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I am reading the first chapter of Akhiezer, Berestetskii QED (1981). They state that Dirac was wrong to assume that the evolution of the wave function is described by

$\psi(t) = e^{-iHt} \psi(t_0)$

They say that in relativity it is also not legit to try to write a single particle formalism; that we only can describe an ensemble of the particles. Why is that?

Actually, why do we assume time reversal invariance in QM at the first place?

MsTais
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1 Answers1

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"They say that in relativity it is also not legit to try to write a single particle formalism; that we only can describe an ensemble of the particles. Why is that?"

Because even if initially you have only one particle, extra particles can be created later (say, in external fields).

akhmeteli
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