1/ A list of the 20 most consequential theoretical breakthroughs in physics over the last 100 years. What did we miss out on? Of course, we had to leave out many important theories because of the arbitrary nature of any top-20 list! #physics #quantum #theoreticalphysics
2/ De Broglie wave-particle duality (1924) conjectures that all particles, e.g. electrons, are also waves with wavelength proportional to the inverse momentum—particles and waves are simultaneous dual properties of matter.
3/ Schrodinger equation (1925) demonstrates the fundamental dynamical equation controlling the microscopic physical world and starts the quantum revolution.
3/ Heisenberg quantum mechanics (1925) creates modern quantum mechanics using non-commuting operators expressed as matrices.
4/ Pauli principle (1925) asserts that fermions with half-integer spins (e.g. electrons, protons) cannot occupy the same quantum state, immediately explaining the periodic table.
6/ Born wave function probability (1926) postulate asserts that the square of the quantum wave function is simply a ‘probability’, thus emphasizing a profound distinction between quantum and classical.
7/ Dirac equation (1928) connects special relativity and quantum mechanics through an elegant generalization of Schrodinger equation.
8/ Fermi weak interaction (1933) defines the beginning of modern particle physics through a phenomenological theory of weak interactions in beta decay.
9/ Schwinger QED (1948) creates the first successful renormalizable quantum field theory of electromagnetic interactions which eventually leads to better than 10 decimal place agreement between theory and experiment.
10/ Ginzburg-Landau mean field theory (1950) creates the general phenomenological field theory, originally to explain superconductivity, underlying a successful description of phases of matter based just on symmetry and order.
11/ Yang-Mills theory (1954) develops the non-Abelian gauge theory by providing an SU(N) Lie group generalization of the U(1) Abelian electromagnetic field theory—this is the cornerstone of the standard model.
12/ BCS theory (1957) creates the successful theory for superconductivity, which also eventually ushers in the subject of ‘spontaneous symmetry breaking’, a key element of the standard model of particle physics.
13/ Gell-Mann (1962-64) develops the SU(3) algebra and postulates quarks for understanding intra-nuclear strong interactions.
14/ Higgs (1963) postulates a new boson, the Higgs particle, and a mechanism, Higgs mechanism, to provide mass in gauge theories.
15/ Bell (1964) proves decisively through an exact inequality that quantum mechanics cannot be both real and local, and as such must be fundamentally different from classical physics.
16/ Weinberg (1967) produces the electroweak unification of gauge theories, creating the modern standard model of particle physics.
17/ T’Hooft (1971) proves the renormalizability of Yang-Mills gauge theory, thus starting the modern theory of particle physics.
18/ Wilson (1971) introduces the renormalization group as a conceptually new way of understanding critical phenomena in phase transitions and also establishes all field theories to be effective field theories with suitable cut-offs.
19/ Laughlin (1983) develops a nonpertubative theory for fractional quantum Hall effect through a paradigmatic correlated wavefunction describing an incompressible quantum fluid with energy gaps.
20/ Witten (1988) introduces the topological quantum field theory as a new theoretical paradigm by incorporating topological invariants in field theories.
21/ Shor (1994) creates the subject of quantum information by introducing the factoring algorithm and the quantum error correction theorem.
22/ Maldacena (1997) conjectures that gravity is dual to conformal field theory through AdS/CFT, creating a deep connection between gauge theories and quantum gravity.
Postscript 1. The theoretical achievements in quantum physics during the 1924-1928 five-year period are an astonishing intellectual triumph of the human mind, unlikely to be ever matched again.
Postscript 2. The theoretical achievements from the last 30 years making the list (Witten, Shor, Maldacena) have a very tenuous connection to laboratory experiments, unlike the achievements of the 1924-1983 period. Perhaps, physics is slowing down after an amazing run. #quantum
