When you break a stick you just break a stick. When you simulate breaking a stick you know everything about the broken stick.
What if you broke the stick to study its material properties? Then you would need to spend months carefully taking samples and measuring all the broken spots.
With a perfect simulation? You're done the moment it ends. All the data is there available with a copy paste
Well of course the simulation is a simulation. They are speaking of the ideal case. A real simulation is an application of a model, the physics of the molecules and structures interacting. They are saying that in the ideal case, once the simulation is complete you have complete knowledge of the entire system at every moment in time. Of course there's a resolution to all this. The time steps are comparatively large to the planck time and the wave functions are approximations, everything is an approximation, that's what makes it a simulation.
But the principle is that within your model, once the simulation is complete you know _everything_. You have measured every aspect of reality possible from your simplified version. If your model was arbitrarily close to reality you really would know everything
What if you broke the stick to study its material properties? Then you would need to spend months carefully taking samples and measuring all the broken spots.
With a perfect simulation? You're done the moment it ends. All the data is there available with a copy paste