“It is impossible to visualize the size and scale of the universe.  In the piece of the universe that we can see, there are roughly two trillion galaxies.  We haven't counted them all, but that's an estimate based on surveys of the local universe.  Two trillion is two thousand billion galaxies.  Let's just say, each galaxy is around the size of the Milky Way -- some are bigger, some are smaller. The Milky Way has 400 hundred billion stars in it.  It takes light over a hundred thousand light years to cross a galaxy.  And there are two trillion in the piece of the universe that we can see.  We are very sure that the piece that we can see is a small bit of  what may be an infinite universe.  We don't know, actually.  I say: don't get worried about that, because nobody can picture it.”

— Brian Cox, Physicist, University of Manchester