I'm not a physicist, I'm a programmer. If I tried to simulate the Many-Worlds Interpretation on a computer, I would rapidly run out of memory keeping track of all of the different possible worlds. How does the universe (or universe of universes) keep track of all of the many worlds without violating a law of conservation of some sort?

If a photon hits two full mirrors at right angles, then its amplitude is changed by i*i = -1. Does it matter whether the second mirror turns the photon back towards its source, or causes the photon to continue in the direction it was going originally? Do you get -1 in both cases?