It is space itself that is expanding, not
some void that lies beyond the edge of the
Imagine a balloon that is covered with cotton
balls that have been glued to it. Those cotton
balls are galaxies, and the rubber of the balloon
is space. Now, blow up the balloon - the cotton
balls will get farther apart from each-other, but
won't be expanding into anything (after all, the
balloon is round - if you walked around it far
enough, you would return to the same spot).
The universe is kind of something like that:
space is getting bigger, and as a result the
distances between galaxies are increasing, but
there is no outside of the universe that matter is
How big is the universe? We don't
know. We can see a distance of about 13.7
billion light years, because the universe is 13.7
billion years old and light only travels so fast.
As the universe gets older, we can see farther,
because light has had more time to travel. There
is no indication that there is an edge of the
universe of any kind in any direction. The
universe may be infinite in size, and yet is still
expanding despite being already infinite.
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