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Astronomy and Cosmology
Cosmology
Low entropy early Universe and the heat death musings
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[QUOTE="PeterDonis, post: 6375134, member: 197831"] Not entropy itself, but something like "maximum possible entropy", yes. There are actually two issues here. One is that the expansion of the universe means that there are, roughly speaking, more microstates available for the universe now than there were right after the Big Bang. That means, roughly speaking, that the "maximum possible entropy" of the universe is much larger now than it was then, since the maximum possible entropy should be something like the logarithm of the number of available microstates. The second issue is that we have to take gravity--or, more precisely, the microstates available in the spacetime geometry--into account when assessing entropy. Roughly speaking, at least a large part of the increase in available microstates due to the expansion of the universe is probably due to more microstates available in the spacetime geometry, not in the "stuff" (matter and energy). However, nobody knows precisely how to describe the microstates available in the spacetime geometry, so this is all very heuristic. Roughly speaking, yes, this is one of the reasons we expect that the correct theory of quantum gravity, if we ever discover it, will tell us that on small enough scales, spacetime is quantized. However, nobody knows precisely how to describe what that means; it is by no means clear that it is as simple as spacetime just being made of 4-dimensional "pixels" each being roughly one Planck-length-sized 4-d volume. [/QUOTE]
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Low entropy early Universe and the heat death musings
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