Schrödinger's cat
Physics can be divided into two types; classic physics and quantum mechanics. Classic physics explains most physical interactions, like why a ball bounces when it drops. It can also be used to predict physical interactions, like what will happen when you drop a ball. However, there are some physical interactions which it does not explain; for instance, how light can be turned into electricity. Quantum mechanics provides a way for physicists to explain why these things happen.