Question: Why does time seem to flow only in one direction?

Liza Sazonova answered on 10 Nov 2020:

As far as we know, travelling back in time is impossible, so time can only go forwards. There are weird and exotic theories to go around that, but nothing close to something we can actually see.
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Why that is the case is a really really tricky question.
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Physicists say “time is the direction of increase of entropy”. That’s a handful of a sentence 🙂 Entropy measures how chaotic or disordered things are, and by physics laws the /global/ entropy in the Universe must always increase.
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For example, if you built a house out of some rocks, you’ve made them more ordered and decreased entropy. But you spent so much energy doing it with your sweat, heat, sound, etc! All this wasted energy was in your body and now it’s scattered in the world in an unordered way. The overall Universe became less orderly, i.e. global entropy increased.
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We are limited to trudging along in this direction of entropy increase, and we see this as going on with our lives – or going “forward in time”.
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Some physics theories let you travel back in time (in theory). For example, if you can fly faster than light, you can go back in time. But doing so would require /infinite/ energy! So even if you manage to propel yourself back in time somehow, you would have to put in so much energy that entropy would still increase.