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The second law suggests that averaged over a large enough space and time, entropy always increases.

The rate of increase obviously depends on local conditions. The increase in Entropy in a year in our solar system (due to the effects of the Sun spewing heat all over the place) is >> the increase in Entropy in, say, a solar-system-sized sphere of intergalactic space. However, the Universe is observed to be reasonably homogenous at very large scales, so it is reasonable to expect that average entropy increase per unit space in the Milky Way is not wildly different from entropy increase in Andromeda (or at least not so wildly different as between the solar system and our hypothesized solar-system-sized intergalactic region). One might expect that averaging two sets of a bunch of galaxies together would bring the average entropy increase of the sets even closer in proportion if not in absolute value.

Anyway, is this average rate of increase in entropy on "large" scales predicted by any of the currently accepted physical theories? Are there any measurements for it?

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  • $\begingroup$ @Qmechanic can you give some advice on making this question on-topic? I'm not familiar enough with the cutting-edge boundaries of physics to know what about this question exceeds them. The second law of thermodynamics seems like it would be on-topic. Is measuring the rate of change of entropy on macro scales not a thing that physicists study? $\endgroup$
    – Him
    Commented Feb 1, 2023 at 21:21
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    $\begingroup$ Hi Him, perhaps try ask in the hbar chat room. $\endgroup$
    – Qmechanic ♦
    Commented Feb 1, 2023 at 21:28
  • $\begingroup$ Why is the rate of entropy increase larger at the sun than on earth? That point imho needs more foundation than a bold statement $\endgroup$
    – planetmaker
    Commented Feb 1, 2023 at 23:15
  • $\begingroup$ @planetmaker I would imagine that since the Sun is generating enormous amounts of heat, that there would be a concomitant increase in entropy. It was my impression that burning a lump of wood increased the entropy of the system. Does the same not apply to the Sun? $\endgroup$
    – Him
    Commented Feb 1, 2023 at 23:18
  • $\begingroup$ @planetmaker I'm not sure whether this comment has any basis in reality, but it seems to suggest that the Sun generally increases entropy at a pretty high rate. $\endgroup$
    – Him
    Commented Feb 1, 2023 at 23:30

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