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TOPIC: Cyclic Universe


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Hořava-Lif****z gravity
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Horava-Lif****z gravity (or Horava gravity) is a theory of quantum gravity proposed by Petr Horava in 2009. It solves the problem of different concepts of time in quantum field theory and general relativity by treating the quantum concept as the more fundamental so that space and time are not equivalent (anisotropic).
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RE: Cyclic Universe
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Title: Oscillating Universe in Horava-Lif****z Gravity
Authors: Kei-ichi Maeda, Yosuke Misonoh, Tsutomu Kobayashi

We study the dynamics of isotropic and homogeneous universes in the generalised Horava-Lif****z gravity, and classify all possible evolutions of vacuum spacetime. In the case without the detailed balance condition, we find a variety of phase structures of vacuum spacetimes depending on the coupling constants as well as the spatial curvature K and a cosmological constant \Lambda. A bounce universe solution is obtained for \Lambda> 0, K= ±1 or \Lambda= 0, K=- 1, while an oscillation spacetime is found for \Lambda\geq 0, K=1, or \Lambda< 0, K= ±1. We also propose a quantum tunnelling scenario from an oscillating spacetime to an inflationary universe, resulting in a macroscopic cyclic universe.

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Title: Conformal formulation of cosmological futures
Authors: Philipp A Hoehn, Susan M Scott

We summarise the new conformal framework of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity. Both new definitions are motivated by, but not restricted to quiescent cosmology and the Weyl curvature hypothesis, which previously only possessed a framework for a classical initial state of the universe, namely the Isotropic Singularity. Some of the features of the framework are briefly discussed.

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I was an author of first comment below.

I agree with you that BH would evaporate rather than accumulate and that is in opposition to proposals of Authors of discussed paper.

In particular there in no longer much need for stable BH remnants to exist.
These were initially proposed because of necessity to conserve quantum information of a system under assumption that Hawking radiation is thermal.
As we now know, that is very unlikely.
On the other hand quantities like barionic number of the system are not necessarily subjected to strict conservation laws.

It is also possible that entire concept of BH is flawed and there are no such animals at all.
Alternatives might include for example MECO (magnetospheric eternally collapsing objects) or fuzzballs (made of string based degenerate matter), later proposed by those working on string theory).
There are also few more exotic proposals like gravastars etc.

In any case such objects, if exist, would exclude possibility of BH existence.
OK, a final product of evolution of MECO or a fuzzball would be a zero-mass BH, but that is nothing, what we need to worry about.

Nevertheless lets return to your proposal of Universe expanding to the point where remaining single elementar particles are the only objects within their own cosmic event horizons.
For me that situation is resembling a Thermal Death scenario, with the exception that every region containing single surviving elemental particle suffer its own thermal death, but whole Universe (which from the perpective of surviving elemental particle would be now a sort of inaccessible "multiverse") would be still left hopelessly out of thermodynamic equilibrium.
This situation is for me a bit aestetically displeasing because it implies that in big picture 2nd law was at the end cheated somehow (as we know Universe is getting more and more out of thermodynamic equilibrium and the process could not be reverted by any means under your scenario).
It is also not clear why your final conditions would necesserely lead to new cycle (Big Bang), though I agree that an entropy of your final single particle world would be very low, and that seems to be the case in pre-inflation Universe, just after Big Bang.

My belief in respect of future of Universe leans towards Big Rip related scenarios.
By now the Big Rip scenario is about the only option, which allows 2nd law to reassert itself in the future (at Big Rip singularity entropy of every point of space of existing Universe would achieve maximum possible value, so the 2nd law would reassert itself at the end).
Maximum possible entropy would also imply the end of arrow of time (end of time).
I am aware that Big Rip is posing some troubles for relativity but many other scenarios also do.
I am aware of some funny implications of this scenario while we are approaching end of time, eg prospects of dark energy contending with strong force binding quarks together or with wormholes running amok towards end (Big Trip).
Nevertheless I think that these difficulties can be ironed out somehow (in particular there are some calculations indicating that strong force would not disturb scenario too much).
It is also worth to note that existing observational evidence is indicating that all important omega factor is likely to be below -1, albeit the issue is still hotly contested.

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Ed ~ thank you for your question.
I don't believe in the classic cyclical scenarios.
Also I believe that the final state of affairs is incorrect; due to the BH evaporation process and space-time expansion, that will lead to an essentially empty universe. Particles would become isolated in their own observable universe with the result that they lose their identity and space and time become meaningless. The universe would now posses conditions that would lead to another big-bang event(s).

-- Edited by Blobrana on Sunday 20th of December 2009 04:31:56 PM

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Blobrana wrote:

Title: The Phantom Bounce: A New Proposal for an Oscillating Cosmology
Authors: Katherine Freese, Matthew G. Brown, William H. Kinney
The classic black hole overproduction of oscillating universes is resolved due to their destruction by the phantom energy.

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So don't you think, that under scenario proposed by Authors of article Planck mass BH would still accumulate with progress off new and new expansion phases and Big Rip phenomenons and as time pass we would end up with Universe which consist solely of Planck mass BHs, eg BH remnants?
Such scenario is still implying some sort of final end of Universe because once it have happened, nothing materially new would be going on upon subsequent expansions/big rip phases where only space of vacuum and BH remnants are eternally "reprocessed" and nothing else can exist.
So that is not truly cyclical scenario.
Once only space and BH remnants exist, that's it. Final state of affairs have been reached and further oscillations are meaningless.

Just other flavor of "Thermal Death" in philosophical sense at least.

 



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Title: Emergence of a Cyclic Universe from the Hagedorn Soup
Authors: Tirthabir Biswas
(Version v3)

One of the challenges of constructing a successful cyclic universe scenario is to be able to incorporate the second law of thermodynamics which typically leads to Tolman's problem of ever shrinking cycles. In this paper we construct a non-singular toy model where as the cycles shrink in the past they also spend more and more time in the entropy conserving Hagedorn phase. Thus in such a scenario the entropy asymptotes to a finite non-zero constant in the infinite past. The universe ``emerges'' from a small (string size) geodesically complete quasi-periodic space-time. This paradigm also naturally addresses some of the classic puzzles of Big Bang cosmology, such as the largeness, horizon and flatness problems.

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RE: Bouncing universe
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(May 23, 2006)

Bounce Preceded Bang
The Big Bang may have been a Big Bounce, say theorists searching for what preceded the birth of our own universe.
If their new mathematical simulations are correct, what came before the Big Bang was a previous universe a lot like our own. It collapsed on itself, then some weird physics caused it to inflate into the universe we have today.


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Title: Bouncing universe and non-BPS branes
Authors: Philipp Höffer v. Loewenfeld, Jin U Kang, Nicolas Moeller, Ivo Sachs
(Version v2)

We describe string frame bouncing universe scenarios involving the creation and annihilation of a non-BPS D9-brane in type IIA superstring theory. We find several classes of solutions, in which the bounce is driven by the tachyon dynamics of the non-BPS brane. The metric and the dilaton are consistently described in terms of the lowest order effective action. The bounce solutions interpolate between contracting and expanding pre-big bang (or post-big bang) solutions. The singular behaviour of our bounce solutions is the same as that of the pre-big bang (or post-big bang) solution. Upon adding a simple dilaton potential the asymptotic curvature singularity is removed but the dilaton still grows without bound. Such a potential may result from \alpha' corrections in the open string sector.

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Title: Bouncing universe and non-BPS branes
Authors: Philipp Höffer v. Loewenfeld, Jin U Kang, Nicolas Moeller, Ivo Sachs

We describe string frame bouncing universe scenarios involving the creation and annihilation of a non-BPS D9-brane in type IIA superstring theory. We find several classes of solutions, in which the bounce is driven by the tachyon dynamics of the non-BPS brane. The metric and the dilaton are consistently described in terms of the lowest order effective action. The bounce solutions interpolate between contracting and expanding pre-big bang (or post-big bang) solutions. The singular behaviour of our bounce solutions is the same as that of the pre-big bang (or post-big bang) solution. Upon adding a simple dilaton potential the asymptotic curvature singularity is removed but the dilaton still grows without bound. Such a potential may result from \alpha' corrections in the open string sector.

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