If you are mainly interested, in what happens with people, accuracy of the rest of simulation is not important, you only need to simulate the parts people see with the resolution they can see, you even can have lots of inconsistencies as long as they are not reproducible.
the problem is the world is chaotic: any approximation, no matter how small, will cause divergence very quickly. (This is actually the main problem with the simulation: how did they get the exact initial conditions and physical constants?).
