I was just reading a bit about our universe and the observable universe which stirred up a few questions. I am mostly a student of mathematics, so I apologies if I am assuming things that are incorrect or if I am not using proper terminology. Maybe some of the quotes from my readings are inaccurate, please feel free to correct. 1) "If the size of the observable earth were a quarter, the entire universe would be the size of earth". How do we know that there is a finite size to the universe? I can see how one would have to subscribe to the finite notion if they accepted the big bang theory. But I see no reason other than that why the universe can't be infinitely large. 2) The cosmic light horizon - is our only limitation on how far we can see into the universe the age of the universe itself? In other words, since light from galaxies beyond our universe hasn't had enough time to get to earth then we can't possibly see it. If yes though, at the time of the big bang, there was a moment when all galaxies and planets and everything was condensed in a singularity. At this time the distance between what is now earth and every other object in space was 0. After the big explosion, unless objects traveled faster than the speed of light to get away from us (which I assume is impossible by the theory of relativity) then we should be able to view light from any object in space. (I don't think I did a very good job at explaining that one)... 3) "Since space is roughly flat..." Can someone justify this claim? How do we know this? 4) If you accept that our Universe only extends a finite length, then is it possible that there are other universes "next to" ours? I am not talking about parallel universes, I am more using the term universe to define an enormous collection of galaxies. Are there any viable theories like this out there? Thanks for your help! I am quite interested in this stuff, but could never find (or fit into my schedule) a class in university about it.