The authors talk about the possibility of replicating the universe rather than simulating it. They conclude that it is not possible to replicate, but I don't think that conclusion has much value. If it were possible to replicate digitally the universe with resources less than those of the entire universe, that would suggest that it is possible for the actual universe to exist in a simpler form. Occam's razor would then suggest that the real universe would simply take that simpler form. So if the universe is as simple as it can be, retaining all its currently observable properties, then it follows that is inherently un-replicable. Or, put another way, the universe is its own replication.<p>Simulation is another matter. Simulation by its nature cuts corners. Otherwise why bother? The challenge of the game of deciding if our universe is a simulation is finding a way to spot the shortcuts taken in the simulation.