According to what I gather from the discussion at https://stackoverflow.com/questions/41063608/why-are-computer-game-physics-engin... it appears that Unity would be deterministic within a given installation if time is calculated within the program without reference to real time. That is, because background processes may cause the computer used to take a different amount of time to do the same thing on different occasions, synchronizing Unity to the actual time can cause velocity calculations to give different results in otherwise identical situations.