Overview: Thirteen discoveries that help explain why matter and energy behave as they do: Galileo's law of falling bodies, Isaac Newton's conclusions of universal gravity, Newton's laws of motion, the second law of thermodynamics, experiments in electromagnetism, Albert Einstein's Special Theory of Relativity and his equation E=mc2, Quantum theory, calculations on the nature of light, James Chadwick's discovery of the neutron, the development of superconductivity, Murray Gell-Mann's proposal of quarks, and the discovery of the strong and weak nuclear forces.