On 13 November 2014 11:29, Bruce Kellett <[email protected]> wrote:
> LizR wrote:
>
>>
>> Why not? Informally, from a quantum viewpoint it makes more states
>> available, in a manner similar to Max Tegmartk's calculation of how far
>> away one's duplicate is in a level 1 multiverse. The analogy used by Paul
>> Davies is that if you have a gas at equilibrium inside a container and
>> expand the container, the gas will stop being at equilibrium in the new
>> configuration. It has more states available, and hence its entropy ceiling
>> has been raised. This seems to me a valid argument. Where has Davies (and
>> Tegmark) gone wrnog?
>>
>
> The problem would seem to be with Davies' analogy. If you expand a
> container containing gas at equilibrium, the temperature will drop and the
> entropy will rise, but this is because you have extracted heat from the
> system. Moving the walls outwards means that molecules that bounce off the
> walls will recoil with lower velocity -- transferring energy from the gas
> to the outside world. This does not happen in the expanding universe. The
> gas cools, but energy is not conserved in the expansion -- it does not go
> anywhere. There is no reservoir at a lower temperature to act as a sink,
> and there is no change in entropy. With no change in entropy, the gas does
> not cease to be at equilibrium if it were initially so, and there is no
> change in the number of available states. This is a peculiarity of GR since
> energy is not globally conserved in an expanding universe.
I think Prof Davies' point is that expansion magnifies any existing
inhomogeneities, at least if the expansion is faster than the relaxation
time of the medium.
However you haven't addressed Max Tegmark's point, that the number of
quantum states available inside a given volume is proportional to the
volume, hence expansion allows more quantum states to exist.
Second, we get the thermodynamic AoT without expansion.
>>
>> In standard BB cosmology, the expansion cools the initial very hot
>> state. But it is not necessary to start with a hot BB to get an AoT.
>> We could image some different mechanism of cosmogenesis whereby the
>> initial state was a relatively thin cool gruel of hydrogen and a few
>> other bits. Something like in the current model when the universe is
>> a few million years old. Imagine it started in that state, but with
>> no further expansion. We would still get gravitational collapse
>> around local inhomogeneities, galaxies and stars would form. Planets
>> and occasionally life would arise. All within a thermodynamic AoT.
>> In other words, we could get to exactly where we are no without any
>> expansion at all. So expansion cannot be a necessary prerequisite
>> for an AoT.
>>
>>
>> You're invoking graviation to create the AOT. I am explicitly trying to
>> explain the AOT without invoking gravitation - obviously the universe has
>> to be smooth, this is what else can occur on top of that.
>>
>
> Gravity is one of the laws of physics. The AoT occurs within physics, so
> why not use gravity to explain what happens? The problems arise -- as I
> have tried to point out -- when you ignore gravity. Cosmogenesis is, after
> all, the quintessential GR/gravitational problem.
Well, space-time starts out smooth to a very good approximation, so you can
look at the behaviour of matter within it to explain at least some features
of the AOT. You haven't yet addressed the formation of nuclei and other
bound states and why that would make no contribution to the AOT, to the
best of my knowledge (I asked for a short simple reply because I don't have
time to wade through huge responses - which is why I also trim anything
irrelevant from my posts).
Also, the presence of hydrogen in the above is unexplained, but you need
>> something like atoms for the 2nd law to operate. It doesn't operate inside
>> a q-g plasma at equilibrium at several trillion degrees, for example. Hence
>> you need to create those little bundles of negative entropy, so to speak,
>> before you have something on which the statistics of the 2nd law can
>> operate.
>>
>>
>> You have to beware of making contingent facts into apparent logical
>> necessities.
>>
>> I will resist making any similarly patronising and irrelevant comments.
>>
>
> The comment is apposite. It is neither patronizing nor irrelevant.
No. You are partonisingly assuming I don't already know about the
possibility of making contingent facts into logical connections (not
necessities). Even if you have shown that there is no logical connection,
which isn't apparent to me (at present, at least), this still reduces to a
merely *ad hominem* remark.
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