On 11/9/2014 7:01 PM, Bruce Kellett wrote:
LizR wrote:
On 8 November 2014 16:53, John Clark <[email protected]
<mailto:[email protected]>> wrote:
On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
> I'd say that expansion of the universe is almost necessary,
not contingent.
I'd say that by about 1850 when people started to have a
understanding of what Entropy was physicists had all they needed to
have known that the universe must have started out in a very very
low entropy state, that is to say they could have predicted the Big
Bang in the early to mid 19th century; and they wouldn't have needed
to go near a telescope to do so. But unfortunately they didn't, it's
one of the great failures of nerve or imagination in the history of
science.
Another feature of the big bang / expanding universe is that it continually raises the
entropy ceiling (maxium entropy that can exist in a given volume).
I think you should stop saying this. It is not true. You have not defined what you mean
by "maximum entropy" nor have you specified how that maximum is calculated. If the
maximum is defined as when all available degrees of freedom are in thermal equilibrium,
then the universe has never been in such a state of maximum entropy,
How about defining the particle maximum as when all mass-energy is in thermal equilibrium
- leaving gravitational modes out. Isn't that how inflation is used to explain the CMB
uniformity?
and it probably will not be until all matter has collapsed into black holes and these
have decayed by Hawking radiation.
At any finite time, one useful concept of maximum entropy is to consider the state in
which all mass energy is in the form of black holes. This has never happened either.
Presumably because inflation was much faster than the time for gravitational
collapse.
Neither of these maxima is in any way affected by the expansion of the universe
as a whole.
So you cannot get around the need to postulate a low entropy condition at the
BB.
I agree that there must have been a low entropy condition, but did it have to be low
relative to various constaints? Of all the ways for the universe to be, being in a
Planck-size volume is a very unlikely one (which is what Penrose points out). But given
that size I don't see why it's conditional entropy could not be high.
Brent
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
