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  • richardmitnick 1:48 pm on January 3, 2021 Permalink | Reply
    Tags: "What if the Universe has no end?", , , , , , Big Bang or Big Bounce, , , 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.

    3
    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.

    4
    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

    4
    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 2:44 pm on December 14, 2016 Permalink | Reply
    Tags: , , , Big Bang or Big Bounce, ,   

    From NOVA: “Did the Universe Start with a Bounce Instead of a Bang?” 

    PBS NOVA

    NOVA

    14 Dec 2016
    Marcus Woo

    1
    Big Bounce could have happened, scientists say. Istock

    For a few physicists, the Big Bang wasn’t the beginning of the universe.

    Rather, they say, the universe existed before that point, stretching forever into the past as well as the future. While the universe is expanding today, it was contracting in the time before the Big Bang. In this picture, the Big Bang isn’t so much a bang but a bounce, a moment when a shrinking universe reversed course and began to grow.

    And according to their theory, the universe could bounce again. Today’s expansion could be followed by collapse in the far future, followed by another bounce. Some physicists have suggested this bouncing could be infinite, reviving a cyclic cosmology first proposed in the 1930s.

    But how that infinitesimally hot and dense point came to be remains an unanswered question. Bouncing theories could promise to explain the origin of the cosmos. Whether a single bounce or endless bounces, a handful of cosmologists have spent the last couple decades tinkering with these ideas. But to others, bounce theories are simply speculative and controversial, and to some, they’re discredited and wrong.

    Much of the debate between Big Bang and Big Bounce proponents revolves around the viability of inflation, the mainstream view of how the universe has come to be the way it is today.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    And although any cosmologist would agree that inflation is, at the very least, incomplete, the vast majority considers it the best model yet. Still, bounce proponents see fundamental flaws in this model.

    “Inflation’s not doing too well,” says Neil Turok, director of the Perimeter Institute for Theoretical Physics. “It’s had its day. It was useful when it was invented in the early 1980s.” But now, he says, we need a new theory, and that theory could be a bouncing universe.

    A Cosmic Growth Spurt

    The standard story of inflation goes like this: shortly after the Big Bang, the universe ballooned rapidly—much faster than its normal expansion. This sudden growth was necessary to create the smooth, flat, and uniform universe that scientists see today.

    Cosmologists first developed inflation in the early 1980s, before balloon-borne experiments and satellites returned increasingly precise data on the state of the early universe. These observations measured the leftover radiation from the Big Bang, a ubiquitous glow called the cosmic microwave background [CMB].

    CMB per ESA/Planck
    CMB per ESA/Planck

    The radiation is patchily distributed, with some spots hotter and cooler than others, an auspicious result since the exact nature of this patchiness was precisely what inflation predicted.

    Inflation also predicted the mass density of the universe, also measured from the cosmic microwave background. “We’ve measured the mass density to better than a half percent accuracy, and it agrees perfectly with what inflation predicts—which is just gorgeous,” says Alan Guth, a physicist at MIT and the first who proposed inflation in 1980.

    “It’s really remarkable how much this simple idea of inflation has done,” says Robert Brandenberger, a physicist at McGill University. Although he’s exploring alternatives to inflation, the theory is the most self-consistent one out there, he says. “It’s successful because it predicted many things—and I emphasize predicted. Early in my career, we didn’t have the data. I saw inflation pass many more tests.”

    Still, while these successes have been more than encouraging for inflation, the evidence has yet to convince everyone. One prediction that might quell some dissent would be the detection of primordial gravitational waves, ripples in the fabric of space and time that originated from fluctuations of the gravity field in the early universe. It almost happened: In March 2014, the BICEP2 experiment at the South Pole claimed to have seen these gravitational waves. But that heralded discovery vanished when astronomers realized the signal could have been entirely due to dust in the galaxy.

    Gravitational Wave Background from BICEP 2
    Gravitational Wave Background from BICEP 2, quickly discredited.

    Inflation is not without its theoretical issues either. Some critics say that inflation requires initial conditions that are too specialized and contrived to be realistic. To get inflation started, the early universe had to be just right.

    Another point of contention is that inflation could imply the existence of an infinite number of universes. In the early 1980s, physicists discovered that inflation goes on forever, stopping only in some regions of space. But in between these pockets, inflation continues, expanding faster than the speed of light. These bubbles are thus closed off from each other, effectively becoming isolated universes with their own laws of physics. According to this theory, we live in one of these bubbles.

    While inflation proponents embrace this so-called multiverse, detractors say it’s absurd. If anything can happen in these bubble universes, then scientific predictions become meaningless. “If you have a theory that can’t be disproved, you should be dissatisfied with that,” Turok says. “That’s the state with inflation and the multiverse, so I would say this is not a scientific theory.”

    Even ardent supporters of inflation would agree the theory is incomplete. It doesn’t say anything about the moment of the Big Bang itself, for example, when the known laws of physics break down at what’s called a singularity.

    What inflation still lacks is a deeper foundation. Physicists have tried connecting inflation with string theory—the best candidate for a so-called theory of everything. But it’s still a work in progress. “With inflation, we basically add something by hand and we say it works, but we don’t have a more theoretical understanding of where it could come from,” says Steffen Gielen of the Perimeter Institute, who works with Turok on bouncing models.

    Bouncing Ideas

    The suggestion that the Big Bang wasn’t the absolute beginning originates from the first half of the 20th century, when physicists proposed a cyclic universe. But at the time, no one understood the details for how the universe could enter and emerge from each bounce.

    Todays’ physicists still have their work cut out for them, but now they have all the tools of modern particle physics and string theory. In 1992, Maurizio Gasperini and Gabriele Veneziano first used these modern ideas to revisit a pre-Big-Bang universe. Ten years later, Turok and Paul Steinhardt, a physicist at Princeton University and one of inflation’s pioneers turned critic, expanded on that work. They have since become two of the most outspoken detractors of inflation and proponents of a bouncing universe.

    A bouncing universe, they argue, could produce the cosmos we see today—but without inflation. The universe doesn’t need a period of super-expansion to reach the smooth, flat state we see today; it can do so while contracting. And because every corner of a shrinking universe would have been in contact with one another, the whole cosmos could settle into a uniform temperature—again, just as we see it today.

    Because so much of the early universe is unknown, theories of cosmology can vary widely. Inflation, for instance, isn’t one particular theory but a class of models, each a bit different in detail. Likewise, physicists have theorized many ways for how a universe can bounce.

    In one case, dubbed a matter bounce, the universe only bounces once. The collapse into the bounce is like a reverse-order Big Bang. Another version, called an ekpyrotic model, can be cyclical, with contraction followed by expansion followed by contraction, and so on. The anamorphic universe might be similarly cyclical.

    Pretty much all models require some sort of new physics. The differences between these models depend on the details, whether it’s new theories or exotic types of matter that halt the inertia of collapse and guide the universe through the bounce. Figuring out what happens at the bounce poses a big challenge, because that point is where the laws of physics fail, just as they do at the start of an inflationary universe.

    At the bounce, the universe collapses into a singularity, in which Einstein’s theory of gravity, general relativity, breaks down. Relativity isn’t currently compatible with quantum mechanics, which is needed at the small scales of the singularity. To unite the two, physicists have been searching for a theory of quantum gravity, which doesn’t yet exist.

    Over the past year, though, physicists have claimed modest progress on how to handle the singularity. Turok and Gielen have outlined how a simplified, toy model of a universe could undergo a quantum bounce. A bouncing universe containing only radiation—not unlike the radiation-dominated cosmos at the Big Bang—could cross the singularity in a way like quantum tunneling: According to quantum mechanics, a particle can spontaneously appear on the other side of a barrier that would otherwise be impenetrable in non-quantum physics. A collapsing universe can act like a particle and tunnel through the barrier-like singularity, appearing on the other side as the expanding universe we know today—and evading the singularity’s problems.

    Meanwhile, Steinhardt and Anna Ijjas of Princeton University have proposed a way the universe could bounce without evoking quantum mechanics. They’ve shown that some exotic, negative energy could prevent a universe from collapsing into a singularity in the first place. By avoiding a singularity, the universe never gets small enough for quantum mechanics to come into play, so you don’t need quantum gravity. The universe then proceeds to expand.

    But while these two proposals might be a small advance, neither marks a radical leap from what’s been done before, Brandenberger says. We’re still far from solving the problem of the singularity. “If we solve the singularity problem by evoking exotic matter, the question is just twisted,” he says. In other words, instead of explaining the singularity, you now have to explain the exotic matter.

    Without new physics, a bounce doesn’t seem likely, according to Guth. “One has to adopt rather special features that one would have to assume in the underlying laws of physics to make the bounce possible,” he says. “To me, that doesn’t seem like a good bet.”

    But it’s still too early to judge, Turok says. The theories aren’t mature enough to be testable yet. Eventually, though, models could start making predictions. Future, more detailed measurements of the cosmic microwave background might support a particular model of inflation or a bouncing universe. Perhaps the most promising evidence would come in the form of primordial gravitational waves, which are about the best indicators of what happened in the moments after the Big Bang (or bounce).

    Depending on what these waves look like, researchers can start ruling out models of both bouncing universes and inflation. While the BICEP2 findings in 2014 were a false alarm, researchers hope other instruments will succeed, including its successor, BICEP3. The Atacama B-mode Search is now operating in the Atacama Desert in Chile, and researchers are planning future experiments with names such as the Primordial Inflation Polarization Explorer, Qubic, and Polarbear.

    The Right Path

    In the end, however, it may not simply come down to an either-or choice between bouncing models or inflation, even though proponents of bouncing models sell their idea as an alternative. “What they’re doing is much more closely allied to inflation than they would have you think,” says Andrew Liddle, a cosmologist at the University of Edinburgh. “I don’t think it’s that radical of a departure.” Many of the mathematical tools used in bouncing models are similar to those used for inflation, he says. And when you apply observations like the cosmic microwave background, both bouncing models and inflation give similar results.

    You can even have both a bounce and inflation. “Now, sociologically, many people who study bounce cosmologies do so because they’re interested in finding an alternative to inflation,” says Sean Carroll, a physicist at the California Institute of Technology. “That’s fine, but if you just said, without any preexisting agendas, does the universe have a bounce, and if so, could it also involve inflation? I think you’d say sure.”

    Still, the debates between bounce proponents and the most outspoken inflation supporters can get contentious, each somewhat dismissive of the other side. The conflict is a reminder that science—and perhaps theoretical physics, in particular—is ultimately a human endeavor, filled with egos and subjectivity. Legacies and Nobel Prizes could be at stake.

    “In the absence of data, you’re welcome to your opinion—opinion is all you have,” Carroll says. “All of these ideas have significant challenges and question marks next to them.” While a problem may be a deal-breaker for one person, it’s only a minor stumbling block to another. When blazing a new trail, the right path is often subjective.

    See the full article here .

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