Regression of Universe

Main Question or Discussion Point

If every particle of the Universe was made to occupy the state at which it was 2 years ago, would there be an action replay of events from (T-2) yrs to T ? Or would subsequent events be different ?:rolleyes:
 

Answers and Replies

Simon Bridge
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Short answer: nobody knows.
This is part of the problem of determinism - and there is currently no solution.
The usual consensus is along the lines that the Universe will not play out exactly the same way twice from the same initial conditions ... this is because of some very sensitive statistical/quantum mechanics effects at the fundamental particle level. But it will be broadly similar.
However, this is an opinion based on an assumption that the underlying physics of the Universe is statistical in nature.
That may not be true: there may be an underlying structure that makes everything deterministic again.
 
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If every particle of the Universe was made to occupy the state at which it was 2 years ago
How can you define "now" without reference to the state of the universe and the particles in it?

This is a purely philosophical question, physics cannot answer philosophical questions and we are not a philosophy forum.
 

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