NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/physics/21517

Internet Message Format | 1992-12-21 | 4.0 KB

Path: sparky!uunet!spool.mu.edu!agate!agate!matt
From: [e-mail] (Matt Austern)
Newsgroups: sci.physics
Subject: Re: TEXAS ASTROPHYSICS MEETING at UCB
Date: 20 Dec 92 23:34:42
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
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In-reply-to: [e-mail]'s message of 20 Dec 92 17:09:19 GMT

In article <[e-mail]> [e-mail] (Steven Timm) writes:

> Mr. Sarfatti suggested that the result was presented at the TEXAS meeting
> (in Berkeley, CA) that the universe would not expand indefinitely.
>
> By this I assume he claims that results were presented that indicate
> that Omega (density/critical density) is greater than or equal to 1.

I certainly don't remember anybody at the conference making any claim
of that nature; the speakers in all of the talks I went to adhered
rather closely to the party line, i.e., that all experimental evidence
suggests that omega is rather less than one, that for aesthetic and/or
theoretical reasons it would nice if omega turned out to be exactly
equal to one, and that there is no reason to think that omega is
greater than one.

There was one speaker, though, who presented a result that was, at
least, reminiscent of what Mr. Sarfatti said; perhaps he is thinking
of Alex Vilenkin's talk on quantum cosmology.

Most of Dr. Vilenkin's talk was on very speculative subjects, but he
spent some of the time on inflation.  (Yes, I know---but that really
was the least speculative part of the talk.  Honest.)  Specifically,
he talked about the rather embarrassing (and rather well known)
problem with inflation: it's very easy to find models in which
inflation occurs, but it's very hard to find ones in which the
inflation stops!  What tends to happen is that when the universe cools
down sufficiently, a phase transition occurs---but only in isolated
bubbles.  The bubbles expand, and more bubbles of the new phase keep
forming, but the space between the bubbles grows faster than the phase
transition can take place, and so most of the universe remains in the
old (metastable) phase, and keeps inflating.

(Think of the phase transition from liquid to gas; when you boil
water, that phase transition starts in bubbles, and then eventually
the bubbles grow and meet.  Well, the problem with inflation is that
the bubbles apparently can't grow fast enough so that they meet.)

Well, as I said, that's a well-known problem, and an equally well
known possibility for solving it is to just accept it: to say that
most of the universe really does just stay in the old phase, and is
still expanding, and will continue to expand forever.  According to
this view, we just happen to live in one of the bubbles of the
lower-energy phase.

What Dr. Vilenkin talked about was a possibility that he called
"eternal inflation."  This is a suggestion that, just as inflation
will not have an end, so, also, it never had a beginning: no matter
how far forward or backwards in time you extrapolate, you will just
see inflation, with bubbles of the new phase continuing to form.

And the result he presented, specifically, was that "eternal
inflation" is impossible: there is nothing wrong with inflation
continuing forever, but, he claimed, it had to begin somewhere.  It
can't have been going on forever.

Unfortunately, I don't remember the reason he gave for thinking that
eternal inflation doesn't work.  I found the whole talk rather too
speculative for my tastes---especially since, as I said, this part
that I just summarized was the most real-world, experimentally
verifiable part of the talk.
--
Matthew Austern                   Just keep yelling until you attract a
[phone]                    crowd, then a constituency, a movement, a
[e-mail]                faction, an army!  If you don't have any
[e-mail]         solutions, become a part of the problem!