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  • richardmitnick 1:48 pm on January 3, 2021 Permalink | Reply
    Tags: "What if the Universe has no end?", Alan Guth-Inflation theory, , , , , , , , 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 11:46 am on October 26, 2019 Permalink | Reply
    Tags: "Putting the “bang” in the Big Bang", Alan Guth-Inflation theory, , The post inflation reheating period sets up the conditions for the Big Bang.   

    From MIT News: “Putting the “bang” in the Big Bang” 

    MIT News

    From MIT News

    October 24, 2019
    Jennifer Chu

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    Image: Christine Daniloff, MIT, NASA/ESA Hubble

    Physicists simulate critical “reheating” period that kickstarted the Big Bang in the universe’s first fractions of a second.

    As the Big Bang theory goes, somewhere around 13.8 billion years ago the universe exploded into being, as an infinitely small, compact fireball of matter that cooled as it expanded, triggering reactions that cooked up the first stars and galaxies, and all the forms of matter that we see (and are) today.

    Just before the Big Bang launched the universe onto its ever-expanding course, physicists believe, there was another, more explosive phase of the early universe at play: cosmic inflation, which lasted less than a trillionth of a second. During this period, matter — a cold, homogeneous goop — inflated exponentially quickly before processes of the Big Bang took over to more slowly expand and diversify the infant universe.

    Recent observations have independently supported theories for both the Big Bang and cosmic inflation. But the two processes are so radically different from each other that scientists have struggled to conceive of how one followed the other.

    Now physicists at MIT, Kenyon College, and elsewhere have simulated in detail an intermediary phase of the early universe that may have bridged cosmic inflation with the Big Bang. This phase, known as “reheating,” occurred at the end of cosmic inflation and involved processes that wrestled inflation’s cold, uniform matter into the ultrahot, complex soup that was in place at the start of the Big Bang.

    “The post inflation reheating period sets up the conditions for the Big Bang, and in some sense puts the ‘bang’ in the Big Bang,” says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. “It’s this bridge period where all hell breaks loose and matter behaves in anything but a simple way.”

    Kaiser and his colleagues simulated in detail how multiple forms of matter would have interacted during this chaotic period at the end of inflation. Their simulations show that the extreme energy that drove inflation could have been redistributed just as quickly, within an even smaller fraction of a second, and in a way that produced conditions that would have been required for the start of the Big Bang.

    The team found this extreme transformation would have been even faster and more efficient if quantum effects modified the way that matter responded to gravity at very high energies, deviating from the way Einstein’s theory of general relativity predicts matter and gravity should interact.

    “This enables us to tell an unbroken story, from inflation to the postinflation period, to the Big Bang and beyond,” Kaiser says. “We can trace a continuous set of processes, all with known physics, to say this is one plausible way in which the universe came to look the way we see it today.”

    The team’s results appear today in Physical Review Letters. Kaiser’s co-authors are lead author Rachel Nguyen, and John T. Giblin, both of Kenyon College, and former MIT graduate student Evangelos Sfakianakis and Jorinde van de Vis, both of Leiden University in the Netherlands.

    “In sync with itself”

    The theory of cosmic inflation, first proposed in the 1980s by MIT’s Alan Guth, the V.F. Weisskopf Professor of Physics, predicts that the universe began as an extremely small speck of matter, possibly about a hundred-billionth the size of a proton.

    This speck was filled with ultra-high-energy matter, so energetic that the pressures within generated a repulsive gravitational force — the driving force behind inflation. Like a spark to a fuse, this gravitational force exploded the infant universe outward, at an ever-faster rate, inflating it to nearly an octillion times its original size (that’s the number 1 followed by 26 zeroes), in less than a trillionth of a second.

    Kaiser and his colleagues attempted to work out what the earliest phases of reheating — that bridge interval at the end of cosmic inflation and just before the Big Bang — might have looked like.

    “The earliest phases of reheating should be marked by resonances. One form of high-energy matter dominates, and it’s shaking back and forth in sync with itself across large expanses of space, leading to explosive production of new particles,” Kaiser says. “That behavior won’t last forever, and once it starts transferring energy to a second form of matter, its own swings will get more choppy and uneven across space. We wanted to measure how long it would take for that resonant effect to break up, and for the produced particles to scatter off each other and come to some sort of thermal equilibrium, reminiscent of Big Bang conditions.”

    The team’s computer simulations represent a large lattice onto which they mapped multiple forms of matter and tracked how their energy and distribution changed in space and over time as the scientists varied certain conditions. The simulation’s initial conditions were based on a particular inflationary model — a set of predictions for how the early universe’s distribution of matter may have behaved during cosmic inflation.

    The scientists chose this particular model of inflation over others because its predictions closely match high-precision measurements of the cosmic microwave background — a remnant glow of radiation emitted just 380,000 years after the Big Bang, which is thought to contain traces of the inflationary period.

    A universal tweak

    The simulation tracked the behavior of two types of matter that may have been dominant during inflation, very similar to a type of particle, the Higgs boson, that was recently observed in other experiments.

    Before running their simulations, the team added a slight “tweak” to the model’s description of gravity. While ordinary matter that we see today responds to gravity just as Einstein predicted in his theory of general relativity, matter at much higher energies, such as what’s thought to have existed during cosmic inflation, should behave slightly differently, interacting with gravity in ways that are modified by quantum mechanics, or interactions at the atomic scale.

    In Einstein’s theory of general relativity, the strength of gravity is represented as a constant, with what physicists refer to as a minimal coupling, meaning that, no matter the energy of a particular particle, it will respond to gravitational effects with a strength set by a universal constant.

    However, at the very high energies that are predicted in cosmic inflation, matter interacts with gravity in a slightly more complicated way. Quantum-mechanical effects predict that the strength of gravity can vary in space and time when interacting with ultra-high-energy matter — a phenomenon known as nonminimal coupling.

    Kaiser and his colleagues incorporated a nonminimal coupling term to their inflationary model and observed how the distribution of matter and energy changed as they turned this quantum effect up or down.

    In the end they found that the stronger the quantum-modified gravitational effect was in affecting matter, the faster the universe transitioned from the cold, homogeneous matter in inflation to the much hotter, diverse forms of matter that are characteristic of the Big Bang.

    By tuning this quantum effect, they could make this crucial transition take place over 2 to 3 “e-folds,” referring to the amount of time it takes for the universe to (roughly) triple in size. In this case, they managed to simulate the reheating phase within the time it takes for the universe to triple in size two to three times. By comparison, inflation itself took place over about 60 e-folds.

    “Reheating was an insane time, when everything went haywire,” Kaiser says. “We show that matter was interacting so strongly at that time that it could relax correspondingly quickly as well, beautifully setting the stage for the Big Bang. We didn’t know that to be the case, but that’s what’s emerging from these simulations, all with known physics. That’s what’s exciting for us.”

    “There are hundreds of proposals for producing the inflationary phase, but the transition between the inflationary phase and the so-called “hot big bang” is the least understood part of the story,” says Richard Easther, professor of physics at the University of Auckland, who was not involved in the research. “This paper breaks new ground by accurately simulating the postinflationary phase in models with many individual fields and complex kinetic terms. These are extremely challenging numerical simulations, and extend the state of the art for studies of nonlinear dynamics in the very early universe.”

    This research was supported, in part, by the U.S. Department of Energy and the National Science Foundation.

    See the full article here .


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  • richardmitnick 12:12 pm on March 23, 2019 Permalink | Reply
    Tags: "This Is Why The Multiverse Must Exist", Alan Guth-Inflation theory, , , ,   

    From Ethan Siegel: “This Is Why The Multiverse Must Exist” 

    From Ethan Siegel
    Mar 22, 2019

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    The multiverse idea states that there are an arbitrarily large number of Universes like our own out there, embedded in our Multiverse. It’s possible, but not necessary, for other pockets within the Multiverse to exist where the laws of physics are different.

    If you accept cosmic inflation and quantum physics, there’s no way out. The Multiverse is real.

    Look out at the Universe all you want, with arbitrarily powerful technology, and you’ll never find an edge. Space goes on as far as we can see, and everywhere we look we see the same things: matter and radiation. In all directions, we find the same telltale signs of an expanding Universe: the leftover radiation from a hot, dense state; galaxies that evolve in size, mass, and number; elements that change abundances as stars live and die.

    But what lies beyond our observable Universe? Is there an abyss of nothingness beyond the light signals that could possibly reach us since the Big Bang? Is there just more Universe like our own, out there past our observational limits? Or is there a Multiverse, mysterious in nature and forever unable to be seen?

    Unless there’s something seriously wrong with our understanding of the Universe, the Multiverse must be the answer. Here’s why.

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    Artist’s logarithmic scale conception of the observable universe. Note that we’re limited in how far we can see back by the amount of time that’s occurred since the hot Big Bang: 13.8 billion years, or (including the expansion of the Universe) 46 billion light years. Anyone living in our Universe, at any location, would see almost exactly the same thing from their vantage point. (WIKIPEDIA USER PABLO CARLOS BUDASSI)

    The Multiverse is an extremely controversial idea, but at its core it’s a very simple concept. Just as the Earth doesn’t occupy a special position in the Universe, nor does the Sun, the Milky Way, or any other location, the Multiverse goes a step farther and claims that there’s nothing special about the entire visible Universe.

    The Multiverse is the idea that our Universe, and all that’s contained within it, is just one small part of a larger structure. This larger entity encapsulates our observable Universe as a small part of a larger Universe that extends beyond the limits of our observations. That entire structure — the unobservable Universe — may itself be part of a larger spacetime that includes many other, disconnected Universes, which may or may not be similar to the Universe we inhabit.

    If this is the idea of the Multiverse, I can understand your skepticism at the notion that we could somehow know whether it does or doesn’t exist. After all, physics and astronomy are sciences that rely on measurable, experimental, or otherwise observational confirmation. If we are looking for evidence of something that exists outside of our visible Universe and leaves no trace within it, it seems that the idea of a Multiverse is fundamentally untestable.

    But there are all sorts of things that we cannot observe that we know must be true. Decades before we directly detected gravitational waves, we knew that they must exist, because we observed their effects.

    Gravitational waves. Credit: MPI for Gravitational Physics/Werner Benger

    Binary pulsars — spinning neutron stars orbiting around one another — were observed to have their revolutionary periods shorten. Something must be carrying energy away, and that thing was consistent with the predictions of gravitational waves.

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    Binary pulsars via Universe Today

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    The rate of orbital decay of a binary pulsar is highly dependent on the speed of gravity and the orbital parameters of the binary system. We have used binary pulsar data to constrain the speed of gravity to be equal to the speed of light to a precision of 99.8%, and to infer the existence of gravitational waves decades before LIGO and Virgo detected them. (NASA (L), MAX PLANCK INSTITUTE FOR RADIO ASTRONOMY / MICHAEL KRAMER (R))

    While we certainly welcomed the confirmation that LIGO and Virgo provided for gravitational waves via direct detection, we already knew that they needed to exist because of this indirect evidence.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    Those who would argue that indirect evidence is no indicator of gravitational waves might still be unconvinced that binary pulsars emit them; LIGO and Virgo didn’t see the gravitational waves that came from the binary pulsars we’ve observed.

    So if we cannot observe the Multiverse directly, what indirect evidence do we have for its existence? How do we know that there’s more unobservable Universe beyond the part we can observe, and how do we know that what we call our Universe is likely just one of many embedded in the Multiverse?

    We look to the Universe itself, and draw conclusions about its nature based on what observations about it reveal.

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    The light from the cosmic microwave background and the pattern of fluctuations from it gives us one way to measure the Universe’s curvature. To the best of our measurements, to within 1 part in about 400, the Universe is perfectly spatially flat. (SMOOT COSMOLOGY GROUP / LAWRENCE BERKELEY LABS)

    When we look out to the edge of the observable Universe, we find that the light rays emitted from the earliest times — from the Cosmic Microwave Background [CMB] — make particular patterns on the sky.

    CMB per ESA/Planck

    Gravitational Wave Background from BICEP 2 which ultimately failed to be correct. The Planck team determined that the culprit was cosmic dust.

    ESA/Planck 2009 to 2013

    These patterns not only reveal the density and temperature fluctuations that the Universe was born with, as well as the matter and energy composition of the Universe, but also the geometry of space itself.

    We can conclude from this that space isn’t positively curved (like a sphere) or negatively curved (like a saddle), but rather spatially flat, indicating that the unobservable Universe likely extends far beyond the part we can access. It never curves back on itself, it never repeats, and it has no empty gaps in it. If it is curved, it has a diameter that’s hundreds of times greater than the part we can see.

    With every second that ticks by, more Universe, just like our own, is revealed to us, consistent with this picture.

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    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that. Over time, we’ll be able to see more of it, eventually revealing approximately 2.3 times as much matter as we can presently view. (FRÉDÉRIC MICHEL AND ANDREW Z. COLVIN, ANNOTATED BY E. SIEGEL)

    That might indicate that there’s more unobservable Universe beyond the part of our Universe we can access, but it doesn’t prove it, and it doesn’t provide evidence for a Multiverse. There are, however, two concepts in physics that have been established far beyond a reasonable doubt: cosmic inflation and quantum physics.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

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

    Alan Guth’s notes:
    5

    Cosmic inflation is the theory that gave rise to the hot Big Bang. Rather than beginning with a singularity, there’s a physical limit to how hot and how dense the initial, early stages of our expanding Universe could have reached. If we had achieved arbitrarily high temperatures in the past, there would be clear signatures that aren’t there:

    large-amplitude temperature fluctuations early on,
    seed density fluctuations limited by the scale of the cosmic horizon,
    and leftover, high-energy relics from early times, like magnetic monopoles.

    6
    Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved or non-smooth space appearing flat. If the Universe is curved, it has a radius of curvature that is at minimum hundreds of times larger than what we can observe. (E. SIEGEL (L); NED WRIGHT’S COSMOLOGY TUTORIAL (R))

    These signatures are all missing. The temperature fluctuations are at the 0.003% level; the density fluctuations exceed the scale of the cosmic horizon; the limits on monopoles and other relics are incredibly stringent. The fact that these signatures aren’t there have an enormous implication to them: the Universe never reached those arbitrarily high temperatures. Something else came before the hot Big Bang to set it up.

    That’s where cosmic inflation comes in. Theorized in the early 1980s [above], it was designed to solve a number of puzzles with the Big Bang, but did what you’d hope for any new physical theory: it made measurable, testable predictions for observable signatures that would appear within our Universe.

    We see the predicted lack of spatial curvature; we see an adiabatic nature to the fluctuations the Universe was born with; we’ve detected a spectrum and magnitude of initial fluctuations that jibe with inflation’s predictions; we’ve seen the superhorizon fluctuations that inflation predicts must arise.

    6
    Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during inflation, giving rise to imperfections in both density and gravitational waves. Whether inflation arose from an eventual singularity or not is unknown, but the signatures of whether it occurred are accessible in our observable Universe. (E. SIEGEL, WITH IMAGES DERIVED FROM ESA/PLANCK AND THE DOE/NASA/ NSF INTERAGENCY TASK FORCE ON CMB RESEARCH)

    We may not know everything about inflation, but we do have a very strong suite of evidence that supports a period in the early Universe where it occurred. It set up and gave rise to the Big Bang, and predicts a set and spectrum of fluctuations that gave rise to the seeds of structure that grew into the cosmic web we observe today. Only inflation, as far as we know, gives us predictions for our Universe that match what we observe.

    “So, big deal,” you might say. “You took a small region of space, you allowed inflation to expand it to some very large volume, and our observable, visible Universe is contained within that volume. Even if this is all right, this only tells us that our unobservable Universe extends far beyond the visible part. You haven’t established the Multiverse at all.”

    And all of that would be correct. But remember, there’s one more ingredient we need to add in: quantum physics.

    7
    (Illustration: Getty Images)

    6
    An illustration between the inherent uncertainty between position and momentum at the quantum level. There is a limit to how well you can measure these two quantities simultaneously, and uncertainty shows up in places where people often least expect it. (E. SIEGEL / WIKIMEDIA COMMONS USER MASCHEN)

    Inflation is treated as a field, like all the quanta we know of in the Universe, obeying the rules of quantum field theory. In the quantum Universe, there are many counterintuitive rules that are obeyed, but the most relevant one for our purposes is the rule governing quantum uncertainty.

    While we conventionally view uncertainty as mutually occurring between two variables — momentum and position, energy and time, angular momentum of mutually perpendicular directions, etc. — there’s also an inherent uncertainty in the value of a quantum field. As time marches forward, a field value that was definitive at an earlier time now has a less certain value; you can only ascribe probabilities to it.

    In other words, the value of any quantum field spreads out over time.

    8
    As time goes on, even for a simple, single particle, its quantum wavefunction that describes its position will spread out, spontaneously, over time. This happens for all quantum particles for a myriad of properties beyond position, such as the field value. (HANS DE VRIES / PHYSICS QUEST)

    Now, let’s combine this: we have an inflating Universe, on one hand, and quantum physics on the other. We can picture inflation as a ball rolling very slowly on top of a flat hill. So long as the ball remains atop the hill, inflation continues. When the ball reaches the end of the flat part, however, it rolls down into the valley below, which converts the energy from the inflationary field itself into matter and energy.

    This conversion signifies the end of cosmic inflation through a process known as reheating, and it gives rise to the hot Big Bang we’re all familiar with. But here’s the thing: when your Universe inflates, the value of the field changes slowly. In different inflating regions, the field value spreads out by randomly different amounts and in different directions. In some regions, inflation ends quickly; in others, it ends more slowly.

    9
    The quantum nature of inflation means that it ends in some “pockets” of the Universe and continues in others. It needs to roll down the metaphorical hill and into the valley, but if it’s a quantum field, the spreading-out means it will end in some regions while continuing in others. (E. SIEGEL / BEYOND THE GALAXY)

    This is the key point that tells us why a Multiverse is inevitable! Where inflation ends right away, we get a hot Big Bang and a large Universe, where a small part of it might be similar to our own observable Universe. But there are other regions, outside of the region where it ends, where inflation continues for longer.

    Where the quantum spreading occurs in just the right fashion, inflation might end there, too, giving rise to a hot Big Bang and an even larger Universe, where a small portion might be similar to our observable Universe.

    But the other regions aren’t still just inflating, they’re also growing. You can calculate the rate at which the inflating regions grow and compare them to the rate at which new Universes form and hot Big Bangs occur. In all cases where inflation gives you predictions that match the observed Universe, we grow new Universes and newly inflating regions faster than inflation can come to an end.

    10
    Wherever inflation occurs (blue cubes), it gives rise to exponentially more regions of space with each step forward in time. Even if there are many cubes where inflation ends (red Xs), there are far more regions where inflation will continue on into the future. The fact that this never comes to an end is what makes inflation ‘eternal’ once it begins, and what gives rise to our modern notion of a Multiverse. (E. SIEGEL / BEYOND THE GALAXY)

    This picture, of huge Universes, far bigger than the meager part that’s observable to us, constantly being created across this exponentially inflating space, is what the Multiverse is all about. It’s not a new, testable scientific prediction, but rather a theoretical consequence that’s unavoidable, based on the laws of physics as they’re understood today. Whether the laws of physics are identical to our own in those other Universes is unknown.

    If you have an inflationary Universe that’s governed by quantum physics, a Multiverse is unavoidable. As always, we are collecting as much new, compelling evidence as we can on a continuous basis to better understand the entire cosmos. It may turn out that inflation is wrong, that quantum physics is wrong, or that applying these rules the way we do has some fundamental flaw. But so far, everything adds up. Unless we’ve got something wrong, the Multiverse is inevitable, and the Universe we inhabit is just a minuscule part of it.

    See the full article here .

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  • richardmitnick 10:15 am on September 12, 2018 Permalink | Reply
    Tags: "The fractal universe" Part 3, Alan Guth-Inflation theory, Andrei Linde-Professor of Physics, , , , , , ,   

    From Stanford University: “The fractal universe” Part 3 

    Stanford University Name
    From Stanford University

    1
    The concept of a multiverse, created in a fiery bloom of matter and radiation, is a central part of the String Theory Landscape. (Image credit: Eric Nyquist)

    September 12, 2018
    Ker Than

    Late one summer night nearly 40 years ago, Andrei Linde was seized by a sudden conviction that he knew how the universe was born. His nocturnal eureka moment would lead to the concept of a multiverse, a central part of the String Theory Landscape. This story is part 3 of a five-part series.

    Late one summer night in 1981, while still a junior research fellow at Lebedev Physical Institute in Moscow, Andrei Linde was struck by a revelation. Unable to contain his excitement, he shook awake his wife, Renata Kallosh, and whispered to her in their native Russian, “I think I know how the universe was born.”

    Kallosh, a theoretical physicist herself, muttered some encouraging words and fell back asleep. “It wasn’t until the next morning that I realized the full impact of what Andrei had told me,” recalled Kallosh, now a professor of physics at the Stanford Institute for Theoretical Physics.

    Linde’s nocturnal eureka moment had to do with a problem in cosmology that he and other theorists, including Stephen Hawking, had struggled with for months.

    A year earlier, a 32-year-old postdoc at SLAC National Accelerator Laboratory named Alan Guth shocked the physics community by proposing a bold modification to the Big Bang theory. According to Guth’s idea, which he called “inflation,” our universe erupted from a vacuum-like state and underwent a brief period of faster-than-light expansion.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

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

    Alan Guth’s notes:
    5

    In less than a billionth of a trillionth of a trillionth of a second, space-time doubled more than 60 times from a subatomic speck to a volume many times larger than the observable universe.

    Guth envisioned the powerful repulsive force fueling the universe’s exponential growth as a field of energy flooding space. As the universe unfurled, this “inflaton field” decayed, and its shed energy was transfigured into a fiery bloom of matter and radiation. This pivot, from nothing to something and timelessness to time, marked the beginning of the Big Bang. It also prompted Guth to famously quip that the inflationary universe was the “ultimate free lunch.”

    As theories go, inflation was a beauty. It explained in one fell swoop why the universe is so large, why it was born hot, and why its structure appears to be so flat and uniform over vast distances. There was just one problem – it didn’t work.

    Tunneling

    To conclude the unpacking of space-time, Guth borrowed a trick from quantum mechanics called “tunneling” to allow his inflaton field to randomly and instantly skip from a higher, less stable energy state to a lower one, thus bypassing a barrier that could not be scaled by classical physics.

    3
    Andrei Linde and Renata Kallosh, both professors of physics. (Image credit: L.A. Cicero)

    But closer inspection revealed that quantum tunneling caused the inflaton field to decay quickly and unevenly, resulting in a universe that was neither flat nor uniform. Aware of the fatal flaw in his theory, Guth wrote at the end of his paper on inflation: “I am publishing this paper in the hope that it will … encourage others to find some way to avoid the undesirable features of the inflationary scenario.”

    Guth’s plea was answered by Linde, who on that fateful summer night realized that inflation didn’t require quantum tunneling to work. Instead, the inflaton field could be modeled as a ball rolling down a hill of potential energy that had a very shallow, nearly flat slope. While the ball rolls lazily downhill, the universe is inflating, and as it nears the bottom, inflation slows further and eventually ends. This provided a “graceful exit” to the inflationary state that was lacking in Guth’s model and produced a cosmos like the one we observe. To distinguish it from Guth’s original model while still paying homage to it, Linde dubbed his model “new inflation.”

    Quantum birth of galaxies

    By the time Linde and Kallosh moved to Stanford in 1990, experiments had begun to catch up with the theory. Space missions were finding temperature variations in the energetic afterglow of the Big Bang – called the cosmic microwave background radiation – that confirmed a startling prediction made by the latest inflationary models. These updated models went by various names – “chaotic inflation,” “eternal inflation,” “eternal chaotic inflation” and many more – but they all shared in common the graceful exit that Linde pioneered.

    According to these models, galaxies like the Milky Way grew from faint wrinkles in the fabric of space-time. The density of matter in these wrinkles was slightly greater compared to surrounding areas and this difference was magnified during inflation, allowing them to attract even more matter. From these dense primordial seeds grew the cosmic structures we see today. “Galaxies are children of random quantum fluctuations produced during the first 10-35 seconds after the birth of the universe,” Linde said.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Inflation predicted that these quantum fluctuations would leave imprints on the universe’s background radiation in the form of hotter and colder regions, and this is precisely what two experiments – dubbed COBE and WMAP – found. “After the COBE and WMAP experiments, inflation started to become part of the standard model of cosmology,” Shamit Kachru said.

    COBE/CMB


    NASA/COBE 1989 to 1993.

    CMB per NASA/WMAP


    NASA/WMAP 2001 to 2010

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    5
    Shamit Kachru, Professor of Physics and Director, Stanford Institute for Theoretical Physics (Image credit: L.A. Cicero)

    The multiverse

    Linde and others later realized that the same quantum fluctuations that produced galaxies can give rise to new inflating regions in the universe. Even though inflation ended in our local cosmic neighborhood 14 billion years ago, it can still continue at the outermost fringes of the universe. The consequence is an ever-expanding sea of inflating space-time dotted with “island universes” or “pocket universes” like our own where inflation has ceased.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    “As a result, the universe becomes a multiverse, an eternally growing fractal consisting of exponentially many exponentially large parts,” Linde wrote. “These parts are so large that for all practical purposes they look like separate universes.”

    Linde took the multiverse idea even further by proposing that each pocket universe could have differing properties, a conclusion that some string theorists were also reaching independently. “It’s not that the laws of physics are different in each universe, but their realizations,” Linde said. “An analogy is the relationship between liquid water and ice. They’re both H2O but realized differently.”

    Linde’s multiverse is like a cosmic funhouse filled with reality-distorting mirrors. Some pocket universes are resplendent with life, while others were stillborn because they were cursed with too few (or too many) dimensions, or with physics incompatible with the formation of stars and galaxies. An infinite number are exact replicas of ours, but infinitely more are only near-replicas. Right now, there could be countless versions of you inhabiting worlds with histories divergent from ours in ways large and small. In an infinitely expanding multiverse, anything that can happen will happen.

    “The inflationary universe is not just the ultimate free lunch, it’s the only lunch where all possible dishes are served,” Linde said.

    While disturbing to some, this eternal aspect of inflation was just what a small group of string theorists were looking for to help explain a surprise discovery that was upending the physics world – dark energy.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    See the full article here .


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    Please help promote STEM in your local schools.

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    Stanford University campus. No image credit

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

    Stanford University Seal

     
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