Friday, October 21, 2016

[ngatfdwd] No arrow of time in the far future

Sean Carroll makes the neat point that we can distinguish between up and down in space because we are spatially near a large object in space, namely the Earth.  In deep space, we would not be able to distinguish between directions.  Analogously we can distinguish between forward and backward in time because we are temporally near a large object in time, namely the Big Bang, when there was very low entropy, and entropy has been noticeably increasing since then.

In the far future, 10^{at least 3 digits} years (though it is fun to write 10^10^10 just because), entropy will have increased almost to the maximum, and analogous to deep space, "we" will not be able to distinguish forward versus backward in time.  Predicting the future will be just as easy as remembering the past: things aren't changing.  It is hard to imagine life existing under such conditions, but who knows, life, uh, finds a way.

The laws of the universe won't have changed: time travel into the past will remain impossible.  However, if will be impossible to tell that you haven't broken the laws of the universe, that you haven't traveled backwards in time.

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