meekerdb wrote:
On 11/6/2014 5:59 PM, Bruce Kellett wrote:
LizR wrote:
On 7 November 2014 12:32, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
I have not seen your arguments for this, being new to the list, but
the expansion of the universe is a universal consequence of general
relativity. So it is built into the laws of physics, and has nothing
to do with whether or not there ever was a period of rapid
inflation.
Expansion or collapse is a consequence of GR, certainly. However I
was thinking on a larger scale with the EI comment, since EI seems to
necessitate the existence of expanding universes. Not sure that it
can be counted as a TOE though, so it's still in need of ultimate
explanation..
The AoT comes from the third law of thermodynamics and has little to
do with the expansion of the universe. Entropy increases in the same
direction as the expansion solely because the universe 'began' in a
state of very low entropy. (The Past Hypothesis).
I didn't realise there was a 3rd law, but anyway - saying the U began
in a low entropy state begs the question - why did it? The big bang
fireball was more or less in thermodynamic equilibrium as far as I
know, and if it had stopped expanding it would have rapidly reached
that stage. My point is to explain the
Sorry -- typo. I meant the second law, of course.
I agree that the past hypothesis, while it explains the thermodynamic
AoT, itself stands in need of explanation. This is the great unsolved
problem of cosmology -- at least according to many cosmologists. The
initial big bang might be assumed to be in thermodynaic equilibrium,
but that is essentially the same assumption as the assumption of low
entropy. The question remains as to why it was in equilibrium. Generic
creation events might actuallybe expected to produce extremely lumpy
universe down to the smallest scaels. I.e., state with very high entropy.
What would be the highest possible (and therefore most probable) initial
state? A single black hole? From an information theoretic viewpoint a
universe inflating up from a Planck scale patch would seem most likely -
doesn't require any information input.
Brent
I know that was Vic's preferred model, but why should one ignore the
possibility of sub-Planckian structure? It is a mere conceit that the
Planck length is some fundamental smallest length. Operationalism is a
sterile philosophy of science.
But it is not really like that. Even if our current observable universe
started out as a Planck-sized sphere before inflation, the
inhomogeneities do not arise pre- or during-inflation. Inhomogeneities
arise at the end of inflation -- the post-inflation reheating is
basically a quantum process so it does not occur at the same time
everywhere. Exiting inflation at different times leads to
inhomogeneities on all scales, and there is no reason to suppose that
these are of bounded magnitude. Inflation models are highly tuned to
give only the degree of inhomogeneity we observe -- which is far from
generic.
Bruce
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