Here is a slightly diferent view of the universe than triggergrin, if it were possible to see it, and it isn't, but here it is if you could.
Since we are within the boundries of existence, we will see the universe as unbounded, and seemingly infinite. If we could travel the speed of light, we would still garner the same information of an infinite universe. That is because the universe is an ongoing process by which it's boundries are increasing at C. Thusly we could never approach these boundries any closer than we are now, no matter what direction we choose.
The universe is no more than the definition of nothing. It is a conceptual definition by fiat i.e there is no other alternative. This is to say that reality is not a physical enerprise. Physical existence can only be brought on by conceptual means. In other words ... we think we are physical entities.
The answer to the question of where does space end? {would be} At the boundries of our universe. It really is that simple! One might ask how far is it to the boundries? It may be so that this is impossible to determine. This could be analogous to the approach of the speed of light, wherein an infinity of energy is required to hit the speed limit. We could say that we observe 99% of the universe, but in reality that last 1% is a trillion times the size of what we consider to be 99%. hence we may never know.
Hows that for barging in with a first post on these forums?