What determines the end of our universe?
Is it defined by the farthest out physical object or is it defined by the farthest out form of energy like light?
This article is good for the subject. It is determined only by the expansion of universe as far as we know. We can still think of the fact that, "If the universe had a beginning (like the Big Bang), then it should definitely have an end"...
For now, the universe is expanding and expanding. It is not defined by light nor a farther object. But instead, a spread-out hypothetical energy called dark energy. The interaction of this energy with gravity causes the acceleration of universe. From 2011, we can slightly incline over the expectation of a Big Rip.