LizR wrote:
On 8 November 2014 11:40, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
LizR wrote:
On 7 November 2014 22:30, Bruce Kellett
<[email protected] <mailto:[email protected]>
<mailto:bhkellett@optusnet.__com.au
<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.
Well, the best thing to do if you don't understand something is to ask
for clarification! (I do that a lot...)
The point is that the existence of an AOT is partly derived from the
existence of bound states like nuclei. In a quark-gluon plasma at
equilibrium at a few trillion degrees, it is safe to say there is no
discernible AOT. All interactions occur with equal probability in either
time direction. But if you cool and spread out the plasma to the point
where nucleons can form, then you have objects which can participate in
entropic processes. So you have started to build the components
necessary for the existence of an AOT. Similar comments can be applied
at lower temperatures.
Several things are needed for an AOT. One is objects like atoms, which
can be arranged into low entropy states. Another is objects like nuclei
that are able to undergo energy-releasing processes. Nuclei are
effectively frozen chunks of negative entropy - a big contribution to
the AOT which didn't exist when they were a q-g plasma.
I thought that was what you probably meant. I questioned it because it
seemed a bit odd to me. There is no reason to suppose that the initial
quark-gluon plasma the instant after the big bang was in equilibrium.
Even if it were in thermal equilibrium in itself, the gravitational
degrees of freedom were not thermalized, so the total state was very far
from a condition of maximum entropy.
The process is then that this plasma cooled (by the additional 1/r
factor for relativistic particles) during the subsequent expansion. The
formation of protons as bound states was then a process that occurred
according to the standard laws of physics -- the bound state is at lower
energy than the separate constituents, so energy was released at lower
temperature, and this itself increased the total entropy. So this
process itself has the thermodynamic AoT. Similar considerations apply
to all later formation of bound states, such as deuterium, helium and
lithium. All released energy at lower temperatures and led to increases
in the total entropy.
This continues all the way to the formation of stars such as the sun.
Aggregates of elementary constituents, loosely bound together by
gravity, underwent collisions that radiated energy (mainly as photons)
and this also increased the total entropy. The sun was formed and
contracted sufficiently to ignite thermonuclear reactions, burning
hydrogen to form helium. The end result, as you say, was that the sun
appears as a low entropy source in a dark universe. But this all happens
by processes governed by the second law of thermodynamics, so the
formation of this low entropy source itself cost a lot of entropy
increase in the rest of the universe. It could be said that it is only
the fact that thermal photons could escape to the wider universe and
carry off that made any of this possible. Photons are not
gravitationally bound, so could escape, but an essential thermodynamic
precondition was that there was a cooler reservoir to receive them.
Gravitational clumping created this reservoir.
Nothing like this could happpen if the entropy were maximized at the BB.
Expansion does not increase the "entropy ceiling", as has been
previously pointed out.
Bruce
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