To predict, Omega doesn't need to simulate. You can predict that water will boil when put on fire without simulating the movement of 10^23 molecules.
Omega even can't use simulation to arrive at his prediction in this scenario. If Omega demands money from simulated agents who then agree to pay, the simulation violates the formulation of the problem, according to which Omega should reward those agents.
If the problem is reformulated as "Omega demands payment only if the agent would counterfactually disagree to pay, OR in a simulation", then we have a completely different problem. For example, if the agent is sufficiently confident about his own decision algorithm, then after Omega's demand he could assign high probability to being in a simulation. The analysis would be more complicated there.
In short, I am only saying that
are together incompatible statements.
You can predict that water will boil when put on fire without simulating the movement of 10^23 molecules.
True but irrelevant. In order to make an accurate prediction, Omega needs, at the very least, to simulate my decision-making faculty in all significant aspects. If my decision-making process decides to recall some particular memory, then Omega needs to simulate that memory in all significant aspects. If my decision-making process decides to wander around the room conducting physics experiments, just to be a jackass, and to peg my decision to the r...
This problem is roughly isomorphic to the branch of Transparent Newcomb (version 1, version 2) where box B is empty, but it's simpler.
Here's a diagram: