Re: [asa] promise trumps biology (multiverses)

One of the successes of Guth's original inflationary model was that it solved the "flatness problem." 30 years ago cosmological parameters weren't known nearly as well as they are now but even then it was realized that the universe was at least moderately close to flatness. & for it to be as close as it is now, it would have had to have been extremely close in the first fraction of a second of the big bang. The inflationary model explains how this could have been so without having to invoke any artificial fine tuning. The exponential expansion consequent upon phase changes of quantum fields would have "inflated" a space of positive curvature so much that it would appear flat over regions the size of our present observable universe.

The possibilities for uniformly expanding universes in general relativity correspond to the possibilities for shooting a rocket away from a planet in Newtonian mechanics. A space of positive curvature corresponds to the rocket being given a speed less than escape speed so that it will eventually stop & fall back to the planet, while a space of negative curvature correspnds to a rocket with speed greater than that needed for escape. The borderline flat space corresponds to the rocket with initial speed exactly equal to escape speed which will never fall back but whose limiting speed would be zero at infinity. The situation is made more complex with a cosmological constant - which now appears to be real, at least as a first approximation for dark energy.

Rotating cosmological models have been considered, the best known being Goedel's, but there's no observational evidence for overall rotation.

I'm getting into this discussion late (in spite of the fact that I started the "promise trumps biology" thread long ago on a totally different topic!) so am not sure what's meant by a "viable universe." I assume that you mean something like "suitable for the evolution of life." It would certainly be possible for life to develop in, e.g., a closed universe that would stop expanding & then contract to a big crunch with a total cosmic lifetime of, e.g., 10^11 years.

Shalom
George
http://home.neo.rr.com/scitheologyglm

----- Original Message -----
From: "gordon brown" <Gordon.Brown@Colorado.EDU>
To: <asa@calvin.edu>
Sent: Wednesday, December 31, 2008 10:05 PM
Subject: RE: [asa] promise trumps biology (multiverses)

> Others (e.g. physicists & astronomers) on this list know a lot more about
> this subject than I do, and so they can correct me if my knowledge of
> cosmic inflation theory is faulty, in which case what I ask in the last
> paragraph of this message is irrelevant.
>
> I have heard that some version of cosmic inflation theory predicts that
> the universe is flat (i.e. Euclidean), has flatness parameter equal to 1,
> is expanding at precisely the minimum possible rate to prevent the
> expansion from eventually stopping, and is not rotating. These properties
> are probably not all independent of one another.
>
> Now the question: Must the flatness parameter be 1 for any possible viable
> universe? If so, it would raise questions about special properties of the
> putative multiverse. If not, then there is a range of possible values,
> and, since 1 just does not look like a number selected at random, it seems
> extremely strange that it is the value that we have, and it would not be
> characterized as mediocre.
>
> Gordon Brown (ASA member)
>
>
>
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Received on Thu Jan 1 10:31:50 2009