So the hypothesis, not a theory as such, is that something happens that is devastating. Sometime in the future a new civilisation rises from the ashes, sets up super computers to figure out where itwent wrong, due to the passage of time, and to hope to avoid similar. The other history simulation idea is similar, but they’re trying to work out how Universes develop and we’re just a side effect, a blink of an eye to them. Both are tragic, one because if we announce ourselves as sentient byproducts they could switch us off; the other because we were always destined to die and fail.