I Proper distance

1. Aug 30, 2017

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

2. Aug 31, 2017

kimbyd

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. Sep 1, 2017

Apashanka Das

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: Sep 1, 2017