(adsbygoogle = window.adsbygoogle || []).push({}); Dirac's "Quantum Mechanics" - the definition of the time evolution operator

I'm reading Dirac's "Principles Of Quantum Mechanics" to learn more about the formal side of the subject.

I have a question about the way he defines the time evolution operator in the book. Either there's a mistake or I'm missing something.

In chapter 27 he says (eqn 1) that [itex]\hat{T}[/itex] is defined such that:

[itex]|P(t)> = \hat{T} |P(0)>[/itex]

Where |P(0)> is a ket at time t=0 , and |P(t)> - at time t

Or equivalently |P(0)> is a ket in the Heisenberg picture, and |P(t)> - in the Schrodinger picture.

So this implies that:

[itex]<P(t)| = <P(0)| \hat{T}^{\dagger} [/itex]

And then in chapter 32, eqn 45 implies that:

[itex]<P(t)| = <P(0)| \hat{T} [/itex]

And I understand, that we can define it both ways, since it's a unitary operator. But we should stick to one way of defining it, and I'm sure Dirac does. So what it is here, that I'm not understanding properly?

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# Dirac's Quantum Mechanics - the definition of the time evolution operator

**Physics Forums | Science Articles, Homework Help, Discussion**