How big is the universe?

Jessica E. asks, "Dr. Volt, how big is the universe?"

Ah, Jessica, this is a far more intriguing question than it at first appears! You see, to this day scientists are still not certain if the universe has a finite size or if it is infinite! At the very least we know it is billions of light years wide (a light year being how far light travels in a year, and given that light moves at around 300,000,000 meters per second that's pretty far itself!). But it is indeed possible that the universe is of infinite size. We may never really know, for in order to even see objects at the edges of the known universe the light must have had time to travel and reach Earth. It is possible, and indeed likely, that there are parts of the universe from which light has yet to reach us.

But let us for a moment assume that the universe is of a finite (albeit very, very large) size. Does this mean the universe has an edge? And end beyond which we can go no further? Not necessarily. Picture a ball. The two-dimensional surface of the ball is of a finite size that we can measure, but that surface doesn't have an edge. If you start and one point and move around the ball you will come back to the point at which you started. The thought is that the universe, if finite, is like a three-dimensional version of that ball: travel far enough and you will eventually come back to the same point as the universe loops back in on itself. It is, to be sure, a strange idea, but since we know that gravity, for example, can warp space-time (thank you, Einstein), the idea is not so far-fetched.