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Time reversal spin

  1. Sep 28, 2015 #1
    Does anyone know why time reversal requires spin to be flipped? It seems like my book assumes that, but I have no idea why.
     
  2. jcsd
  3. Sep 28, 2015 #2

    stevendaryl

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    Well, it's obvious that orbital angular momentum reverses sign under time reversal, because it's [itex]\vec{L} = \vec{r} \times \vec{p}[/itex], and momentum reverses sign. Since angular momentum can move from spin to orbital, I don't think it would be consistent to reverse one and not the other. But I don't know of a proof.
     
  4. Sep 29, 2015 #3

    DrDu

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    Spin is angular momentum in the rest frame. Angular momentum has to change sign under time reversal by definition.
     
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