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Originally Posted by transplant99
I wasn't aware they were sure how big the universe was, therefore, how would they know what makes up the parts they cannot see?
Just curious.
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The cosmic background radiation is the signature of the big bang; it's a view of the universe as early as is possible with electromagnetic radiation. Any earlier and the universe was opaque. If we could detect gravity waves (if they even exist) we could peer back further, but I don't think they've done that yet.
With this cosmic background radiation they are able to tell how big the universe is, and the signature gives the variation of the stuff in the universe, so no need to directly observe every part of the universe.