The current belief is that the universe will continue to expand to a point, then will contract back to a point and there will be another big bang. I disagree, as I don't believe the big bang to be an accurate theory. However, I don't know. No one knows. It's all just best guesses based of theory and what we can observe, which at this point in human history isn't a hell of a lot. I think black holes and dark matter play an important part. But we know next to nothing about either of them.