It’s an appealing idea. However, a moment’s reflection tells us that very few investigations could actually proceed in this manner. For one thing, we rarely (if ever) have access to the complete initial data required for the laws to deliver an unequivocal answer. Suppose we wanted to calculate the state of the world just one second from now. If the laws are relativistic – that is, if they stipulate that no influence can travel faster than light – our initial state description would need to cover a radius of 300,000 km. Only then could we account for any possible influences that might reach our location within one second. For all practical purposes this is, of course, impossible. And so we find that, even in physics, we need inferences that require much less than complete states as input.