Even were we to imagine some technology and technology advanced civilization capable of simulating an entire world, the minds within them, and anything that such minds can perceive and be affected by (i.e. we can perceive and be affected by atoms, electrons, quarks, etc but we can not perceive or be affected by an atom or particle say 100 million light years away) - even if we postulate such an enormous computing capacity - the capacity has to be finite. Even were the "computer" running the simulation the size of a world or a star or a galaxy, it is still a finite thing. Thus the simulation (the amount of our universe which we can perceive) must be "digitized" somehow - it can not go on forever and must break down at extremely small scales. So there must be a smallest "distance" or "time unit" and things like that in the universe in which we live. If we lived in a universe where the physics was "analog" or "fractal" (for want of a better word) where regardless of how small a time period we look at (or a distance or an energy unit) there can always be something smaller this would entirely disprove the simulation(I think) theory as the capacity of the computing machine needed to create such a universe would be infinite leaving no room for the "programmers". In our universe we do live with a physics which has smallest possible units of distance, time and energy which does not prove or disprove the simulation theory but does give one something to think about.