hmm, bathroomcoffee you do know what you are talking about :) yes, by using the theory of relativity both things can be predicted. A finite universe and an infinite one. it was by a guy named, Alexander Friedman, who used the theory of relativity and stated that the finite universe will have more enery inside it than a infinite universe. .. Using even the theory of relativity, which says universe is finite or infinite depends on its density, but when it was calculated by, i think it was Friedman again,?? the result was close to its critical density, which suggest universe is finite. but we dont know for certain. and when talking about gravitational constant, we cannot be sure that every corner of the galaxy holds the same constant. Yes, the once we have seen which are many light yrs away might match, what we know, but what about the rest which we havent even seen, it might be of something that we have not seen.. and lastly, we would like to consider an infinite universe because it is easier to imagine then a 3 D universe.. Aliciaa, the answer to your question also lies in the enery or the density of that matter, if the universe is infinite right now, it was certainly infinite even when big bang took place so, the density might have been very huge, but it is finite, then the desity should have been very small..