But there is another problem about really knowing the curvature of the universe. Much of our exploration of space depends on an assumption: that where we sit in the universe isn’t particularly special. It’s called the Copernican principle. Once we thought we were at the centre of it all. But Copernicus put paid to that. So we now believe that what the universe looks like around us is pretty much what it looks like everywhere. That is certainly what the evidence tells us. But it need not be the case. It’s possible that the bit of the universe we see is rather special.
