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I was looking at reviews for Sakurai's Quantum Mechanics textbook, and some mentioned it being outdated, specifically mentioning his use of imaginary time. Is this idea deliberately avoided in modern treatments?

I can't see why a simple parameter change t->it, would be or not be an outdated concept. It doesn't make things significantly prettier, but it doesn't hurt anything either.

With that said I've never before heard the specific phrase imaginary time so maybe it is outdated.

user2264247
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    The question "is this something most people think" is an opinion based question, but the part of imaginary time is covered under: http://physics.stackexchange.com/q/123156, http://physics.stackexchange.com/q/46798, http://physics.stackexchange.com/q/107443, and http://physics.stackexchange.com/q/121380 – Kyle Kanos Mar 05 '15 at 13:18
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    possible duplicate of Special relativity and imaginary coefficient of the time coordinate – Kyle Kanos Mar 05 '15 at 13:18
  • Unfortunately, your interesting question was closed by some not so interesting robots. I suggest to reformulate, but without the "Is this something most people think?" sentence. Try to give it a general objectivist roundup. They are not evil, they are only buggy. And register with a real name, so you will have much better chances. Good luck! – peterh Mar 05 '15 at 23:07
  • I've edited the question. Is this better? – user2264247 Mar 06 '15 at 03:20
  • Imaginary time, or, more generally, the use of $\mathbb{C}^4$ rather than $\mathbb{R}^{3+1}$ breaks the significance of signature. See my discussion of this here – Selene Routley Mar 06 '15 at 03:29
  • While it was closed with the majority voters saying it was primarily opinion based, there are still (at least) 4 separate questions on this site that explain what imaginary time is and why it is outdated. – Kyle Kanos Mar 06 '15 at 03:29
  • It is a good question, it's just been asked and answered previously. – Kyle Kanos Mar 06 '15 at 03:30
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    I see. I was looking for an explanation relating to QM so the questions mentioning Minkowski space didn't seem right. But I guess the answer is essentially the same. It hides essential mathematical features without truly simplifying anything. – user2264247 Mar 06 '15 at 04:17
  • @user2264247 Good summary. It is a good question because I guess all students of science first experience $\mathbb{C}$ as a kind of kingdom of enlightenment and power: their first experience of an algebraically closed field, one wherein the beautiful differentiability rigidity holds and so forth. Our first meeting is so intoxicating that one takes a little time to understand that the increased power of $\mathbb{C}$ means that it can't model restrictions that we need to model. Puncture $\mathbb{C}$ - you get a topological space that is still connected: puncture $\mathbb{R}$ and you sunder ... – Selene Routley Mar 06 '15 at 04:24
  • ... the space in two so there is a fundamental topoligical difference and indeed this observation yields one proof of the fundamental theorem of algebra. The discussion of signature is another expression of this kind of idea: signature is REALLY significant physically: Greg Egan explains this better than I can here: also see Greg Egan's in depth discussion of what all branches of physics would look like in a trivially signatured World – Selene Routley Mar 06 '15 at 04:32

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