Dear Dr. B: What do physicists mean when they say time doesn�t exist?

That was a question Brian Clegg didn�t ask but should have asked. What he asked instead in a recent blogpost was: �When physicists say many processes are independent of time, are they cheating?� He then answered his own question with yes. Let me explain first what�s wrong with Brian�s question, then I�ll tell you something about the existence of time.
What is time-reversal invariance?

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