LizR wrote:
On 7 November 2014 22:30, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
No, my main problem with identifying the expansion of the universe
as the origin of the arrow of time is that the expansion of the
universe really has essential zero impact on the everyday physics of
our experience, but we see a consistent AoT associated with
increasing entropy in every phenomenon of our everyday experience.
Sure, what happened in the early universe has had lasting
consequences for our everyday life, but any connection with the
expansion is too remote to provide a plausible explanation of the
consistency of our experience of time. So the increase of entropy
itself -- whose universality is easily understood -- is itself the
origin of the AoT.
So you don't think that the creation of bound states in the BB fireball
is a significant contribution to the entropy gradient?
No, and I don't really understand what you are trying to get at with
this. In the early stages of the Big Bang we had a period of
nucleo-synthesis in which the temperature was high enough for protons to
have enough energy to fuse together in collisions, so amounts of
deuterium, helium and lithium were formed. The exact amounts of these is
a significant test of the hot BB theory since we know enough about
nuclear physics to understand these processes. Once the expansion cooled
things further, nucleo-synthesis stopped and could only start again when
collapsing dust created stars which could ignite nuclear reactions --
and ultimately lead to supernovae which cook higher elements.
But all these as standard processes and proceed according to the second
law of thermodynamics just as much as the laws of nuclear physics. I
find it strange that you refer to this as 'creating negative entropy' or
some such.
The entropy gradient can only exist because at any point in time the
actual entropy of matter and radiation is much less than its possible
maximum. This is as true in the early stages of nucleo-synthesis in the
BB as it is now. We can get on entropy gradient only if the initial
entropy was very much lower than might have been expected for a generic
universe.
The entropy gradient between the sun and earth is important, and life of
earth depends on the existence of a cold dark universe into which we can
dump our waste heat.
I don't think you can cite the "remoteness of the Hubble flow" (as it
were) as a reason to discount expansion as a source of the AOT (I assume
you think that because bound systems are effectively separated out from
it?). All the matter around us was once in the big bang fireball, and if
that's where the conditions that created the entropy gradient originated
then we would expect there to be a connection, although it may not be an
immediately obvious one.
The entropy gradient certainly originated at the beginning because it
was a low entropy state. It was not the low entropy was somehow created
by processes at that time. If the hot BB was a quark plasma at
more-or-less thermal equilibrium, that is a relatively high entropy
state for that form of matter, but that does not excite all the
available degrees of freedom. It is only the quarks that are in thermal
equilibrium, they are not in equilibrium with the gravitational and
other degres of freedom, so relative to the maximum possible, that
plasma was a low entropy state.
Bruce
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