the information loss problem is indeed solved, to study other types of matter that exert pressure, and other types of matter clouds, to see if our shock wave result remains qualitatively unchanged. If this turns out to be the case, then shock waves could be a universal signature that marks the death of a black hole.”

    See the full article here .

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  • richardmitnick 10:00 am on April 10, 2022 Permalink | Reply
    Tags: "A New Tool for Finding Dark Matter Digs Up Nothing", , , , , Dark Matter-the nonluminous stuff that holds galaxies together., Dark photons are hypothetical light-like particles that would mostly interact with other dark matter particles but would occasionally strike normal atoms., , If scientists do find dark matter that would be the discovery of decades., , , Quantum Gravity, , Scalar-field dark matter, Scalar-field dark matter would subtly alter the properties of other particles and fundamental forces., Scientists are developing a novel interferometer at Caltech to look for signs that space-time is pixelated., , With nearly 100 gravitational waves now recorded the landscape of invisible black holes is unfurling. But that’s only part of the story.   

    From Quanta Magazine: “A New Tool for Finding Dark Matter Digs Up Nothing” 

    From Quanta Magazine

    March 21, 2022
    Thomas Lewton

    1
    Researchers recently searched for a kind for dark matter that would expand and contract the beam splitter at the heart of a gravitational wave detector. Credit: GIPhotoStock/Science Source.

    Even the strongest gravitational waves that pass through the planet, created by the distant collisions of black holes, only stretch and compress each mile of Earth’s surface by one-thousandth the diameter of an atom. It’s hard to conceive of how small these ripples in the fabric of space-time are, let alone detect them. But in 2016, after physicists spent decades building and fine-tuning an instrument called the Laser Interferometer Gravitational-Wave Observatory (LIGO), they got one.

    _____________________________________________________________________________________
    LIGOVIRGOKAGRA

    Caltech /MIT Advanced aLigo.

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

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    KAGRA Large-scale Cryogenic Gravitational Wave Telescope Project (JP).
    _____________________________________________________________________________________

    LIGO Virgo Kagra Masses in the Stellar Graveyard. Credit: Frank Elavsky and Aaron Geller at Northwestern University.

    With nearly 100 gravitational waves now recorded the landscape of invisible black holes is unfurling. But that’s only part of the story.

    Gravitational wave detectors are picking up some side gigs.

    “People have started to ask: ‘Maybe there’s more to what we get out of these machines than just gravitational waves?’” said Rana Adhikari, a physicist at The California Institute of Technology.

    Inspired by the extreme sensitivity of these detectors, researchers are devising ways to use them to search for other elusive phenomena: above all, Dark Matter-the nonluminous stuff that holds galaxies together.

    In December, a team led by Hartmut Grote of Cardiff University [Prifysgol Caerdydd] (WLS) reported in Nature that they had used a gravitational wave detector to look for scalar-field dark matter, a lesser-known candidate for the missing mass in and around galaxies. The team didn’t find a signal, ruling out a large class of scalar-field dark matter models. Now the stuff can only exist if it affects normal matter very weakly — at least a million times more weakly than was previously thought possible.

    “It’s a very nice result,” said Keith Riles, a gravitational wave astronomer at The University of Michigan who wasn’t involved in the research.

    Until a few years ago, the leading candidate for dark matter was a slow-moving, weakly interacting particle similar to other elementary particles — a sort of heavy neutrino. But experimental searches for these so-called WIMPs keep coming up empty-handed [Nature], making room for myriad alternatives.

    2
    Dark matter could be made up of particles with a vast range of possible masses. Credit: Samuel Velasco/Quanta Magazine

    “We’ve kind of reached the stage in dark matter searches where we’re looking everywhere,” said Kathryn Zurek, a theoretical physicist at Caltech.

    In 1999, three physicists proposed that dark matter might be made of particles that are so light and numerous that they’re best thought of collectively, as a field of energy that permeates the universe. This “scalar field” has a value at each point in space, and the value oscillates with a characteristic frequency.

    Scalar-field dark matter would subtly alter the properties of other particles and fundamental forces. The electron’s mass and the strength of the electromagnetic force, for example, would oscillate with the oscillating amplitude of the scalar field.

    For years, physicists have wondered whether gravitational wave detectors could spot such a wobble. These detectors sense slight disturbances using an approach called interferometry. First, laser light enters a “beam splitter,” which divides the light, sending beams in two directions at right angles to each other, like arms of an L. The beams reflect off mirrors at the ends of both arms, then return to the hinge of the L and recombine. If the returning laser beams have been pushed out of sync — for instance, by a passing gravitational wave, which briefly lengthens one arm of the interferometer while contracting the other — a distinct interference pattern of dark and light fringes forms.

    Could scalar-field dark matter push the beams out of sync and cause an interference pattern? “The common thinking,” said Grote, was that any distortions would affect both arms equally, canceling out. But then in 2019, Grote had a realization [Physical Review Research]. “One morning I woke up and the idea came to me suddenly: The beam splitter is exactly what we need.”

    The beam splitter is a block of glass that acts like a leaky mirror, reflecting, on average, half of the light that strikes its surface, while the other half passes through. If scalar-field dark matter is present, then whenever the field reaches its peak amplitude, the strength of the electromagnetic force weakens; Grote realized that this would cause atoms in the glass block to shrink. When the field’s amplitude drops, the glass block will expand. This wobble will subtly shift the distance traveled by the reflected light without affecting the transmitted light; thus, an interference pattern will appear.

    With the aid of computers, Sander Vermeulen, Grote’s graduate student, searched through data from the GEO600 gravitational wave detector in Germany looking for interference patterns resulting from several million different frequencies of scalar-field dark matter.

    2
    GEO600 | The MPG Institute for Gravitational Physics[MPG Institut für Gravitationsphysik][Albert Einstein Institute](DE)

    He saw nothing. “It’s disappointing because if you do find dark matter that would be the discovery of decades,” Vermeulen said.

    But the search was only ever “a fishing expedition,” said Zurek. The scalar field’s frequency and the strength of its effect on other particles (and therefore the beam splitter) could be almost anything. GEO600 only detects a specific range of frequencies.

    For this reason, the failure to find scalar-field dark matter with the GEO600 detector doesn’t rule out its existence. “It’s more a demonstration that we have a new tool now to look for dark matter,” said Grote. “We will go on searching.” He also plans to use interferometers to search for axions, another popular dark matter candidate.

    Meanwhile, Riles and his colleagues have been searching for signs of “dark photons” in data from LIGO [Communications Physics], which has detectors in Livingston, Louisiana, and Hanford, Washington, and its partner, the Virgo detector near Pisa, Italy [both above]. Dark photons are hypothetical light-like particles that would mostly interact with other dark matter particles but would occasionally strike normal atoms. If they’re all around us, then at any given moment, they’ll happen to push on one mirror in an interferometer more than the other, changing the relative lengths of the arms. “There will tend to be an imbalance in one direction, just a random fluctuation,” Riles said. “So you try to exploit that.”

    Dark photon wavelengths can be as wide as the sun, so any random fluctuations that disturb the mirrors of the interferometer in Hanford would have the same effect at the Livingston detector, nearly 5,000 kilometers away, and correlated effects in Pisa. But the researchers found no such correlations in the data. Their result, reported last year, means that dark photons, if real, must be at least 100 times weaker than previously allowed.

    Adhikari proposes [Physical Review D] that gravitational wave detectors could even find “human-sized” dark matter particles weighing hundreds of kilograms. As these heavy particles flew through the detector, they would gravitationally attract LIGO’s mirrors and laser beams. “You’d see a little bit of a winking in the beam’s power as the particle flies through,” said Adhikari. “The entire L-shape detector is a sort of a net that can get these particles.”

    What else could these sensitive instruments catch? Adhikari is developing a novel interferometer at Caltech to look for signs that space-time is pixelated, as some quantum theories of gravity suppose. “That’s always the dream of physicists. Can we measure quantum gravity in the lab?” Conventional wisdom holds that a detector capable of probing such tiny distances would be so big that it would collapse into a black hole under its own weight. Zurek, however, has been working on an idea that could make quantum gravity detectable with Adhikari’s setup or another experiment at Grote’s lab in Cardiff.

    In other quantum gravity theories, space-time isn’t pixelated; instead, it’s a 3D hologram that emerges out of a 2D system of quantum particles. Zurek thinks this, too, might be detectable with gravitational wave detectors. Small quantum fluctuations in the 2D space would be amplified when holographically projected into 3D, potentially making waves in space-time big enough for an interferometer to pick up.

    “When we started working on this, people were like: ‘What are you talking about? You’re completely nuts,” Zurek said. “Now people are starting to listen.”

    See the full article here.


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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 11:53 am on February 13, 2022 Permalink | Reply
    Tags: "Symmetries Reveal Clues About the Holographic Universe", , , How might our universe emerge like a hologram out of a two-dimensional sheet? An infinitely distant “celestial sphere” could hold answers., In the bizarre curves of AdS space a finite boundary can encapsulate an infinite world., One of the most promising of those efforts treats gravity as something like a hologram—a three-dimensional effect that pops out of a flat two-dimensional surface., Our best theory of gravity describes it as bent spacetime., Physicists want to determine the rules for a CFT that can give rise to gravity in a world without the curves of AdS space., , Quantum Gravity, Quantum gravity reproduces the predictions of general relativity., Recent research results have given physicists hope that they’re on the right track., They’re looking for a CFT for flat space—a celestial CFT.,   

    From WIRED: “Symmetries Reveal Clues About the Holographic Universe” 

    From WIRED

    Feb 13, 2022
    Katie McCormick

    How might our universe emerge like a hologram out of a two-dimensional sheet? An infinitely distant “celestial sphere” could hold answers.

    1
    Researchers have long studied how gravity might emerge from a two-dimensional surface in hyperbolic spaces such as this one. In our own universe, the surface would be infinitely far away. Illustration: Kwok Wai Chung.

    We’ve known about gravity since Newton’s apocryphal encounter with the apple, but we’re still struggling to make sense of it. While the other three forces of nature are all due to the activity of quantum fields, our best theory of gravity describes it as bent spacetime. For decades, physicists have tried to use quantum field theories to describe gravity, but those efforts are incomplete at best.

    One of the most promising of those efforts treats gravity as something like a hologram—a three-dimensional effect that pops out of a flat two-dimensional surface. Currently, the only concrete example of such a theory is the AdS/CFT correspondence, in which a particular type of quantum field theory, called a conformal field theory (CFT), gives rise to gravity in so-called anti-de Sitter (AdS) space. In the bizarre curves of AdS space a finite boundary can encapsulate an infinite world. Juan Maldacena, the theory’s discoverer, has called it a “universe in a bottle.”

    But our universe isn’t a bottle. Our universe is (largely) flat. Any bottle that would contain our flat universe would have to be infinitely far away in space and time. Physicists call this cosmic capsule the “celestial sphere.”

    Physicists want to determine the rules for a CFT that can give rise to gravity in a world without the curves of AdS space. They’re looking for a CFT for flat space—a celestial CFT.

    The celestial CFT would be even more ambitious than the corresponding theory in AdS/CFT. Since it lives on a sphere of infinite radius, concepts of space and time break down. As a consequence, the CFT wouldn’t depend on space and time; instead, it could explain how space and time come to be.

    Recent research results have given physicists hope that they’re on the right track. These results use fundamental symmetries to constrain what this CFT might look like. Researchers have discovered a surprising set of mathematical relationships between these symmetries—relationships that have appeared before in certain string theories, leading some to wonder if the connection is more than coincidence.

    “There’s a very large, amazing animal out here,” said Nima Arkani-Hamed, a theoretical physicist at The Institute for Advanced Study in Princeton, New Jersey. “The thing we’re going to find is going to be pretty mind-blowing, hopefully.”

    Symmetries on the Sphere

    Perhaps the primary way that physicists probe the fundamental forces of nature is by blasting particles together to see what happens. The technical term for this is “scattering.” At facilities such as the Large Hadron Collider, particles fly in from distant points, interact, then fly out to the detectors in whatever transformed state has been dictated by quantum forces.

    If the interaction is governed by any of the three forces other than gravity, physicists can in principle calculate the results of these scattering problems using quantum field theory. But what many physicists really want to learn about is gravity.

    Luckily, Steven Weinberg showed [Physical Review Journals Archive] in the 1960s that certain quantum gravitational scattering problems—ones that involve low-energy gravitons—can be calculated. In this low-energy limit, “we’ve nailed the behavior,” said Monica Pate of Harvard University. “Quantum gravity reproduces the predictions of general relativity.” Celestial holographers like Pate and Sabrina Pasterski of Princeton University are using these low-energy scattering problems as the starting point to determine some of the rules the hypothetical celestial CFT must obey.

    They do this by looking for symmetries. In a scattering problem, physicists calculate the products of scattering—the “scattering amplitudes”—and what they should look like when they hit the detectors. After calculating these amplitudes, researchers look for patterns the particles make on the detector, which correspond to rules or symmetries the scattering process must obey. The symmetries demand that if you apply certain transformations to the detector, the outcome of a scattering event should remain unchanged.

    Just as quantum interactions can be translated into scattering amplitudes that then lead to symmetries, researchers working on quantum gravity hope to translate scattering problems into symmetries on the celestial sphere, then use these symmetries to fill out the celestial CFT rulebook.

    “We’re trying to just start from the basic ingredients of the dictionary,” said Pasterski, referring to the symmetries, “and then move up from there.”

    In November, a group led by Andrew Strominger of Harvard University published a paper [Physical Review Letters] that describes the “symmetry algebra” the celestial CFT must obey. The algebra dictates how different symmetry transformations combine to form new transformations. By studying the structure of the composition of the transformations, Strominger and his colleagues, including Pate, have managed to further constrain the potential CFT. They discovered that the group of symmetries on the celestial sphere obeyed a thoroughly studied and well-established algebra—one that has already appeared in certain string theories and is related to the description of well-known quantum systems such as the quantum Hall effect.

    “The fact that the structure you landed on is something that people have explored and played with before gives you encouragement that maybe there’s something to it,” said David Skinner, a theoretical physicist at The University of Cambridge.

    Infinite Issues

    When you have a theory that applies to an infinitely distant sphere, problems arise. Consider two particles that come together and scatter apart. If they scatter apart at any nonzero angle, by the time they reach the infinitely distant celestial sphere, they will also be infinitely far apart. The notion of distance breaks down. Our normal theories rely on locality, in which the strength of interactions between objects depends on their distance from one another. But if everything is infinitely far from everything else, the CFT must transcend locality.

    Even more perplexing: What is the concept of time on the celestial sphere, which is infinitely far in both the past and in the future? It has no meaning here.

    Arkani-Hamed considers the fact that concepts of space and time break down on the celestial sphere to be a feature, not a bug. It offers the potential to explain spacetime as an emergent property of a more fundamental theory.

    Others temper their enthusiasm. “I think it’s exciting, but I think there’s a long way to go,” said Skinner. “There are some things that I would say are major challenges to overcome.”

    Arkani-Hamed doesn’t disagree. “The whole thing is sort of grasping and figuring out what the question is. But the stakes are also similarly high.”

    See the full article here .

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  • richardmitnick 2:35 pm on January 21, 2022 Permalink | Reply
    Tags: "In a Numerical Coincidence Some See Evidence for String Theory", "Massive Gravity", "String universality": a monopoly of string theories among viable fundamental theories of nature, , Asymptotically safe quantum gravity, , Graviton: A graviton is a closed string-or loop-in its lowest-energy vibration mode in which an equal number of waves travel clockwise and counterclockwise around the loop., Lorentz invariance: the same laws of physics must hold from all vantage points., , , , Quantum Gravity, , ,   

    From Quanta Magazine (US): “In a Numerical Coincidence Some See Evidence for String Theory” 

    From Quanta Magazine (US)

    January 21, 2022
    Natalie Wolchover

    1
    Dorine Leenders for Quanta Magazine.

    In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly.

    Quantum gravity researchers use “α” to denote the size of the biggest quantum correction to Albert Einstein’s Theory of General Relativity.

    Recently, three physicists calculated a number pertaining to the quantum nature of gravity. When they saw the value, “we couldn’t believe it,” said Pedro Vieira, one of the three.

    Gravity’s quantum-scale details are not something physicists usually know how to quantify, but the trio attacked the problem using an approach that has lately been racking up stunners in other areas of physics. It’s called the bootstrap.

    To bootstrap is to deduce new facts about the world by figuring out what’s compatible with known facts — science’s version of picking yourself up by your own bootstraps. With this method, the trio found a surprising coincidence: Their bootstrapped number closely matched the prediction for the number made by string theory. The leading candidate for the fundamental theory of gravity and everything else, string theory holds that all elementary particles are, close-up, vibrating loops and strings.

    Vieira, Andrea Guerrieri of The Tel Aviv University (IL), and João Penedones of The EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH) reported their number and the match with string theory’s prediction in Physical Review Letters in August 2021. Quantum gravity theorists have been reading the tea leaves ever since.

    Some interpret the result as a new kind of evidence for string theory, a framework that sorely lacks even the prospect of experimental confirmation, due to the pointlike minuteness of the postulated strings.

    “The hope is that you could prove the inevitability of string theory using these ‘bootstrap’ methods,” said David Simmons-Duffin, a theoretical physicist at The California Institute of Technology (US). “And I think this is a great first step towards that.”

    2
    From left: Pedro Vieira, Andrea Guerrieri and João Penedones.
    Credit: Gabriela Secara / The Perimeter Institute for Theoretical Physics (CA); Courtesy of Andrea Guerrieri; The Swiss National Centres of Competence in Research (NCCRs) [Pôle national suisse de recherche en recherche][Schweizerisches Nationales Kompetenzzentrum für Forschung](CH) SwissMAP (CH)

    Irene Valenzuela, a theoretical physicist at the Institute for Theoretical Physics at The Autonomous University of Madrid [Universidad Autónoma de Madrid](ES), agreed. “One of the questions is if string theory is the unique theory of quantum gravity or not,” she said. “This goes along the lines that string theory is unique.”

    Other commentators saw that as too bold a leap, pointing to caveats about the way the calculation was done.

    Einstein, Corrected

    The number that Vieira, Guerrieri and Penedones calculated is the minimum possible value of “α” (alpha). Roughly, “α” is the size of the first and largest mathematical term that you have to add to Albert Einstein’s gravity equations in order to describe, say, an interaction between two gravitons — the presumed quantum units of gravity.

    Albert Einstein’s 1915 Theory of General Relativity paints gravity as curves in the space-time continuum created by matter and energy. It perfectly describes large-scale behavior such as a planet orbiting a star. But when matter is packed into too-small spaces, General Relativity short-circuits. “Some correction to Einsteinian gravity has to be there,” said Simon Caron-Huot, a theoretical physicist at McGill University (CA).

    Physicists can tidily organize their lack of knowledge of gravity’s microscopic nature using a scheme devised in the 1960s by Kenneth Wilson and Steven Weinberg: They simply add a series of possible “corrections” to General Relativity that might become important at short distances. Say you want to predict the chance that two gravitons will interact in a certain way. You start with the standard mathematical term from Relativity, then add new terms (using any and all relevant variables as building blocks) that matter more as distances get smaller. These mocked-up terms are fronted by unknown numbers labeled “α”, “β”, “γ” and so on, which set their sizes. “Different theories of quantum gravity will lead to different such corrections,” said Vieira, who has joint appointments at The Perimeter Institute for Theoretical Physics (CA), and The International Centre for Theoretical Physics at The South American Institute for Fundamental Research [Instituto sul-Americano de Pesquisa Fundamental] (BR). “So these corrections are our first way to tell such possibilities apart.”

    In practice, “α” has only been explicitly calculated in string theory, and even then only for highly symmetric 10-dimensional universes. The English string theorist Michael Green and colleagues determined in the 1990s that in such worlds “α” must be at least 0.1389. In a given stringy universe it might be higher; how much higher depends on the string coupling constant, or a string’s propensity to spontaneously split into two. (This coupling constant varies between versions of string theory, but all versions unite in a master framework called “M-theory”, where string coupling constants correspond to different positions in an extra 11th dimension.)

    Meanwhile, alternative quantum gravity ideas remain unable to make predictions about “α”. And since physicists can’t actually detect gravitons — the force of gravity is too weak — they haven’t been able to directly measure “α” as a way of investigating and testing quantum gravity theories.

    Then a few years ago, Penedones, Vieira and Guerrieri started talking about using the bootstrap method to constrain what can happen during particle interactions. They first successfully applied the approach to particles called pions. “We said, OK, here it’s working very well, so why not go for gravity?” Guerrieri said.

    Bootstrapping the Bound

    The trick of using accepted truths to constrain unknown possibilities was devised by particle physicists in the 1960s, then forgotten, then revived to fantastic effect over the past decade by researchers with supercomputers, which can solve the formidable formulas that bootstrapping tends to produce.

    Guerrieri, Vieira and Penedones set out to determine what “α” has to be in order to satisfy two consistency conditions. The first, known as unitarity, states that the probabilities of different outcomes must always add up to 100%. The second, known as Lorentz invariance, says that the same laws of physics must hold from all vantage points.

    The trio specifically considered the range of values of “α” permitted by those two principles in supersymmetric 10D universes. Not only is the calculation simple enough to pull off in that setting (not so, currently, for “α” in 4D universes like our own), but it also allowed them to compare their bootstrapped range to string theory’s prediction that “α” in that 10D setting is 0.1389 or higher.

    Unitarity and Lorentz invariance impose constraints on what can happen in a two-graviton interaction in the following way: When the gravitons approach and scatter off each other, they might fly apart as two gravitons, or morph into three gravitons or any number of other particles. As you crank up the energies of the approaching gravitons, the chance they’ll emerge from the encounter as two gravitons changes — but unitarity demands that this probability never surpass 100%. Lorentz invariance means the probability can’t depend on how an observer is moving relative to the gravitons, restricting the form of the equations. Together the rules yield a complicated bootstrapped expression that “α” must satisfy. Guerrieri, Penedones and Vieira programmed the Perimeter Institute’s computer clusters to solve for values that make the two-graviton interactions unitary and Lorentz-invariant.

    The computer spit out its lower bound for “α”: 0.14, give or take a hundredth — an extremely close and potentially exact match with string theory’s lower bound of 0.1389. In other words, string theory seems to span the whole space of allowed “α” values — at least in the 10D place where the researchers checked. “That was a huge surprise,” Vieira said.

    10-Dimensional Coincidence

    What might the numerical coincidence mean? According to Simmons-Duffin, whose work a few years ago helped drive the bootstrap’s resurgence, “they’re trying to tackle a question [that’s] fundamental and important. Which is: To what extent does string theory as we know it cover the space of all possible theories of quantum gravity?”

    String theory emerged in the 1960s as a putative picture of the stringy glue that binds composite particles called mesons. A different description ended up prevailing for that purpose, but years later people realized that string theory could set its sights higher: If strings are small — so small they look like points — they could serve as nature’s elementary building blocks. Electrons, photons and so on would all be the same kind of fundamental string strummed in different ways. The theory’s selling point is that it gives a quantum description of gravity: A graviton is a closed string, or loop, in its lowest-energy vibration mode, in which an equal number of waves travel clockwise and counterclockwise around the loop. This feature would underlie macroscopic properties of gravity like the corkscrew-patterned polarization of gravitational waves.

    But matching the theory to all other aspects of reality takes some fiddling. To get rid of negative energies that would correspond to unphysical, faster-than-light particles, string theory needs a property called “Supersymmetry”, which doubles the number of its string vibration modes. Every vibration mode corresponding to a matter particle must come with another mode signifying a force particle. String theory also requires the existence of 10 space-time dimensions for the strings to wiggle around in. Yet we haven’t found any supersymmetric partner particles, and our universe looks 4D, with three dimensions of space and one of time.

    Standard Model of Supersymmetry

    Both of these data points present something of a problem.

    If string theory describes our world, Supersymmetry must be broken here. That means the partner particles, if they exist, must be far heavier than the known set of particles — too heavy to muster in experiments. And if there really are 10 dimensions, six must be curled up so small they’re imperceptible to us — tight little knots of extra directions you can go in at any point in space. These “compactified” dimensions in a 4D-looking universe could have countless possible arrangements, all affecting strings (and numbers like “α”) differently.

    Broken Supersymmetry and invisible dimensions have led many quantum gravity researchers to seek or prefer alternative, non-stringy ideas.

    Mordehai Milgrom, MOND theorist, is an Israeli physicist and professor in the department of Condensed Matter Physics at The Weizmann Institute of Science (IL) in Rehovot, Israel http://cosmos.nautil.us

    MOND Rotation Curves with MOND Tully-Fisher

    MOND 1

    But so far the rival approaches have struggled to produce the kind of concrete calculations about things like graviton interactions that string theory can.

    Some physicists hope to see string theory win hearts and minds by default, by being the only microscopic description of gravity that’s logically consistent. If researchers can prove “string universality,” as this is sometimes called — a monopoly of string theories among viable fundamental theories of nature — we’ll have no choice but to believe in hidden dimensions and an inaudible orchestra of strings.

    To string theory sympathizers, the new bootstrap calculation opens a route to eventually proving string universality, and it gets the journey off to a rip-roaring start.

    Other researchers disagree with those implications. Astrid Eichhorn, a theoretical physicist at The South Danish University [Syddansk Universitet](DK) and The Ruprecht Karl University of Heidelberg [Ruprecht-Karls-Universität Heidelberg](DE) who specializes in a non-stringy approach called asymptotically safe quantum gravity, told me, “I would consider the relevant setting to collect evidence for or against a given quantum theory of gravity to be four-dimensional and non-supersymmetric” universes, since this “best describes our world, at least so far.”

    Eichhorn pointed out that there might be unitary, Lorentz-invariant descriptions of gravitons in 4D that don’t make any sense in 10D. “Simply by this choice of setting one might have ruled out alternative quantum gravity approaches” that are viable, she said.

    Vieira acknowledged that string universality might hold only in 10 dimensions, saying, “It could be that in 10D with supersymmetry, there’s only string theory, and when you go to 4D, there are many theories.” But, he said, “I doubt it.”

    Another critique, though, is that even if string theory saturates the range of allowed “α” values in the 10-dimensional setting the researchers probed, that doesn’t stop other theories from lying in the permitted range. “I don’t see any practical way we’re going to conclude that string theory is the only answer,” said Andrew Tolley of Imperial College London (UK).

    Just the Beginning

    Assessing the meaning of the coincidence will become easier if bootstrappers can generalize and extend similar results to more settings. “At the moment, many, many people are pursuing these ideas in various variations,” said Alexander Zhiboedov, a theoretical physicist at The European Organization for Nuclear Research [Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) [CERN], Europe’s particle physics laboratory.

    Guerrieri, Penedones and Vieira have already completed a “dual” bootstrap calculation, which bounds “α” from below by ruling out solutions less than the minimum rather than solving for viable “α” values above the bound, as they did previously. This dual calculation shows that their computer clusters didn’t simply miss smaller allowed “α” values, which would correspond to additional viable quantum gravity theories outside string theory’s range.

    They also plan to bootstrap the lower bound for worlds with nine large dimensions, where string theory calculations are still under some control (since only one dimension is curled up), to look for more evidence of a correlation. Aside from “α”, bootstrappers also aim to calculate “β” and “γ” — the allowed sizes of the second- and third-biggest quantum gravity corrections— and they have ideas for how to approach harder calculations about worlds where supersymmetry is broken or nonexistent, as it appears to be in reality. In this way they’ll try to carve out the space of allowed quantum gravity theories, and test string universality in the process.

    Claudia de Rham, a theorist at Imperial College, emphasized the need to be “agnostic,” noting that bootstrap principles are useful for exploring more ideas than just string theory. She and Tolley have used positivity — the rule that probabilities are always positive — to constrain a theory called “Massive Gravity”, which may or may not be a realization of string theory. They discovered potentially testable consequences, showing that massive gravity only satisfies positivity if certain exotic particles exist. De Rham sees bootstrap principles and positivity bounds as “one of the most exciting research developments at the moment” in fundamental physics.

    “No one has done this job of taking everything we know and taking consistency and putting it together,” said Zhiboedov. It’s “exciting,” he added, that theorists have work to do “at a very basic level.”

    See the full article here .


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    Formerly known as Simons Science News, Quanta Magazine (US) is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 2:07 pm on November 10, 2021 Permalink | Reply
    Tags: "Laws of Logic Lead to New Restrictions on the Big Bang", “de Sitter” space, , Cosmologists Close in on Logical Laws for the Big Bang, , Inflation theory, , , Quantum Gravity, The universe’s first moments have always been a mysterious era when the quantum nature of gravity would have been on full display.,   

    From Quanta Magazine (US) : “Laws of Logic Lead to New Restrictions on the Big Bang” 

    From Quanta Magazine (US)

    November 10, 2021
    Charlie Wood

    Cosmologists Close in on Logical Laws for the Big Bang

    Physicists are translating commonsense principles into strict mathematical constraints on how our universe must have behaved at the beginning of time.


    Patterns in the ever-expanding arrangement of galaxies might reveal secrets of the universe’s first moments.Credit: Dave Whyte for Quanta Magazine.

    1
    Cosmologists Close In on Logical Laws for the Big Bang Credit: Quanta Magazine

    For over 20 years, physicists have had reason to feel envious of certain fictional fish: specifically, the fish inhabiting the fantastic space of M.C. Escher’s Circle Limit III woodcut, which shrink to points as they approach the circular boundary of their ocean world. If only our universe had the same warped shape, theorists lament, they might have a much easier time understanding it.

    2
    M.C. Escher’s Circle Limit III (1959). Credit: M.C. Escher.

    Escher’s fish lucked out because their world comes with a cheat sheet — its edge. On the boundary of an Escher-esque ocean, anything complicated happening inside the sea casts a kind of shadow, which can be described in relatively simple terms. In particular, theories addressing the quantum nature of gravity can be reformulated on the edge in well-understood ways. The technique gives researchers a back door for studying otherwise impossibly complicated questions. Physicists have spent decades exploring this tantalizing link.

    Inconveniently, the real universe looks more like the Escher world turned inside out. This “de Sitter” space has a positive curvature; it expands continuously everywhere. With no obvious boundary on which to study the straightforward shadow theories, theoretical physicists have been unable to transfer their breakthroughs from the Escher world.

    “The closer we get to the real world, the fewer tools we have and the less we understand the rules of the game,” said Daniel Baumann, a cosmologist at The University of Amsterdam [Universiteit van Amsterdam](NL).

    But some Escher advances may finally be starting to bleed through. The universe’s first moments have always been a mysterious era when the quantum nature of gravity would have been on full display. Now multiple groups are converging on a novel way to indirectly evaluate descriptions of that flash of creation. The key is a new notion of a cherished law of reality known as unitarity, the expectation that all probabilities must add up to 100%. By determining what fingerprints a unitary birth of the universe should have left behind, researchers are developing powerful tools to check which theories clear this lowest of bars in our shifty and expanding space-time.

    Unitarity in de Sitter space “was not understood at all,” said Massimo Taronna, a theoretical physicist at The National Institute for Nuclear Physics[Institutio Nzaionale di Fisica Nucleare](IT). “There is a huge jump that has happened in the last couple of years.”

    Spoiler Alert

    The unfathomable ocean that theorists aim to plumb is a brief but dramatic stretch of space and time that many cosmologists believe set the stage for all we see today. During this hypothetical era, known as inflation, the infant universe would have ballooned at a truly incomprehensible rate, inflated by an unknown entity akin to Dark Energy.

    Cosmologists are dying to know exactly how inflation might have happened and what exotic fields might have driven it, but this era of cosmic history remains hidden. Astronomers can see only the output of inflation — the arrangement of matter hundreds of thousands of years after the Big Bang, as revealed by the cosmos’s earliest light.
    CMB per European Space Agency(EU) Planck.

    Their challenge is that countless inflationary theories match the final observable state. Cosmologists are like film buffs struggling to narrow down the possible plots of Thelma and Louise from its final frame: the Thunderbird hanging frozen in midair.

    Yet the task may not be impossible. Just as currents in the Escher-like ocean can be deciphered from their shadows on its boundary, perhaps theorists can read the inflationary story from its final cosmic scene. In recent years, Baumann and other physicists have sought to do just that with a strategy called bootstrapping.

    Cosmic bootstrappers strive to winnow the crowded field of inflationary theories with little more than logic. The general idea is to disqualify theories that fly in the face of common sense — as translated into stringent mathematical requirements. In this way, they “hoist themselves up by their bootstraps,” using math to evaluate theories that can’t be distinguished using current astronomical observations.

    One such commonsense property is unitarity, an elevated name for the obvious fact that the sum of the odds of all possible events must be 1. Put simply, flipping a coin must produce a heads or a tails. Bootstrappers can tell at a glance whether a theory in the Escher-like “anti-de Sitter” space is unitary by looking at its shadow on the boundary, but inflationary theories have long resisted such simple treatment, because the expanding universe has no obvious edge.

    Physicists can check a theory for unitarity by laboriously calculating its predictions from moment to moment and verifying that the odds always add up to 1, the equivalent of watching a whole movie with an eye for plot holes. What they really want is a way to glance at the end of an inflationary theory — the film’s final frame — and instantly know whether unitarity has been violated during any previous scene.

    But the concept of unitarity is linked closely to the passage of time, and they’ve struggled to understand what shape the fingerprints of unitarity would take in this final frame, which is a static, timeless snapshot. “For many years the confusion was, ‘How the hell can I get information about time evolution … in an object where time doesn’t exist at all?’” said Enrico Pajer, a theoretical cosmologist at The University of Cambridge (UK).

    Last year, Pajer helped bring the confusion to an end. He and his colleagues found a way to figure out if a particular theory of inflation is unitary by looking only at the universe it produces.

    In the Escher world, checking shadow theories for unitarity can be done on a cocktail napkin. These boundary theories are, in practice, quantum theories of the sort we might use to understand particle collisions. To check one for unitarity, physicists describe two particles pre-crash with a mathematical object called a matrix, and post-crash with another matrix. For a unitarity collision, the product of the two matrices is 1.

    Where do physicists get these matrices? They start with the pre-crash matrix. When space holds still, a movie of a particle collision looks the same played forward or backward, so researchers can apply a simple operation to the initial matrix to find the final matrix. Multiply those two together, check the product, and they’re done.

    But expanding space ruins everything. Cosmologists can work out the post-inflation matrix. Unlike particle collisions, however, an inflating cosmos looks quite different in reverse, so until recently it was unclear how to determine the pre-inflation matrix.

    “For cosmology we would have to exchange the end of inflation with the beginning of inflation,” Pajer said, “which is crazy.”

    Last year, Pajer, along with his colleagues Harry Goodhew and Sadra Jazayeri, figured out how to calculate the initial matrix. The Cambridge group rewrote the final matrix to accommodate complex numbers as well as real numbers. They also defined a transformation involving swapping positive energies for negative energies — analogous to what physicists might do in the particle collision context.

    But had they found the right transformation?

    Pajer then set out to verify that these two matrices really do capture unitarity. Using a more generic theory of inflation, Pajer and Scott Melville, also at Cambridge, played the birth of the universe forward frame by frame, looking for illegal unitarity violations in the traditional way. In the end, they showed that this painstaking process gave the same result as the matrix method.

    The new method allows them to skip the moment-by-moment calculation. For a general theory involving particles of any mass and any spin communing via any force, they could see if it is unitary by checking the final outcome. They had discovered how to reveal the plot without watching the movie.

    The new matrix test, known as the cosmological optical theorem, soon proved its power. Pajer and Melville found that a lot of possible theories violated unitarity. In fact, the researchers ended up with so few valid possibilities that they wondered if they could make some predictions. Even without a specific theory of inflation in hand, could they tell astronomers what to search for?

    Cosmic Triangle Test

    One revealing imprint of inflation is the way galaxies are distributed across the sky. The simplest pattern is the two-point correlation function, which, roughly speaking, gives the odds of finding two galaxies separated by particular distances. In other words, it tells you where the universe’s matter is.

    Our universe’s matter is spread out in a special way, observations have found, with dense spots stuffed full of galaxies that come in a variety of sizes. The theory of inflation arose in part to explain this peculiar finding.

    3
    Lucy Reading-Ikkanda/Quanta Magazine.

    The universe started out quite smooth overall, the thinking goes, but quantum wiggles imprinted space with tiny dollops of extra matter. As space expanded, these dense spots stretched out even as the tiny ripples continued to arise. When inflation stopped, the young cosmos was left with dense spots ranging from small to large, which would go on to become galaxies and galaxy clusters.

    All theories of inflation nail this two-point correlation function. To distinguish between competing theories, researchers need to measure subtler, higher-point correlations — relationships between the angles formed by a trio of galaxies, for instance.

    Typically, cosmologists propose a theory of inflation involving certain exotic particles, and then play it forward to calculate the three-point correlation functions it would leave in the sky, giving astronomers a target to search for. In this way, researchers tackle theories one by one. “There are many, many, many possible things you could look for. Infinitely many, in fact,” said Daan Meerburg, a cosmologist at the The University of Groningen [Rijksuniversiteit Groningen] (NL).

    Pajer has turned that process around. Inflation is thought to have left ripples in the fabric of space in the form of gravitational waves. Pajer and his collaborators started with all possible three-point functions describing these gravitational waves and checked them with the matrix test, eliminating any functions that failed unitarity.

    In the case of a certain type of gravitational wave, the group found that unitary three-point functions are few and far between. In fact, only three pass the test, the researchers announced in a preprint posted in September. The result “is very remarkable,” said Meerburg, who was not involved. If astronomers ever detect primordial gravitational waves — and efforts are ongoing — these will be the first signs of inflation to look for.

    Positive Signs

    The cosmological optical theorem guarantees that the probabilities of all possible events add up to 1, just as a coin is certain to have two sides. But there is another way of thinking about unitarity: The odds of each event must be positive. No coin can have a negative chance of landing on tails.

    Victor Gorbenko, a theoretical physicist at Stanford University (US), Lorenzo Di Pietro of The University of Trieste [Università degli Studi di Trieste](IT), and Shota Komatsu of The European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) [CERN] recently approached unitarity in de Sitter space from this perspective. What would the sky look like, they wondered, in bizarro universes that broke this law of positivity?

    Taking inspiration from the Escher world, they were intrigued by the fact that anti-de Sitter space and de Sitter space share one fundamental feature: Viewed properly, each can look the same at all scales. Zoom in near the boundary of Escher’s Circle Limit III woodcut, and the shrimpy fish have identical proportions to the whoppers in the middle. Similarly, quantum ripples in the inflating universe generated dense spots large and small. This common property, “conformal symmetry,” allowed Gorbenko’s group to port a popular mathematical technique for breaking apart boundary theories between the two worlds.


    Video: David Kaplan explores the leading cosmological explanation for the origin of the universe.
    Filming by Petr Stepanek. Editing and motion graphics by MK12. Music by Pete Calandra and Scott P. Schreer.

    In practice, this tool let them take the end of inflation in any universe — the hodgepodge of density ripples — and break it into a sum of wavelike patterns. For unitary universes, they found, each wave would have a positive coefficient. Any theories predicting negative waves would be no good. They described their test in a preprint in August. Simultaneously, an independent group led by João Penedones of The EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH)arrived at the same result.

    The positivity test is more exact than the cosmological optical theorem, but less ready for real data. Both positivity groups made simplifications, including stripping out gravity and assuming flawless de Sitter structure, that will need to be modified to fit our messy, gravitating universe. But Gorbenko calls these steps “concrete and doable.”

    Cause for Hope

    Now that bootstrappers are closing in on the notion of what unitarity looks like for the outcome of a de Sitter expansion, they can move on to other classic bootstrapping rules, such as the expectation that causes should come before effects. It’s not currently clear how to see the traces of causality in a timeless snapshot, but the same was once true of unitarity.

    “That’s the most exciting thing that we still don’t fully understand,” said Taronna, who has been working with Charlotte Sleight, a theoretical physicist at Durham University (UK), to reformulate Escher-world results for a more realistic universe. “We don’t know what is not causal in de Sitter.”

    As bootstrappers learn the ropes of de Sitter space, they hope to zero in on a few correlation functions that next-generation telescopes might actually spot — and the few theories of inflation, or even gravity, that could have produced them. If they can pull it off, our swollen universe might someday look as transparent as the world of Escher’s fish.

    “After many years of working in de Sitter,” Taronna said, “we are finally starting to understand what the rules of a mathematically consistent theory of quantum gravity are.”

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Formerly known as Simons Science News, Quanta Magazine (US) is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 3:23 pm on September 7, 2021 Permalink | Reply
    Tags: "One Lab’s Quest to Build Space-Time Out of Quantum Particles", , , , Pairs of atoms could be entangled together and then each pair would itself be entangled with another pair and so on forming a kind of tree., Physicists have been suggesting for over a decade that gravity — and even space-time itself — may emerge from a strange quantum connection called entanglement., , , Quantum Gravity, , , Testing quantum gravity without black holes or galaxy-size particle accelerators., The Standard Model despite its success is clearly incomplete.   

    From Quanta Magazine (US) and Stanford University (US) : “One Lab’s Quest to Build Space-Time Out of Quantum Particles” 

    From Quanta Magazine (US)

    and

    Stanford University Name

    Stanford University (US)

    September 7, 2021
    Adam Becker

    1
    Quantum particles entangled in a “tree-like” structure correspond to various configurations of space-time.
    Credit: Olena Shmahalo & Samuel Velasco/Quanta Magazine; Photo: Felix Mittermeier.

    The prospects for directly testing a theory of quantum gravity are poor, to put it mildly. To probe the ultra-tiny Planck scale, where quantum gravitational effects appear, you would need a particle accelerator as big as the Milky Way galaxy. Likewise, black holes hold singularities that are governed by quantum gravity, but no black holes are particularly close by — and even if they were, we could never hope to see what’s inside. Quantum gravity was also at work in the first moments of the Big Bang, but direct signals from that era are long gone, leaving us to decipher subtle clues that first appeared hundreds of thousands of years later.

    But in a small lab just outside Palo Alto, the Stanford University professor Monika Schleier-Smith and her team are trying a different way to test quantum gravity without black holes or galaxy-size particle accelerators. Physicists have been suggesting for over a decade that gravity — and even space-time itself — may emerge from a strange quantum connection called entanglement. Schleier-Smith and her collaborators are reverse-engineering the process. By engineering highly entangled quantum systems in a tabletop experiment, Schleier-Smith hopes to produce something that looks and acts like the warped space-time predicted by Albert Einstein’s theory of general relativity.

    In a paper posted in June, her team announced their first experimental step along this route: a system of atoms trapped by light, with connections made to order, finely controlled with magnetic fields. When tuned in the right way, the long-distance correlations in this system describe a treelike geometry, similar to ones seen in simple models of emergent space-time. Schleier-Smith and her colleagues hope to build on this work to create analogues to more complex geometries, including those of black holes. In the absence of new data from particle physics or cosmology — a state of affairs that could continue indefinitely — this could be the most promising route for putting the latest ideas about quantum gravity to the test.

    The Perils of Perfect Predictions

    For five decades, the prevailing theory of particle physics, the Standard Model, has met with almost nothing but success — to the endless frustration of particle physicists.

    The problem lies in the fact that the Standard Model despite its success is clearly incomplete. It doesn’t include gravity, despite the long search for a theory of quantum gravity to replace general relativity. Nor can it explain dark matter or dark energy, which account for 95% of all the stuff in the universe. (The Standard Model also has trouble with the fact that neutrinos have mass — the sole particle physics phenomenon it has failed to predict.)

    Moreover, the Standard Model itself dictates that beyond a certain threshold of high energy — one closely related to the Planck scale — it almost certainly fails.

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    Monika Schleier-Smith’s lab at Stanford is a dense maze of cables and optical equipment. “But at the end of the day,” she said, “You can make a system that is clean and controlled.”
    Credit: Dawn Harmer/DOE’s SLAC National Accelerator Laboratory (US).

    Physicists are desperate for puzzling experimental data that might help to guide them as they build the Standard Model’s replacement. String theory, still the leading candidate to replace the Standard Model, has often been accused of being untestable. But one of the strangest features of string theory suggests a way to test some ideas about quantum gravity that don’t require impractical feats of galactic architecture.

    String theory is filled with dualities — relations between different physical systems that share the same mathematical structure. Perhaps the most surprising and consequential of these dualities is a connection between a type of quantum theory in four dimensions without gravity, known as a conformal field theory (CFT), and a particular kind of five-dimensional space-time with gravity, known as an anti-de Sitter (AdS) space. This AdS/CFT correspondence, as it’s known, was first discovered in 1997 by the physicist Juan Maldacena, now at the Institute for Advanced Study (US).

    Because the CFT has one fewer dimension than the AdS space, the former can be thought of as lying on the surface of the latter, like the two-dimensional skin of a three-dimensional apple. Yet the quantum theory on the surface still fully captures all the features of the volume inside — as if you could tell everything about the interior of an apple just by looking at its skin. This is an example of what physicists call holography: a lower-dimensional space giving rise to a higher-dimensional space, like a flat hologram producing a 3D image.

    In the AdS/CFT correspondence, the interior or “bulk” space emerges from relationships between the quantum components on the surface. Specifically, the geometry of the bulk space is built from entanglement, the “spooky” quantum connections that infamously troubled Einstein. Neighboring regions of the bulk correspond to highly entangled portions of the surface. Distant regions of the bulk correspond to less entangled parts of the surface. If the surface has a simple and orderly set of entanglement relations, the corresponding bulk space will be empty. If the surface is chaotic, with all its parts entangled with all the others, the bulk will form a black hole.

    The AdS/CFT correspondence is a deep and fruitful insight into the connections between quantum physics and general relativity. But it doesn’t actually describe the world we live in. Our universe isn’t a five-dimensional anti-de Sitter space — it’s an expanding four-dimensional space with a “flat” geometry.

    So over the past few years, researchers have proposed another approach. Rather than starting from the bulk — our own universe — and looking for the kind of quantum entanglement pattern that could produce it, we can go the other way. Perhaps experimenters could build systems with interesting entanglements — like the CFT on the surface — and search for any analogues to space-time geometry and gravity that emerge.

    That’s easier said than done. It’s not yet possible to build a system like any of the strongly interacting quantum systems known to have gravitational duals. But theorists have only mapped out a small fraction of possible systems — many others are too complex to study theoretically with existing mathematical tools. To see if any of those systems actually yield some kind of space-time geometry, the only option is to physically construct them in the lab and see if they also have a gravitational dual. “These experimental constructions might help us discover such systems,” said Maldacena. “There might be simpler systems than the ones we know about.” So quantum gravity theorists have turned to experts in building and controlling entanglement in quantum systems, like Schleier-Smith and her team.

    Quantum Gravity Meets Cold Atoms

    “There’s something really just elegant about the theory of quantum mechanics that I’ve always loved,” said Schleier-Smith. “If you go into the lab, you’ll see there’s cables all over the place and all kinds of electronics we had to build and vacuum systems and messy-looking hardware. But at the end of the day, you can make a system that is clean and controlled in such a way that it does nicely map onto this sort of elegant theory that you can write down on paper.”

    This messy elegance has been a hallmark of Schleier-Smith’s work since her graduate days at The Massachusetts Institute of Technology (US), where she used light to coax collections of atoms into particular entangled states and demonstrated how to use these quantum systems to build more precise atomic clocks. After MIT, she spent a few years at the MPG Institute for Quantum Optics [MPG Institut für Quantenoptik](DE) in Garching, Germany, before landing at Stanford in 2013. A couple of years later, Brian Swingle, a theoretical physicist then at Stanford working on string theory, quantum gravity and other related subjects, reached out to her with an unusual question. “I wrote her an email saying, basically, ‘Can you reverse time in your lab?’” said Swingle. “And she said yes. And so we started talking.”

    Swingle wanted to reverse time in order to study black holes and a quantum phenomenon known as scrambling. In quantum scrambling, information about a quantum system’s state is rapidly dispersed across a larger system, making it very hard to recover the original information. “Black holes are very good scramblers of information,” said Swingle. “They hide information very well.” When an object is dropped into a black hole, information about that object is rapidly hidden from the rest of the universe. Understanding how black holes obscure information about the objects that fall into them — and whether that information is merely hidden or actually destroyed — has been a major focus of theoretical physics since the 1970s.

    In the AdS/CFT correspondence, a black hole in the bulk corresponds to a dense web of entanglement at the surface that scrambles incoming information very quickly. Swingle wanted to know what a fast-scrambling quantum system would look like in the lab, and he realized that in order to confirm scrambling was taking place as rapidly as possible, researchers would need to tightly control the quantum system in question, with the ability to perfectly reverse all interactions. “The sort of obvious way to do it required the ability to effectively fast forward and rewind the system,” said Swingle. “And that’s not something you can do in an everyday kind of experiment.” But Swingle knew Schleier-Smith’s lab might be able to control the entanglement between atoms carefully enough to perfectly reverse all their interactions, as if time were running backward. “If you have this nice, isolated, well-controlled, highly engineered quantum many-body system, then maybe you have a chance,” he said.

    So Swingle reached out to Schleier-Smith and told her what he wanted to do. “He explained to me this conjecture that this process of scrambling — that there’s a fundamental speed limit to how fast that can happen,” said Schleier-Smith. “And that if you could build a quantum system in the lab that scrambles at this fundamental speed limit, then maybe that would be some kind of an analogue of a black hole.” Their conversations continued, and in 2016, Swingle and Schleier-Smith co-authored a paper, along with Patrick Hayden, another theorist at Stanford, and Gregory Bentsen, one of Schleier-Smith’s graduate students at the time, outlining a feasible method for creating and probing fast quantum scrambling in the lab.

    That work left Schleier-Smith contemplating other quantum gravitational questions that her lab could investigate. “That made me think … maybe these are actually good platforms for being able to realize some toy models of quantum gravity that are hard to realize by other means,” she said. She started to consider a setup where pairs of atoms could be entangled together and then each pair would itself be entangled with another pair and so on forming a kind of tree. “It seemed kind of far-fetched to actually do it, but at least I could sort of imagine on paper how you would design a system where you can do that,” she said. But she wasn’t sure if this actually corresponded to any known model of quantum gravity.

    3
    A view of the vacuum chamber at the center of the experiment. This view, taken several years ago, is now impossible, as there have been too many elements placed around the apparatus.
    4
    Inside the control room where researchers control the experiment and analyze the data. Credit: Khoi Huynh. Courtesy of Monika Schleier-Smith.

    Intense and affable, Schleier-Smith has an infectious enthusiasm for her work, as her student Bentsen discovered. He had started his doctoral work at Stanford in theoretical physics, but Schleier-Smith managed to pull him into her group anyhow. “I sort of convinced him to do experiments,” she recalled, “but he maintained an interest in theory as well, and liked to chat with theorists around the department.” She discussed her new idea with Bentsen, who discussed it with Sean Hartnoll, another theorist at Stanford. Hartnoll in turn played matchmaker, connecting Schleier-Smith and Bentsen with Steven Gubser, a theorist at Princeton University (US). (Gubser later died in a rock-climbing accident.)

    At the time, Gubser was working on a twist on the AdS/CFT correspondence. Rather than using the familiar kind of numbers that physicists generally use, he was using a set of alternative number systems known as the p-adic numbers. The key distinction between the p-adics and ordinary “real” numbers is the way the size of a number is defined. In the p-adics, a number’s size is determined by its prime factors. There’s a p-adic number system for each prime number: the 2-adics, the 3-adics, the 5-adics, and so on. In each p-adic number system, the more factors a number has that are multiples of p, the smaller that number is. So, for example, in the 2-adics, 44 is much closer to 0 than it is to 45, because 44 has two factors that are multiples of 2, while 45 doesn’t have any. But in the 3-adics, it’s the reverse; 45 is closer to 0 than to 44, because 45 has two factors that are multiples of 3. Each p-adic number system can also be represented as a kind of tree, with each branch containing numbers that all have the same number of factors that are multiples of p.

    4
    In p-adic geometry, different branches share the same number of factors that are multiples of p.
    Samuel Velasco/Quanta Magazine.

    Using the p-adics, Gubser and others had discovered a remarkable fact about the AdS/CFT correspondence. If you rewrite the surface theory using the p-adic numbers rather than the reals, the bulk is replaced with a kind of infinite tree. Specifically, it’s a tree with infinite branches packed into a finite space, resembling the structure of the p-adic numbers themselves. The p-adics, Gubser wrote, are “naturally holographic.”

    “The structure of p-adic numbers that [Gubser] told me about reminded me of the way Monika’s atoms interacted with each other,” said Hartnoll, “so I put them in touch.” Gubser co-authored a paper in 2019 with Schleier-Smith, Bentsen and others. In the paper, the team described how to get something resembling the p-adic tree to emerge from entangled atoms in an actual lab. With the plan in hand, Schleier-Smith and her team got to work.

    Building Space-Time in the Lab

    Schleier-Smith’s lab at Stanford is a dense forest of mirrors, lenses and fiber-optic cables that surround a vacuum chamber at the center of the room. In that vacuum chamber, 18 tiny collections of rubidium atoms — about 10,000 to a group — are arranged in a line and cooled to phenomenally low temperatures, a fraction of a degree above absolute zero. A specially tuned laser and a magnetic field that increases from one end of the chamber to the other allow the experimenters to choose which groups of atoms become correlated with each other.

    Using this lab setup, Schleier-Smith and her research group were able to get the two groups of atoms at the ends of the line just as correlated as neighboring groups were in the middle of the line, connecting the ends and turning the line into a circle of correlations. They then coaxed the collection of atoms into a treelike structure. All of this was accomplished without moving the atoms at all — the correlation “geometry” was wholly disconnected from the actual spatial geometry of the atoms.

    While the tree structure formed by the interacting atoms in Schleier-Smith’s lab isn’t a full-blown realization of p-adic AdS/CFT, it’s “a first step towards holography in the laboratory,” said Hayden. Maldacena, the originator of the AdS/CFT correspondence, agrees: “I’m very excited about this,” he said. “Our subject has been always very theoretical, and so this contact with experiment will probably raise more questions.”

    Hayden sees this as the way of the future. “Instead of trying to understand the emergence of space-time in our universe, let’s actually just make toy universes in the lab and study the emergence of space-time there,” he said. “And that sounds like a crazy thing to do, right? Like kind of mad-scientist kind of crazy, right? But I think it really is likely to be easier to do that than to directly test quantum gravity.”

    Schleier-Smith is also optimistic about the future. “We’re still at the stage of getting more and more control, characterizing the quantum states that we have. But … I would love to get to that point where we don’t know what will happen,” she said. “And maybe we measure the correlations in the system, and we learn that there’s a geometric description, some holographic description that we didn’t know was there. That would be cool.”

    See the full article here .


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    Please help promote STEM in your local schools.

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    Stanford University campus
    Stanford University (US)

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members.

    Stanford University, officially Leland Stanford Junior University, is a private research university located in Stanford, California. Stanford was founded in 1885 by Leland and Jane Stanford in memory of their only child, Leland Stanford Jr., who had died of typhoid fever at age 15 the previous year. Stanford is consistently ranked as among the most prestigious and top universities in the world by major education publications. It is also one of the top fundraising institutions in the country, becoming the first school to raise more than a billion dollars in a year.

    Leland Stanford was a U.S. senator and former governor of California who made his fortune as a railroad tycoon. The school admitted its first students on October 1, 1891, as a coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was damaged by the 1906 San Francisco earthquake. Following World War II, provost Frederick Terman supported faculty and graduates’ entrepreneurialism to build self-sufficient local industry in what would later be known as Silicon Valley.

    The university is organized around seven schools: three schools consisting of 40 academic departments at the undergraduate level as well as four professional schools that focus on graduate programs in law, medicine, education, and business. All schools are on the same campus. Students compete in 36 varsity sports, and the university is one of two private institutions in the Division I FBS Pac-12 Conference. It has gained 126 NCAA team championships, and Stanford has won the NACDA Directors’ Cup for 24 consecutive years, beginning in 1994–1995. In addition, Stanford students and alumni have won 270 Olympic medals including 139 gold medals.

    As of October 2020, 84 Nobel laureates, 28 Turing Award laureates, and eight Fields Medalists have been affiliated with Stanford as students, alumni, faculty, or staff. In addition, Stanford is particularly noted for its entrepreneurship and is one of the most successful universities in attracting funding for start-ups. Stanford alumni have founded numerous companies, which combined produce more than $2.7 trillion in annual revenue, roughly equivalent to the 7th largest economy in the world (as of 2020). Stanford is the alma mater of one president of the United States (Herbert Hoover), 74 living billionaires, and 17 astronauts. It is also one of the leading producers of Fulbright Scholars, Marshall Scholars, Rhodes Scholars, and members of the United States Congress.

    Stanford University was founded in 1885 by Leland and Jane Stanford, dedicated to Leland Stanford Jr, their only child. The institution opened in 1891 on Stanford’s previous Palo Alto farm.

    Jane and Leland Stanford modeled their university after the great eastern universities, most specifically Cornell University. Stanford opened being called the “Cornell of the West” in 1891 due to faculty being former Cornell affiliates (either professors, alumni, or both) including its first president, David Starr Jordan, and second president, John Casper Branner. Both Cornell and Stanford were among the first to have higher education be accessible, nonsectarian, and open to women as well as to men. Cornell is credited as one of the first American universities to adopt this radical departure from traditional education, and Stanford became an early adopter as well.

    Despite being impacted by earthquakes in both 1906 and 1989, the campus was rebuilt each time. In 1919, The Hoover Institution on War, Revolution and Peace was started by Herbert Hoover to preserve artifacts related to World War I. The Stanford Medical Center, completed in 1959, is a teaching hospital with over 800 beds. The DOE’s SLAC National Accelerator Laboratory(US)(originally named the Stanford Linear Accelerator Center), established in 1962, performs research in particle physics.

    Land

    Most of Stanford is on an 8,180-acre (12.8 sq mi; 33.1 km^2) campus, one of the largest in the United States. It is located on the San Francisco Peninsula, in the northwest part of the Santa Clara Valley (Silicon Valley) approximately 37 miles (60 km) southeast of San Francisco and approximately 20 miles (30 km) northwest of San Jose. In 2008, 60% of this land remained undeveloped.

    Stanford’s main campus includes a census-designated place within unincorporated Santa Clara County, although some of the university land (such as the Stanford Shopping Center and the Stanford Research Park) is within the city limits of Palo Alto. The campus also includes much land in unincorporated San Mateo County (including the SLAC National Accelerator Laboratory and the Jasper Ridge Biological Preserve), as well as in the city limits of Menlo Park (Stanford Hills neighborhood), Woodside, and Portola Valley.

    Non-central campus

    Stanford currently operates in various locations outside of its central campus.

    On the founding grant:

    Jasper Ridge Biological Preserve is a 1,200-acre (490 ha) natural reserve south of the central campus owned by the university and used by wildlife biologists for research.
    SLAC National Accelerator Laboratory is a facility west of the central campus operated by the university for the Department of Energy. It contains the longest linear particle accelerator in the world, 2 miles (3.2 km) on 426 acres (172 ha) of land.
    Golf course and a seasonal lake: The university also has its own golf course and a seasonal lake (Lake Lagunita, actually an irrigation reservoir), both home to the vulnerable California tiger salamander. As of 2012 Lake Lagunita was often dry and the university had no plans to artificially fill it.

    Off the founding grant:

    Hopkins Marine Station, in Pacific Grove, California, is a marine biology research center owned by the university since 1892.
    Study abroad locations: unlike typical study abroad programs, Stanford itself operates in several locations around the world; thus, each location has Stanford faculty-in-residence and staff in addition to students, creating a “mini-Stanford”.

    Redwood City campus for many of the university’s administrative offices located in Redwood City, California, a few miles north of the main campus. In 2005, the university purchased a small, 35-acre (14 ha) campus in Midpoint Technology Park intended for staff offices; development was delayed by The Great Recession. In 2015 the university announced a development plan and the Redwood City campus opened in March 2019.

    The Bass Center in Washington, DC provides a base, including housing, for the Stanford in Washington program for undergraduates. It includes a small art gallery open to the public.

    China: Stanford Center at Peking University, housed in the Lee Jung Sen Building, is a small center for researchers and students in collaboration with Beijing University [北京大学](CN) (Kavli Institute for Astronomy and Astrophysics at Peking University(CN) (KIAA-PKU).

    Administration and organization

    Stanford is a private, non-profit university that is administered as a corporate trust governed by a privately appointed board of trustees with a maximum membership of 38. Trustees serve five-year terms (not more than two consecutive terms) and meet five times annually.[83] A new trustee is chosen by the current trustees by ballot. The Stanford trustees also oversee the Stanford Research Park, the Stanford Shopping Center, the Cantor Center for Visual Arts, Stanford University Medical Center, and many associated medical facilities (including the Lucile Packard Children’s Hospital).

    The board appoints a president to serve as the chief executive officer of the university, to prescribe the duties of professors and course of study, to manage financial and business affairs, and to appoint nine vice presidents. The provost is the chief academic and budget officer, to whom the deans of each of the seven schools report. Persis Drell became the 13th provost in February 2017.

    As of 2018, the university was organized into seven academic schools. The schools of Humanities and Sciences (27 departments), Engineering (nine departments), and Earth, Energy & Environmental Sciences (four departments) have both graduate and undergraduate programs while the Schools of Law, Medicine, Education and Business have graduate programs only. The powers and authority of the faculty are vested in the Academic Council, which is made up of tenure and non-tenure line faculty, research faculty, senior fellows in some policy centers and institutes, the president of the university, and some other academic administrators, but most matters are handled by the Faculty Senate, made up of 55 elected representatives of the faculty.

    The Associated Students of Stanford University (ASSU) is the student government for Stanford and all registered students are members. Its elected leadership consists of the Undergraduate Senate elected by the undergraduate students, the Graduate Student Council elected by the graduate students, and the President and Vice President elected as a ticket by the entire student body.

    Stanford is the beneficiary of a special clause in the California Constitution, which explicitly exempts Stanford property from taxation so long as the property is used for educational purposes.

    Endowment and donations

    The university’s endowment, managed by the Stanford Management Company, was valued at $27.7 billion as of August 31, 2019. Payouts from the Stanford endowment covered approximately 21.8% of university expenses in the 2019 fiscal year. In the 2018 NACUBO-TIAA survey of colleges and universities in the United States and Canada, only Harvard University(US), the University of Texas System(US), and Yale University(US) had larger endowments than Stanford.

    In 2006, President John L. Hennessy launched a five-year campaign called the Stanford Challenge, which reached its $4.3 billion fundraising goal in 2009, two years ahead of time, but continued fundraising for the duration of the campaign. It concluded on December 31, 2011, having raised a total of $6.23 billion and breaking the previous campaign fundraising record of $3.88 billion held by Yale. Specifically, the campaign raised $253.7 million for undergraduate financial aid, as well as $2.33 billion for its initiative in “Seeking Solutions” to global problems, $1.61 billion for “Educating Leaders” by improving K-12 education, and $2.11 billion for “Foundation of Excellence” aimed at providing academic support for Stanford students and faculty. Funds supported 366 new fellowships for graduate students, 139 new endowed chairs for faculty, and 38 new or renovated buildings. The new funding also enabled the construction of a facility for stem cell research; a new campus for the business school; an expansion of the law school; a new Engineering Quad; a new art and art history building; an on-campus concert hall; a new art museum; and a planned expansion of the medical school, among other things. In 2012, the university raised $1.035 billion, becoming the first school to raise more than a billion dollars in a year.

    Research centers and institutes

    DOE’s SLAC National Accelerator Laboratory(US)
    Stanford Research Institute, a center of innovation to support economic development in the region.
    Hoover Institution, a conservative American public policy institution and research institution that promotes personal and economic liberty, free enterprise, and limited government.
    Hasso Plattner Institute of Design, a multidisciplinary design school in cooperation with the Hasso Plattner Institute of University of Potsdam [Universität Potsdam](DE) that integrates product design, engineering, and business management education).
    Martin Luther King Jr. Research and Education Institute, which grew out of and still contains the Martin Luther King Jr. Papers Project.
    John S. Knight Fellowship for Professional Journalists
    Center for Ocean Solutions
    Together with UC Berkeley(US) and UC San Francisco(US), Stanford is part of the Biohub, a new medical science research center founded in 2016 by a $600 million commitment from Facebook CEO and founder Mark Zuckerberg and pediatrician Priscilla Chan.

    Discoveries and innovation

    Natural sciences

    Biological synthesis of deoxyribonucleic acid (DNA) – Arthur Kornberg synthesized DNA material and won the Nobel Prize in Physiology or Medicine 1959 for his work at Stanford.
    First Transgenic organism – Stanley Cohen and Herbert Boyer were the first scientists to transplant genes from one living organism to another, a fundamental discovery for genetic engineering. Thousands of products have been developed on the basis of their work, including human growth hormone and hepatitis B vaccine.
    Laser – Arthur Leonard Schawlow shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for his work on lasers.
    Nuclear magnetic resonance – Felix Bloch developed new methods for nuclear magnetic precision measurements, which are the underlying principles of the MRI.

    Computer and applied sciences

    ARPANETStanford Research Institute, formerly part of Stanford but on a separate campus, was the site of one of the four original ARPANET nodes.

    Internet—Stanford was the site where the original design of the Internet was undertaken. Vint Cerf led a research group to elaborate the design of the Transmission Control Protocol (TCP/IP) that he originally co-created with Robert E. Kahn (Bob Kahn) in 1973 and which formed the basis for the architecture of the Internet.

    Frequency modulation synthesis – John Chowning of the Music department invented the FM music synthesis algorithm in 1967, and Stanford later licensed it to Yamaha Corporation.

    Google – Google began in January 1996 as a research project by Larry Page and Sergey Brin when they were both PhD students at Stanford. They were working on the Stanford Digital Library Project (SDLP). The SDLP’s goal was “to develop the enabling technologies for a single, integrated and universal digital library” and it was funded through the National Science Foundation, among other federal agencies.

    Klystron tube – invented by the brothers Russell and Sigurd Varian at Stanford. Their prototype was completed and demonstrated successfully on August 30, 1937. Upon publication in 1939, news of the klystron immediately influenced the work of U.S. and UK researchers working on radar equipment.

    RISCARPA funded VLSI project of microprocessor design. Stanford and UC Berkeley are most associated with the popularization of this concept. The Stanford MIPS would go on to be commercialized as the successful MIPS architecture, while Berkeley RISC gave its name to the entire concept, commercialized as the SPARC. Another success from this era were IBM’s efforts that eventually led to the IBM POWER instruction set architecture, PowerPC, and Power ISA. As these projects matured, a wide variety of similar designs flourished in the late 1980s and especially the early 1990s, representing a major force in the Unix workstation market as well as embedded processors in laser printers, routers and similar products.
    SUN workstation – Andy Bechtolsheim designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation, which led to Sun Microsystems.

    Businesses and entrepreneurship

    Stanford is one of the most successful universities in creating companies and licensing its inventions to existing companies; it is often held up as a model for technology transfer. Stanford’s Office of Technology Licensing is responsible for commercializing university research, intellectual property, and university-developed projects.

    The university is described as having a strong venture culture in which students are encouraged, and often funded, to launch their own companies.

    Companies founded by Stanford alumni generate more than $2.7 trillion in annual revenue, equivalent to the 10th-largest economy in the world.

    Some companies closely associated with Stanford and their connections include:

    Hewlett-Packard, 1939, co-founders William R. Hewlett (B.S, PhD) and David Packard (M.S).
    Silicon Graphics, 1981, co-founders James H. Clark (Associate Professor) and several of his grad students.
    Sun Microsystems, 1982, co-founders Vinod Khosla (M.B.A), Andy Bechtolsheim (PhD) and Scott McNealy (M.B.A).
    Cisco, 1984, founders Leonard Bosack (M.S) and Sandy Lerner (M.S) who were in charge of Stanford Computer Science and Graduate School of Business computer operations groups respectively when the hardware was developed.[163]
    Yahoo!, 1994, co-founders Jerry Yang (B.S, M.S) and David Filo (M.S).
    Google, 1998, co-founders Larry Page (M.S) and Sergey Brin (M.S).
    LinkedIn, 2002, co-founders Reid Hoffman (B.S), Konstantin Guericke (B.S, M.S), Eric Lee (B.S), and Alan Liu (B.S).
    Instagram, 2010, co-founders Kevin Systrom (B.S) and Mike Krieger (B.S).
    Snapchat, 2011, co-founders Evan Spiegel and Bobby Murphy (B.S).
    Coursera, 2012, co-founders Andrew Ng (Associate Professor) and Daphne Koller (Professor, PhD).

    Student body

    Stanford enrolled 6,996 undergraduate and 10,253 graduate students as of the 2019–2020 school year. Women comprised 50.4% of undergraduates and 41.5% of graduate students. In the same academic year, the freshman retention rate was 99%.

    Stanford awarded 1,819 undergraduate degrees, 2,393 master’s degrees, 770 doctoral degrees, and 3270 professional degrees in the 2018–2019 school year. The four-year graduation rate for the class of 2017 cohort was 72.9%, and the six-year rate was 94.4%. The relatively low four-year graduation rate is a function of the university’s coterminal degree (or “coterm”) program, which allows students to earn a master’s degree as a 1-to-2-year extension of their undergraduate program.

    As of 2010, fifteen percent of undergraduates were first-generation students.

    Athletics

    As of 2016 Stanford had 16 male varsity sports and 20 female varsity sports, 19 club sports and about 27 intramural sports. In 1930, following a unanimous vote by the Executive Committee for the Associated Students, the athletic department adopted the mascot “Indian.” The Indian symbol and name were dropped by President Richard Lyman in 1972, after objections from Native American students and a vote by the student senate. The sports teams are now officially referred to as the “Stanford Cardinal,” referring to the deep red color, not the cardinal bird. Stanford is a member of the Pac-12 Conference in most sports, the Mountain Pacific Sports Federation in several other sports, and the America East Conference in field hockey with the participation in the inter-collegiate NCAA’s Division I FBS.

    Its traditional sports rival is the University of California, Berkeley, the neighbor to the north in the East Bay. The winner of the annual “Big Game” between the Cal and Cardinal football teams gains custody of the Stanford Axe.

    Stanford has had at least one NCAA team champion every year since the 1976–77 school year and has earned 126 NCAA national team titles since its establishment, the most among universities, and Stanford has won 522 individual national championships, the most by any university. Stanford has won the award for the top-ranked Division 1 athletic program—the NACDA Directors’ Cup, formerly known as the Sears Cup—annually for the past twenty-four straight years. Stanford athletes have won medals in every Olympic Games since 1912, winning 270 Olympic medals total, 139 of them gold. In the 2008 Summer Olympics, and 2016 Summer Olympics, Stanford won more Olympic medals than any other university in the United States. Stanford athletes won 16 medals at the 2012 Summer Olympics (12 gold, two silver and two bronze), and 27 medals at the 2016 Summer Olympics.

    Traditions

    The unofficial motto of Stanford, selected by President Jordan, is Die Luft der Freiheit weht. Translated from the German language, this quotation from Ulrich von Hutten means, “The wind of freedom blows.” The motto was controversial during World War I, when anything in German was suspect; at that time the university disavowed that this motto was official.
    Hail, Stanford, Hail! is the Stanford Hymn sometimes sung at ceremonies or adapted by the various University singing groups. It was written in 1892 by mechanical engineering professor Albert W. Smith and his wife, Mary Roberts Smith (in 1896 she earned the first Stanford doctorate in Economics and later became associate professor of Sociology), but was not officially adopted until after a performance on campus in March 1902 by the Mormon Tabernacle Choir.
    “Uncommon Man/Uncommon Woman”: Stanford does not award honorary degrees, but in 1953 the degree of “Uncommon Man/Uncommon Woman” was created to recognize individuals who give rare and extraordinary service to the University. Technically, this degree is awarded by the Stanford Associates, a voluntary group that is part of the university’s alumni association. As Stanford’s highest honor, it is not conferred at prescribed intervals, but only when appropriate to recognize extraordinary service. Recipients include Herbert Hoover, Bill Hewlett, Dave Packard, Lucile Packard, and John Gardner.
    Big Game events: The events in the week leading up to the Big Game vs. UC Berkeley, including Gaieties (a musical written, composed, produced, and performed by the students of Ram’s Head Theatrical Society).
    “Viennese Ball”: a formal ball with waltzes that was initially started in the 1970s by students returning from the now-closed Stanford in Vienna overseas program. It is now open to all students.
    “Full Moon on the Quad”: An annual event at Main Quad, where students gather to kiss one another starting at midnight. Typically organized by the Junior class cabinet, the festivities include live entertainment, such as music and dance performances.
    “Band Run”: An annual festivity at the beginning of the school year, where the band picks up freshmen from dorms across campus while stopping to perform at each location, culminating in a finale performance at Main Quad.
    “Mausoleum Party”: An annual Halloween Party at the Stanford Mausoleum, the final resting place of Leland Stanford Jr. and his parents. A 20-year tradition, the “Mausoleum Party” was on hiatus from 2002 to 2005 due to a lack of funding, but was revived in 2006. In 2008, it was hosted in Old Union rather than at the actual Mausoleum, because rain prohibited generators from being rented. In 2009, after fundraising efforts by the Junior Class Presidents and the ASSU Executive, the event was able to return to the Mausoleum despite facing budget cuts earlier in the year.
    Former campus traditions include the “Big Game bonfire” on Lake Lagunita (a seasonal lake usually dry in the fall), which was formally ended in 1997 because of the presence of endangered salamanders in the lake bed.

    Award laureates and scholars

    Stanford’s current community of scholars includes:

    19 Nobel Prize laureates (as of October 2020, 85 affiliates in total)
    171 members of the National Academy of Sciences
    109 members of National Academy of Engineering
    76 members of National Academy of Medicine
    288 members of the American Academy of Arts and Sciences
    19 recipients of the National Medal of Science
    1 recipient of the National Medal of Technology
    4 recipients of the National Humanities Medal
    49 members of American Philosophical Society
    56 fellows of the American Physics Society (since 1995)
    4 Pulitzer Prize winners
    31 MacArthur Fellows
    4 Wolf Foundation Prize winners
    2 ACL Lifetime Achievement Award winners
    14 AAAI fellows
    2 Presidential Medal of Freedom winners

    Stanford University Seal

    Formerly known as Simons Science News, Quanta Magazine (US) is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 10:03 pm on August 24, 2021 Permalink | Reply
    Tags: "This Physicist Discovered an Escape From Hawking’s Black Hole Paradox", , In 1974 Stephen Hawking calculated that black holes’ secrets die with them., , Quantum Gravity,   

    From Quanta Magazine (US) : “This Physicist Discovered an Escape From Hawking’s Black Hole Paradox” 

    From Quanta Magazine (US)

    August 23, 2021
    Natalie Wolchover

    1
    Netta Engelhardt puzzles over the fates of black holes in her office at the Massachusetts Institute of Technology. Credit: Tira Khan for Quanta Magazine.

    In 1974 Stephen Hawking calculated that black holes’ secrets die with them. Random quantum jitter on the spherical outer boundary, or “event horizon,” of a black hole will cause the hole to radiate particles and slowly shrink to nothing. Any record of the star whose violent contraction formed the black hole — and whatever else got swallowed up after — then seemed to be permanently lost.

    Hawking’s calculation posed a paradox — the infamous “black hole information paradox” — that has motivated research in fundamental physics ever since. On the one hand, quantum mechanics, the rulebook for particles, says that information about particles’ past states gets carried forward as they evolve — a bedrock principle called “unitarity.” But black holes take their cues from general relativity, the theory that space and time form a bendy fabric and gravity is the fabric’s curves. Hawking had tried to apply quantum mechanics to particles near a black hole’s periphery, and saw unitarity break down.

    So do evaporating black holes really destroy information, meaning unitarity is not a true principle of nature? Or does information escape as a black hole evaporates? Solving the information paradox quickly came to be seen as a route to discovering the true, quantum theory of gravity, which general relativity approximates well everywhere except black holes.

    In the past two years, a network of quantum gravity theorists, mostly millennials, has made enormous progress on Hawking’s paradox. One of the leading researchers is Netta Engelhardt, a 32-year-old theoretical physicist at The Massachusetts Institute of Technology (US). She and her colleagues have completed a new calculation that corrects Hawking’s 1974 formula; theirs indicates that information does, in fact, escape black holes via their radiation. She and Aron Wall identified an invisible surface that lies inside a black hole’s event horizon, called the “quantum extremal surface.” In 2019, Engelhardt and others showed that this surface seems to encode the amount of information that has radiated away from the black hole, evolving over the hole’s lifetime exactly as expected if information escapes.

    Engelhardt received a 2021 New Horizons in Physics Prize “for calculating the quantum information content of a black hole and its radiation.” Ahmed Almheiri of The Institute for Advanced Study (US), a frequent collaborator, noted her “deeply rooted intuition for the intricate workings of gravity,” particularly in the discovery of quantum extremal surfaces.

    Engelhardt set her sights on quantum gravity when she was 9 years old. She moved to Boston from Israel that year with her family, and, not knowing any English, read every book in Hebrew she could find in her house. The last was Hawking’s A Brief History of Time. “What that book did for me was trigger a desire to understand the fundamental building blocks of the universe,” she said. “From then on, I was sort of finding my own way, watching different popular science videos and asking questions of anybody who might have the answers, and narrowing down what I wanted to work on.” She ultimately found her way to Hawking’s paradox.

    When Quanta Magazine caught up with Engelhardt in a recent video call, she emphasized that the full solution to the paradox — and the quantum theory of gravity — is a work in progress. We discussed that progress, which centrally involves the concept of entropy, and the search for a “reverse algorithm” that would allow someone to reconstruct a black hole’s past. The conversation has been condensed and edited for clarity.

    Would you say you and your colleagues have solved the black hole information paradox?

    Not yet. We’ve made a lot of progress toward a resolution. That’s part of what makes the field so exciting; we’re moving forward — and we’re not doing it so slowly, either — but there’s still a lot that we have to uncover and understand.

    Could you summarize what you’ve figured out so far?

    Certainly. Along the way there have been a number of very important developments. One I will mention is a 1993 paper by Don Page [Physical Review Letters]. Page said, suppose that information is conserved. Then the entropy of everything outside of a black hole starts out at some value, increases, then has to go back down to the original value once the black hole has evaporated altogether. Whereas Hawking’s calculation predicts that the entropy increases, and once the black hole is evaporated completely, it just plateaus at some value and that’s it.

    3
    Samuel Velasco/Quanta Magazine.

    So the question became, which entropy curve is right. Normally, entropy is the number of possible indistinguishable configurations of a system. What’s the best way to understand entropy in this black hole context?

    You could think of this entropy as ignorance of the state of affairs in the black hole interior. The more possibilities there are for what could be going on in the black hole interior, the more ignorant you will be about which configuration the system is in. So this entropy measures ignorance.

    Page’s discovery was that if you assume that the evolution of the universe doesn’t lose information, then, if you start out with zero ignorance about the universe before a black hole forms, eventually you’re going to end up with zero ignorance once the black hole is gone, since all the information that went in has come back out. That’s in conflict with what Hawking derived, which was that eventually you end up with ignorance.

    You characterize Page’s insight and all other work on the information paradox prior to 2019 as “understanding the problem better.” What happened in 2019?

    The activity that started in 2019 is the steps towards actually resolving the problem. The two papers that kicked this off were work by myself, Ahmed Almheiri, Don Marolf and Henry Maxfield3 and, in parallel, the second paper, which came out at the same time, by Geoff Penington. We submitted our papers on the same day and coordinated because we knew we were both onto the same thing.

    The idea was to calculate the entropy in a different way. This is where Don Page’s calculation was very important for us. If we use Hawking’s method and his assumptions, we get a formula for the entropy which is not consistent with unitarity. Now we want to understand how we could possibly do a calculation that would give us the curve of the entropy that Page proposed, which goes up then comes back down.

    And for this we relied on a proposal that Aron Wall and I gave in 2014: the quantum extremal surface proposal, which essentially states that the so-called quantum-corrected area of a certain surface inside the black hole is what computes the entropy. We said, maybe that’s a way to do the quantum gravity calculation that gives us a unitary result. And I will say: It was kind of a shot in the dark.

    When did you realize that it worked?

    This entire time is a bit of a daze in my mind, it was so exciting; I think I slept maybe two hours a night for weeks. The calculation came together over a period of three weeks, I want to say. I was at Princeton University (US) at the time. We just had a meeting on campus. I have a very distinct memory of driving home, and I was thinking to myself, wow, this could be it.

    The crux of the matter was, there’s more than one quantum extremal surface in the problem. There’s one quantum extremal surface that gives you the wrong answer — the Hawking answer. To correctly calculate the entropy, you have to pick the right one, and the right one is always the one with the smallest quantum-corrected area. And so what was really exciting — I think the moment we realized this might really actually work out — is when we found that exactly at the time when the entropy curve needs to “turn over” [go from increasing to decreasing], there’s a jump. At that time, the quantum extremal surface with the smallest quantum-corrected area goes from being the surface that would give you Hawking’s answer to a new and unexpected one. And that one reproduces the Page curve.

    What are these quantum extremal surfaces, exactly?

    Let me try to intuit a little bit what a classical, non-quantum extremal surface feels like. Let me begin with just a sphere. Imagine that you place a light bulb inside of it, and you follow the light rays as they move outward through the sphere. As the light rays get farther and farther away from the light bulb, the area of the spheres that they pass through will be getting larger and larger. We say that the cross-sectional area of the light rays is getting larger.

    That’s an intuition that works really well in approximately flat space where we live. But when you consider very curved space-time like you find inside a black hole, what can happen is that even though you’re firing your light rays outwards from the light bulb, and you’re looking at spheres that are progressively farther away from the bulb, the cross-sectional area is actually shrinking. And this is because space-time is very violently curved. It’s something that we call focusing of light rays, and it’s a very fundamental concept in gravity and general relativity.

    The extremal surface straddles this line between the very violent situation where the area is decreasing, and a normal situation where the area increases. The area of the surface is neither increasing nor decreasing, and so intuitively you can think of an extremal surface as kind of lying right at the cusp of where you’d expect strong curvature to start kicking in. A quantum extremal surface is the same idea, but instead of area, now you’re looking at quantum-corrected area. This is a sum of area and entropy, which is neither increasing nor decreasing.

    What does the quantum extremal surface mean? What’s the difference between things that are inside versus outside?

    Recall that when the Page curve turns over, we expect that our ignorance of what the black hole contains starts to decrease, as we have access to more and more of its radiation. So the radiation emitted by the hole must start to “learn” about the black hole interior.

    It’s the quantum extremal surface that divides the space-time in two: Everything inside the surface, the radiation can already decode. Everything outside of it is what remains hidden in the black hole system, what’s not contained in the information of the radiation. As the black hole emits more radiation, the quantum extremal surface moves outwards and encompasses an ever-larger volume of the black hole interior. By the time that black hole evaporates altogether, the radiation has to be able to decode everything that way.

    Now that we have an explicit calculation that gives us a unitary answer, that gives us so many tools to start asking questions that we could never ask before, like where does this formula come from, what does it mean about what type of theory quantum gravity is? Also, what is the mechanism in quantum gravity that restores unitarity? It has something to do with the quantum extremal surface formula.

    Most of the justification for the quantum extremal surface formula comes from studying black holes in “Anti-de Sitter” (AdS) space — saddle-shaped space with an outer boundary. Whereas our universe has approximately flat space, and no boundary. Why should we think that these calculations apply to our universe?

    First, we can’t really get around the fact that our universe contains both quantum mechanics and gravity. It contains black holes. So our understanding of the universe is going to be incomplete until we have a description of what happens inside a black hole. The information problem is such a difficult problem to solve that any progress — whether it’s in a toy model or not — is making progress towards understanding phenomena that happen in our universe.

    Now at a more technical level, quantum extremal surfaces can be computed in different kinds of space-times, including flat space like in our universe. And in fact there already have been papers written on the behavior of quantum extremal surfaces within different kinds of space-times and what types of entropy curves they would give rise to.

    We have a very firm interpretation of the quantum extremal surface in AdS space. We can extrapolate and say that in flat space there exists some interpretation of the quantum extremal surface which is analogous, and I think that’s probably true. It has many nice properties; it looks like it’s the right thing. We get really interesting behavior and we expect to get unitarity as well, and so, yes, we do expect that this phenomenon does translate, although the interpretation is going to be harder.

    You said at the beginning of our conversation that we don’t know the solution to the information paradox yet. Can you explain what a solution looks like?

    A full resolution of the information paradox would have to tell us exactly how the black hole information comes out. If I’m an observer that’s sitting outside of a black hole and I have extremely sophisticated technology and all the time in the world — a quantum computer taking incredibly sophisticated measurements, all the radiation of that black hole — what does it take for me to actually decode the radiation to reconstruct, for instance, the star that collapsed and formed the black hole? What process do I need to put my quantum computer through? We need to answer that question.

    So you want to find the reverse algorithm that unscrambles the information in the radiation. What’s the connection between that algorithm and quantum gravity?

    This algorithm that decodes the Hawking radiation is coming from the process in which quantum gravity encodes the radiation as it evaporates at the black hole horizon. The emergence of the black hole interior from quantum gravity and the dynamics of the black hole interior, the experience of an object that falls into the black hole — all of that is encoded in this reverse algorithm that quantum gravity has to spit out. All of those are tied up in the question of “how does the information get encoded in the Hawking radiation?”

    You’ve lately been writing papers about something called “a python’s lunch”. What’s that?

    It’s one thing to ask how can you decode the Hawking radiation; you also might ask, how complex is the task of decoding the Hawking radiation. And, as it turns out, extremely complex. So maybe the difference between Hawking’s calculation and the quantum extremal surface calculation that gives unitarity is that Hawking’s calculation is just dropping the high-complexity operations.

    It’s important to understand the complexity geometrically. And in 2019 there was a paper by some of my colleagues that proposed that whenever you have more than one quantum extremal surface, the one that would be wrong for the entropy can be used to calculate the complexity of decoding the black hole radiation. The two quantum extremal surfaces can be thought of as sort of constrictions in the space-time geometry, and those of us who have read Le Petit Prince see an elephant inside a python, and so it has become known as a python’s lunch.

    We proposed that multiple quantum extremal surfaces are the exclusive source of high complexity. And these two papers that you’re referring to are essentially an argument for this “strong python’s lunch” proposal. That is very insightful for us because it identifies the part of the geometry that Hawking’s calculation knows about and part of the geometry that Hawking’s calculation doesn’t know about. It’s working towards putting his and our calculations in the same language so that we know why one is right, and the other is wrong.

    Where would you say we currently stand in our effort to understand the quantum nature of gravity?

    I like to think of this as a puzzle, where we have all the edge pieces and we’re missing the center. We have many different insights about quantum gravity. There are many ways in which people are trying to understand it. Some by constraining it: What are things that it can’t do? Some by trying to construct aspects of it: things that it must do. My personal preferred approach is more to do with the information paradox, because it’s so pivotal; it’s such an acute problem. It’s clearly telling us: Here’s where you messed up. And to me that says, here’s a place where we can begin to fix our pillars, one of which must be wrong, of our understanding of quantum gravity.

    See the full article here .


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    Formerly known as Simons Science News, Quanta Magazine (US) is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 10:52 am on June 21, 2021 Permalink | Reply
    Tags: "Klarman postdoc seeks ‘theory of everything’ by approximation", Attempting to unify gravity with other fundamental forces of physics., , , , , Quantum Gravity, ,   

    From Cornell Chronicle (US) : “Klarman postdoc seeks ‘theory of everything’ by approximation” 

    From Cornell Chronicle (US)

    June 21, 2021
    Kate Blackwood
    cunews@cornell.edu

    1
    Francesco Sgarlata.

    Two pillar theories in physics – general relativity and quantum mechanics – stand up well on their own, but are incompatible with each other.

    “These two theories describe two different regimes of phenomena,” said Francesco Sgarlata, a Klarman Postdoctoral Fellow in physics in the College of Arts and Sciences (A&S).

    2

    Quantum mechanics, he said, describes physical phenomena at atomic or sub-atomic scales; general relativity describes very large phenomena.

    “The two theories are both correct in that they both predict very well, and we don’t have any violation of these theories. However, the two theories are inconsistent with each other,” Sgarlata said, adding that the inconsistencies show up in processes at extremely small scales.

    A member of the first cohort of six Klarman Fellows, Sgarlata is using his three-year fellowship to join theoretical physicists at Cornell and around the world in trying to solve this inconsistency.

    Physicists have long sought a “theory of everything,” or theory of quantum gravity, that would unify quantum mechanics and general relativity. In recent decades, researchers have tried a top-down approach, trying to come up with a unifying theory, such as string theory.

    Sgarlata, in contrast, is taking a bottom-up approach to finding a theory of quantum gravity, which attempts to unify gravity with other fundamental forces of physics.

    “We seek an approximation,” he said. “We don’t know what this theory of everything is. [Instead,] we are trying to write down some theory which can be seen as an approximation of quantum gravity, and we study what conditions this theory will have in order to be a good approximation of quantum gravity.”

    Sgarlata is working with Cornell’s theoretical physics community, including his faculty host, Csaba Csaki, professor of physics (A&S), and Thomas Hartman, associate professor of physics (A&S), to “identify some hidden properties of quantum gravity,” one at a time – and then build from there.

    “Francesco’s research is on the fundamental properties of particles and forces,” Hartman said. “His goal is to understand what particles are consistent with basic principles of relativity and quantum mechanics, and how these particles can interact.”

    Sgarlata’s background is in particle physics, Hartman said, while his own background is in black hole physics and string theory.

    “There is a lot of overlap, but these are two different perspectives,” Hartman said, “so this is a great opportunity for us to collaborate on new ideas. We are working on joining forces and combining our approaches.”

    To find conditions necessary to support a theory of quantum gravity, Sgarlata and collaborators focus on “first principles” – those we experience in everyday life but are difficult to prove mathematically. One example is causality – the link between cause and effect.

    “If I punch you, you will start feeling pain after I punch you, not before,” Sgarlata said. “We assume that this theory of everything respects causality.”

    Other first principles the researchers consider are unitarity (probabilities must add up to 1); and locality (particles only interact with neighboring particles.)

    From a “swampland” of possible theories arise islands of probable theories, Sgarlata said, narrowing the scope. “We get some constraints on the parameters of the theory,” he said.

    Hartman said that Sgarlata uses methods from particle physics to develop and interpret theories of physics at high energies.

    “In some cases, his methods can even be used to understand some corners of the more mysterious theory of quantum gravity at ultrashort distances,” Hartman said. “Over the next couple years, I think Francesco’s research at Cornell will lead to better insight into fundamental particles and new connections between particles, gravity and black holes.”

    The Klarman Fellowship, Sgarlata said, offers independence to pursue research collaborations toward solving the biggest problems in physics.

    “We have the tools to understand features of quantum gravity,” he said. “Today we are reinterpreting these concepts in a more modern way, and we are discovering new concepts of physics just by our interpretations.”

    See the full article here .


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    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

    Cornell University (US) is a private, statutory, Ivy League and land-grant research university in Ithaca, New York. Founded in 1865 by Ezra Cornell and Andrew Dickson White, the university was intended to teach and make contributions in all fields of knowledge—from the classics to the sciences, and from the theoretical to the applied. These ideals, unconventional for the time, are captured in Cornell’s founding principle, a popular 1868 quotation from founder Ezra Cornell: “I would found an institution where any person can find instruction in any study.”

    The university is broadly organized into seven undergraduate colleges and seven graduate divisions at its main Ithaca campus, with each college and division defining its specific admission standards and academic programs in near autonomy. The university also administers two satellite medical campuses, one in New York City and one in Education City, Qatar, and Jacobs Technion-Cornell Institute(US) in New York City, a graduate program that incorporates technology, business, and creative thinking. The program moved from Google’s Chelsea Building in New York City to its permanent campus on Roosevelt Island in September 2017.

    Cornell is one of the few private land grant universities in the United States. Of its seven undergraduate colleges, three are state-supported statutory or contract colleges through the SUNY – The State University of New York (US) system, including its Agricultural and Human Ecology colleges as well as its Industrial Labor Relations school. Of Cornell’s graduate schools, only the veterinary college is state-supported. As a land grant college, Cornell operates a cooperative extension outreach program in every county of New York and receives annual funding from the State of New York for certain educational missions. The Cornell University Ithaca Campus comprises 745 acres, but is much larger when the Cornell Botanic Gardens (more than 4,300 acres) and the numerous university-owned lands in New York City are considered.

    Alumni and affiliates of Cornell have reached many notable and influential positions in politics, media, and science. As of January 2021, 61 Nobel laureates, four Turing Award winners and one Fields Medalist have been affiliated with Cornell. Cornell counts more than 250,000 living alumni, and its former and present faculty and alumni include 34 Marshall Scholars, 33 Rhodes Scholars, 29 Truman Scholars, 7 Gates Scholars, 55 Olympic Medalists, 10 current Fortune 500 CEOs, and 35 billionaire alumni. Since its founding, Cornell has been a co-educational, non-sectarian institution where admission has not been restricted by religion or race. The student body consists of more than 15,000 undergraduate and 9,000 graduate students from all 50 American states and 119 countries.

    History

    Cornell University was founded on April 27, 1865; the New York State (NYS) Senate authorized the university as the state’s land grant institution. Senator Ezra Cornell offered his farm in Ithaca, New York, as a site and $500,000 of his personal fortune as an initial endowment. Fellow senator and educator Andrew Dickson White agreed to be the first president. During the next three years, White oversaw the construction of the first two buildings and traveled to attract students and faculty. The university was inaugurated on October 7, 1868, and 412 men were enrolled the next day.

    Cornell developed as a technologically innovative institution, applying its research to its own campus and to outreach efforts. For example, in 1883 it was one of the first university campuses to use electricity from a water-powered dynamo to light the grounds. Since 1894, Cornell has included colleges that are state funded and fulfill statutory requirements; it has also administered research and extension activities that have been jointly funded by state and federal matching programs.

    Cornell has had active alumni since its earliest classes. It was one of the first universities to include alumni-elected representatives on its Board of Trustees. Cornell was also among the Ivies that had heightened student activism during the 1960s related to cultural issues; civil rights; and opposition to the Vietnam War, with protests and occupations resulting in the resignation of Cornell’s president and the restructuring of university governance. Today the university has more than 4,000 courses. Cornell is also known for the Residential Club Fire of 1967, a fire in the Residential Club building that killed eight students and one professor.

    Since 2000, Cornell has been expanding its international programs. In 2004, the university opened the Weill Cornell Medical College in Qatar. It has partnerships with institutions in India, Singapore, and the People’s Republic of China. Former president Jeffrey S. Lehman described the university, with its high international profile, a “transnational university”. On March 9, 2004, Cornell and Stanford University(US) laid the cornerstone for a new ‘Bridging the Rift Center’ to be built and jointly operated for education on the Israel–Jordan border.

    Research

    Cornell, a research university, is ranked fourth in the world in producing the largest number of graduates who go on to pursue PhDs in engineering or the natural sciences at American institutions, and fifth in the world in producing graduates who pursue PhDs at American institutions in any field. Research is a central element of the university’s mission; in 2009 Cornell spent $671 million on science and engineering research and development, the 16th highest in the United States. Cornell is classified among “R1: Doctoral Universities – Very high research activity”.

    For the 2016–17 fiscal year, the university spent $984.5 million on research. Federal sources constitute the largest source of research funding, with total federal investment of $438.2 million. The agencies contributing the largest share of that investment are the Department of Health and Human Services and the National Science Foundation(US), accounting for 49.6% and 24.4% of all federal investment, respectively. Cornell was on the top-ten list of U.S. universities receiving the most patents in 2003, and was one of the nation’s top five institutions in forming start-up companies. In 2004–05, Cornell received 200 invention disclosures; filed 203 U.S. patent applications; completed 77 commercial license agreements; and distributed royalties of more than $4.1 million to Cornell units and inventors.

    Since 1962, Cornell has been involved in unmanned missions to Mars. In the 21st century, Cornell had a hand in the Mars Exploration Rover Mission. Cornell’s Steve Squyres, Principal Investigator for the Athena Science Payload, led the selection of the landing zones and requested data collection features for the Spirit and Opportunity rovers. NASA-JPL/Caltech(US) engineers took those requests and designed the rovers to meet them. The rovers, both of which have operated long past their original life expectancies, are responsible for the discoveries that were awarded 2004 Breakthrough of the Year honors by Science. Control of the Mars rovers has shifted between National Aeronautics and Space Administration(US)’s JPL-Caltech (US) and Cornell’s Space Sciences Building.

    Further, Cornell researchers discovered the rings around the planet Uranus, and Cornell built and operated the telescope at Arecibo Observatory located in Arecibo, Puerto Rico(US) until 2011, when they transferred the operations to SRI International, the Universities Space Research Association (US) and the Metropolitan University of Puerto Rico [Universidad Metropolitana de Puerto Rico](US).

    The Automotive Crash Injury Research Project was begun in 1952. It pioneered the use of crash testing, originally using corpses rather than dummies. The project discovered that improved door locks; energy-absorbing steering wheels; padded dashboards; and seat belts could prevent an extraordinary percentage of injuries.

    In the early 1980s, Cornell deployed the first IBM 3090-400VF and coupled two IBM 3090-600E systems to investigate coarse-grained parallel computing. In 1984, the National Science Foundation began work on establishing five new supercomputer centers, including the Cornell Center for Advanced Computing, to provide high-speed computing resources for research within the United States. As an National Science Foundation (US) center, Cornell deployed the first IBM Scalable Parallel supercomputer.

    In the 1990s, Cornell developed scheduling software and deployed the first supercomputer built by Dell. Most recently, Cornell deployed Red Cloud, one of the first cloud computing services designed specifically for research. Today, the center is a partner on the National Science Foundation XSEDE-Extreme Science Engineering Discovery Environment supercomputing program, providing coordination for XSEDE architecture and design, systems reliability testing, and online training using the Cornell Virtual Workshop learning platform.

    Cornell scientists have researched the fundamental particles of nature for more than 70 years. Cornell physicists, such as Hans Bethe, contributed not only to the foundations of nuclear physics but also participated in the Manhattan Project. In the 1930s, Cornell built the second cyclotron in the United States. In the 1950s, Cornell physicists became the first to study synchrotron radiation.

    During the 1990s, the Cornell Electron Storage Ring, located beneath Alumni Field, was the world’s highest-luminosity electron-positron collider. After building the synchrotron at Cornell, Robert R. Wilson took a leave of absence to become the founding director of DOE’s Fermi National Accelerator Laboratory(US), which involved designing and building the largest accelerator in the United States.

    Cornell’s accelerator and high-energy physics groups are involved in the design of the proposed ILC-International Linear Collider(JP) and plan to participate in its construction and operation. The International Linear Collider(JP), to be completed in the late 2010s, will complement the CERN Large Hadron Collider(CH) and shed light on questions such as the identity of dark matter and the existence of extra dimensions.

    As part of its research work, Cornell has established several research collaborations with universities around the globe. For example, a partnership with the University of Sussex(UK) (including the Institute of Development Studies at Sussex) allows research and teaching collaboration between the two institutions.

     
  • richardmitnick 9:20 am on June 18, 2021 Permalink | Reply
    Tags: "Physicists Nearly Reach Elusive Quantum Ground State on The Largest 'Object' Yet", Achieving the quantum ground state of a cloud of atoms isn't easy. You need to cool the atom by applying just the right amount of force to stop its vibrations., , , , , , , , Quantum Gravity, , , The work represents a new way to probe the quantum realm.   

    From Massachusetts Institute of Technology (US) via Science Alert (AU) : “Physicists Nearly Reach Elusive Quantum Ground State on The Largest ‘Object’ Yet” 

    MIT News

    From Massachusetts Institute of Technology (US)

    via

    http://www.sciencealert.com/”> Science Alert (AU)

    17 JUNE 2021
    MICHELLE STARR

    1
    One of LIGO’s mirrors. Credit: Caltech/ MIT Advanced aLIGO (US).

    Very rarely is anything completely still. All normal matter in the Universe is made of humming particles, minding their own business and vibrating at their own frequencies.

    If we can get them to slow down as much as possible, the material enters what is known as the motional ground state. In this state, physicists can perform tests of quantum mechanics and quantum gravity, probing the boundary with classical physics to search for a way to unify the two.

    Previously, this has been performed in the nanoscale; but now, for the first time, it’s been done on a massive ‘object’ – the collective motions of the four mirrors of the LIGO gravitational wave interferometer, known as an optomechanical oscillator, with an effective mass of 10 kilograms (22 pounds).

    Caltech /MIT Advanced aLigo .

    The work represents a new way to probe the quantum realm.

    “Nobody has ever observed how gravity acts on massive quantum states,” said mechanical engineer Vivishek Sudhir of MIT.

    “We’ve demonstrated how to prepare kilogram-scale objects in quantum states. This finally opens the door to an experimental study of how gravity might affect large quantum objects, something hitherto only dreamed of.”

    Achieving the quantum ground state of a cloud of atoms isn’t easy. You need to cool the atom by applying just the right amount of force to stop its vibrations. If you don’t cool it enough, it merely slows; so you need to know the exact energy level and direction of the atom’s vibrations in order to apply the appropriate force to stop it.

    This is called ‘feedback cooling’, and on the nanoscale it’s simpler to do, because it’s easier to isolate the smaller groups of atoms and minimize interference. The larger you go, though, the harder it becomes to handle that interference.

    LIGO is one of the most precise instruments for measuring fine motion. It’s designed to detect tiny ripples in space-time generated by collisions between massive objects up to billions of light-years away.

    It consists of an L-shaped vacuum chamber, with laser lights beamed along its two 4-kilometer (2.5-mile) tunnels, and sent to a beam splitter to four mirrors, one at each end of each tunnel. When space-time ripples, the mirrors distort the light, producing an interference pattern that scientists can decode to determine the cause. And it’s so sensitive that it can detect a change just one ten-thousandth the width of a proton, or 10-19 meters.

    Each of LIGO’s four 40-kilogram mirrors is suspended, and it’s their collective motion that makes up the oscillator. The balance of the mirrors effectively reduces 160 kilograms of total weight to a single object of just 10 kilograms.

    “LIGO is designed to measure the joint motion of the four 40-kilogram mirrors,” Sudhir said. “It turns out you can map the joint motion of these masses mathematically, and think of them as the motion of a single 10-kilogram object.”

    By precisely measuring the motion of this oscillator, the team hoped to work out exactly the rate of feedback cooling required to induce the motional ground state… and then, obviously, apply it.

    Unfortunately the very act of measuring throws a degree of randomness into the equation, making it difficult to predict the kinds of nudges needed to sap the energy out of the mirror’s atoms.

    To correct for this, the team cleverly studied each photon to estimate the activity of previous collisions, continuously building a more accurate map of how to apply the correct forces and achieve cooling.

    Then, they applied the calculated force using electromagnets attached to the backs of the mirrors.

    It worked. The oscillator stopped moving, almost completely. Its remaining energy was equivalent to a temperature of 77 nanokelvin (-273.15 degrees Celsius, or -459.67 degrees Fahrenheit).

    Its motional ground state, 10 nanokelvin, is extremely close, especially considering the room temperature starting point. And 77 nanokelvin is also very close to the temperatures used in motional ground state studies on the nanoscale.

    Moreover, it opens the door to some exciting possibilities. Macro-scale demonstrations and measurements of quantum phenomena – and maybe even applications for the same.

    But quantum gravity is the big kicker. Kilogram-mass objects are more susceptible to gravity; the team’s work raises hope to use this mass regime to study the quantum realm.

    “Preparing something in the ground state is often the first step to putting it into exciting or exotic quantum states,” said physicist Chris Whittle of MIT and the LIGO collaboration.

    “So this work is exciting because it might let us study some of these other states, on a mass scale that’s never been done before.”

    The research has been published in Science.

    See the full article here .


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    MIT Seal

    USPS “Forever” postage stamps celebrating Innovation at MIT.

    MIT Campus

    Massachusetts Institute of Technology (US) is a private land-grant research university in Cambridge, Massachusetts. The institute has an urban campus that extends more than a mile (1.6 km) alongside the Charles River. The institute also encompasses a number of major off-campus facilities such as the MIT Lincoln Laboratory, the Bates Center, and the Haystack Observatory, as well as affiliated laboratories such as the Broad and Whitehead Institutes.

    Founded in 1861 in response to the increasing industrialization of the United States, Massachusetts Institute of Technology (US) adopted a European polytechnic university model and stressed laboratory instruction in applied science and engineering. It has since played a key role in the development of many aspects of modern science, engineering, mathematics, and technology, and is widely known for its innovation and academic strength. It is frequently regarded as one of the most prestigious universities in the world.

    As of December 2020, 97 Nobel laureates, 26 Turing Award winners, and 8 Fields Medalists have been affiliated with MIT as alumni, faculty members, or researchers. In addition, 58 National Medal of Science recipients, 29 National Medals of Technology and Innovation recipients, 50 MacArthur Fellows, 80 Marshall Scholars, 3 Mitchell Scholars, 22 Schwarzman Scholars, 41 astronauts, and 16 Chief Scientists of the U.S. Air Force have been affiliated with Massachusetts Institute of Technology (US) . The university also has a strong entrepreneurial culture and MIT alumni have founded or co-founded many notable companies. Massachusetts Institute of Technology (US) is a member of the Association of American Universities (AAU).

    Foundation and vision

    In 1859, a proposal was submitted to the Massachusetts General Court to use newly filled lands in Back Bay, Boston for a “Conservatory of Art and Science”, but the proposal failed. A charter for the incorporation of the Massachusetts Institute of Technology, proposed by William Barton Rogers, was signed by John Albion Andrew, the governor of Massachusetts, on April 10, 1861.

    Rogers, a professor from the University of Virginia (US), wanted to establish an institution to address rapid scientific and technological advances. He did not wish to found a professional school, but a combination with elements of both professional and liberal education, proposing that:

    “The true and only practicable object of a polytechnic school is, as I conceive, the teaching, not of the minute details and manipulations of the arts, which can be done only in the workshop, but the inculcation of those scientific principles which form the basis and explanation of them, and along with this, a full and methodical review of all their leading processes and operations in connection with physical laws.”

    The Rogers Plan reflected the German research university model, emphasizing an independent faculty engaged in research, as well as instruction oriented around seminars and laboratories.

    Early developments

    Two days after Massachusetts Institute of Technology (US) was chartered, the first battle of the Civil War broke out. After a long delay through the war years, MIT’s first classes were held in the Mercantile Building in Boston in 1865. The new institute was founded as part of the Morrill Land-Grant Colleges Act to fund institutions “to promote the liberal and practical education of the industrial classes” and was a land-grant school. In 1863 under the same act, the Commonwealth of Massachusetts founded the Massachusetts Agricultural College, which developed as the University of Massachusetts Amherst (US)). In 1866, the proceeds from land sales went toward new buildings in the Back Bay.

    Massachusetts Institute of Technology (US) was informally called “Boston Tech”. The institute adopted the European polytechnic university model and emphasized laboratory instruction from an early date. Despite chronic financial problems, the institute saw growth in the last two decades of the 19th century under President Francis Amasa Walker. Programs in electrical, chemical, marine, and sanitary engineering were introduced, new buildings were built, and the size of the student body increased to more than one thousand.

    The curriculum drifted to a vocational emphasis, with less focus on theoretical science. The fledgling school still suffered from chronic financial shortages which diverted the attention of the MIT leadership. During these “Boston Tech” years, Massachusetts Institute of Technology (US) faculty and alumni rebuffed Harvard University (US) president (and former MIT faculty) Charles W. Eliot’s repeated attempts to merge MIT with Harvard College’s Lawrence Scientific School. There would be at least six attempts to absorb MIT into Harvard. In its cramped Back Bay location, MIT could not afford to expand its overcrowded facilities, driving a desperate search for a new campus and funding. Eventually, the MIT Corporation approved a formal agreement to merge with Harvard, over the vehement objections of MIT faculty, students, and alumni. However, a 1917 decision by the Massachusetts Supreme Judicial Court effectively put an end to the merger scheme.

    In 1916, the Massachusetts Institute of Technology (US) administration and the MIT charter crossed the Charles River on the ceremonial barge Bucentaur built for the occasion, to signify MIT’s move to a spacious new campus largely consisting of filled land on a one-mile-long (1.6 km) tract along the Cambridge side of the Charles River. The neoclassical “New Technology” campus was designed by William W. Bosworth and had been funded largely by anonymous donations from a mysterious “Mr. Smith”, starting in 1912. In January 1920, the donor was revealed to be the industrialist George Eastman of Rochester, New York, who had invented methods of film production and processing, and founded Eastman Kodak. Between 1912 and 1920, Eastman donated $20 million ($236.6 million in 2015 dollars) in cash and Kodak stock to MIT.

    Curricular reforms

    In the 1930s, President Karl Taylor Compton and Vice-President (effectively Provost) Vannevar Bush emphasized the importance of pure sciences like physics and chemistry and reduced the vocational practice required in shops and drafting studios. The Compton reforms “renewed confidence in the ability of the Institute to develop leadership in science as well as in engineering”. Unlike Ivy League schools, Massachusetts Institute of Technology (US) catered more to middle-class families, and depended more on tuition than on endowments or grants for its funding. The school was elected to the Association of American Universities (US)in 1934.

    Still, as late as 1949, the Lewis Committee lamented in its report on the state of education at Massachusetts Institute of Technology (US) that “the Institute is widely conceived as basically a vocational school”, a “partly unjustified” perception the committee sought to change. The report comprehensively reviewed the undergraduate curriculum, recommended offering a broader education, and warned against letting engineering and government-sponsored research detract from the sciences and humanities. The School of Humanities, Arts, and Social Sciences and the MIT Sloan School of Management were formed in 1950 to compete with the powerful Schools of Science and Engineering. Previously marginalized faculties in the areas of economics, management, political science, and linguistics emerged into cohesive and assertive departments by attracting respected professors and launching competitive graduate programs. The School of Humanities, Arts, and Social Sciences continued to develop under the successive terms of the more humanistically oriented presidents Howard W. Johnson and Jerome Wiesner between 1966 and 1980.

    Massachusetts Institute of Technology (US) ‘s involvement in military science surged during World War II. In 1941, Vannevar Bush was appointed head of the federal Office of Scientific Research and Development and directed funding to only a select group of universities, including MIT. Engineers and scientists from across the country gathered at Massachusetts Institute of Technology (US) ‘s Radiation Laboratory, established in 1940 to assist the British military in developing microwave radar. The work done there significantly affected both the war and subsequent research in the area. Other defense projects included gyroscope-based and other complex control systems for gunsight, bombsight, and inertial navigation under Charles Stark Draper’s Instrumentation Laboratory; the development of a digital computer for flight simulations under Project Whirlwind; and high-speed and high-altitude photography under Harold Edgerton. By the end of the war, Massachusetts Institute of Technology (US) became the nation’s largest wartime R&D contractor (attracting some criticism of Bush), employing nearly 4000 in the Radiation Laboratory alone and receiving in excess of $100 million ($1.2 billion in 2015 dollars) before 1946. Work on defense projects continued even after then. Post-war government-sponsored research at MIT included SAGE and guidance systems for ballistic missiles and Project Apollo.

    These activities affected Massachusetts Institute of Technology (US) profoundly. A 1949 report noted the lack of “any great slackening in the pace of life at the Institute” to match the return to peacetime, remembering the “academic tranquility of the prewar years”, though acknowledging the significant contributions of military research to the increased emphasis on graduate education and rapid growth of personnel and facilities. The faculty doubled and the graduate student body quintupled during the terms of Karl Taylor Compton, president of Massachusetts Institute of Technology (US) between 1930 and 1948; James Rhyne Killian, president from 1948 to 1957; and Julius Adams Stratton, chancellor from 1952 to 1957, whose institution-building strategies shaped the expanding university. By the 1950s, Massachusetts Institute of Technology (US) no longer simply benefited the industries with which it had worked for three decades, and it had developed closer working relationships with new patrons, philanthropic foundations and the federal government.

    In late 1960s and early 1970s, student and faculty activists protested against the Vietnam War and Massachusetts Institute of Technology (US) ‘s defense research. In this period Massachusetts Institute of Technology (US) ‘s various departments were researching helicopters, smart bombs and counterinsurgency techniques for the war in Vietnam as well as guidance systems for nuclear missiles. The Union of Concerned Scientists was founded on March 4, 1969 during a meeting of faculty members and students seeking to shift the emphasis on military research toward environmental and social problems. Massachusetts Institute of Technology (US) ultimately divested itself from the Instrumentation Laboratory and moved all classified research off-campus to the MIT (US) Lincoln Laboratoryfacility in 1973 in response to the protests. The student body, faculty, and administration remained comparatively unpolarized during what was a tumultuous time for many other universities. Johnson was seen to be highly successful in leading his institution to “greater strength and unity” after these times of turmoil. However six Massachusetts Institute of Technology (US) students were sentenced to prison terms at this time and some former student leaders, such as Michael Albert and George Katsiaficas, are still indignant about MIT’s role in military research and its suppression of these protests. (Richard Leacock’s film, November Actions, records some of these tumultuous events.)

    In the 1980s, there was more controversy at Massachusetts Institute of Technology (US) over its involvement in SDI (space weaponry) and CBW (chemical and biological warfare) research. More recently, Massachusetts Institute of Technology (US) ‘s research for the military has included work on robots, drones and ‘battle suits’.

    Recent history

    Massachusetts Institute of Technology (US) has kept pace with and helped to advance the digital age. In addition to developing the predecessors to modern computing and networking technologies, students, staff, and faculty members at Project MAC, the Artificial Intelligence Laboratory, and the Tech Model Railroad Club wrote some of the earliest interactive computer video games like Spacewar! and created much of modern hacker slang and culture. Several major computer-related organizations have originated at MIT since the 1980s: Richard Stallman’s GNU Project and the subsequent Free Software Foundation were founded in the mid-1980s at the AI Lab; the MIT Media Lab was founded in 1985 by Nicholas Negroponte and Jerome Wiesner to promote research into novel uses of computer technology; the World Wide Web Consortium standards organization was founded at the Laboratory for Computer Science in 1994 by Tim Berners-Lee; the MIT OpenCourseWare project has made course materials for over 2,000 Massachusetts Institute of Technology (US) classes available online free of charge since 2002; and the One Laptop per Child initiative to expand computer education and connectivity to children worldwide was launched in 2005.

    Massachusetts Institute of Technology (US) was named a sea-grant college in 1976 to support its programs in oceanography and marine sciences and was named a space-grant college in 1989 to support its aeronautics and astronautics programs. Despite diminishing government financial support over the past quarter century, MIT launched several successful development campaigns to significantly expand the campus: new dormitories and athletics buildings on west campus; the Tang Center for Management Education; several buildings in the northeast corner of campus supporting research into biology, brain and cognitive sciences, genomics, biotechnology, and cancer research; and a number of new “backlot” buildings on Vassar Street including the Stata Center. Construction on campus in the 2000s included expansions of the Media Lab, the Sloan School’s eastern campus, and graduate residences in the northwest. In 2006, President Hockfield launched the MIT Energy Research Council to investigate the interdisciplinary challenges posed by increasing global energy consumption.

    In 2001, inspired by the open source and open access movements, Massachusetts Institute of Technology (US) launched OpenCourseWare to make the lecture notes, problem sets, syllabi, exams, and lectures from the great majority of its courses available online for no charge, though without any formal accreditation for coursework completed. While the cost of supporting and hosting the project is high, OCW expanded in 2005 to include other universities as a part of the OpenCourseWare Consortium, which currently includes more than 250 academic institutions with content available in at least six languages. In 2011, Massachusetts Institute of Technology (US) announced it would offer formal certification (but not credits or degrees) to online participants completing coursework in its “MITx” program, for a modest fee. The “edX” online platform supporting MITx was initially developed in partnership with Harvard and its analogous “Harvardx” initiative. The courseware platform is open source, and other universities have already joined and added their own course content. In March 2009 the Massachusetts Institute of Technology (US) faculty adopted an open-access policy to make its scholarship publicly accessible online.

    Massachusetts Institute of Technology (US) has its own police force. Three days after the Boston Marathon bombing of April 2013, MIT Police patrol officer Sean Collier was fatally shot by the suspects Dzhokhar and Tamerlan Tsarnaev, setting off a violent manhunt that shut down the campus and much of the Boston metropolitan area for a day. One week later, Collier’s memorial service was attended by more than 10,000 people, in a ceremony hosted by the Massachusetts Institute of Technology (US) community with thousands of police officers from the New England region and Canada. On November 25, 2013, Massachusetts Institute of Technology (US) announced the creation of the Collier Medal, to be awarded annually to “an individual or group that embodies the character and qualities that Officer Collier exhibited as a member of the Massachusetts Institute of Technology (US) community and in all aspects of his life”. The announcement further stated that “Future recipients of the award will include those whose contributions exceed the boundaries of their profession, those who have contributed to building bridges across the community, and those who consistently and selflessly perform acts of kindness”.

    In September 2017, the school announced the creation of an artificial intelligence research lab called the MIT-IBM Watson AI Lab. IBM will spend $240 million over the next decade, and the lab will be staffed by MIT and IBM scientists. In October 2018 MIT announced that it would open a new Schwarzman College of Computing dedicated to the study of artificial intelligence, named after lead donor and The Blackstone Group CEO Stephen Schwarzman. The focus of the new college is to study not just AI, but interdisciplinary AI education, and how AI can be used in fields as diverse as history and biology. The cost of buildings and new faculty for the new college is expected to be $1 billion upon completion.

    The Caltech/MIT Advanced aLIGO (US) was designed and constructed by a team of scientists from California Institute of Technology (US), Massachusetts Institute of Technology (US) , and industrial contractors, and funded by the National Science Foundation (US) .

    MIT/Caltech Advanced aLigo .

    It was designed to open the field of gravitational-wave astronomy through the detection of gravitational waves predicted by general relativity. Gravitational waves were detected for the first time by the LIGO detector in 2015. For contributions to the LIGO detector and the observation of gravitational waves, two Caltech physicists, Kip Thorne and Barry Barish, and Massachusetts Institute of Technology (US) physicist Rainer Weiss won the Nobel Prize in physics in 2017. Weiss, who is also an Massachusetts Institute of Technology (US) graduate, designed the laser interferometric technique, which served as the essential blueprint for the LIGO.

    The mission of Massachusetts Institute of Technology (US) is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the Massachusetts Institute of Technology (US) community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

     
  • richardmitnick 10:28 am on February 11, 2021 Permalink | Reply
    Tags: , "Researchers gather numerical evidence of quantum chaos in the Sachdev-Ye-Kitaev model", , , , , Chaos in quantum systems composed of strongly interacting particles also known as “many-body chaos”, , , Quantum Gravity,   

    From UC Berkeley via phys.org: “Researchers gather numerical evidence of quantum chaos in the Sachdev-Ye-Kitaev model” 

    From UC Berkeley

    via


    phys.org

    February 11, 2021
    Ingrid Fadelli , Phys.org

    1
    A schematic phase diagram showing the behavior of the Sachdev-Ye-Kitaev model for different regimes of temperature and system size. From high to low temperature, the model transitions from behaving like interacting particles, to a semiclassical black hole, to a highly quantum black hole. Credit: Kobrin et al.

    Over the past few years, many physicists worldwide have conducted research investigating chaos in quantum systems composed of strongly interacting particles, also known as “many-body chaos”. The study of many-body chaos has broadened the current understanding of quantum thermalization (i.e., the process through which quantum particles reach thermal equilibrium by interacting with one another) and revealed surprising connections between microscopic physics and the dynamics of black holes.

    Researchers at University of California, Berkeley have recently carried out a study [Physical Review Letters] examining many-body chaos in the context of a renowned physical construct called the Sachdev-Ye-Kitaev (SYK) model. The SYK model describes a cluster of randomly interacting particles and was the first microscopic quantum system predicted to exhibit many-body chaos.

    “Our work is motivated by the fundamental question of how quickly information can spread in strongly-interacting quantum systems,” Bryce Kobrin, one of the researchers who carried out the study, told Phys.org. “A few years ago, a beautiful theoretical prediction emerged which suggested that in certain high-dimensional systems, information spreads exponentially fast, analogous to the butterfly effect in classical chaos.”

    In addition to hypothesizing this rapid spread of information in certain high-dimensional systems, previous studies proved that there is a universal speed limit on the rate at which this ‘chaos’ can develop. Interestingly, the only known or hypothesized systems that reach this limit are closely related to black holes, or more specifically, quantum theories that describe black holes. A major surprise was when researchers predicted that the SYK model also saturates the universal bound on chaos. This insight led to further analyses indicating that the low-temperature properties of the SYK model are, in effect, equivalent to that of a charged black hole.

    Although these ideas have been supported by theoretical calculations, verifying their validity and observing quantum chaos in numerical simulations has so far proved to be an enduring challenge. Kobrin and his colleagues set out to investigate the chaotic nature of the SYK model. They did this by simulating the dynamics of exceptionally large systems using cutting-edge numerical techniques they developed. Subsequently, they analyzed the data they collected using a method based on calculations from quantum gravity.

    “As a function of temperature, we observed the system change from behaving like ordinary interacting particles to agreeing precisely with the predicted behavior of a quantum black hole,” Kobrin said. “By developing new procedures to analyze our results, we determined the rate of chaos and explicitly showed that, at low temperatures, it approached the theoretical upper bound.”

    Kobrin and his colleagues gathered direct numerical evidence of a new dynamical phenomenon, namely many-body chaos, which translates chaos from classical mechanics to strongly interacting quantum systems. Their findings also highlight the valuable interplay between quantum simulations and quantum gravity theories.

    While in their recent study the researchers used the numerical tools that they created to examine many-body chaos in the SYK model in the future the same techniques could be applied to other models that are difficult to examine using common analysis frameworks. Ultimately, this could aid the ongoing search for quantum systems that exhibit the same behavior as black holes. Finally, the methods employed by this team of researchers could also inspire the development of experimental techniques to simulate quantum dynamics on controllable quantum hardware, for instance using arrays of cold atoms or trapped ions.

    “I am excited to investigate other phenomena at the intersection between quantum information and quantum gravity,” Kobrin said. “For example, it is predicted that by coupling together two copies of the SYK model, one can form a so-called traversable wormhole through which information can be communicated. This is a highly counterintuitive result which demonstrates that quantum chaos can, in fact, help move information from one place to another.”

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

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