Physicist: A woman on the subway, about two stations away from her stop, asked us “what are relativity and quantum mechanics?”So, this is a two-stop elevator pitch for the two most pivotal sciences since slicedbreadology. Relativity: Speed is just distance over time (as in “miles per hour”). Normally when you change you’re own speed, the speeds of everything else changes (for your point of view). Relativity is the study of how distance and time change with speed, and the consequences that follow from those changes. If particles were like ordinary objects, but smaller like tiny billiard balls, then you’d expect them to act like ordinary (but tiny) objects.