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
A guy called Edwin Hubble noticed that the further away a galaxy is, the faster it is moving away from us. That means that on average everything we see is moving away from everything else. It follows that everything must have been closer together in the past.
As far as we know there is no edge to the universe, the stars and galaxies just keep going forever. There is no edge so the universe isn’t expanding into anything, it is just expanding.
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