If the universe is expanding, what is it expanding into? It’s actually a great question, with a subtle answer. The universe doesn’t have to expand “into anything” if it doesn’t have an edge, in other words if it is infinitely large. Take a look at this Escher print of an infinite grid. As far as the eye can see, the grid goes on forever. Now imagine each of the sticks between nodes all getting longer. The nodes would begin to separate, and this Escher
universe would begin to expand. But it isn’t expanding into anything, it is just getting larger. That’s exactly the same as what we notice about our own universe. All the galaxies appear to be moving away from each other. But there is no edge to the universe, and therefore there also isn’t a center to the universe (which is also the reason the Big Bang didn’t happen at a point). At least we haven’t seen an edge yet.
Here’s another version I like of this print done by Escher. Flying fish as far as the eye can see!
Update 1/25/2012 – A reader wrote to inform me that these Escher works were not actually paintings, but rather prints. I’ve corrected the post.News