Is the universe finite or infinite? Will it recollapse or expand forever?
We don’t really know in either case. Since the Big Bang happened a finite time ago (about 14 billion years), and since light travels at a finite speed, there is an unbreakable upper limit to how far away we can see in the universe. Up to the limits of the observable universe, what we observe is consistent with a uniform distribution of matter and energy that could easily extend forever. On the other hand, it might eventually turn into something very different, beyond what we can see; indeed, this might arise naturally as a result of inflation (see the really early universe). Similarly, we can straightforwardly extrapolate the current evolution of our universe, dominated by dark energy, to predict a future in which the universe continues to expand for all time (see the dark universe). However, the dark energy might someday change its character into something different, in which case the universe might very well collapse. So, given how little we currently understand about the nature of d
