# If the univese is finite will I see my light again.

1. Jun 24, 2011

### tkav1980

As the thread title says, if the universe is finite will i see my light again. I understand that parts of space-time are expanding faster than c, therefore even in a finite yet expanding universe the light will never reach the "boundry". By boundry i mean more of a turning point where the curvature of space takes my Photon on a long trip eventually leading to its point of origion. I'm picturing 2 ants on a baloon standing next to each other. The first ant gets in his little space ship and zips off in a straight line, well a line he percieves to be straight. heading into the distance until his friend can't see him anymore. from the perspective of both ants everything in every direction is perfectly flat. But eventually our second ant turns around to find his friend rapidly aproaching from the other direction. Our first ant followed, in a straight line, the natural curvature of the baloon and ended up right where he started.

I'm trying to read a book thats a bit out of my league and im at a part of the book that talks about spatial curvature. I tend to think better in pictures so i want to make sure my picture is right before i move on to trying to teach myself the math.

2. Jun 24, 2011

### bcrowell

Staff Emeritus
In a finite universe with zero cosmological constant, I think the answer to your question is definitely yes, because every particle in the entire universe is ultimately reunited in a Big Crunch. I don't know if you'd actually see your own light before the Big Crunch, but you're guaranteed to see it at some point.

Our real universe is nearly flat, and it has a nonzero cosmological constant. So I guess if you want an answer for the real universe, we should be talking about a cosmology that has the observed value of the cosmological constant, and that is not quite flat but just barely closed (say at one end of the error bars for the best current empirical bounds on the curvature). In that case, I don't know the answer.

3. Jun 24, 2011

### tkav1980

So, to picture the ever so slight curvature of space in our real Universe, I'm on the right track?

Sorry this is a bit elementary but my last Physics class was 10 years ago, and I'm determined to get through "The Road to Reality" no matter how long it takes. Anyway, Thank you for your responce, now on to the Math section for some truly annyoing questions for those guys.