Exactly. To draw a computing analogy, in order for it to work we'd have to be able to make virtual machines that outperform the machines they're running on, and

Exactly. To draw a computing analogy, in order for it to work we'd have to be able to make virtual machines that outperform the machines they're running on, and recursively. In order for it to work, each simulated universe would have to progress to the point we have in ours, and also be able to simulate getting to this point much faster than it took to get there itself. It quickly starts to sound like perfect compression or perpetual motion.