system
Given the following post, respond as if you're commenting on Reddit:
human
How do we know that space/ the universe is expanding and not matter "shrinking" in relation to space?

How do we know that the universe is expanding and not matter "shrinking"? I have no physics background so as far I can see the observable effects would be the same: As matter gets smaller/is shrinking, but space is'nt, it would seem like every galaxy is moving away from us. Also there would be no need for dark energy etc ...
This might be a ridiculous question, but I just could not find an answer myself how we know for certain that this isn't the case.
gpt
When observing very distant objects, we observe the phenomena of red-shift, where the light waves from the galaxies and quasars have be stretched as a result of the expansion of the universe. Objects which are further away appear to be moving away much faster than objects which are nearer--the red-shift is more stark. If matter were simply shrinking, the effects of red-shift would come solely from the actual movement of distant objects from us. Nearly everything in the universe is moving away from us and some of these objects are "moving" faster than the speed of light, which would be impossible with the shrinking matter theory.