alt Hacker News > Combining quantum mechanics and General Relativity is all well and good, but there‘s one key mystery it doesn’t address: why does time only seem to flow in one direction?
Time still flows and ebbs, we just lack the ability to sense it just like a cork in a river doesn't feel the water flowing past.
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there is no flow per se, as it’s a subjective experience. it’s just that our current environment (specifically human environment) is predominantly structured in a way that the past makes an imprint on the present (in terms of biological memory, historical records, etc) and the future generally being unpredictable because we kinda don’t want it to be too predictable (eg you don’t want to be too predictable when a tiger is chasing you for example)
but in other environments (talking about same universe here!) the future is more predictable than here on earth, for example motions of planetary bodies can be predicted way in advance within error bars as in the past, and when you have that kind of relatively symmetrical system, any subjective experiences within those systems would be much less inclined to feel that time flows on way or the other. (of course, the only kind of subjective experiencers we know are made of biological stuff which structurally remembers the past and leaves the future open as form of evolved ability, so this timelessness experience may be harder to imagine for us)
For the "canonical" physics explanation, see:
https://en.wikipedia.org/wiki/Past_hypothesis
You can happily run physics backwards and forwards, and there's no difference. But assuming that entropy was very low in the distant past is very useful and lets us talk about fascinating things, like what happened last tuesday (or 12 billion years ago)
If you just know the current state of the a system, there isn't really any difference between running time backwards and forwards. Of course, if you know exactly the state of every particle, field, etc, and the past hypothesis is true, running time one way will lead to lowering entropy, and the other way will lead to raising entropy. But if you're a mere mortal and just know the macrostate, either way you run time, the entropy of the system will increase.