Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Bill S on 16/09/2017 20:35:53
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Popular science literature often raises questions about a “boundary condition” at the Big Bang, which necessitated a low entropy scenario.
In the FLRW model the Universe in its first instant is miniscule (a single quantum, as Lemaître described it). This “Primordial Atom” contained all the matter and energy of the Universe, which completely filled the tiny space it occupied. In that first “quantum” matter/energy occupied all the available space; there was no room for “manoeuvre”; entropy could not have started evolving until more space became available (?).
What does it mean to equate this to a low entropy boundary condition? Surely, in that first instant, entropy was at the maximum possible for the conditions, albeit for only the briefest instant.
I suspect that this is a poor way to describe it, but it is what tends to come out of Pop Sci. Possibly I should be talking in terms of thermal equilibrium, restricted degrees of freedom and low/high entropy. However, the low entropy boundary condition is frequently met. A particular example is the writing of Sean Carroll.
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For those unfamiliar with the subject the FLRW model is detailed here.
https://en.m.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric
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Also of interest may be Roger Penrose's conformal cyclic cosmology where the universe is cyclic. This derives from the FLRW model.
https://en.m.wikipedia.org/wiki/Conformal_cyclic_cosmology
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Have a look through the CCC article Bill. It covers the low entropy past within each cycle. It also has a solution to the information paradox.
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I have "Cycles of Time", but have not yet found time to read it. Must do something about that.
Fortunately, I think I have found a way to deal with the problems I have always had with infinite sequences, eternal repetitions and the like. If I ever post about it; it will have to be in "New Theories" :)
For the time being, though, I'll just use it to save myself lots of tortuous discussions.