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Question regarding the universes origin

  1. Jul 31, 2014 #1
    According to the Poincare recurrence theorem - certain systems will, after a sufficiently long but finite time, return to a state very close to the initial state.

    and according to wikipedia - a quantum fluctuation or vacuum fluctuation is the temporary change in the amount of energy in a point in space,as explained in Werner Heisenberg's uncertainty principle.

    and according to wikipedia again - a bubble of lower-energy vacuum could come to exist by chance or otherwise in our universe, and catalyze the conversion of our universe to a lower energy state in a volume expanding at nearly the speed of light, destroying all that we know without forewarning. Chaotic Inflation theory suggests that the universe may be in either a false vacuum or a true vacuum state.

    Is it possible that in a universe such as ours that expands forever and reaches heat death will have regions where all these occurrences happen at the same time; thereby birthing a new stable universe that is part of, yet separate from our own.
     
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  3. Jul 31, 2014 #2

    marcus

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    That's a guess. there are a variety of guesses like that which have been proposed. To make progress we need a model of how our OWN expansion started (call it big bang, loop big bounce, Penrose conformal cycle, Steinhardt cyclic bounce, eternal inflation fluctuation…) and that model should be TESTABLE, namely falsifiable by some observation of ancient light, structure formation etc etc.

    Lots of models have been proposed (bounce models are increasingly popular of late) for what could have preceded our expansion, what came before our "bang"… the important thing to look for in these models is some way of testing or falsifying by observation.

    Paul Steinhardt (princeton) gave a great talk back in June about this, at the Strings conference. There's a video. He gave a cogent critique of the inflation paradigm and all that quantum fluctuation stuff. He has a model that does not depend on random fluctuations, but achieves more or less the same results that inflation is known for. From what I hear the talk upset some of the conferees. :biggrin:

    Something completely different, that appeals to me, is a proposal by Barrau and Linsefors that is oddly similar to your own. I'll get a link.
    http://arxiv.org/abs/1406.3706
    Our Universe from the cosmological constant
    Aurelien Barrau, Linda Linsefors
    (Submitted on 14 Jun 2014)
    In this article, we consider a bouncing Universe, as described for example by Loop Quantum Cosmology. If the current acceleration is due to a true cosmological constant, this constant is naturally conserved through the bounce and the Universe should also be in a (contracting) de Sitter phase in the remote past. We investigate here the possibility that the de Sitter temperature in the contracting branch fills the Universe with radiation and causes the bounce and the subsequent inflation and reheating. We also consider the possibility that this gives rise to a cyclic model of the Universe and suggest some possible tests.
    5 pages

    Paul Steinhardt is very well known, an established senior figure, and an excellent speaker. I'll get a link to his 28 minute talk later in case you are interested. By contrast Barrau and Linsefors are bright young people, less well known. Barrau's area of expertise is in testing other people's cosmological models, determining if and how it can be done. It's not every day he comes out with his own proposal!
     
    Last edited: Jul 31, 2014
  4. Jul 31, 2014 #3
    "In the far future, huge patches of our universe, with
    radii larger than the Hubble scale, will be completely
    empty. They will be pure dS spaces. If the model sug-
    gested in this work is correct, these empty spaces will
    give birth to new universe through the process of spon-
    taneous symmetry breaking described above. When this
    leads to a contraction, which will inevitably occur, a new
    universe filled with radiation – and then matter – will
    appear."

    Can you further explain what the author of this paper means by "breakage of SUSY", and how does this breakage relate to matter forming spontaneously in these hypothetical sub-manifolds.
     
  5. Jul 31, 2014 #4

    marcus

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    I won't be able to satisfy your curiosity, certainly not completely. Others may want to help. First off, SUSY stands for "supersymmetry" a special very complex extra symmetry that has not been shown to exist, no evidence for it was found at LHC.
    But there is lots of NON-SUPER plain ordinary symmetry in standard everyday physics that has been tested and passed the tests so far.

    I don't think Barrau and Linsefors mention SUSY anywhere. So the question is, in that passage you quoted, what ARE they talking about (since they aren't talking about SUSY)?

    Well they refer to the "process of symmetry breaking described above…" so lets look back and see what that is.

    Here it is, on page 2, in the middle of the righthand column:

    ==quote http://arxiv.org/abs/1406.3706 ==
    ... If standard fields, e.g. radiation, are introduced in a dS space, the time symmetry will be broken. In the simplest case, we end up with a homogenous universe that evolves in time. We focus on this simple case.

    We suggest a scenario where the radiation from the dS horizon spontaneously breaks the symmetry of the dS structure. Out of this, one gets a homogenous universe with a tiny amount of radiation, an arbitrary curvature, and a Hubble factor with arbitrary sign. If the Universe is expanding, the radiation will be diluted away and one gets back to an empty dS space. But if the Universe is contracting, something interesting happens. Let us start with the Friedmann equation…
    ==endquote==
    back later…oops, family stuff takes precedence. Have to get back to this later. the main thing is that in Gen Rel there is a simple geometry that approximately fits expanding U, called "de Sitter space", or "dS". It has many equally good choices of time coordinate. No preferred one. That means a high degree of spacetime geometry SYMMETRY. It's a bit like the familiar space of Special Rel, where when you have reference frames of two relatively moving observers there is no PREFERRED frame---that is the basic symmetry of SR. The two are equally good. democracy of frames.
    But in SR there is no expansion or contraction of distances. dS space is LIKE Special Rel in having frame democracy, but with the extra feature of expansion contraction of distances. And which of the two is happening depends on your choice of time coordinate.
    A small amount of radiation is enough to choose a preferred time coordinate and thus break that symmetry. that is what they are talking about. have to go….
     
    Last edited: Aug 1, 2014
  6. Aug 1, 2014 #5

    marcus

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    So how does the presence of radiation, think for example of our CMB, the background of ancient light, choose a preferred time coordinate for us?

    Well that's been our practical experience in cosmology! The Background gives us a criterion of rest. If you move relative to the CMB you detect a doppler warm spot ahead of you and a cool spot behind. We can define a class of observers who are at rest relative to ancient light. They all experience the same time and that time is universe standard time. It is also called Friedman time and is the time the Friedman equation model of the cosmos runs on.

    So that Background light actually breaks the ideal symmetry of GR according to which there is no preferred frame, no preferred idea of rest, no preferred time coordinate.

    So in answer to your question, namely what symmetry breaking are Barrau Linsefors talking about?
    the answer is they are talking about a pure dS space, that has perfect dS symmetry with NO preferred time coordinate, and then a faint glow of radiation appears and that gives a criterion of rest, and a preferred class of observers, or frames, and a preferred time. So it breaks the initial symmetry of the dS geometry.

    I hope that explanation is on the right level and doesn't put you off. Glad to be talking about this, it is an interesting new idea of how the U could regenerate itself. And the idea works by putting together familiar components, tried and true well studied stuff. It is not fantasy. And it apparently is testable---that is Aurelien Barrau's specialty, he's a cosmology phenomenologist---a cosmic model tester.
    So I'm happy to be talking about the paper.

    I didn't talk about where the radiation comes from, in their model. If you are interested I'll talk about that tomorrow, or someone else will jump in. dS space has a temperature because of its accelerated expansion. Any observer is surrounded by an event horizon which is kind of like a very gentle inside-out BH horizon, that glows with cool thermal radiation by roughly the same physics as a BH horizon glows. Black holes have a temperature called "Hawking temperature" and the dS horizon has analogous temperature.. So if you are in dS space there is certain to be a possibly very faint radiation. Maybe get back to this tomorrow. It is late now.
     
  7. Aug 1, 2014 #6
    Poincaré's recurrence theorem and "Tryon's moment"

    It’s important to note that the observable universe appears not to be one of the dynamic systems for which Poincaré recurrence theorem. Stated informally, for it to apply a physical system, that system must be contained in a fixed volume, allowing no parts of it to escape that volume. Described classically (ie without effects like Hawking radiation or other quantum phenomena), the inside of a black hole is such a system. Were the universe more massive (by naive calculations, about 3 time more) that is, were it inside a black hole, nothing, not even light, would escape it, and it would be the kind of dynamic system to which the recurrence theorem applies. It appears not to be – nearly all the universe’s light is constantly increasing its volume, its radius increasing at the speed of light.

    I’d be better able to understand you and comment if you said where (in what articles) in wikipedia you were getting your information, but your statement seem to match my understanding of the subject.
    The idea that the universe – big bang, expansion, the present stelliferous era, its future heat death, and everything in between – is a large-scale quantum fluctuation is the core of Edward Tryon’s 1973 proposal, which he’s semi-famously quoted as summarizing "the universe is simply one of those things that happens from time to time.", which is sometimes referred to as “nothing cosmology”, “nothing physics”, or “nothing theory”. I don’t think this is a very well-developed subject, in large part because, as marcus points out, models need to be testable/falsifiable to be truly scientific, and it’s difficult to imagine experiments to falsify Tryon’s hypothesis. (“Wait and eventually observe it happening” isn’t a very satisfying experiment design)

    Nothing is the hypothesis suggests that a universe-birthing quantum fluctuation would occur in many different regions of our universe at the same time (the concept of “at the same time” in very large objects like the universe is usually problematical, but I think OK in this context). Tryon’s “from time to time” is understood to suggest a very long time, vastly many powers of 10 times the present age of the universe (this estimate gives 10^(10^56)) years), and to be effectively random, so the likelihood of several occurring at or around the same time is very small.

    Though I imagine that Tryon imagined the UBQF happening in heat death old age of a universe, there’s no obvious reason that it couldn’t happen at any time. Because the old age of the universe is a much longer duration than its present age, the probability of “Tryon’s moment” occurring in an era but the universe’s old age is very small, but, per the theory, if we were very unlucky, a big bang could occur today, very close to us, expanding in less than 10^-11 seconds to devour us and everything in a primordial quark-gluon plasma.
     
  8. Aug 1, 2014 #7
    Questions:

    1. What is meant by "preferred" time coordinate?
    2. How does radiation break ds symmetry?
    "If standard fields, e.g. radiation, are introduced in a dS space, the time symmetry will be broken"
    3. Forgive me for my ignorance on this subject, I'm an applied math student, but how does radiation "break" time symmetry. Does this have to do with entropy?
    4. I have read that the universe is increasing in expansion because of dark energy and that after heat death no usable energy will exist. So, how can radiation still exist in a universe thats already totally cold? is the amount of radiation necessary to break time/spacial symmetry and form a "de sitter universe" very small or infinitesimal?
     
  9. Aug 2, 2014 #8

    marcus

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    Hiyo Silver :biggrin:, thanks for the good questions! I'm not always the best qualified to answer (and was kind of overloaded with reallife things yesterday) so'd be happy if someone else would chime in. but I'll try to respond.

    1. it just means somehow distinguished or picked out. In pure GR there is pure egalitarian demography. When yu have a solution to the GR equation there are million different possible observer world lines threading it and each obs has his own clock. Nothing picks one out. Nothing physical chooses and highlights one particular worldline or class of worldlines above the rest.

    But if there is a soup of radiation like the CMB that picks out one. It makes it possible for us (in cosmology) to have an "official" time. I make the point repeatedly in the Balloon Model thread. In cosmology we have a criterion of rest. Yu can say what you mean by being "at rest with respect to the universe" or at rest relative to the ancient light. The Hubble Law is defined using that idea, the distances it talks about are between stationary points and the rate of their growth is in terms of universe standard time. the law v(t) = H(t)D(t) would not be true for an observer moving relative to Background.

    So for us, for anyone professional or amateur doing standard Hubble Law cosmology, the original symmetry of Gen Rel has been, happily enough, broken by our being given a distinguish criterion of rest and a distinguished choice of time. Don't think of "broken" as having a "bad" connotation. It can be a help. Like on Earth we have a distinguished direction North (because the earth rotates) on a sphere that does not rotated all directions are equal and there is nothing physical that distinguishes.So rotation breaks symmetry, thank goodness.

    2. In cosmology the CMB gives us a criterion of rest because if you move relative to it you see a doppler hot spot ahead of you. They generalize this. I am not sure how they do this. Here is how I THINK they reason. in dS space any observer is surrounded by a large sphere which is his event horizon because of the accelerated expansion. The Lambda. What defines dS space is the positive cosmological constant. Some people call that "dark energy" a dS space is a space that has nothing in it except dark energy (if you like that way of thinking about Lambda)

    That event horizon is like a hawking black hole event horizon turned inside out. Whatever drifts away from you and crosses it is gone forever (because of acceleration). The cosmic event horizon is called CEH by some people. It has a TEMPERATURE just like a BH event horizon has a temperature. Therefore it glows with radiation. This glow gives the observer a criterion of rest.

    this seems like weird reasoning to me, but I can't see anything wrong with it.

    4. A universe with positive Lambda, i.e. with "dark energy", is never completely empty because Lambda is a constant. Look at the the title of the paper.
    What they are saying is that a universe with a positive cosmological constant will always (when it gets empty enough) regenerate.

    I certainly find this unintuitive but mathematically I do not see any fault in it. So I have to entertain the possibility that it is right. If it is right I will have to gradually cultivate my intuition so as to accept it. In the meanwhile I wait to hear what other people say (they may be more insightful or experienced than I and I may learn something)

    Yes it's very strange but it might just be right.

    I'll repeat the link, given earlier.
    http://arxiv.org/abs/1406.3706
    Our Universe from the cosmological constant
    Aurelien Barrau, Linda Linsefors
    (Submitted on 14 Jun 2014)
    In this article, we consider a bouncing Universe, as described for example by Loop Quantum Cosmology. If the current acceleration is due to a true cosmological constant, this constant is naturally conserved through the bounce and the Universe should also be in a (contracting) de Sitter phase in the remote past. We investigate here the possibility that the de Sitter temperature in the contracting branch fills the Universe with radiation and causes the bounce and the subsequent inflation and reheating. We also consider the possibility that this gives rise to a cyclic model of the Universe and suggest some possible tests.
    5 pages
     
  10. Aug 2, 2014 #9
    So, and hopefully I'm not totally misunderstanding what is being said. A solution to Einsteins GR equations yields of multitude of possible world lines that are collapsed to one world line because of the presence of radiation.

    This singular worldline is the "official time" and "official space"(I guess official is just some abstract way of saying "the observer relative to the universe".). This observer, because of his position occupies a reverse event horizon that supplies "free energy" because of the radiation expelled from it. So, does this mean that when the universe becomes totally "ds", it will in effect regenerate completely?
     
  11. Aug 2, 2014 #10

    marcus

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    That is the direction they are arguing, but they hedge and some things about the argument are not yet clear to me.

    1. In the dS universe, once you single out an observer world line there is a contracting phase, a narrow waist like an hourglass, and an expanding phase. The observer can be in either contracting or expanding. They refer to this and say if expanding then nothing happens! It just thins out.
    But if contracting, this will somehow concentrate and amplify the energy (my interpretation) and eventually there will be a bounce and a regeneration.

    They argue that either of those two cases can occur and if you wait long enough the right thing will happen. I think you can find the passage where they talk about that.

    2. One thing I don't understand. It sounds to me like they are talking about a large PIECE of almost empty universe rather than the whole universe. So that puzzles me. But maybe with the cosmo constant Lamba resulting CEH we can think of a huge tract of universe being causally disconnected from the rest---because signals from beyond the CEH cannot reach it. Sorry, this is very vague I know.

    3. Another thing I don't feel I understand is how the faint (Hawking radiation-like) glow from an observer's distant CEH can serve as a "time-compass" to break the equality and single out a time direction.
    It seems CIRCULAR. I think you have to have an observer in order to define a CEH in the first place. So you already have that observer's preferred time. Obviously I need to read their paper again. Maybe I'll have some time today. I have to admit there is some vagueness and circularity in my understanding of the paper. That may be just me, however. My past experience with the work of those two authors tells me that Barrau and Linsefors have a lot on the ball--I respect their impressive ability and the senior author's track record. So I have to take a wait and see attitude and watch how their idea is treated by others.
     
  12. Aug 3, 2014 #11
    Big Bounce =/= quantum bounce

    Barrau and Linsefors’ model strikes me as an elaboration on the Tryon’s vague idea that the Big Bang (which, in B&L’s model, is better called “the quantum bounce”) is a large scale quantum vacuum fluctuation.

    The simplified, personalized sketch on the model I get from a read of their paper (reading first Philippe Brax‘s 2009 "Gif Lectures on Cosmic Acceleration", the “pedagogical review” it recommends) is this:
    • In the future universe, cosmic expansion increases so greatly it’s a “pure de Sitter universe” – that is, 3+ space +1 time dimensions with cosmological constant (which can be taken as a similar to dark energy and the metric expansion of space) much greater than 0, thus expanding at a rate faster than the speed of light, resulting in “de Sitter horizons” on many volume of empty space, such that they get no light or other radiation from anywhere else in the universe. Causally disconnected, these volumes can be considered separate, empty universes
    • A tiny amount of radiation gets into one of these dS universes
    • If the dS universe is expanding, this radiation “dilutes to nothing” – I think it could also be described as getting expelled from its dS horizon, and nothing happens.
    • If the dSU is contracting (I don’t understand how this could be – wouldn’t this imply a CC<0, making it an anti-dS universe?), its volume gets small, and this tiny amount or radiation quick constitutes a large energy density.
    • Classically, this results in an infinitely mass-energy dense singularity producing “crunch”. Since classical physics is only an approximation of reality, though, something like loop quantum gravity explains that a “quantum bounce” occurs.
    • This quantum bounce takes the place of the Big Bang in the usual origin of the universe model. What follows is the same as described in the usual model.
    The emphasis and subtext of Tryon’s 40-year old "the universe is simply one of those things that happens from time to time" “vacuum genesis” hypothesis is that the conditions of the pre-genesis universe – such as the sign or magnitude of its cosmological constant - aren’t important. There’s a non-zero probability of a “the universe happening” genesis – that is, an event equivalent in the usual model’s Big Bang or B&L’s quantum bounce – in any given time interval.

    From B&L’s paper, I get the impression that their model gives a 0 probability of genesis when the pre-universe is expanding, and 1 probability when it’s contracting, but that an expanding dS universe will eventually become a contracting (anti?) dS universe.

    This could be rephrased in a Tryon-esque way as “an empty contracting universe is simply one of those things that happens from time to time”.

    For a non-specialist like me, it’s important to keep the various phrases for different cosmology ideas distinct. In this case, B&L’s “quantum bounce” is not at all the same as what folk like physicists de Sitter and Gamow thought of (and what undergrad physics student turned professional SF writer Poul Anderson described so convincingly in his 1970 novel Tau Zero) as the “Big Bounce”. The old Big Bounce is a feature in cyclic universe models, many of which can be well-approximated with classical, mass-energy conserving physics in un-expanding or contracting space. B&L’s quantum bounce, like (and arguably equivalently to) Tryon’s large-scale vacuum fluctuation, and Penrose and Gurzadyan’s 5-year old conformal cyclic cosmology, is a different kind oc cyclic universe model, where each parent universe dies an “expansion death” which results in conditions and/or very long time intervals that permit a “spontaneous cosmic genesis”.
     
  13. Aug 3, 2014 #12

    marcus

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    In response, have a quick look at http://en.wikipedia.org/wiki/Hyperboloid the hyperboloid of one sheet and the corresponding equation.

    This is not to study! :biggrin: just glance at to see the "hourglass" shape of the hyp-loid and its equation -t2 + u2 + v2 = 1

    http://en.wikipedia.org/wiki/De_Sitter_space

    The deSitter space (positive Lambda) has a contracting phase and an expanding phase. it is analogous to the "hourglass" picture and the equation, as you can see, is essentially the same.

    It lives in 5D minkowski space. It is a 4D submanifold, with the induced metric.

    -t2 + w2 + x2 + y2 + z2 = 1

    where 1 can be replaced by any other positive number. In Wikipedia they say α2.

    It is analogous to a SPHERE but in Minkowski space instead of Euclidean.
    So it has a contracting "hemisphere" and an expanding one. The "alpha squared" number is conceptually related to the reciprocal of the cosmological constant Lambda. Small positive Lambda corresponds to large positive "alpha squared" in the language of the Wiki article.
    The cosmo constant Lambda is what is somewhat misleadingly called "dark energy". It is not known to correspond to any energy, in the Einstein equation it is a small intrinsic curvature (I think you know about that.)

    You draw some interesting analogies and comparisons! I think your pedagogical summary of the Barrau Linsefors scenario for universe regenerating itself is basically right, but as I said I don't entirely understand how it works and am in a wait-and-see mode.
     
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