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island
#5
Jan26-06, 06:36 PM
P: n/a
Phillip Helbig---remove CLOTHES to reply wrote:

> I recently saw Roger Penrose on the BBC television programme "Hard
> Talk". Having recently read his magnum opus THE ROAD TO REALITY, it was
> clear that a half-hour programme would have to remain superficial. Of
> course, Penrose touched on two of his main themes, the possible role of
> quantum theory in consciousness (I don't think his case is very strong
> here, though I am sympathetic to his ideas about unification, if that's
> the word, of GR with QM) and the low entropy of the big bang.


> I want to talk about the latter point here.


> Penrose has been presenting this puzzle for decades now. I'm surprised
> that it seems to be ignored if it has not been refuted. If it has been
> refuted, can someone point me to a paper which does so?


> Let me state briefly the puzzle. The standard answer to the question of
> the origin of the second law of thermodynamics, i.e. why entropy usually
> increases, is that there are more ways to be disorderly than to be
> orderly. Thus, entropy should increase from time t to time t+dt.
> However, this argument itself cannot assume any arrow of time (it is
> actually trying to explain the arrow of time), so one could just as well
> say that entropy should increase increase from time t to time t-dt. In
> other words, if there are many more disordered states, then a given
> ordered state is much more likely to have arisen from a disorderly
> state. However, observations (e.g. smoothness of the CMB) indicate that
> entropy really does decrease as one goes back in time. Thus, the big
> bang was in a very special state, not some "generic" state. Penrose
> claims that no current theories about the early universe explain this
> and, again, if someone has refuted this argument I would like to know.


I don't know of any, personally, but I wouldn't be inclined to refute it
anyway, other than to add that I don't think that you have to have
specially low entropy prior to a big bang to increase entropy
indefinitely. For example, if we had a big bang right now, then time
would restart and the process would start over, while the
"characteristics" of this universe get "conovolved" forward to the next
universe, which would be flat for this reason, and would not have a
horizon issue, since it already has volume when a big bang occurs.

I've previously discussed a mechanism for this in this forum:

http://www.lns.cornell.edu/spr/2005-01/msg0066400.html

Christine Dantas, http://christinedantas.blogspot.com/ recommended this
paper to me, http://br.arxiv.org/abs/gr-qc?papernum=0205075 which I
found to be interesting and relevant, because it makes the cosmological
constant into a source term, and "invites particle physics to interact
with general relativity" 'It behaves like a perfect fluid with the
energy density and an isotropic pressure. The conserved quantity is now
the sum of matter and vacuum together'

This paper is interesting for similar reasons:

http://arxiv.org/abs/hep-th/9903255

> From what I could gather from the interview, his answer to the question
> of where the special state of the big bang came from is the following:
> it arises out of the end state of a "previous" universe. He doesn't
> depart from what is now considered to be the standard model of
> cosmology, i.e. the universe continues to expand (i.e. no big crunch).
> After a long time, most matter will end up in black holes. After a
> longer time (Barrow and Tipler estimate such time scales in their book
> THE ANTHROPIC COSMOLOGICAL PRINCIPLE), these will decay due to Hawking
> radiation. (Yes, the timescale is REALLY LONG.) There is then a
> universe of radiation, and Penrose then claims that it "loses track of
> time". I'm not sure how he gets from here to the special state of the
> big bang, perhaps he relies on the fact that, after a very long time,
> even a special state will appear.


I like the idea and the outcome for selfish reasons, but I hope that his
mechanism isn't really that weak and "uncertainly rationalized" so as to
avoid causality and the first principles. I think that it's a huge
mistake to give up on explainations for fine-tuning from first
principles. It can't be coincidence that the anthropic principle
defines the thermodynamic structuring that produces far-from-equilibrium
dissipative structures, (like us)... in order to minimize the amount of
work that is required in the effort toward maximum entropy. What we
actually know is that the second law indicates that entropy always
increases due to a perpetually inherent imbalance in the energy that
cannot be reconciled. I can believe that, from the actual available
observational evidence, without projecting anything beyond what the
second law is telling us... and given my previously referenced mechanism
for this to be forever true... I do believe it.