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  • richardmitnick 1:48 pm on January 3, 2021 Permalink | Reply
    Tags: "What if the Universe has no end?", , , , , , , , Hawking radiation, In fact it’s possible that time has existed forever., Mirror Universe theory, , , , , Roger Penrose’s “Conformal Cyclic Cosmology” theory (CCC)   

    From BBC (UK): “What if the Universe has no end?” 

    From BBC (UK)

    19th January 2020 [Year End Wrap Up]
    Patchen Barss

    1
    Credit: Getty Images.

    The Big Bang is widely accepted as being the beginning of everything we see around us, but other theories that are gathering support among scientists are suggesting otherwise.

    The usual story of the Universe has a beginning, middle, and an end.

    It began with the Big Bang 13.8 billion years ago when the Universe was tiny, hot, and dense. In less than a billionth of a billionth of a second, that pinpoint of a universe expanded to more than a billion, billion times its original size through a process called “cosmological inflation”.

    Next came “the graceful exit”, when inflation stopped. The universe carried on expanding and cooling, but at a fraction of the initial rate. For the next 380,000 years, the Universe was so dense that not even light could move through it – the cosmos was an opaque, superhot plasma of scattered particles. When things finally cooled enough for the first hydrogen atoms to form, the Universe swiftly became transparent. Radiation burst out in every direction, and the Universe was on its way to becoming the lumpy entity we see today, with vast swaths of empty space punctuated by clumps of particles, dust, stars, black holes, galaxies, radiation, and other forms of matter and energy.

    Eventually these lumps of matter will drift so far apart that they will slowly disappear, according to some models. The Universe will become a cold, uniform soup of isolated photons.

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    The Universe we can currently see is made up of clumps of particles, dust, stars, black holes, galaxies, radiation. Credit: NASA/JPL-Caltech/ESA/CXC/STScI.

    It’s not a particularly dramatic ending, although it does have a satisfying finality.

    But what if the Big Bang wasn’t actually the start of it all?

    Perhaps the Big Bang was more of a “Big Bounce”, a turning point in an ongoing cycle of contraction and expansion. Or, it could be more like a point of reflection, with a mirror image of our universe expanding out the “other side”, where antimatter replaces matter, and time itself flows backwards. (There might even be a “mirror you” pondering what life looks like on this side.)

    Or, the Big Bang might be a transition point in a universe that has always been – and always will be – expanding. All of these theories sit outside mainstream cosmology, but all are supported by influential scientists.

    The growing number of these competing theories suggests that it might now be time to let go of the idea that the Big Bang marked the beginning of space and time. And, indeed, that it may even have an end.

    Many competing Big Bang alternatives stem from deep dissatisfaction with the idea of cosmological inflation.

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    Scars left by the Big Bang in a weak microwave radiation that permeates the entire cosmos provides clues about what the early Universe looked like. Credit: NASA.

    “I have to confess, I never liked inflation from the beginning,” says Neil Turok, the former director of the Perimeter Institute for Theoretical Physics in Waterloo, Canada.

    “The inflationary paradigm has failed,” adds Paul Steinhardt, Albert Einstein professor in science at Princeton University, and proponent of a “Big Bounce” model.

    “I always regarded inflation as a very artificial theory,” says Roger Penrose, emeritus Rouse Ball professor of mathematics at Oxford University. “The main reason that it didn’t die at birth is that it was the only thing people could think of to explain what they call the ‘scale invariance of the Cosmic Microwave Background temperature fluctuations’.”

    The Cosmic Microwave Background (or “CMB”) has been a fundamental factor in every model of the Universe since it was first observed in 1965.

    CMB per ESA/Planck.

    It’s a faint, ambient radiation found everywhere in the observable Universe that dates back to that moment when the Universe first became transparent to radiation.

    The CMB is a major source of information about what the early Universe looked like. It is also a tantalising mystery for physicists. In every direction scientists point a radio telescope, the CMB looks the same, even in regions that seemingly could never have interacted with one another at any point in the history of a 13.8 billion-year- old universe.

    “The CMB temperature is the same on opposite sides of the sky and those parts of the sky would never have been in causal contact,” says Katie Mack, a cosmologist at North Carolina State University. “Something had to connect those two regions of the Universe in the past. Something had to tell that part of the sky to be the same temperature as that part of the sky.”

    Without some mechanism to even out the temperature across the observable Universe, scientists would expect to see much larger variations in different regions.

    Inflation offers a way to solve this so-called “homogeneity problem”. With a period of insane expansion stretching out the Universe so rapidly that almost the entire thing ended up far beyond the region we can observe and interact with. Our observable universe expanded from one tiny homogeneous region within that primordial hot mess, producing the uniform CMB. Other regions beyond what we can observe might look very different.

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    Theoretical physicists are increasingly finding that inflation theory fails to account for the spread of matter and energy observed in the Universe. Credit: NASA, ESA.

    “Inflation seems to be the thing that has enough support from the data that we can take it as the default,” says Mack. ”It’s the one I teach in my classes. But I always say that we don’t know for sure that this happened. But it seems to fit the data pretty well, and is what most people would say is most likely.”

    Inflation

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    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lamda Cold Dark Matter Accerated Expansion of The universe http scinotions.com the-cosmic-inflation-suggests-the-existence-of-parallel-universes
    Alex Mittelmann, Coldcreation


    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    But there have always been shortcomings with the theory. Notably, there is no definitive mechanism to trigger inflationary expansion, or a testable explanation for how the graceful ending could happen. One idea put forward by proponents of inflation is that theoretical particles made up something called an “inflation field” that drove inflation and then decayed into the particles we see around us today.

    But even with tweaks like this, inflation makes predictions that have, at least thus far, not been confirmed. The theory says spacetime should be warped by primordial gravitational waves that ricocheted out across the Universe with the Big Bang. But while certain types of gravitational waves have been detected, none of these primordial ones have yet been found to support the theory.

    Quantum physics also forces inflation theories into very messy territory. Rare quantum fluctuations are predicted to cause inflation to break space up into an infinite number of patches with wildly different properties – a “multiverse” in which literally every imaginable outcome occurs.

    “The theory is completely indecisive,” says Steinhardt. “It can only say that the observable Universe might be like this or that or any other possibility you can imagine, depending on where we happen to be in the multiverse. Nothing is ruled out that is physically conceivable.”

    Steinhardt, who was one of the original architects of inflationary theory, ultimately got fed up with the lack of predictiveness and untestability.

    “Do we really need to imagine that there exist an infinite number of messy universes that we have never seen and never will see in order to explain the one simple and remarkably smooth Universe we actually observe?” he asks. “I say no. We have to look for a better idea.”

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    Rather than being a beginning, the Big Bang could have been a moment of transition from one period of space and time to another – more of a bounce. Credit: Alamy.

    The problem might have to do with the Big Bang itself, and with the idea that there was a beginning to space and time.

    The “Big Bounce” theory agrees with the Big Bang picture of a hot, dense universe 13.8 billion years ago that began to expand and cool. But rather than being the beginning of space and time, that was a moment of transition from an earlier phase during which space was contracting.

    With a bounce rather than a bang, Steinhardt says, distant parts of the cosmos would have plenty of time to interact with each other, and to form a single smooth universe in which the sources of CMB radiation would have had a chance to even out.

    In fact, it’s possible that time has existed forever.

    “And if a bounce happened in our past, why could there not have been many of them?” says Steinhardt. “In that case, it is plausible that there is one in our future. Our expanding universe could start to contract, returning to that dense state and starting the bounce cycle again.”

    Steinhardt and Turok worked together on some early versions of the Big Bounce model, in which the Universe shrunk to such a tiny size that quantum physics took over from classical physics, leaving the predictions uncertain. But more recently, another of Steinhardt’s collaborators, Anna Ijjas, developed a model in which the Universe never gets so small that quantum physics dominates.

    “It’s a rather prosaic, conservative idea described at all times by classical equations,” Steinhardt says. “Inflation says there’s a multiverse, that there’s an infinite number of ways the Universe might come out, and we just happen to live in the one that is smooth and flat. That’s possible but not likely. This Big Bounce model says this is how the Universe must be.”

    Neil Turok has also been exploring another avenue for a simpler alternative to inflationary theory, the “Mirror Universe”. It predicts that another universe dominated by antimatter, but governed by the same physical laws as our own, is expanding outwards on the other side of the Big Bang – a kind of “anti-universe”, if you like.

    “I take one thing away from the observations of the last 30 years, which is that the Universe is unbelievably simple,” he says. “At large scales, it is not chaotic. It is not random. It’s incredibly ordered and regular and requires very few numbers to describe everything.”

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    Our forward-time flowing universe could have a perfect reflection that also extends out in reverse from the event we call the Big Bang. Credit: Alamy.

    With this in mind, Turok sees no place for a multiverse, higher dimensions, or new particles to explain what can be seen when we look up at the heavens. The Mirror Universe offers all that – and might also solve one of the Universe’s big mysteries.

    If you add up all the known mass in a galaxy – stars, nebulae, black holes and so on – the total doesn’t create enough gravity to explain the motion within and between galaxies. The remainder seems to be made up of something we cannot currently see – Dark Matter. This mysterious stuff accounts for about 85% of the matter in the universe.

    The Mirror Universe model predicts that the Big Bang produced a particle known as “right-handed neutrinos” in abundance. While particle physicists have yet to directly see any of these particles, they are pretty sure they exist. And it is these that make up dark matter, according to those who support the Mirror Universe theory.

    “It’s the only particle on that list (of particles in the Standard Model) that has the two requisite properties that we haven’t directly observed it yet, and it could be stable,” says Latham Boyle, another leading proponent of the Mirror Universe theory and a colleague of Turok at the Perimeter Institute.

    Perhaps the most challenging alternative to the Big Bang and inflation is Roger Penrose’s “Conformal Cyclic Cosmology” theory (CCC). Like the Big Bounce, it involves a universe that might have existed forever. But in CCC, it never goes through a period of contraction – it only ever expands.

    “The view I have is that the Big Bang was not the beginning,” says Penrose. “The entire picture of what we know nowadays, the whole history of the Universe, is what I call one ‘aeon’ in a succession of aeons.”

    Penrose’s model predicts that much of the matter in the Universe will eventually be dragged into ultra-massive black holes. As the Universe expands and cools to near absolute zero, those black holes will “boil away” through a phenomenon called Hawking Radiation.

    “You have to think in terms of something like a googol years, which means a number one with 100 zeros,” says Penrose. “That’s the number of years or more for the really big ones to finally evaporate away. And then you’ve got a universe really dominated by photons (particles of light).”

    Penrose says at this point, the Universe begins to look much as it did at its start, setting the stage for the start of another aeon.

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    Conformal Cyclic Cosmology predicts that much of the Universe will be pulled into enormous black holes that will then boil away. Credit: NASA/JPL-Caltech.

    One of the predictions of CCC is that there might be a record of the previous aeon in the cosmic microwave background radiation that originally inspired the inflation model. When hyper-massive black holes collide, the impact creates a huge release of energy in the form of gravitational waves. When giant black holes finally evaporate, they release a huge amount of energy in the form of low-frequency photons. Both of these phenomena are so powerful, Penrose says, that they can “burst through to the other side” of a transition from one aeon to the next, each leaving its own kind of “signal” embedded in the CMB like an echo from the past.

    Penrose calls the patterns left behind by evaporating black holes “Hawking Points”.

    For the first 380,000 years of the current aeon, these would have been nothing more than tiny points in the cosmos, but as the Universe has expanded, they would appear as “splotches” across the sky.

    Penrose has been working with Polish, Korean and Armenian cosmologists to see if these patterns can actually be found by comparing measurements of the CMB with thousands of random patterns.

    “The conclusion we come to is that we see these spots in the sky with 99.98% confidence,” Penrose says. The physics world has, however, remained largely skeptical of these results to date and there has been limited interest among cosmologists about even attempting to replicate Penrose’s analysis.

    It is unlikely that we will ever be able to directly observe what happened in the first moments after the Big Bang, let alone the moments before. The opaque superheated plasma that existed in the early moments will likely forever obscure our view. But there are other potentially observable phenomena such as primordial gravitational waves, primordial black holes, right-handed neutrinos, that could provide us some clues about which of the theories about our universe are correct.

    “As we develop new theories and new models of cosmology, those will give us other interesting predictions that can that we can look for,” says Mack. “The hope is not necessarily that we’re going to see the beginning more directly, but that maybe through some roundabout way we’ll better understand the structure of physics itself.”

    Until then, the story of our universe, its beginnings and whether it has an end, will continue to be debated.

    See the full article here .

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  • richardmitnick 12:05 pm on September 8, 2019 Permalink | Reply
    Tags: , , , , , , Craig Callender, Hawking radiation, Second law of thermodynamics,   

    From WIRED: “Are We All Wrong About Black Holes?” 

    Wired logo

    From WIRED

    09.08.2019
    Brendan Z. Foster

    1
    Craig Callender, a philosopher of science at the University of California San Diego, argues that the connection between black holes and thermodynamics is less ironclad than assumed.Photograph: Peggy Peattie/Quanta Magazine

    In the early 1970s, people studying general relativity, our modern theory of gravity, noticed rough similarities between the properties of black holes and the laws of thermodynamics. Stephen Hawking proved that the area of a black hole’s event horizon—the surface that marks its boundary—cannot decrease. That sounded suspiciously like the second law of thermodynamics, which says entropy—a measure of disorder—cannot decrease.

    Yet at the time, Hawking and others emphasized that the laws of black holes only looked like thermodynamics on paper; they did not actually relate to thermodynamic concepts like temperature or entropy.

    Then in quick succession, a pair of brilliant results—one by Hawking himself—suggested that the equations governing black holes were in fact actual expressions of the thermodynamic laws applied to black holes. In 1972, Jacob Bekenstein argued that a black hole’s surface area was proportional to its entropy [Physical Review D], and thus the second law similarity was a true identity. And in 1974, Hawking found that black holes appear to emit radiation [Nature]—what we now call Hawking radiation—and this radiation would have exactly the same “temperature” in the thermodynamic analogy.

    This connection gave physicists a tantalizing window into what many consider the biggest problem in theoretical physics—how to combine quantum mechanics, our theory of the very small, with general relativity. After all, thermodynamics comes from statistical mechanics, which describes the behavior of all the unseen atoms in a system. If a black hole is obeying thermodynamic laws, we can presume that a statistical description of all its fundamental, indivisible parts can be made. But in the case of a black hole, those parts aren’t atoms. They must be a kind of basic unit of gravity that makes up the fabric of space and time.

    Modern researchers insist that any candidate for a theory of quantum gravity must explain how the laws of black hole thermodynamics arise from microscopic gravity, and in particular, why the entropy-to-area connection happens. And few question the truth of the connection between black hole thermodynamics and ordinary thermodynamics.

    But what if the connection between the two really is little more than a rough analogy, with little physical reality? What would that mean for the past decades of work in string theory, loop quantum gravity, and beyond? Craig Callender, a philosopher of science at the University of California, San Diego, argues that the notorious laws of black hole thermodynamics may be nothing more than a useful analogy stretched too far [Phil Sci]. The interview has been condensed and edited for clarity.

    Why did people ever think to connect black holes and thermodynamics?

    Callender: In the early ’70s, people noticed a few similarities between the two. One is that both seem to possess an equilibrium-like state. I have a box of gas. It can be described by a small handful of parameters—say, pressure, volume, and temperature. Same thing with a black hole. It might be described with just its mass, angular momentum, and charge. Further details don’t matter to either system.

    Nor does this state tell me what happened beforehand. I walk into a room and see a box of gas with stable values of pressure, volume and temperature. Did it just settle into that state, or did that happen last week, or perhaps a million years ago? Can’t tell. The black hole is similar. You can’t tell what type of matter fell in or when it collapsed.

    The second feature is that Hawking proved that the area of black holes is always non-decreasing. That reminds one of the thermodynamic second law, that entropy always increases. So both systems seem to be heading toward simply described states.

    Now grab a thermodynamics textbook, locate the laws, and see if you can find true statements when you replace the thermodynamic terms with black hole variables. In many cases you can, and the analogy improves.

    Hawking then discovers Hawking radiation, which further improves the analogy. At that point, most physicists start claiming the analogy is so good that it’s more than an analogy—it’s an identity! That’s a super-strong and surprising claim. It says that black hole laws, most of which are features of the geometry of space-time, are somehow identical to the physical principles underlying the physics of steam engines.

    Because the identity plays a huge role in quantum gravity, I want to reconsider this identity claim. Few in the foundations of physics have done so.

    So what’s the statistical mechanics for black holes?

    Well, that’s a good question. Why does ordinary thermodynamics hold? Well, we know that all these macroscopic thermodynamic systems are composed of particles. The laws of thermodynamics turn out to be descriptions of the most statistically likely configurations to happen from the microscopic point of view.

    Why does black hole thermodynamics hold? Are the laws also the statistically most likely way for black holes to behave? Although there are speculations in this direction, so far we don’t have a solid microscopic understanding of black hole physics. Absent this, the identity claim seems even more surprising.

    What led you to start thinking about the analogy?

    Many people are worried about whether theoretical physics has become too speculative. There’s a lot of commentary about whether holography, the string landscape—all sorts of things—are tethered enough to experiment. I have similar concerns. So my former Ph.D. student John Dougherty and I thought, where did it all start?

    To our mind a lot of it starts with this claimed identity between black holes and thermodynamics. When you look in the literature, you see people say, “The only evidence we have for quantum gravity, the only solid hint, is black hole thermodynamics.”

    If that’s the main thing we’re bouncing off for quantum gravity, then we ought to examine it very carefully. If it turns out to be a poor clue, maybe it would be better to spread our bets a little wider, instead of going all in on this identity.

    What problems do you see with treating a black hole as a thermodynamic system?

    I see basically three. The first problem is: What is a black hole? People often think of black holes as just kind of a dark sphere, like in a Hollywood movie or something; they’re thinking of it like a star that collapsed. But a mathematical black hole, the basis of black hole thermodynamics, is not the material from the star that’s collapsed. That’s all gone into the singularity. The black hole is what’s left.

    The black hole isn’t a solid thing at the center. The system is really the entire space-time.

    Yes, it’s this global notion for which black hole thermodynamics was developed, in which case the system really is the whole space-time.

    Here is another way to think about the worry. Suppose a star collapses and forms an event horizon. But now another star falls past this event horizon and it collapses, so it’s inside the first. You can’t think that each one has its own little horizon that is behaving thermodynamically. It’s only the one horizon.

    Here’s another. The event horizon changes shape depending on what’s about to be thrown into it. It’s clairvoyant. Weird, but there is nothing spooky here so long as we remember that the event horizon is only defined globally. It’s not a locally observable quantity.

    The picture is more counterintuitive than people usually think. To me, if the system is global, then it’s not at all like thermodynamics.

    The second objection is: Black hole thermodynamics is really a pale shadow of thermodynamics. I was surprised to see the analogy wasn’t as thorough as I expected it to be. If you grab a thermodynamics textbook and start replacing claims with their black hole counterparts, you will not find the analogy goes that deep.


    Craig Callender explains why the connection between black holes and thermodynamics is little more than an analogy.

    For instance, the zeroth law of thermodynamics sets up the whole theory and a notion of equilibrium — the basic idea that the features of the system aren’t changing. And it says that if one system is in equilibrium with another — A with B, and B with C — then A must be in equilibrium with C. The foundation of thermodynamics is this equilibrium relation, which sets up the meaning of temperature.

    The zeroth law for black holes is that the surface gravity of a black hole, which measures the gravitational acceleration, is a constant on the horizon. So that assumes temperature being constant is the zeroth law. That’s not really right. Here we see a pale shadow of the original zeroth law.

    The counterpart of equilibrium is supposed to be “stationary,” a technical term that basically says the black hole is spinning at a constant rate. But there’s no sense in which one black hole can be “stationary with” another black hole. You can take any thermodynamic object and cut it in half and say one half is in equilibrium with the other half. But you can’t take a black hole and cut it in half. You can’t say that this half is stationary with the other half.

    Here’s another way in which the analogy falls flat. Black hole entropy is given by the black hole area. Well, area is length squared, volume is length cubed. So what do we make of all those thermodynamic relations that include volume, like Boyle’s law? Is volume, which is length times area, really length times entropy? That would ruin the analogy. So we have to say that volume is not the counterpart of volume, which is surprising.

    The most famous connection between black holes and thermodynamics comes from the notion of entropy. For normal stuff, we think of entropy as a measure of the disorder of the underlying atoms. But in the 1970s, Jacob Bekenstein said that the surface area of a black hole’s event horizon is equivalent to entropy. What’s the basis of this?

    This is my third concern. Bekenstein says, if I throw something into a black hole, the entropy vanishes. But this can’t happen, he thinks, according to the laws of thermodynamics, for entropy must always increase. So some sort of compensation must be paid when you throw things into a black hole.

    Bekenstein notices a solution. When I throw something into the black hole, the mass goes up, and so does the area. If I identify the area of the black hole as the entropy, then I’ve found my compensation. There is a nice deal between the two—one goes down while the other one goes up—and it saves the second law.

    When I saw that I thought, aha, he’s thinking that not knowing about the system anymore means its entropy value has changed. I immediately saw that this is pretty objectionable, because it identifies entropy with uncertainty and our knowledge.

    There’s a long debate in the foundations of statistical mechanics about whether entropy is a subjective notion or an objective notion. I’m firmly on the side of thinking it’s an objective notion. I think trees unobserved in a forest go to equilibrium regardless of what anyone knows about them or not, that the way heat flows has nothing to do with knowledge, and so on.

    Chuck a steam engine behind the event horizon. We can’t know anything about it apart from its mass, but I claim it can still do as much work as before. If you don’t believe me, we can test this by having a physicist jump into the black hole and follow the steam engine! There is only need for compensation if you think that what you can no longer know about ceases to exist.

    Do you think it’s possible to patch up black hole thermodynamics, or is it all hopeless?

    My mind is open, but I have to admit that I’m deeply skeptical about it. My suspicion is that black hole “thermodynamics” is really an interesting set of relationships about information from the point of view of the exterior of the black hole. It’s all about forgetting information.

    Because thermodynamics is more than information theory, I don’t think there’s a deep thermodynamic principle operating through the universe that causes black holes to behave the way they do, and I worry that physics is all in on it being a great hint for quantum gravity when it might not be.

    Playing the role of the Socratic gadfly in the foundations of physics is sometimes important. In this case, looking back invites a bit of skepticism that may be useful going forward.

    See the full article here .

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  • richardmitnick 9:03 am on July 31, 2019 Permalink | Reply
    Tags: A0620-00- a binary star system 3300 light-years away- holds a dark secret: One of its stars isn’t a star at all but rather a black hole., , Along Unruh’s imaginary river a waterfall plunges at a supersonic speed—faster than the speed of sound in water., , , , , Black holes were first theorized in 1784 by English clergyman and astronomer John Michell., Building black hole models, , Eight years later in 1980 Unruh realized that the equations of motion for sound in the waterfall analogy were identical to those describing light at the horizon of a black hole., , Hawking radiation, In 1972 William “Bill” Unruh a physicist at the University of British Columbia Vancouver connected gravity to fluid dynamics in an analogy, Most physicists believe that black holes don’t truly destroy information and that information is preserved in Hawking radiation but that conjecture may be impossible to test directly., physicists use everything from water to exotic ultracold states of matter to mimic black holes, , Stephen Hawking revolutionized the field by proposing that that something could in fact escape from a black hole., Today, Unruh’s work was rediscovered as physicists began probing gravity theoretically and experimentally with analog models., What happens if a fellow fish goes over the falls? You- a blind fish- cannot know; you will never hear it scream because the waterfall will drag the sound down faster than it can travel up., William “Bill” Unruh: “Imagine that you are a blind fish and are also a physicist living in a river” Unruh wrote.   

    From Symmetry: “Gravity’s Waterfall” 

    Symmetry Mag
    From Symmetry

    07/30/19
    Daniel Garisto

    Physicists are using analog black holes to better understand gravity.

    1
    Illustration by Sandbox Studio, Chicago with Ariel Davis

    A0620-00, a binary star system 3300 light-years away, holds a dark secret: One of its stars isn’t a star at all, but a black hole. As far as we know, this is the black hole closest to our planet. Astronomers know it’s there only because its partner star appears to be dancing alone, pulled along by an invisible lead.

    In recent years, scientists have found ways to study black holes, listening to the gravitational waves they unleash when they collide, and even creating an image of one by combining information from radio telescopes around the world.

    MIT /Caltech Advanced aLigo


    VIRGO Collaboration

    But our knowledge of black holes remains limited. No one will ever be able to test a real one in a lab, and with current technology, it would take about 50 million years for a probe to reach A0620-00.

    So scientists are figuring out how to make do with substitutes—analogs to black holes that may hold answers to mysteries about gravity and quantum mechanics.

    Building black hole models

    In 1972, William “Bill” Unruh, a physicist at the University of British Columbia, Vancouver, connected gravity to fluid dynamics in an analogy: “Imagine that you are a blind fish, and are also a physicist, living in a river,” Unruh wrote.

    Along Unruh’s imaginary river, a waterfall plunges at a supersonic speed—faster than the speed of sound in water. What happens if a fellow fish goes over the falls? You, a blind fish, cannot know; you will never hear it scream because the waterfall will drag the sound down faster than it can travel up.

    Unruh used this piscine drama to explain a property of black holes: Like sound that passes over the edge of the supersonic waterfall, light that crosses the horizon of a black hole cannot escape.

    The analogy turned out to be more accurate than Unruh initially thought. Eight years later, in 1980, he realized that the equations of motion for sound in the waterfall analogy were identical to those describing light at the horizon of a black hole.

    At the time, his research drew little attention—it was cited just four times in the decade after it was published. But in the ’90s, Unruh’s work was rediscovered as physicists began probing gravity theoretically and experimentally with analog models.

    Today, physicists use everything from water to exotic ultracold states of matter to mimic black holes. Proponents of the analogs say that these models have confirmed theoretical predictions about black holes. But many physicists still doubt that analogs can predict what happens where gravity warps spacetime so violently.

    Black holes were first theorized in 1784, by English clergyman and astronomer John Michell, who calculated that for a large enough star, “all light emitted from such a body would be made to return towards it, by its own proper gravity.”

    The idea was mostly put aside until the 20th century, when Einstein’s general theory of relativity overturned the paradigm of Newtonian gravity. Luminaries like Karl Schwarzchild, Subrahmanyan Chandrasekhar and John Archibald Wheeler developed theory about these monsters from which nothing could escape. But in 1974, a young physicist named Stephen Hawking revolutionized the field by proposing that that something could, in fact, escape from a black hole.

    Due to random quantum fluctuations in the fabric of spacetime, pairs of virtual particles and antiparticles pop into existence all the time, throughout the universe. Most of the time, these pairs annihilate instantly, disappearing back into the void. But, Hawking theorized, the horizon of a black hole could separate a pair: One particle would be sucked in, while the other would zoom away as a now real particle.

    Because of a mathematical quirk in Hawking radiation, swallowed virtual particles effectively have negative energy. Black holes that gobble up these particles shrink. To an observer, Hawking radiation would look a lot like a black hole spitting up what it swallowed and getting smaller.

    However, Hawking radiation is random and carries no information about the inside of a black hole—remember that the emitted particle comes from just outside the horizon. This creates a paradox: Quantum mechanics rests on the premise that information is never destroyed, but if particles emitted as Hawking radiation are truly random, information would be lost forever.

    Most physicists believe that black holes don’t truly destroy information and that information is preserved in Hawking radiation, but that conjecture may be impossible to test directly. “The temperature of Hawking radiation is very small—it’s much smaller than the background radiation of the universe,” says Hai Son Nguyen, a physicist at the Institute of Nanotechnology of Lyon. “That’s why we will never be able to observe Hawking radiation from a real black hole.”

    What about something that behaved a lot like a black hole? In his 1980 paper, Unruh calculated that phonons—quantum units of sound analogous to photons, quantum units of light—would be the Hawking radiation emitted from his analog black hole.

    Unruh was initially bleak about the prospects of actually making such a measurement, calling it “an extremely slim possibility.” But as more physicists joined Unruh in theorizing about analogs to black holes in the ’90s, the possibility of measuring Hawking radiation became a difficult, but achievable goal.

    Over the waterfall

    There are many different analog models of black holes, but they all have one aspect in common: a horizon. Mathematically, horizons are defined as the boundary beyond which events cannot escape—like the edge of Unruh’s waterfall. Because they can separate pairs of particles, any horizon creates a form of Hawking radiation.

    “Understanding of the phenomenology associated with the presence of horizons in different analog systems provides hints about phenomena that might also be present in the gravitational realm,” writes Carlos Barceló, a theoretical physicist at the Astrophysical Institute of Andalucia.

    Often, it’s useful to start with a simple analog like water, says Silke Weinfurtner, a physicist at the University of Nottingham. It’s possible to create a horizon by running water quickly enough over an obstacle; if the conditions are just right, surface waves are thwarted at the obstacle.

    But to properly measure the smallest—quantum-level—effects of a black hole, you need a quantum analog. Bose-Einstein condensates, or BECs, are typically ultracold gases like rubidium that are ruled by quantum effects odd enough to qualify them as another state of matter. Subtle quantum effects like Hawking radiation hidden by the noise present in normal fluids become apparent in BECs.

    Analog black holes can even use light as a fluid. The fluid is made of quasiparticles called polaritons, which are the collective state of a photon that couples to an electric field. Enough polaritons behave as a quantum fluid of light. So when the flow of polaritons goes faster than the speed of sound in the polariton fluid, just like Unruh’s waterfall, a horizon forms. Hawking radiation from this fluid of light still comes in the form of phonons.

    Some black hole analogs are “optical” because their Hawking radiation comes in photons. In optical fibers—like the type we send data through—intense laser pulses can create a horizon. The pulse changes the physical properties of the fiber, slowing down the speed of light within the fiber. This makes the leading edge of the pulse a horizon: Slowed light cannot escape past the pulse any more than sound can escape up out of Unruh’s waterfall.

    To date, though, experimental evidence of Hawking radiation in any of these analogs has been lacking in support—with one exception.

    In May, Jeff Steinhauer published his latest paper, with the strongest evidence yet for Hawking radiation. Steinhauer, a physicist at the Technion in Haifa, Israel, has been working on the problem for over a decade, chipping away relentlessly at the extremely difficult experimental task, largely on his own.

    Focusing a laser on rubidium gas, a BEC, Steinhauer created a high-energy region. Particles move from high-energy regions to low-energy regions, so the rubidium gas wanted to escape the laser. The edge of the laser here functioned as the horizon for the rubidium gas, similar to a waterfall that it could go over but not come back up. Steinhauer used the set-up to study the Hawking radiation resulting from quantum fluctuations separated by the horizon.

    The temperature of Hawking radiation—how much energy the emitted phonons have, in this case—depends on the slope of the horizon, or waterfall. The steeper it is, the higher the energy of the radiation. This is why Hawking radiation is low temperature for a black hole: A weak force like gravity doesn’t make for a steep horizon.

    By measuring the slope, and then separately measuring the energy of radiated phonons, Steinhauer was able to get corroboration for his data.

    Previous experiments from Steinhauer and others have claimed to find Hawking radiation [PhysicsWorld], but have lacked the rigor of this latest result. This time, Steinhauer and some other physicists believe he has observed Hawking radiation.

    “I think we verified Hawking’s calculation,” Steinhauer says. “He had a calculation with certain assumptions and approximations, and we have the same approximations, and so mathematically it’s equivalent.”

    However, Steinhauer points out, it’s quite possible that Hawking radiation works differently for black holes because of quantum gravity. Critics also claim phonons may not be perfect analogs to photons.

    Many physicists who work on quantum gravity are dismissive of the latest results, according to reporting in Quanta.

    Weinfurtner acknowledges the criticism and agrees that analogs cannot strictly prove anything about black holes. But to physicists working on analogs, the facsimiles of black holes are already worthwhile. “What we’re doing is already on its own really interesting,” she says. “We’re deepening our understanding of the analog gravity systems, and the hope is that such experiments stimulate new theoretical black hole studies.”

    3

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:44 am on January 21, 2019 Permalink | Reply
    Tags: , , , , , Hawking radiation, , , ,   

    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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    Please help promote STEM in your local schools.

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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 7:24 am on August 30, 2018 Permalink | Reply
    Tags: An eternal cycle of Big Bang events, Big Bang, , Conformal Cyclic Cosmology, , Hawking Points- anomalous high energy features in the CMB, Hawking radiation, Roger Penrose, ,   

    From University of Oxford via COSMOS: “Black holes from a previous universe shine light on our own” 

    U Oxford bloc

    From University of Oxford

    via

    COSMOS

    30 August 2018
    Stephanie Rowlands

    Cold spots are a hot topic in Conformal Cyclic Cosmology.

    1
    Stephen Hawking suggested evidence of previous universes could be detected in the cosmic microwave background. Has he been proved right? Jemal Countess/Getty Images

    Cosmologists say they have found remnants of a bygone universe in the afterglow of the Big Bang found in the Cosmic Microwave Background (CMB).

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    The discovery gives weight to the controversial theory of Conformal Cyclic Cosmology, or CCC, that suggests our universe is just one of many, built from the remains of a previous one in the Big Bang 13.6 billion years ago.

    The theory describes an eternal cycle of Big Bang events, repeating into the far distant future, the end of our universe giving rise to a new one.

    A team led by Oxford University mathematics emeritus Roger Penrose, a former collaborator of the late Stephen Hawking, claims in a new paper lodged on the preprint server arXiv to have found signs of so-called Hawking Points, anomalous high energy features in the CMB.

    3
    Inside Penrose’s universe
    06 Dec 2010
    Cycles of Time: An Extraordinary New View of the Universe
    Roger Penrose
    2010 Bodley Head £25.00 hb 320pp

    Click to access paul.pdf

    Penrose and colleagues say that these anomalies were made from the last moments of black holes evaporating through “Hawking radiation”.

    Although black holes are famous for never releasing any light, Hawking proposed a subtle way for light and particles to escape over time.

    Through quantum mechanical effects, every black hole slowly shrinks and fades, losing its energy through Hawking radiation.

    “This burst of energy from a now decayed black hole then spreads out quickly in our newly formed universe, leaving a warm central point with a cooling spot around it,” says astronomer Alan Duffy from Australia’s Swinburne University and Lead Scientist of the Royal Institution of Australia, who was not involved in the research.

    “In other words, they have proposed that we can search for an echo of a previous universe in the CMB.”

    Conformal Cyclic Cosmology strongly conflicts with the current standard model explaining the evolution of the universe.

    “Unlike previous cyclic universe models, there is no ‘Big Crunch’ where everything comes together again,” explains Duffy.

    “Instead CCC links the similarity of the current accelerating expansion of the universe by dark energy with early expansion of inflation in the Big Bang.”

    While mathematically the two epochs of expansion are similar, not all cosmologists are convinced that the Big Bang eventually leads to another Big Bang from a future empty universe.

    The results from Penrose and colleagues are likely to be met with skepticism by many mainstream cosmologists.

    Penrose first claimed [Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity] to have detected Hawking points in 2010. Other researchers shot down the claim in flames, arguing that his discoveries were nothing more than random noise contained in the data.

    NASA/WMAP 2001 to 2010


    Inflationary Universe. NASA/WMAP


    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    See the full article here.


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Oxford campus

    Oxford is a collegiate university, consisting of the central University and colleges. The central University is composed of academic departments and research centres, administrative departments, libraries and museums. The 38 colleges are self-governing and financially independent institutions, which are related to the central University in a federal system. There are also six permanent private halls, which were founded by different Christian denominations and which still retain their Christian character.

    The different roles of the colleges and the University have evolved over time.

     
  • richardmitnick 10:01 am on January 26, 2017 Permalink | Reply
    Tags: Accelerating mirror, , Black hole paradox, , Hawking radiation, , , Shooting electron waves through plasma could reveal if black holes permanently destroy information,   

    From Science Alert: “Shooting electron waves through plasma could reveal if black holes permanently destroy information” 

    ScienceAlert

    Science Alert

    25 JAN 2017
    MIKE MCRAE

    1
    Interstellar/Paramount Pictures

    Without having to enter a black hole ourselves…

    One of the greatest dilemmas in astrophysics is the black hole paradox – if black holes really do destroy every scrap of information that enters them.

    Now, physicists might have finally come up with a way to test the paradox once and for all, by accelerating a wave of negatively charged electrons through a cloud of plasma.

    As far as objects in space go, black holes need little introduction. Get too close, and their concentrated mass will swallow you, never to return.

    But in the 1970s, physicists including Stephen Hawking proposed that black holes weren’t necessarily forever.

    Thanks to the peculiarities of quantum mechanics, particles did indeed radiate away from black holes, Hawking hypothesised, which means, theoretically, black holes could slowly evaporate away over time.

    This poses the paradox. Information – the fundamental coding of stuff in the Universe – can’t just disappear. That’s a big rule. But when a black hole evaporates away, where does its bellyful of information go?

    A clue might be found in the nature of the radiation Hawking described. This form of radiation arises when a pair of virtual particles pops into existence right up against a black hole’s line of no return – the ‘event horizon’.

    Usually, such paired particles cancel each other out, and the Universe is none the wiser. But in the case of Hawking radiation, one of these particles falls across the horizon into the gravitational grip of the black hole. The other barely escapes off into the Universe as a bona fide particle.

    Physicists have theorised that this escaped particle preserves the information of its twin thanks to the quirks of quantum dynamics. In this case, the phenomenon of entanglement would allow the particles to continue share a connection, even separated by time and space, leaving a lasting legacy of whatever was devoured by the black hole.

    To demonstrate this, physicists could catch a particle that has escaped a black hole’s event horizon, and then wait for the black hole to spill its guts in many, many years, to test if there’s indeed a correlation between one of the photons and its entangled twin. Which, let’s face it, isn’t exactly practical.

    Now, Pisin Chen from the National Taiwan University and Gerard Mourou from École Polytechnique in France have described a slightly easier method.

    They suggest that a high-tech ‘accelerating mirror’ should provide the same opportunity of separating entangled particles.

    That sounds strange, but as a pair of particles zips into existence in this hypothetical experiment, one would reflect from the accelerating mirror as the other became trapped at the boundary. Just as it might happen in a black hole.

    Once the mirror stopped moving, the ‘trapped’ photon would be freed, just as the energy would be released from a dying black hole.

    Chen’s and Mourou’s mirror would be made by pulsing an X-ray laser through a cloud of ionised gas in a plasma wakefield accelerator. The pulse would leave a trail of negatively charged electrons, which would serve nicely as a mirror.

    By altering the density of the plasma on a small enough scale, the ‘mirror’ would accelerate away from the laser pulse.

    As clever as the concept is, the experiment is still in its ‘thought bubble ‘stage. Even with established methods and trusted equipment, entanglement is tricky business to measure.

    And Hawking radiation itself has yet to be observed as an actual thing.

    Yet Chen’s and Mourou’s model could feasibly be built using existing technology, and as the researchers point out in their paper, could also serve to test other hypotheses on the physics of black holes.

    It sounds far more appealing than waiting until the end of time in front of a black hole, at least.

    This research was published in Physical Review Letters.

    See the full article here .

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  • richardmitnick 7:35 pm on August 15, 2016 Permalink | Reply
    Tags: , Hawking radiation,   

    From Technion: “Technion Scientist is First to Observe Hawking Radiation” 

    Technion bloc

    Technion

    August 15, 2016
    Kevin Hattori

    The eminent British scientist Stephen Hawking made predictions, 42 years ago, about elusive radiation emanating from black holes.

    Known as Hawking radiation, this phenomenon is too weak to observe with current techniques, and remained a “holy grail” for the fields of atomic physics, nonlinear optics, solid state physics, condensed matter superfluids, astrophysics, cosmology, and particle physics. It remained as such until Prof. Jeff Steinhauer’s observations of Hawking radiation in an analogue (model) black hole created at his Atomic Physics Lab in the Technion-Israel institute of Technology Faculty of Physics.

    1
    Technion-Israel Institute of Technology Professor Jeff Steinhauer

    Steinhauer’s latest findings, published today in Nature Physics, describe the first observation of thermal, quantum Hawking radiation in any system. “We observe a thermal distribution of Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole,” says Steinhauer. “This confirms Hawking’s prediction regarding black hole thermodynamics.”

    Pairs of phonons (particles of sound) appear spontaneously in the void at the event horizon (in layman’s terms, this is “the point of no return” in spacetime, beyond which events cannot affect an outside observer) of the analogue black hole. One of the phonons travels away from the black hole as Hawking radiation, and the other partner phonon falls into the black hole. The pairs have a broad spectrum of energies. It is the correlations between these pairs that allow for the detection of the Hawking radiation.

    The Hawking and partner particles within a pair can have a quantum connection called “entanglement.” Steinhauer explains: “Using a technique we developed, we saw that high energy pairs were entangled, while low energy pairs were not. This entanglement verifies an important element in the discussion of the information paradox (the idea that information that falls into a black hole is destroyed or lost) as well as the firewall controversy (the theory that a wall of fire – resulting from the breaking of the entanglement between the Hawking particles and their partners – exists at the event horizon of a black hole).”

    This observation of Hawking radiation, performed in a Bose-Einstein condensate (a quantum state of matter where a clump of super-cold atoms behaves like a single atom), verifies Hawking’s semiclassical calculation, which is viewed as a milestone in the quest for quantum gravity. The observation of its entanglement verifies important elements in the discussion of information loss in a real black hole.

    Steinhauer has been working exclusively on the proof since 2009 in his hand-assembled lab, replete with lasers and dozens of mirrors, lenses, and magnetic coils to simulate a black hole. Motivated by an overriding curiosity regarding the laws of physics since he was a child, Steinhauer says that evidence for the existence of quantum Hawking radiation brings us one step further in our endless journey of discovering the laws of the universe. This understanding itself is important to human beings, as is the applications of the laws of physics in society.

    Through the Wormhole, a Science Channel TV show hosted and narrated by Academy Award winner Morgan Freeman, featured Steinhauer back in 2012. Here, he discussed his creation of an analogue black hole in the lab and his hopes of using it to observe Hawking radiation. The analogue black hole takes advantage of his pioneering ultra-high resolution imaging system.

    In 2014, Steinhauer succeeded in doing this, publishing his results in a top science journal of the first observation of Hawking radiation in any system. This earlier work demonstrated self-amplifying Hawking radiation, which reflected from the inner horizon, returned to the outer horizon, and caused additional Hawking radiation. In contrast, his latest research endorses the existence of quantum Hawking radiation, the spontaneous appearance of Hawking pairs.

    See the full article here .

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    Technion Campus

    A science and technology research university, among the world’s top ten,
    dedicated to the creation of knowledge and the development of human capital and leadership,
    for the advancement of the State of Israel and all humanity.

     
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