True, it sounds impossible because there can't be a minimal limitation for frames rates. I can see that.

Except if the physics engine doesn't have to do real time calculations and then synchronize it with the graphics.
Or am I wrong here?

What I want to do is simply calculate the outcome of a scene with multiple objects and some variables. Then the calculations can happen a lot faster then real time and with it's own clock. Not the frame rate clock. So if I start the exact same calculations right after the last one, the result would have to be exactly the same, because nothing has changed! The only thing that changes in real time is the time it takes to finish a cycle, right?