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Concerning the importance of preffered time coordinates

  1. Aug 18, 2011 #1
    I have been reading around in general relativity, and see that, for Quantum Field Theory in Curved Spacetime, the notion of a preferred time coordinate comes up quite often (to distinguish positive frequencies). Why must the coordinate be 'preffered,' i.e. why must it be a consequence of the manifold's structure.

    I understand this may sound like a stupid question, but any spacetime manifold admits at least one timelike (or two null coordinates) coordinate - why not simply use this?
  2. jcsd
  3. Aug 22, 2011 #2


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    I don't there's any fundamental reason, isn't it just a matter of practicality. The things you want to do, such as separate the wave equation to define positive frequencies, write down a Green's function, etc, can be carried out explicitly in cases where the time coordinate has simple global properties.
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