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 Be the first pioneers to continue the Astronomy Discussions at our new Astronomy meeting place...The Space and Astronomy Agora Hawking Cosmology, Age Of Universe And Phantom Energy Forum List | Follow Ups | Post Message | Back to Thread TopicsPosted by Richard Ruquist on May 30, 2003 14:59:19 UTC

Every morning the first thing I always do on the internet is to check all the papers posted to the physics and math archives found at

http://arxiv.org/

I do not know about math, but every physicist in the world posts his or her paper there first before they are accepted and usually even submitted to journals. Often this is the only place physics papers are posted.

Something over 100 papers are posted each day. I check only astrophysics, cosmology, high energy phenemology and theory, general physics and quantum mechanices, which is about 1/3 the total number of categories.

So everything of significance in physics gets posted there and is seen by every good physicist. Stafford could post there. There are no rejections. But there is no appropriate category for my Dark Matter survey paper.

So anyway this morning there seemed to be three papers in the astrophysics category that might be of particular interest to some of the posters here as cosmology has been a topic recently. Copied below are the links and abstracts for each paper.
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http://arxiv.org/abs/astro-ph/0305562

Cosmology from the Top Down
Authors: Stephen Hawking
Comments: Talk presented at Davis Inflation Meeting, 2003 (astro-ph/0304225)
Report-no: DavisInflation/2003/pelly

In this talk, I want to put forward a different approach to cosmology, that can address its central problem, why is the universe to way it is. Does string theory, or M theory, predict the distinctive features of our universe, like a spatially flat four-dimensional expanding universe with small fluctuations, and the standard model of physics. Most physicists would rather believe that string theory uniquely predicts the universe, than the alternatives. These are that the initial state of the universe is prescribed by an outside agency, code named GOD. Or that there are many universes, and that our universe is picked out by the antropic principle.
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http://arxiv.org/abs/astro-ph/0305556

Implications of the WMAP Age Measurement for Stellar Evolution and Dark Energy
Authors: Lawrence M. Krauss (Case Western Reserve University)
Comments: 12 pages, 3 figures, submitted to Ap. J
Report-no: CWRU-P15-03
The WMAP satellite has provided a new measurement of the age of the Universe, of $13.7 \pm 0.2$ Gyr. A comparison of this limit with constraints from stellar evolution imply that the oldest globular clusters in the Milky Way galaxy have a reasonable probability of have formed significantly after reionization. At the same time, one can derive a direct {\it upper limit} on the time after the big bang before globular clusters in our galaxies formed of $\approx 3$ Gyr, which significantly reduces our uncertainty since before the CMB age estimate. The WMAP age constraint can also be shown to provide a stringent {\it lower bound} on the equation of state of dark energy. A precise value of this lower bound would require a global analysis of the WMAP parameter constraints. However, making conservative assumptions about allowed parameter ranges and correlations one derives a lower bound of $w > -1.22$. Combining this with the WMAP-quoted upper limit on $w$ thus gives roughly symmetric 95% confidence range $w =-1 \pm 0.22$.
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http://arxiv.org/abs/astro-ph/0305559

You need not be afraid of phantom energy
Author: Pedro F. Gonzalez-Diaz (IMAFF, CSIC, Madrid)
Comments: 4 pages, RevTex, to appear as a Rapid Communication in Phys. Rev. D
Report-no: IMAFF-RCA-03-04
Phantom energy which violates the dominant-energy condition and is not excluded by current constraints on the equation of state may be dominating the evolution of the universe now. It has been pointed out that in such a case the fate of the universe may be a big rid where the expansion is so violent that all galaxies, planet and even atomic nuclei will be successively ripped apart in finite time. Here we show however that there are certain unified models for dark energy which are stable to perturbations in matter density where the presence of phantom energy does not lead to such a cosmic doomsday.

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Hawking is a very well-known physicist. Krauss is a well-known astronomer and cosmology, better known in cosmology than even Hawking. (He is saying that the universe is 13.7+_0.2 billion years old, by the way)

Gonzalez-Diaz is unknown, at least to me, but has the most interesting cosmology of the three. Allow me to quote from his paper as his abstract does not do it justice:

"...It is that in a finite time the universe will undergo a catastrophic 'big rip'...the scale factor blows up in a finite time because its cosmic acceleration is larger than that induced by the coamological constant, making in this way every component of the universe go beyond the horizon of all other universe components in a finite time....where the universe dies after ripping apart successively, all galaxies, our solar system, the Earth itself, and finally molecules, atoms, nuclei and nucleons."

Phantom energy is just dark energy having an equation of state with the particular properties to cause a 'BIG RIP'.

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So everything of importance as well as many crank papers get published in the Cornell archives. People like Witten and Seiberg of Princeton's Advanced Institute publish papers from 20 to 70 pages long, full of math. I prefer to read the 5-10 page papers that are more words than equations. Like Hawkings talk is entirely words. People publish chapters of books there to get some review before binding. I recommend checking out the archives to just get an idea of what physics is currently being done the world over.

yanniru