If the known universe was spherical would it be possible to move outside of it the same way a rocket can leave the Earth?
Justin, New Zealand
Oh that’s an interesting question. Could it be possible to leave our Universe? Probably not, but you don’t ask exactly that. You picked a specific universe. A spherical one.
To be spherical or at least curved, the Universe has to be dense enough. Its density needs to be higher than a certain quantity we call the critical density. Our Universe is spot-on that value, suggesting that the real cosmos is flat (in three-dimensions) and infinite. The curved, closed Universe would have a finite size, and we would inhabit the three-dimensional surface of a higher-dimensional sphere.
That said, leaving the universe still wouldn’t be an easy task. We can leave Earth and go into space because (as far as we can tell) the laws of physics are the same everywhere. This might not be the case in the “outside” of the Universe. We have no evidence one way or another.
It could be similar to the novel flatland, and the multiverse is made of universes of different dimensions all next to each other. Or ...