system
Given the following post, respond as if you're commenting on Reddit:
human
in the FAQ it is stated that one proof of the universe's expansion is that "more distant galaxies are packed closer together". What sort of measurements have been made to show this?
gpt
Telescope observations were done to establish two things.  

1) The distance to galaxies using Supernova Light curves and redshifts.

2) How seperated the galaxies are (basically galaxies "per square inch")

Its found that at larger distances, there are more galaxies per unit area at that distance.

So at 10 billion ly we might have 5 galaxies per unit area.  At 12, the average is 8, at 13 the average is 14 per unit area.

&#x200B;

Its essentially a matter of sectioning off a portion of the sky and counting.  Then comparing that to the distances for each galaxy.