The laws of Physics literally determine the outcome of most events in the universe. A simple example is Newton’s law of motion (Published in 1687) is all that is needed to predict the path of the Voyager spacecraft through our planetary system. In fact, the path of Voyager was predetermined and plotted well before anything was built so that engineers can be sure of what will happen. The act of predicting and plotting of the path ahead of time is a simulation.
Multiphysics simulation is simply accounting for the combined effects of more than one of the laws of physics to predict what will happen ahead of time.