Corpus ID: 235390555

Causality and gravity

  title={Causality and gravity},
  author={J. Donoghue and G. Menezes},
In our classical world, causality is taken to mean that there is no effect before its cause. Technically, we therefore use retarded propagators, which vanish for propagation backwards-in-time, to describe classical physics. Quantum physics is a bit different. Using Feynman boundary conditions, propagators do have a backwards-in-time propagation for so-called negative energy modes. Indeed this is required [1] in order to obtain a more general definition of causality that field operators commute… Expand
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