What would need to be true for the universe to be recollapsing in nature?

For the universe to be recollapsing, it is essential that dark energy does not play a significant role and that there is a considerable amount of matter in the universe. In scenarios where the density of matter exceeds a certain critical value, gravitational forces can overcome the expansion driven by the initial conditions of the Big Bang. This would lead to a situation where the universe's expansion eventually halts and reverses, resulting in a collapse back on itself.

If dark energy were to exist and influence the universe significantly, it would counteract gravitational forces, leading to accelerated expansion rather than recollapse. The presence of dark energy is associated with a lower density of matter overall, making it less likely for the universe to collapse again. Therefore, the state of the universe being dominated by matter — to a degree that counterbalances any expanding forces — is the necessary condition for a recollapsing universe.