I understand how they can tell how big a planet is or how hot a star is. The thing I don’t understand is how do they know the universe is expanding? We cant see the edge of the universe also things are moving away and towards us. So how do they know its expanding? Also, what is it expanding to? For example, at the edge of the universe, is there a wall or is there complete nothingness? Like what is it expanding towards?
Edit: hopefully I used the right flair. I wanted to use “Astronomy” but there isn’t a flair for that
In: Physics
It’s like droping a huge drop of ketchup on the floor. The only ketchup there is is the blob you let fall. But it would extend as the time passes.
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