It seems to me that any accurate, large scale universe simulation is impossible as a matter of principle. The amount of energy it would take to run, having to simulate every particle in the universe realistically and simultaneously for trillions of years, would be as much or nearly as much energy/matter as there is in the universe. Otherwise the creation of such a simulation would violate things like the law of the conservation of energy in thermodynamics. So that the universe exists at all means that there is no simulation being run, meaning that if any "ancestor" universe exists it also cannot simultaneously exist AND run "our" universe, but we exist so it can't exist, or at least we are not a simulation.