* Astronomy

Blobrana · L

RE: Cyclic Universe

Blobrana · L

Title: Cyclic Universe and Infinite Past
Authors: Paul H. Frampton

We address two questions about the past for infinitely cyclic cosmology. The first is whether it can contain an infinite length null geodesic into the past in view of the Borde-Guth-Vilenkin (BGV) "no-go" theorem, The second is whether, given that a small fraction of spawned universes fail to cycle, there is an adequate probability for a successful universe after an infinite time. We give positive answers to both questions then show that in infinite cyclicity the total number of universes has always been infinite, given an appropriate definition of time t = - \infty.

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Blobrana · L

Title: The Return of a Static Universe and the End of Cosmology
Authors: Lawrence M. Krauss (1,2), Robert J. Scherrer (2) ((1) Case Western Reserve University, (2) Vanderbilt University)

We demonstrate that as we extrapolate the current \Lambda CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

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Blobrana · L

Quintom Matter

Blobrana · L

RE: Cyclic Universe

Blobrana · L

What gruesome fate awaits our universe? Some physicists have argued that it is doomed to be ripped apart by runaway dark energy, while others think it is bouncing through an endless series of big bangs and big crunches. Now these two ideas are being combined to create another option, in which our universe ultimately shatters into billions of pieces, with each shard growing into a whole new universe. The model could solve the mystery of why our early universe was surprisingly well ordered.
One of the problems that cosmological models must explain revolves around the amount of disorder in the way that particles in our universe are arranged, which is marked by a quantity called entropy. Cosmologists believe that the universe started out in an ordered, low-entropy state after the big bang, and is gradually becoming more of a mess. But just why it started out so well ordered, when it is much more likely for particles and energy to be created in a greater state of disarray, is something of a puzzle.

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Blobrana · L

One of the oldest questions in theoretical cosmology is whether an infinitely oscillatory universe which avoids an initial singularity can be consistently constructed. As realised by Friedmann and especially by Tolman (also LeMaitre, Einstein, De Sitter ....) one principal obstacle is the second law of thermodynamics which dictates that the entropy increases from cycle to cycle. If the cycles thereby become longer, extrapolation into the past will lead back to an initial singularity again, thus removing the motivation to consider an oscillatory universe in the first place. This led to the abandonment of the oscillatory universe by the majority of workers.
Nevertheless, an oscillatory universe is an attractive alternative to the Big Bang. One new ingredient in the cosmic make-up is the dark energy discovered only in 1998 and so it natural to ask whether this can avoid the difficulties with entropy which have dogged previous attempts. Some work has been started to exploit the dark energy in allowing cyclicity possibly without apparently the need for inflation in Steinhardt et al Another new ingredient is the use of branes and a fourth spatial dimension as in Randall et al, Binetruy et al which have examined the consequences for cosmology. The Big Rip and replacement of dark energy by modified gravity have been explored in PHF and Takahashi.

The cyclic model proposed by Dr. Paul Frampton, Louis J. Rubin Jr. distinguished professor of physics in UNC's College of Arts & Sciences, and co-author Lauris Baum, a UNC graduate student in physics, has four key parts: expansion, turnaround, contraction and bounce.

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Blobrana · L

Title: On Cyclic Universes
Authors: P.H. Frampton

Dark energy in a brane world reconciles an infinitely cyclic cosmology with the second law of thermodynamics. At turnaround one causal patch with no matter and vanishing entropy is retained for the contraction.

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Blobrana · L

Title: Was the universe open or closed before inflation?
Authors: Eduard Masso, Subhendra Mohanty, Gabriel Zsembinszki

If the spatial curvature of the universe at the beginning of inflation is negative, there is an enhancement of the temperature anisotropy of the Cosmic Background Radiation at large angles. On the other hand if at the start of inflation the universe was closed with curvature there will be a suppression of temperature anisotropy at the scale of the present horizon. The observation of a low quadrupole anisotropy by WMAP suggests that the universe was closed with (Omega-1) of order unity at the time when the perturbation scales of the size of our present horizon were exiting the inflationary horizon.

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Blobrana · L

Big crunches wipe the slate clean
There is no such thing as karma, at least not for stars and galaxies in a universe cycling through a series of big bangs and big crunches. Apparently whatever happens to stars and galaxies in the present universe doesn't affect them in their next incarnation.

The cyclic universe model was proposed in 2002 by Paul Steinhardt of Princeton University and Neil Turok of the University of Cambridge. In their model, the universe bounces through a series of big bangs and crunches, with each cycle lasting about a trillion years. The model solves some of the problems with the standard big bang theory, and the researchers have also used it to explain the mystery of why the cosmological constant, which governs the rate of acceleration of the universe's expansion, is so small.
However, the model has been dogged by a problem. If the fluctuations in each new universe are ones left over from the previous cycle, how did the fluctuations in the universe at the start of the chain originate?

Source

Title: Life, The Universe, and Nothing: Life and Death in an Ever-Expanding Universe
Authors: Lawrence M. Krauss and Glenn D. Starkman, Departments of Physics and Astronomy Case Western Reserve University

Current evidence suggests that the cosmological constant is not zero, or that we live in an open universe. We examine the implications for the future under these assumptions, and find that they are striking. If the Universe is cosmological constant-dominated, our ability to probe the evolution of large scale structure will decrease with time — presently observable distant sources will disappear on a time-scale comparable to the period of stellar burning.
Moreover, while the Universe might expand forever, the integrated conscious lifetime of any civilization will be finite, although it can be astronomically long. We find that this latter result is far more general. In the absence of possible exotic and uncertain strong gravitational effects, the total information recoverable by any civilization over the entire history of our universe is finite, and assuming that consciousness has a physical computational basis, life cannot be eternal.

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-- Edited by Blobrana at 16:33, 2006-08-15