Reversing the momentum of every object and evolving it forward in time is the same gives you the same kind of answer as just evolving backward in time. The earth moving round the sun is a physical system that has very small numbers of moving parts, so there's no entropy increase or decrease. If you retrodict the past, without a past hypothesis, you predict the opposite of that, which is, you predict radiation flowing from the sun into the past.
Welcome to the March 2022 Ask Me Anything episode of Mindscape! These monthly excursions are funded by Patreon supporters (who are also the ones asking the questions). I take the large number of questions asked by Patreons, whittle them down to a more manageable size — based primarily on whether I have anything interesting to say about them, not whether the questions themselves are good — and sometimes group them together if they are about a similar topic. Enjoy!
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