Understanding the Role of a(t)*dr in Calculating Actual Distance

  • #1
Apashanka Das
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
 
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  • #2
Apashanka Das said:
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
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:
https://arxiv.org/pdf/astro-ph/9905116.pdf
 
  • #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?
 
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