Quantum physics is the study of the very, very small. What is the smallest possible constituent of matter? Originally believed to be the atom, we now know that even the protons and neutrons that make up the atomic nucleus can be divided into smaller particles called quarks. Objects behave counterintuitively on such tiny scales, with particles appearing to act like waves, and vice versa. The bizarre idea that the state of a system isn't defined until it is observed gives rise to the famous thought experiment known as Schrödinger's Cat.