Re: Penrose and Entropy


carlip-nospam@xxxxxxxxxxxxxxxxxxx wrote:
rev.goetz <jimgoetz316@xxxxxxxxx> wrote:
Roger Penrose calculates entropy by the number of photons per baryon.
And whenever I asked a physics graduate student about this, they where
not sure why.

This is the "specific entropy," the entropy per baryon. This is
a useful quantity because it's conserved during almost the entire
expansion of the Universe, so a measurement now gives you useful
information about the very early Universe. (The specific entropy
is not exactly the number of photons per baryon, but at the present
stage of the evolution of the Universe, it's the same order of
magnitude. That's because most of the entropy is in photons, and
because the entropy per unit volume of black body radiation is
equal to the number of photons per unit volume times a factor of
order one.)

Steve Carlip

If specific entropy is conserved during almost the entire expansion of
the Universe, then does it only increase mostly in black holes?

And what causes the number of photons to increase? And what converts
into photons?For example, the early universe now has roughly 10^8
photons per baryon while black holes have at least 10^20 photons per
baryon.

James

.

Relevant Pages

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