Physics seems to be very diverse, with so many fields stretching in various different directions: quantum theory, general relativity, cosmology, particle physics. Yet, in all those fields physical laws are formulated in much the same way. Since the time of Galileo and Newton, in traditional physics the fundamental objects have been considered trajectories, dynamical laws and initial conditions. Physical laws say what will happen to a physical object at some later time, given the dynamical laws and the initial conditions at an earlier time. So, for example, one describes what happens to a football, which is kicked with a certain initial speed in a certain direction, via an equation of motion and a prediction about what trajectory the ball will follow, and where it will end up, given those initial conditions.