In nuclear physics, the discoveries of Ernest Rutherford, Niels Bohr, J. J. Thomson and James Chadwick made people really understand what is inside an atom: electrons, protons and neutrons. J. Robert Oppenheimer studied here and later went on to develop the atomic bomb. In astronomy, Paul Dirac, Stephen Hawking, John Herschel and Georges Lemaître found out many things about the universe, from the Big Bang to black holes.