By the end of the 1800s, the periodic table arranged the elements of matter into a pattern ordered by atomic weight. In 1897, J.J. Thomson found the first subatomic particle, the electron. In 1908, Ernest Rutherford’s scattering experiment revealed the nucleus. Einstein’s theory of special relativity showed that space and time can change in different reference frames. E=mc2 Quantum mechanics: Particles can behave like waves, energy can exist in quanta, and particles behave by probability, not certainty. Quantum pioneers Werner Heisenberg and Niels Bohr. The fundamental particles of matter are leptons and quarks. Everything we see in nature can be understood as the interplay of the particles and forces of the Standard Model. The physics of the ultimately small is deeply connected to the physics of the ultimately large; matter-antimatter, the early universe, dark matter, the expanding universe. A Century of Discovery Discoveries of the 20th century revolutionized our understanding of matter, space and time. Atoms The Standard Model Protons The Cosmic Connection Quantum Mechanics Dark Matter Special Relativity The Expanding Universe Quarks and Leptons