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  • richardmitnick 5:50 pm on March 6, 2019 Permalink | Reply
    Tags: Black Holes, For an arbitrary process whose scrambling properties might not be known this method could be used to test whether—or even how much—it scrambles, If information is successfully teleported from one atom to another it means that the state of the first atom is spread out across all of the atoms, If the information was lost successful teleportation would not be possible, In terms of the difficulty of quantum algorithms that have been run we’re toward the top of that list, In the case of the new experiment Information seems lost but it’s actually still hidden in the correlations between the different particles, Information seems lost but it’s actually still hidden in the correlations between the different particles, it means that the state of the first atom is spread out across all of the atoms, , Quantum scrambling: a chaotic shuffling of the information stored among a collection of quantum particles, Researchers at the Joint Quantum Institute have implemented an experimental test for quantum scrambling, The final step relies on quantum teleportation—a method for transferring information between two quantum particles that are potentially very far apart, The protocol may one day help verify the calculations of quantum computers which harness the rules of quantum physics to process information in novel ways, the teleportation is over modest distances—just 35 microns separates the first atom from the seventh, This is a very complicated experiment to run and it takes a very high level of control, This is something that only happens if the information is scrambled   

    From Joint Quantum Institute: “Ion experiment aces quantum scrambling test” 

    JQI bloc

    From Joint Quantum Institute

    March 6, 2019
    Chris Cesare

    1
    Artist conception of information falling into a black hole. Researchers have implemented an experimental test for quantum scrambling, a chaotic shuffling of the information stored among a collection of quantum particles. The experiment was originally inspired by the physics of black holes. Quantum scrambling is one suggestion for how information can fall into a black hole and come out as random-looking radiation. Perhaps, the argument goes, it’s not random at all, and black holes are just excellent scramblers. (Credit E. Edwards/JQI)

    Researchers at the Joint Quantum Institute have implemented an experimental test for quantum scrambling, a chaotic shuffling of the information stored among a collection of quantum particles. Their experiments on a group of seven atomic ions, reported in the March 7 issue of Nature, demonstrate a new way to distinguish between scrambling—which maintains the amount of information in a quantum system but mixes it up—and true information loss. The protocol may one day help verify the calculations of quantum computers, which harness the rules of quantum physics to process information in novel ways.

    “In terms of the difficulty of quantum algorithms that have been run, we’re toward the top of that list,” says Kevin Landsman, a graduate student at JQI and the lead author of the new paper. “This is a very complicated experiment to run, and it takes a very high level of control.”

    The research team, which includes JQI Fellow and UMD Distinguished University Professor Christopher Monroe and JQI Fellow Norbert Linke, performed their scrambling tests by carefully manipulating the quantum behavior of seven charged atomic ions using well-timed sequences of laser pulses. They found that they could correctly diagnose whether information had been scrambled throughout a system of seven atoms with about 80% accuracy.

    “With scrambling, one particle’s information gets blended or spread out into the entire system,” Landsman says. “It seems lost, but it’s actually still hidden in the correlations between the different particles.”

    Quantum scrambling is a bit like shuffling a fresh deck of cards. The cards are initially ordered in a sequence, ace through king, and the suits come one after another. Once it’s sufficiently shuffled, the deck looks mixed up, but—crucially—there’s a way to reverse that process. If you kept meticulous track of how each shuffle exchanged the cards, it would be simple (though tedious) to “unshuffle” the deck by repeating all those exchanges and swaps in reverse.

    Quantum scrambling is similar in that it mixes up the information stored inside a set of atoms and can also be reversed, which is a key difference between scrambling and true, irreversible information loss. Landsman and colleagues used this fact to their advantage in the new test by scrambling up one set of atoms and performing a related scrambling operation on a second set. A mismatch between the two operations would indicate that the process was not scrambling, causing the final step of the method to fail.

    That final step relied on quantum teleportation—a method for transferring information between two quantum particles that are potentially very far apart. In the case of the new experiment, the teleportation is over modest distances—just 35 microns separates the first atom from the seventh—but it is the signature by which the team detects scrambling: If information is successfully teleported from one atom to another, it means that the state of the first atom is spread out across all of the atoms—something that only happens if the information is scrambled. If the information was lost, successful teleportation would not be possible. Thus, for an arbitrary process whose scrambling properties might not be known, this method could be used to test whether—or even how much—it scrambles.

    The authors say that prior tests for scrambling couldn’t quite capture the difference between information being hidden and lost, largely because individual atoms tend to look similar in both cases. The new protocol, first proposed by theorists Beni Yoshida of the Perimeter Institute in Canada, and Norman Yao at the University of California, Berkeley, distinguishes the two cases by taking correlations between particular particles into account in the form of teleportation.

    “When our colleague Norm Yao told us about this teleportation litmus test for scrambling and how it needed at least seven qubits capable of running many quantum operations in a sequence, we knew that our quantum computer was uniquely-suited for the job,” says Linke.

    The experiment was originally inspired by the physics of black holes. Scientists have long pondered what happens when something falls into a black hole, especially if that something is a quantum particle. The fundamental rules of quantum physics suggest that regardless of what a black hole does to a quantum particle, it should be reversible—a prediction that seems at odds with a black hole’s penchant for crushing things into an infinitely small point and spewing out radiation. But without a real black hole to throw things into, researchers have been stuck speculating.

    Quantum scrambling is one suggestion for how information can fall into a black hole and come out as random-looking radiation. Perhaps, the argument goes, it’s not random at all, and black holes are just excellent scramblers. The paper discusses this motivation, as well as an interpretation of the experiment that compares quantum teleportation to information going through a wormhole.

    “Regardless of whether real black holes are very good scramblers, studying quantum scrambling in the lab could provide useful insights for the future development of quantum computing or quantum simulation,” Monroe says.

    In addition to Landsman, Monroe and Linke, the new paper had four other coauthors: Caroline Figgatt, now at Honeywell in Colorado; Thomas Schuster at UC Berkeley; Beni Yoshida at the Perimeter Institute for Theoretical Physics; and Norman Yao at UC Berkeley and Lawrence Berkeley National Laboratory.

    See the full article here .


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    JQI supported by Gordon and Betty Moore Foundation

    We are on the verge of a new technological revolution as the strange and unique properties of quantum physics become relevant and exploitable in the context of information science and technology.

    The Joint Quantum Institute (JQI) is pursuing that goal through the work of leading quantum scientists from the Department of Physics of the University of Maryland (UMD), the National Institute of Standards and Technology (NIST) and the Laboratory for Physical Sciences (LPS). Each institution brings to JQI major experimental and theoretical research programs that are dedicated to the goals of controlling and exploiting quantum systems.

     
  • richardmitnick 3:07 pm on February 6, 2019 Permalink | Reply
    Tags: , , , Black Holes, , , , ,   

    From Niels Bohr Institute: “Catching a glimpse of the gamma-ray burst engine” 

    University of Copenhagen

    Niels Bohr Institute bloc

    From Niels Bohr Institute

    16 January 2019

    A gamma-ray burst registered in December of 2017 turns out to be “one of the closets GRBs ever observed”. The discovery is featured in Nature [co-authors are: Jonathan Selsing, Johan Fynbo, Jens Hjorth and Daniele Malesani from the Niels Bohr Institute, Giorgos Leloudas from the Technical University of Denmark and Kasper Heintz from University of Iceland] – and it has yielded valuable information about the formation of the most luminous phenomenon in the universe. Scientists from the Niels Bohr Institute at the University of Copenhagen helped carrying out the analysis.

    Jonatan Selsing frequently receives text messages from a certain sender regarding events in space. It happens all around the clock, and when his cell phone goes ‘beep’ he knows that yet another gamma-ray burst (GRB) notification has arrived. Which, routinely, raises the question: Does this information – originating from the death of a massive star way back, millions if not billions of years ago – merit further investigation?

    1
    The development in a dying star until the gamma ray burst forms. Attribution: National Science Foundation

    Gamma ray bursts – bright signals from space

    “GRBs represent the brightest phenomenon known to science – the luminous intensity of a single GRB may in fact exceed that of all stars combined! And at the same time GRBs – which typically last just a couple of seconds – represent one of the best sources available, when it comes to gleaning information about the initial stages of our universe”, explains Jonatan Selsing.

    He is astronomer and postdoc at Cosmic Dawn Center at the Niels Bohr Institute in Copenhagen. And he is one of roughly 100 astronomers in a global network set up to ensure that all observational resources needed can be instantaneously mobilized when the GRB-alarm goes off.

    Quick action must be taken when a gamma ray burst is registered

    The alarm sits on board the international Swift-telescope which was launched in 2004 – and has orbited Earth ever since with the mission of registering GRBs.

    NASA Neil Gehrels Swift Observatory

    Swift is capable of constantly observing one third of the night sky, and when the telescope registers a GRB – which on average happens a couple of times per week – it will immediately text the 100 astronomers. The message will tell where in space the GRB has been observed – whereupon the astronomer on duty must make a here-and-now decision:

    Is there reason to assume that this specific GRB is of such importance that we should ask the VLT-telescope in Chile to immediately take a closer look at it?

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    Or should we consider the information from Swift sheer routine, and leave it at that?

    On December 5th 2017 – just around 09 o’clock in the morning Copenhagen time – the GRB-alarm went off. Luca Izzo, Italian astronomer, was on duty – and Izzo did not harbor the slightest doubt: He right away alerted VLT – the Very Large Telescope in Chile – which is run by 11 European countries, including Germany, Great Britain, Italy, France, Sweden and Denmark.

    At that time it was early in the morning in Chile – 05 o’clock – and dawn was rapidly approaching, tells Jonatan Selsing: “For VLT to take a closer look at the GRB, action had to be taken immediately – since the telescope is only capable of working against a background of the night sky. And fortunately this was exactly what happened, when Izzo contacted VLT”.

    This is also why Luca Izzo is listed as first author of the scientific article describing this GRB – an article which has just been published in Nature, one of the world’s most influential scientific journals. The article is based on analyses of the VLT-recordings, and the recordings reveal that this GRB in more than one respect can be described as unusual, says Jonatan Selsing:

    “Not least because this is one of the closest GRBs ever observed. GRB171205A – which has since become the official name of this gamma-ray burst – originated a mere 500 million years ago, and has ever since traveled through space at the speed of light, i.e. at 300.000 kilometer per second”. Working closely with a number of his colleagues at the Niels Bohr Institute, Jonatan Selsing contributed to the Nature-article with an analysis which – put simply – represents “a glimpse” of the very engine behind a gamma-ray burst.

    Gamma ray bursts are the results of violent events in space

    When a massive star – rotating at very high speed – dies, its core may collapse, thus creating a so-called black hole.

    This computer-simulated image of a supermassive black hole at the core of a galaxy. Credit NASA, ESA, and D. Coe, J. Anderson

    A massive star may weigh up to 300 times more than the Sun, and due to combustion the star is transforming light elements to heavier elements. This process, which takes place in the core, is the source of energy not only in massive stars, but in all stars.

    Ashes – the by-product of combustion – may over time become such a heavy load that a massive star can no longer carry its own weight, which is why it finally collapses. When that happens, the outer layers will gradually fall towards the core – towards the black hole – at which point a disc is formed.

    Due to the star’s rotation, the disc will function as a dynamo creating a gigantic magnetic field – which will emit two jets, both going away from the black hole at a velocity close to the speed of light. During this process, the dying star is also releasing – spewing – matter, which lightens up with extreme intensity.
    This light is the very gamma-ray burst – the GRB itself. And the matter which is released from the center of the star is set free in the form of a so-called jet cocoon.

    The gamma ray burst confirms our assumptions about the elements stars produce

    “One of the unique features of GRB171205A is that it proved possible to determine which elements this gamma-ray burst released via the jet cocoon 500 million years ago. That was measured here at the Niels Bohr Institute, and that is our contribution to the Nature-article. These measurements were carried out via X-shooter – an extremely sensitive piece of equipment mounted on the VLT-telescope”, says Jonatan Selsing.

    X-shooter analyzed the VLT-footage of the gamma-ray burst – and this analysis led to the conclusion that the jet cocoon from GRB171205A contained iron, cobalt and nickel which had formed in the center of the star, explains Jonatan Selsing:

    “This corresponds with our theoretical expectations – and therefore also corroborates our model for a star-collapse of this magnitude. Being able to establish that it actually did happen in this way is, however, really special. That’s when you get a glimpse of the very engine behind a gamma-ray burst”.

    ESO X-shooter on VLT on UT2 at Cerro Paranal, Chile


    ESO X-shooter on VLT on UT2 at Cerro Paranal, Chile

    See the full article here .


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    Niels Bohr Institute Campus

    The Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

    The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

    The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient

     
  • richardmitnick 2:25 pm on January 22, 2019 Permalink | Reply
    Tags: , , , Black Holes, , , Sagittarius A*   

    From Harvard-Smithsonian Center for Astrophysics: “Lifting the Veil on the Black Hole at the Heart of Our Galaxy” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    January 22, 2019

    Tyler Jump
    Public Affairs
    Center for Astrophysics | Harvard & Smithsonian
    +1 617-495-7462
    tyler.jump@cfa.harvard.edu

    1

    A black hole four million times as massive as our Sun lurks at the center of the Milky Way. This black hole, called Sagittarius A* (Sgr A*), swallows nearby material that glows brightly as it approaches the event horizon.

    SGR A and SGR A* from Penn State and NASA/Chandra

    This galactic furnace is key to understanding black holes, but our view of it is obscured by lumpy clouds of electrons throughout the Galaxy. These clouds stretch, blur, and crinkle the image of Sgr A*, making it appear as though the black hole is blocked by an enormous sheet of frosted glass.

    Now, a team of astronomers, led by Radboud University PhD student Sara Issaoun, have finally been able to see through these clouds and to study what makes the black hole glow. Issaoun completed this work while participating in the Predoctoral Program at the Smithsonian Astrophysical Observatory in Cambridge, MA.

    “The source of the radiation from Sgr A* has been debated for decades,” says Michael Johnson of the Center for Astrophysics | Harvard and Smithsonian (CfA). “Some models predict that the radiation comes from the disk of material being swallowed by the black hole, while others attribute it to a jet of material shooting away from the black hole. Without a sharper view of the black hole, we can’t exclude either possibility.”

    The team used the technique of Very Long Baseline Interferometry (VLBI), which combines many telescopes to form a virtual telescope the size of the Earth. The decisive advance was equipping the powerful ALMA array of telescopes in northern Chile with a new phasing system. This allowed it to join the GMVA, a global network of twelve other telescopes in North America and Europe.

    GMVA The Global VLBI Array

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    “ALMA itself is a collection of more than 50 radio dishes. The magic of the new ALMA Phasing System is to allow all these dishes to function as a single telescope, which has the sensitivity of a single dish more than 75 meters across. That sensitivity, and its location high in the Andes mountains, makes it perfect for this Sgr A* study,” says Shep Doeleman of the CfA, who was Principal Investigator of the ALMA Phasing Project.

    “The breakthrough in image quality came from two factors,” explains Lindy Blackburn, a radio astronomer at the CfA. “By observing at high frequencies, the image corruption from interstellar material was less significant, and by adding ALMA, we doubled the resolving power of our instrument.”

    The new images show that the radiation from Sgr A* has a symmetrical morphology and is smaller than expected – it spans a mere 300 millionth of a degree. “This may indicate that the radio emission is produced in a disk of infalling gas rather than by a radio jet,” explains Issaoun, who tested computer simulations against the images. “However, that would make Sgr A* an exception compared to other radio-emitting black holes. The alternative could be that the radio jet is pointing almost directly at us.”

    Issaoun’s supervisor Heino Falcke, Professor of Radio Astronomy at Radboud University, was surprised by this result. Last year, Falcke would have considered this new jet model implausible, but recently another set of researchers came to a similar conclusion using ESO’s Very Large Telescope Interferometer of optical telescopes and an independent technique. “Maybe this is true after all,” concludes Falcke, “and we are looking at this beast from a very special vantage point.”

    To learn more will require pushing these telescopes to even higher frequencies. “The first observations of Sgr A* at 86 GHz date from 26 years ago, with only a handful of telescopes. Over the years, the quality of the data has improved steadily as more telescopes join,” says J. Anton Zensus, director of the Max Planck Institute for Radio Astronomy.

    Michael Johnson is optimistic. “If ALMA has the same success in joining the Event Horizon Telescope at even higher frequencies, then these new results show that interstellar scattering will not stop us from peering all the way down to the event horizon of the black hole.”

    The results were published in The Astrophysical Journal.

    See the full article here .

    See also here.


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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 11:44 am on January 21, 2019 Permalink | Reply
    Tags: A huge flare from a black hole helps reveal how matter and energy are expelled, , , “Light echoes” — time lags between the x-ray light coming from two different areas around the black hole, , Black Holes, , , MAXI J1820+070,   

    From Scientific American: “Erupting Black Hole Shows Intriguing ‘Light Echoes'” 

    Scientific American

    From Scientific American

    Jan 11, 2019
    Clara Moskowitz

    1
    A black hole called MAXI J1820+070 emitted a huge flare of X-ray light that astronomers monitored over time to study how black holes swallow and spit out matter. Photo: NASA’s Goddard Space Flight Center.

    A huge flare from a black hole helps reveal how matter and energy are expelled

    We tend to think black holes gobble up all the matter around them — but they can actually spew out as much as they suck in. And sometimes they seem to go downright crazy.

    Astronomers recently spotted one black hole, nearly 10,000 light-years from Earth, belching out an enormous explosion of x-ray light. Measurements of this tantrum have given scientists one of the clearest pictures yet of what happens when black holes erupt with energy. “One of our big questions is how do we go from this process of material flowing into the black hole to this process of flowing out?” says astronomer Erin Kara of the University of Maryland, College Park, lead author of a paper on the findings, published this week in Nature. “We know this is happening but we don’t understand how it works in detail.” Kara presented the discovery Wednesday at the American Astronomical Society’s annual meeting in Seattle.

    The outburst began on March 11, 2018, and quickly transformed a black hole that had been totally invisible to telescopes into one of the brightest objects (in terms of x-ray light) in the entire sky. The object, called MAXI J1820+070, was first spotted by the Monitor of All-sky X-ray Image (MAXI) experiment on the International Space Station. Another observatory on the station, the Neutron star Interior Composition Explorer (NICER), monitored the flare with near-daily observations over the next few months.

    JAXA MAXI on the ISS

    NASA/NICER on the ISS

    Not only did astronomers measure the black hole brightening extremely over this time, they also observed what they called “light echoes” — time lags between the x-ray light coming from two different areas around the black hole. Some light travels straight from a region called the corona, made of electrons and other charged particles close in to the black hole. Farther out and perpendicular to the corona is the “accretion disk” — a wider pancake of gas swirling around the hole and falling into it. Other light comes out of the corona and bounces off this disk, arriving at the NICER detectors later. As NICER watched the eruption, the time between echoes became shorter and shorter, indicating the distance between the disk and corona was shrinking. The scientists had evidence the boundaries of the disk were not changing, so they concluded the corona itself must be getting shorter and thus light did not have to travel so far to reach the disk. “This is the clearest detection to date of these light echoes off of the gas falling into a stellar-mass black hole in our own galaxy,” says Dan Wilkins, an astrophysicist at Stanford University who was not involved in the study. “Being able to detect a change in the time delays between the echoes over the course of the outburst means we can start to learn about what is happening around the black hole.”

    2
    This illustration shows X-rays from the black hole’s corona (blue) echoing off its accretion disk (orange). Timing these echoes helped scientists determine that the corona was shrinking over time. Photo: NASA’s Goddard Space Flight Center

    Zeroing in on the corona is especially helpful because scientists think this region is likely the base from which powerful beams of particles and light, called relativistic jets, are launched. These jets travel close to light-speed and can be spotted coming from black holes across the universe. “The big fun of this paper, from my point of view, is that we really can ‘see’ the corona shrinking during the evolution of the outburst,” says Stephen Eikenberry of the University of Florida, a co-author on the new paper. “I don’t know of any real theoretical prediction for this ‘shrinkage’ nor of any prior observation of it, so this result will already require overhauling of the theories we have for jet formation.”

    The black hole in this study holds about 10 times the mass of the sun. The new observations should help astronomers understand not just star-size black holes like this one but also the gargantuan “supermassive” black holes that are located at the centers of galaxies and contain millions of times more mass. “These stellar-mass systems are a convenient analogue for supermassive black holes,” Kara says. “They have similar components, but we see outbursts over several weeks and months whereas for supermassive black holes it’s years.” The new findings support one theory for how supermassive black hole coronas are structured — called the “lamppost model” — which posits coronas are lightbulb-shaped blobs above and below the black hole, as opposed to diffuse clouds. “These new observations are exactly in line with the lamppost model,” Wilkins says. “Indeed, we observed very similar behavior during flares from supermassive black holes, seeing a change in the size of the corona.”

    Astronomers hope NICER, which launched in June 2017, and other new observatories will observe many more outbursts in the future and help fill in the missing details of erupting black holes. “It’s a really exciting time to be doing this,” says Joey Neilsen, a physicist at Villanova University and a co-author of the new paper. “We’re getting to a point where the observations are actually ahead of the theory. New missions are allowing us to see things that we hadn’t necessarily thought of before.”

    See the full article here .


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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 10:44 am on January 21, 2019 Permalink | Reply
    Tags: , , , Black Holes, , , , , ,   

    Weizmann Institute of Science via Science Alert: “We Just Got Lab-Made Evidence of Stephen Hawking’s Greatest Prediction About Black Holes” 

    Weizmann Institute of Science logo

    Weizmann Institute of Science

    via

    ScienceAlert

    Science Alert

    21 JAN 2019
    MICHELLE STARR

    Scientists may have just taken a step towards experimentally proving the existence of Hawking radiation. Using an optical fibre analogue of an event horizon – a lab-created model of black hole physics – researchers from Weizmann Institute of Science in Rehovot, Israel report that they have created stimulated Hawking radiation.

    Under general relativity, a black hole is inescapable. Once something travels beyond the event horizon into the heart of the black hole, there’s no return. So intense is the gravitational force of a black hole that not even light – the fastest thing in the Universe – can achieve escape velocity.

    Under general relativity, therefore, a black hole emits no electromagnetic radiation. But, as a young Stephen Hawking theorised in 1974, it does emit something when you add quantum mechanics to the mix.

    This theoretical electromagnetic radiation is called Hawking radiation; it resembles black body radiation, produced by the temperature of the black hole, which is inversely proportional to its mass (watch the video below to get a grasp of this neat concept).

    This radiation would mean that black holes are extremely slowly and steadily evaporating, but according to the maths, this radiation is too faint to be detectable by our current instruments.

    So, cue trying to recreate it in a lab using black hole analogues. These can be built from things that produce waves, such as fluid and sound waves in a special tank, from Bose-Einstein condensates, or from light contained in optical fibre.

    “Hawking radiation is a much more general phenomenon than originally thought,” explained physicist Ulf Leonhardt to Physics World. “It can happen whenever event horizons are made, be it in astrophysics or for light in optical materials, water waves or ultracold atoms.”

    These won’t, obviously, reproduce the gravitational effects of a black hole (a good thing for, well, us existing), but the mathematics involved is analogous to the mathematics that describe black holes under general relativity.

    This time, the team’s method of choice was an optical fibre system developed by Leonhardt some years ago.

    The optical fibre has micro-patterns on the inside, and acts as a conduit. When entering the fibre, light slows down just a tiny bit. To create an event horizon analogue, two differently coloured ultrafast pulses of laser light are sent down the fibre. The first interferes with the second, resulting in an event horizon effect, observable as changes in the refractive index of the fibre.

    The team then used an additional light on this system, which resulted in an increase in radiation with a negative frequency. In other words, ‘negative’ light was drawing energy from the ‘event horizon’ – an indication of stimulated Hawking radiation.

    While the findings were undoubtedly cool, the end goal for such research is to observe spontaneous Hawking radiation.

    Stimulated emission is exactly what it sounds like – emission that requires an external electromagnetic stimulus. Meanwhile the Hawking radiation emanating from a black hole would be of the spontaneous variety, not stimulated.

    There are other problems with stimulated Hawking radiation experiments; namely, they are rarely unambiguous, since it’s impossible to precisely recreate in the lab the conditions around an event horizon.

    With this experiment, for example, it’s difficult to be 100 percent certain that the emission wasn’t created by an amplification of normal radiation, although Leonhardt and his team are confident that their experiment did actually produce Hawking radiation.

    Either way, it’s a fascinating achievement and has landed another mystery in the team’s hands, too – they found the result was not quite as they expected.

    “Our numerical calculations predict a much stronger Hawking light than we have seen,” Leonhardt told Physics World.

    “We plan to investigate this next. But we are open to surprises and will remain our own worst critics.”

    The research has been published in the journal Physical Review Letters.

    See the full article here .

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    Weizmann Institute Campus

    The Weizmann Institute of Science is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

    Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

    The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

     
  • richardmitnick 3:04 pm on January 9, 2019 Permalink | Reply
    Tags: , , , Black Holes, , , , The findings are the first evidence that the corona shrinks as a black hole feeds or accretes   

    From MIT News: “Astronomers observe evolution of a black hole as it wolfs down stellar…” 

    MIT News
    MIT Widget

    From MIT News

    January 9, 2019
    Jennifer Chu

    1
    X-ray echoes, mapped by NASA’s Neutron star Interior Composition Explorer (NICER), revealed changes to the accretion disk and corona of black hole MAXI J1820+070.
    Image: NASA’s Goddard Space Flight Center

    NASA/NICER

    …Halo of highly energized electrons around the black hole contracts dramatically during feeding frenzy.

    On March 11, an instrument aboard the International Space Station detected an enormous explosion of X-ray light that grew to be six times as bright as the Crab Nebula, nearly 10,000 light years away from Earth. Scientists determined the source was a black hole caught in the midst of an outburst — an extreme phase in which a black hole can spew brilliant bursts of X-ray energy as it devours an avalanche of gas and dust from a nearby star.

    Now astronomers from MIT and elsewhere have detected “echoes” within this burst of X-ray emissions, that they believe could be a clue to how black holes evolve during an outburst. In a study published today in the journal Nature, the team reports evidence that as the black hole consumes enormous amounts of stellar material, its corona — the halo of highly-energized electrons that surrounds a black hole — significantly shrinks, from an initial expanse of about 100 kilometers (about the width of Massachusetts) to a mere 10 kilometers, in just over a month.

    The findings are the first evidence that the corona shrinks as a black hole feeds, or accretes. The results also suggest that it is the corona that drives a black hole’s evolution during the most extreme phase of its outburst.

    “This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution,” says Jack Steiner, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself.”

    Steiner’s MIT co-authors include Ronald Remillard and first author Erin Kara.

    X-ray echoes

    The black hole detected on March 11 was named MAXI J1820+070, for the instrument that detected it. The Monitor of All-sky X-ray Image (MAXI) mission is a set of X-ray detectors installed in the Japanese Experiment Module of the International Space Station (ISS), that monitors the entire sky for X-ray outbursts and flares.

    Soon after the instrument picked up the black hole’s outburst, Steiner and his colleagues started observing the event with NASA’s Neutron star Interior Composition Explorer, or NICER, another instrument aboard the ISS, which was designed partly by MIT, to measure the amount and timing of incoming X-ray photons.

    “This boomingly bright black hole came on the scene, and it was almost completely unobscured, so we got a very pristine view of what was going on,” Steiner says.

    A typical outburst can occur when a black hole sucks away enormous amounts of material from a nearby star. This material accumulates around the black hole, in a swirling vortex known as an accretion disk, which can span millions of miles across. Material in the disk that is closer to the center of the black hole spins faster, generating friction that heats up the disk.

    “The gas in the center is millions of degrees in temperature,” Steiner says. “When you heat something that hot, it shines out as X-rays. This disk can undergo avalanches and pour its gas down onto the central black hole at about a Mount Everest’s worth of gas per second. And that’s when it goes into outburst, which usually lasts about a year.”

    Scientists have previously observed that X-ray photons emitted by the accretion disk can ping-pong off high-energy electrons in a black hole’s corona. Steiner says some of these photons can scatter “out to infinity,” while others scatter back onto the accretion disk as higher-energy X-rays.

    By using NICER, the team was able to collect extremely precise measurements of both the energy and timing of X-ray photons throughout the black hole’s outburst. Crucially, they picked up “echoes,” or lags between low-energy photons (those that may have initially been emitted by the accretion disk) and high-energy photons (the X-rays that likely had interacted with the corona’s electrons). Over the course of a month, the researchers observed that the length of these lags decreased significantly, indicating that the distance between the corona and the accretion disk was also shrinking. But was it the disk or the corona that was shifting in?

    To answer this, the researchers measured a signature that astronomers know as the “iron line” — a feature that is emitted by the iron atoms in an accretion disk only when they are energized, such as by the reflection of X-ray photons off a corona’s electrons. Iron, therefore, can measure the inner boundary of an accretion disk.

    When the researchers measured the iron line throughout the outburst, they found no measurable change, suggesting that the disk itself was not shifting in shape, but remaining relatively stable. Together with the evidence of a diminishing X-ray lag, they concluded that it must be the corona that was changing, and shrinking as a result of the black hole’s outburst.

    “We see that the corona starts off as this bloated, 100-kilometer blob inside the inner accretion disk, then shrinks down to something like 10 kilometers, over about a month,” Steiner says. “This is the first unambiguous case of a corona shrinking while the disk is stable.”

    “NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before,” Kara adds. “Previously these light echoes off the inner accretion disk were only seen in supermassive black holes, which are millions to billions of solar masses and evolve over millions of years. Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human time scales.”

    While it’s unclear what is exactly causing the corona to contract, Steiner speculates that the cloud of high-energy electrons is being squeezed by the overwhelming pressure generated by the accretion disk’s in-falling avalanche of gas.

    The findings offer new insights into an important phase of a black hole’s outburst, known as a transition from a hard to a soft state. Scientists have known that at some point early on in an outburst, a black hole shifts from a “hard” phase that is dominated by the corona’s energy, to a “soft” phase that is ruled more by the accretion disk’s emissions.

    “This transition marks a fundamental change in a black hole’s mode of accretion,” Steiner says. “But we don’t know exactly what’s going on. How does a black hole transition from being dominated by a corona to its disk? Does the disk move in and take over, or does the corona change and dissipate in some way? This is something people have been trying to unravel for decades And now this is a definitive piece of work in regards to what’s happening in this transition phase, and that what’s changing is the corona.”

    This research is supported, in part, by NASA through the NICER mission and the Astrophysics Explorers Program.

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

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    The mission of MIT 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 MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:22 pm on December 17, 2018 Permalink | Reply
    Tags: Black Holes, Black holes expand by increasing in complexity inwardly – a feature we just don't see connected while watching from afar, , Why Don't Black Holes Swallow All of Space? This Explanation Is Blowing Our Minds   

    From Science Alert: “Why Don’t Black Holes Swallow All of Space? This Explanation Is Blowing Our Minds” 

    ScienceAlert

    From Science Alert

    16 DEC 2018
    MIKE MCRAE

    1
    (GM Stock Films/istock)

    Black holes are great at sucking up matter. So great, in fact, that not even light can escape their grasp (hence the name).

    But given their talent for consumption, why don’t black holes just keep expanding and expanding and simply swallow the Universe? Now, one of the world’s top physicists has come up with a new explanation.

    Conveniently, the idea could also unite the two biggest theories in all of physics.

    The researcher behind this latest explanation is none other than Stanford University physicist Leonard Susskind, also known as one of the fathers of string theory.

    Leonard Susskind by Linda Cicero-Stanford News Service

    He recently gave his two cents on the paradox in a series of papers, which basically suggest that black holes expand by increasing in complexity inwardly – a feature we just don’t see connected while watching from afar.

    In other words, they expand in, not out.

    Weirder still, this hypothesis might have a parallel in the expansion of our own Universe, which also seems to be growing in a counterintuitive way.

    “I think it’s a very, very interesting question whether the cosmological growth of space is connected to the growth of some kind of complexity,” Susskind was quoted in The Atlantic.

    “And whether the cosmic clock, the evolution of the universe, is connected with the evolution of complexity. There, I don’t know the answer.”

    Susskind might be speculating on the Universe’s evolution, but his thoughts on why black holes grow in more than they do out is worth unpacking.

    To be clear though, for now this work has only been published on the pre-print site arXiv.org, so it’s yet to be peer reviewed. That means we need to take it with a big grain of salt for now. On top of that, this type of research is, by its very nature, theoretical.

    But there are some pretty cool idea in here worth unpacking. To do that, we need to go back to basics for a moment. So … hang tight.

    For the uninitiated, black holes are dense masses that distort space to the extent that even light (read: information) lacks the escape velocity required to make an exit.

    The first solid theoretical underpinnings for such an object emerged naturally out of the mathematics behind Einstein’s general relativity back in 1915. Since then physical objects matching those predictions have been spotted, often hanging around the centre of galaxies.

    A common analogy is to imagine the dimensions of space plus time as a smooth rubber sheet. Much as a heavy object dimples the rubber sheet, mass distorts the geometry of spacetime.

    The properties of our Universe’s rubber sheet means it can form deep gravity funnel that stretches ‘down’ without stretching much further ‘out’.

    Most objects expand ‘out’ as you add material, not ‘in’. So how do we even begin to picture this? Rubber sheets are useful analogies, but only up to a certain point.

    To understand how matter behaves against this super stretchy backdrop, we need to look elsewhere. Luckily physics has a second rulebook on ‘How the Universe Works’ called quantum mechanics, which describes how particles and their forces interact.

    The two rule books of GR and QM don’t always agree, though. Small things interpreted through the lens of general relativity don’t make much sense. And big things like black holes produce gibberish when the rules of quantum mechanics are applied.

    This means we’re missing something important – something that would allow us to interpret general relativity’s space-bending feature in terms of finite masses and force-mediating particles.

    One contender is something called anti-de Sitter/conformal field theory correspondence, which is shortened to Ads/CFT. This is a ‘string theory meets four dimensional space’ kind of idea, aiming to bring the best of both quantum mechanics and general relativity together.

    Based on its framework, the quantum complexity of a black hole – the number of steps required to return it to a pre-black hole state – is reflected in its volume. The same thinking is what lies behind another brain-breaking idea called the holographic principle.

    The exact details aren’t for the faint hearted, but are freely available on arXiv.org if you want to get your mathematics fix for the day.

    It might sound a bit like downloading movies onto your desktop only to find it’s now ‘bigger’ on the inside. As ludicrous as it sounds, in the extreme environment of a black hole more computational power might indeed mean more internal volume. At least this is what Susskind’s Ads/CFT modelling suggests.

    String theory itself is one of those nice ideas begging for an empirical win, so we’re still a long way from marrying quantum mechanics and general relativity.

    Susskind’s suggestion that quantum complexity is ultimately responsible for the volume of a black hole has physicists thinking through the repercussions. After all, black holes aren’t like ordinary space, so we can’t expect ordinary rules to apply.

    But if anybody is worth listening to on the subject, it’s probably this guy.

    This research is available on arXiv.org.

    See the full article here .


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  • richardmitnick 11:12 am on November 23, 2018 Permalink | Reply
    Tags: , , , Black Holes, Black holes: from absurd idea to fact of nature, , Sir Arthur Eddington publicly ridiculed Chandrasekhar in an infamous encounter at the Royal Astronomical Society in 1935, , , Yet history proved Eddington wrong   

    From COSMOS Magazine: “Black holes: from absurd idea to fact of nature” Subrahmanyan Chandrasekhar 

    Cosmos Magazine bloc

    From COSMOS Magazine

    22 November 2018
    Paul Davies

    1
    Subrahmanyan Chandrasekhar meets the press in 1983, shortly after winning the Nobel Prize.
    Bettmann / Contributor / Getty Images

    2
    Credit Mark Garlick / Science Photo Library

    In 1930 a 20-year-old Indian student named Subrahmanyan Chandrasekhar was sailing from Madras to England to pursue his studies in astrophysics. During the voyage he toyed with equations describing the stability of stars. And from a few lines of this mathematics, a momentous discovery emerged.

    Astronomers of the day had only a sketchy understanding of what makes stars tick. They knew that a star is a ball of hot gas engaging in a cosmic balancing act. The gas tries to expand out into the vacuum of the surrounding space but gravity holds it back. In stars like the sun, an equilibrium is achieved, but only as long as the gas burns fuel to generate heat, which we now know is produced by nuclear reactions in the core.

    However, uncertainty surrounded the question of what happens when the fuel runs out. It seemed that gravity would inevitably gain the upper hand, causing the star to contract, and the smaller the radius, the fiercer the gravitational force would become at the surface. Astronomers had long been familiar with tiny stars known as white dwarfs, which contain a mass comparable to the sun but squashed into a volume roughly the size of the Earth. These burned-out stellar remnants are so dense that their atoms are pressed cheek by jowl. Further compression would mean the atoms themselves would be crushed, which was initially assumed to be impossible due to the laws of quantum physics.

    From his nautical calculations Chandrasekhar discovered otherwise. The equations suggested that if a star has a big enough mass, the crushing effect of its immense gravity would cause the atomic electrons to approach the speed of light, rendering the stellar material more squishy and heralding the further gravitational collapse of the star. In the absence of any other factor, the ball of matter would implode totally and vanish down its own gravitational well, forming an object that today we call a black hole. But in the early 1930s such an object was considered too outlandish to take seriously.

    Chandrasekhar was able to calculate the critical mass above which this gravitational instability would set in. The answer he obtained was 1.44 solar masses, now known as the Chandrasekhar limit. On reaching England, he announced his result, only to find it was ignored or dismissed as nonsense from a young upstart. The most distinguished astronomer of the day, Sir Arthur Eddington, publicly ridiculed Chandrasekhar in an infamous encounter at the Royal Astronomical Society in 1935, declaring that there should be a law of nature “to prevent a star from behaving in this absurd way!”

    Yet history proved Eddington wrong. If a burned-out star has a mass exceeding Chandrasekhar’s limit, it does indeed collapse. One possible fate is to form a so-called neutron star, in which the atoms are crushed into neutrons and the object stabilises at a radius about the size of Sydney. Neutron stars were discovered in the 1960s and today form an important branch of astronomy. Most of them have masses not far from the Chandrasekhar limit. More massive stars end their days by totally collapsing. When they shrink to a few kilometres across, their gravity is so great that even light cannot escape, and a black hole results.

    Although it took decades for the concept of a black hole to be fully understood and accepted, the basic idea was hiding in plain sight since just after Albert Einstein first published his general theory of relativity in 1915. Chandrasekhar acknowledged this in his 1983 Nobel Prize address, where he wrote: “This important result is implicit in a fundamental paper by Karl Schwarzschild published in 1916”. Although the theoretical possibility of a black hole was inherent all along in Einstein’s theory, it took the youthful genius of Chandrasekhar to prove that such an object could result from the transformation of a dying star.

    By the time of the Prize, the existence of black holes had become firmly established, and Subrahmanyan Chandrasekhar’s calculations fully vindicated. Yet he was so stung by Eddington’s derision, he decided to leave the UK in 1937 and settle in the US, where he followed a distinguished career until his death in 1995.

    Chandrasekhar died leaving open a fascinating question. Might there exist an intermediate state between a neutron star and a black hole? This would be an object above 1.44 solar masses, too heavy to form a neutron star, but prevented from total collapse by an exotic form of ultra-dense matter such as a soup of quarks – the constituents of protons and neutrons. To date nobody has discovered a quark star, but the notion remains a theoretical possibility, perhaps awaiting the attention of another student genius with the insight to settle the matter.

    See the full article here .


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    Please help promote STEM in your local schools.

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  • richardmitnick 7:35 am on November 2, 2018 Permalink | Reply
    Tags: "Hotspot discovery proves Waterloo astrophysicist’s black hole theory", , , , Black Holes, , ,   

    From University of Waterloo: “Hotspot discovery proves Waterloo astrophysicist’s black hole theory” 

    U Waterloo bloc

    From University of Waterloo

    October 31, 2018

    The recent detection of flares circling black holes has proven a decade-old theory – co-developed by Waterloo physicist Avery Broderick – about how black holes grow and consume matter.

    “It’s extremely exciting to see our theoretical musing come to life and that tracking these types of flares about black holes is possible,” said Avery Broderick, an Associate Faculty member at the University of Waterloo and Perimeter Institute, who predicted the flares 13 years ago with collaborator Avi Loeb.

    Recently, a discovery by the GRAVITY Collaboration has detailed the detection of three flares — visual hotspots — emanating from a black hole known as Sagittarius A*, or Sgr A*, which sits at the centre of the Milky Way.

    ESO VLTI GRAVITY

    Astronomy & Astrophysics

    Sgr A* from ESO VLT


    SgrA* NASA/Chandra


    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    The team detected a wobble of emissions coming from the flares, enabling the scientists to detect the growing orbit, known as an accretion disk, of the black hole itself.

    The idea of using the emissions from visual hotspots to map the behaviour of black holes was first suggested by Broderick and Loeb in 2005 when both were working at the Harvard-Smithsonian Center for Astrophysics.

    The pair’s 2005 [MNRAS] paper and a 2006
    [Journal of Physics: Conference Series] follow-up paper outlined computer models and highlighted their proposal that the flares were being caused by the confluence of two extreme events: the bending of light around the black hole and the generation of hot spots by magnetic reconfigurations (known as magnetic reconnection) which accelerated charged particles to relativistic speeds around Sgr A*. They showed how the hotspots could be used as visual probes to trace out structures in the accretion disk and spacetime itself.

    “Black holes are gravitational masters of their domain, and anything that drifts too close will be blended into a superheated disk of plasma surrounding them,” said Broderick. “The matter trapped in the black hole’s growing retinue then flows towards the event horizon — the point at which no light can escape — and consumed by the black hold via mechanisms that aren’t yet fully understood.

    The study, published today in Astronomy and Astrophysics, detected the flares emanating from Sgr A* earlier this year on the European Southern Observatory’s Very Large Telescope in Chile.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    While the hotspots couldn’t be fully revolved using the telescope, the GRAVITY Collaboration recognized the wobble of emission from the flares as the associated hotspots orbited the supermassive black hole.

    “The lives of black holes have become substantially more clear today. My hope is that the same features seen by GRAVITY will be imaged in the near future, allowing us to unlock the nature of gravity. I’m optimistic that we won’t have long to wait,” said Broderick.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Waterloo campus

    In just half a century, the University of Waterloo, located at the heart of Canada’s technology hub, has become a leading comprehensive university with nearly 36,000 full- and part-time students in undergraduate and graduate programs.

    Consistently ranked Canada’s most innovative university, Waterloo is home to advanced research and teaching in science and engineering, mathematics and computer science, health, environment, arts and social sciences. From quantum computing and nanotechnology to clinical psychology and health sciences research, Waterloo brings ideas and brilliant minds together, inspiring innovations with real impact today and in the future.

    As home to the world’s largest post-secondary co-operative education program, Waterloo embraces its connections to the world and encourages enterprising partnerships in learning, research, and commercialization. With campuses and education centres on four continents, and academic partnerships spanning the globe, Waterloo is shaping the future of the planet.

     
  • richardmitnick 12:56 pm on October 15, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , , , ,   

    From The Guardian: “Black holes and soft hair: why Stephen Hawking’s final work is important” 

    The Guardian Logo

    From The Guardian

    Malcolm Perry, who worked with Hawking on his final paper, explains how it improves our understanding of one of universe’s enduring mysteries.

    10 Oct 2018
    Ian Sample

    Black Hole Entropy and Soft Hair was completed in the days before the physicist’s death in March.

    1
    An artist’s impression of a star being torn apart by a black hole. Photograph: NASA’s Goddard Space Flight Center.

    Stephen Hawking by Jason Bye/REX/Shutterstock

    The information paradox is perhaps the most puzzling problem in fundamental theoretical physics today. It was discovered by Stephen Hawking 43 years ago, and until recently has puzzled many.

    Starting in 2015, Stephen, Andrew Strominger and I started to wonder if we could understand a way out of this difficulty by questioning the basic assumptions that underlie the difficulties. We published our first paper on the subject in 2016 and have been working hard on this problem ever since.

    The most recent work, and perhaps the last paper that Stephen was involved in, has just come out. While we have not solved the information paradox, we hope that we have paved the way, and we are continuing our intensive work in this area.

    Physics is really about being able to predict the future given how things are now. For example, if you throw a ball, once you know its initial position and velocity, then you can figure out where it will be in the future. That kind of reasoning is fine for what we call classical physics but for small things, like atoms and electrons, the rules need some modifications, as described by quantum mechanics. In quantum mechanics, instead of describing precise outcomes, one finds that one can only calculate the probabilities for various things to happen. In the case of a ball being thrown, one would not know its precise trajectory, but only the probability that it would be in some particular place given its initial conditions.

    What Hawking discovered was that in black hole physics, there seemed to be even greater uncertainty than in quantum mechanics. However, this kind of uncertainty seemed to be completely unacceptable in that it resulted in many of the laws of physics appearing to break down. It would deprive us of the ability to predict anything about the future of a black hole.

    That might not have mattered – except that black holes are real physical objects. There are huge black holes at the centres of many galaxies. We know this because observations of the centre of our galaxy show that there is a compact object with a mass of a few million times that of our sun there; such a huge concentration of mass could only be a black hole. Quasars, extremely luminous objects at the centres of very distant galaxies, are powered by matter falling onto black holes. The observatory Ligo has recently discovered ripples in spacetime, gravitational waves, produced by the collision of black holes.

    The root of the problem is that it was once thought that black holes were completely described by their mass and their spin. If you threw something into a black hole, once it was inside you would be unable to tell what it was that was thrown in.

    These ideas were encapsulated in the phrase “a black hole has no hair”. We can often tell people apart by looking their hair, but black holes seemed to be completely bald. Back in 1974, Stephen discovered that black holes, rather than being perfect absorbers, behave more like what we call “black bodies”. A black body is characterised by a temperature, and all bodies with a temperature produce thermal radiation.

    If you go to a doctor, it is quite likely your temperature will be measured by having a device pointed at you. This is an infrared sensor and it measures your temperature by detecting the thermal radiation you produce. A piece of metal heated up in a fire will glow because it produces thermal radiation.

    Black holes are no different. They have a temperature and produce thermal radiation. The formula for this temperature, universally known as the Hawking temperature, is inscribed on the memorial to Stephen’s life in Westminster Abbey. Any object that has a temperature also has an entropy. The entropy is a measure of how many different ways an object could be made from its microscopic ingredients and still look the same. So, for a particular piece of red hot metal, it would be the number of ways the atoms that make it up could be arranged so as to look like the lump of metal you were observing. Stephen’s formula for the temperature of a black hole allowed him to find the entropy of a black hole.

    The problem then was: how did this entropy arise? Since all black holes appear to be the same, the origin of the entropy was at the centre of the information paradox.

    What we have done recently is to discover a gap in the mathematics that led to the idea that black holes are totally bald. In 2016, Stephen, Andy and I found that black holes have an infinite collection of what we call “soft hair”. This discovery allows us to question the idea that black holes lead to a breakdown in the laws of physics.

    Stephen kept working with us up to the end of his life, and we have now published a paper that describes our current thoughts on the matter. In this paper, we describe a way of calculating the entropy of black holes. The entropy is basically a quantitative measure of what one knows about a black hole apart from its mass or spin.
    While this is not a resolution of the information paradox, we believe it provides some considerable insight into it. Further work is needed but we feel greatly encouraged to continue our research in this area. The information paradox is intimately tied up with our quest to find a theory of gravity that is compatible with quantum mechanics.

    Einstein’s general theory of relativity is extremely successful at describing spacetime and gravitation on large scales, but to see how the world works on small scales requires quantum theory. There are spectacularly successful theories of the non-gravitational forces of nature as explained by the “standard model” of particle physics. Such theories have been exhaustively tested and the recent discovery of the Higgs particle at Cern by the Large Hadron Collider is a marvellous confirmation of these ideas.

    Yet the incorporation of gravitation into this picture is still something that eludes us. As well as his work on black holes, Stephen was pursuing ideas that he hoped would lead to a unification of gravitation with the other forces of nature in a way that would unite Einstein’s ideas with those of quantum theory. Our work on black holes does indeed shed light on this other puzzle. Sadly, Stephen is no longer with us to share our excitement about the possibility of resolving these issues, which have now been around for half a century.

    The origins of the puzzle can be traced back to Albert Einstein. In 1915, Einstein published his theory of general relativity, a tour-de-force that described how gravity arises from the spacetime-bending effects of matter, and so why the planets circle the sun. But Einstein’s theory made important predictions about black holes too, notably that a black hole can be completely defined by only three features: its mass, charge, and spin.

    Nearly 60 years later, Hawking added to the picture. He argued that black holes also have a temperature. And because hot objects lose heat into space, the ultimate fate of a black hole is to evaporate out of existence. But this throws up a problem. The rules of the quantum world demand that information is never lost. So what happens to all the information contained in an object – the nature of a moon’s atoms, for instance – when it tumbles into a black hole?

    “The difficulty is that if you throw something into a black hole it looks like it disappears,” said Perry. “How could the information in that object ever be recovered if the black hole then disappears itself?”

    In the latest paper, Hawking and his colleagues show how some information at least may be preserved. Toss an object into a black hole and the black hole’s temperature ought to change. So too will a property called entropy, a measure of an object’s internal disorder, which rises the hotter it gets.

    The physicists, including Sasha Haco at Cambridge and Andrew Strominger at Harvard, show that a black hole’s entropy may be recorded by photons that surround the black hole’s event horizon, the point at which light cannot escape the intense gravitational pull. They call this sheen of photons “soft hair”.

    “What this paper does is show that ‘soft hair’ can account for the entropy,” said Perry. “It’s telling you that soft hair really is doing the right stuff.”

    It is not the end of the information paradox though. “We don’t know that Hawking entropy accounts for everything you could possibly throw at a black hole, so this is really a step along the way,” said Perry. “We think it’s a pretty good step, but there is a lot more work to be done.”

    Days before Hawking died, Perry was at Harvard working on the paper with Strominger. He was not aware how ill Hawking was and called to give the physicist an update. It may have been the last scientific exchange Hawking had. “It was very difficult for Stephen to communicate and I was put on a loudspeaker to explain where we had got to. When I explained it, he simply produced an enormous smile. I told him we’d got somewhere. He knew the final result.”

    Among the unknowns that Perry and his colleagues must now explore are how information associated with entropy is physically stored in soft hair and how that information comes out of a black hole when it evaporates.

    “If I throw something in, is all of the information about what it is stored on the black hole’s horizon?” said Perry. “That is what is required to solve the information paradox. If it’s only half of it, or 99%, that is not enough, you have not solved the information paradox problem.

    “It’s a step on the way, but it is definitely not the entire answer. We have slightly fewer puzzles than we had before, but there are definitely some perplexing issues left.”

    Marika Taylor, professor of theoretical physics at Southampton University and a former student of Hawking’s, said: “Understanding the microscopic origin of this entropy – what are the underlying quantum states that the entropy counts? – has been one of the great challenges of the last 40 years.

    “This paper proposes a way to understand entropy for astrophysical black holes based on symmetries of the event horizon. The authors have to make several non-trivial assumptions so the next steps will be to show that these assumptions are valid.”

    Juan Maldacena, a theoretical physicist at Einstein’s alma mater, the Institute for Advanced Studies in Princeton, said: “Hawking found that black holes have a temperature. For ordinary objects we understand temperature as due to the motion of the microscopic constituents of the system. For example, the temperature of air is due to the motion of the molecules: the faster they move, the hotter it is.

    “For black holes, it is unclear what those constituents are, and whether they can be associated to the horizon of a black hole. In some physical systems that have special symmetries, the thermal properties can be calculated in terms of these symmetries. This paper shows that near the black hole horizon we have one of these special symmetries.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
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