Quantum Theory - Timeline

J.J Thomson - Credited with Electron Discovery Showed Cathode Rays were composed of unknown negatively charged particles

Max Planck 1900 - Originator of Quantum theory o His findings were counter to all existing physical study. - Suggested radiation is quantized – Travels in discrete amounts

Albert Einstein 1905 - Takes Planck’s ideas seriously, proposes quantum of light – the photon which behaves like a particle. - Explained equivalence of mass and energy - Suggested particle-wave duality of photons o The Equivalence principle - Special relativity - Explains the curvature of space-time 1912

Ernest Rutherford 1911 - Leads team of Hans Geiger and Ernest Marsden to conduct famous alpha particle, gold foil experiment

Ernest Rutherford - He infers the existence of the nucleus as result of the experiment. 1919

Niels Bohr 1913 - Constructs a theory of atomic structure based on quantum ideas - Developed the complementarity principle. o Bohr’s Postulates - Electrons in an atom exist in Stationary states - Transmission between stationary states produces/absorbs EM radiation - The Angular momentum of stationary electron is quantised

James Chadwick 1921 - With the assistance of E.S Bieler conclude the existence of a strong force binding the nucleus together

James Chadwick 1931 - Discovers the existence of the Neutron.

Louis de Broglie 1924 - Postulated the wave nature of electrons and suggested that all matter has wave properties. o The “de Broglie hypothesis” led to the birth of wave mechanics. o “If particles can act as wave, waves can act as particles” - Davisson and Gerner experiment o Confirmed the wave nature of electrons

Wolfgang Pauli 1925 – January - Applies quantum understanding to the hydrogen atom. - Formulates exclusion principle for electrons in an atom. o No two electrons could exist in the same quantum - Identified by four quantum numbers including his new two-valued degree of freedom. Later called Electron Spin

Enrico Fermi: - Alongside C.N Yang suggest that a pion is a composite structure of a nucleon and an anti-nucleon. (Highly radical idea) 1949

Enrico Fermi 1933-34 - Puts forward the theory of beta decay that introduces the weak interaction. First theory to explicitly use neutrinos and particle flavour changes. - Created first nuclear reactor - Experimented with inducing radioactivity with recently discovered neutrons, discovered slow neutrons were easily captured. o Fermi Age Equation