Re: Quintessence and Curvature

ebunn_at_lfa221051.richmond.edu
Date: 03/11/05 

Date: Fri, 11 Mar 2005 08:30:41 +0000 (UTC)

In article <422e4f0f$1@news101.his.com>,
FearlessFerret <ff@repliestonewsgrouponly.com> wrote:

>Long ago (BQ, Before Quintessence) I learned that if the universe
>contains enough mass expanding at a low enough rate, it would collapse
>in on itself in finite time and exhibits 'positive curvature'. In the
>converse case, the universe is 'negatively curved'.
>
>If there is such a thing as Quintessence(*), is it possible to make a
>similarly concise statement about global curvature?

No.

Suppose that the quintessence behaves in exactly the same way as a
cosmological constant, and suppose that the only other constituent of
the Universe is ordinary matter. Then the state of the Universe is
described by two density parameters, Omega_matter and Omega_lambda.
In the two-dimensional Omega_matter-Omega_lambda plane, there are all
sorts of different possibilities: Universes with positive, zero, and
negative curvature that either recollapse or expand forever.

And it's even worse than that, because the quintessence may not behave
like a cosmological constant.

>(*) As far as I can see, observational evidence for Q continues to
>mount. Has its existence really achieved the status of 'consensus'?
>Would anyone care to point out any Big Names who are doubtful of this?

Among people working in cosmology, there's a pretty strong consensus
that you can't explain the data with a Universe containing nothing but
matter. Plenty of people have a healthy level of uncertainty about
exactly what that extra piece of the puzzle is.

There are still some astrophysicists who think that all of us
cosmologists are engaged in wildly unjustified speculation. In my
opinion, that position is getting very hard to justify.

-Ted 

-- 
[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]

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