You don't really need quantum mechanics for this argument, though. Even in a non-quantum world, non-linear and, in particular, chaotic systems effectively preve

You don't really need quantum mechanics for this argument, though. Even in a non-quantum world, non-linear and, in particular, chaotic systems effectively prevent you from predicting the future. While you could do it in theory, in practice you would need do know every single variable very precisely because the outcome of chaotic systems can change drastically due to a small change in initial conditions (which is colloquially known as the butterfly effect). Quantum mechanics just makes this even harder or downright impossible (think of determining the exact values of the wave function or predicting the outcome of measurements). But even if we did know all the variables, we'd then still need to simulate every single atom to predict the future, so we'd basically be building another universe. So, you're right, in that sense the universe is the most efficient computer simulating our physical reality.