[codeulike]

Lets say you have that 300 qubit quantum computer, and you only need to simulate your own light cone. Trouble is, that quantum computer is also in your light cone. So to accurately simulate your light cone, your simulation has to include itself, recursively. Hence: not going to happen.

[cthalupa]

Not if you're only attempting to prove or disprove free will and run the simulation after the fact. If you can get perfect knowledge of the starting conditions for everything in the light cone, run it, and then compare it against what actually occurred.

It might not work for telling the future, but if you limit the computation to see if it accurately models what is now history, you don't need it to simulate itself.