Expert: James Gort - 2/27/2007

Question
Does time stop when you reach the boundary of the finite universe?

If the universe was a singularity prior to the big bang and the big bang created space time, I'm guessing that time stops when you reach the edges of universal expansion.

Answer
Hello Paul,

Yes, you could say that "time stops" outside of the space-time boundary of the universe, in the sense that there is no time defined there.  One way to think of it (in traditional terms) is the space-time "wrinkle" propagating out (into nothingness) at the speed of light.  Since gravity disturbances seem to propagate at that speed, it's a good analogy.  If you could somehow "ride" the propagating edge outward, you'd be travelling at the speed of light.  Of course, Einstein said you really can't (as matter) travel at the speed of light, but as you approach that speed, time seems to slow for you (relevant to a distant observer).  So at the "edge", time would "stop" (again, relative to a distant observer).

Now, a leap of faith.  Suppose you built a powerful rocket that could travel near the speed of light.  For the sake of argument, you'll stay close to home (in our own solar system).  As you approach the speed of light, one theory says that you're ACTUALLY approaching the "space-time edge" of our universe!  So the "edge" is not really a PLACE (in this example, the PLACE is in our own solar system), but it is a condition of space-time (at the speed of light, space-time is warped to its maximum, and so this is really the "edge").  That's difficult to put your mind around, because we usually think in three dimensions rather than four.  But taking it one step further, if our rocket ship could somehow surpass the speed of light (with today's physics, impossible, but who knows?), then we would have crossed the "edge" and reached outside of our universe.

All of which is theory, of course, but certainly food for thought!  Eat hearty!

Prof. James Gort