(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You want to count all the galaxies out to a certain distance R(naught). If the universe were not expanding, then N (number of galaxies) would be proportional to R^3. Justify/derive.

For an expanding universe, take into account the finite time that light takes to reach us and just describe (without derivation) the relation that would be observed between N and R.

2. Relevant equations

3. The attempt at a solution

Is this as simple as saying that the density is mass/volume, so the more volume of space you have, the more galaxies you have? That seems to easy for this class...

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Galaxy counts and the expansion of the universe

**Physics Forums | Science Articles, Homework Help, Discussion**