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I Proper distance

  1. Aug 30, 2017 #1
    actually I want to clarify that is the proper distance a(t)*dr is the elementary length along the radial direction which is changing with respect to time and if integrating a(t)*dr and dr ,which may be considered the actual distance
  2. jcsd
  3. Aug 31, 2017 #2


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    What is done in these coordinates is to fix the calculation to be at a specific time. The proper distance will be different at different times because the universe is expanding, meaning objects within the universe are getting further apart.

    Anyway, if you want a good, detailed breakdown of the distance measures used in cosmology, this is a good summary:
  4. Sep 1, 2017 #3
    actually what is the difference between dr and a(t)*dr in terms of distance?Which shall be considered the exact distance between two points say at time t?
    Last edited by a moderator: Sep 1, 2017
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