A Timeline of Quantum Physics |

1897
Pieter Zeeman shows that light is radiated
by the motion of charged particles in an atom, and
Joseph John (J. J.) Thomson discovers the electron.
1900 Max Planck explains blackbody radiation in the context of quantized
energy emission: Quantum theory is born.
1905
Albert Einstein proposes that light, which
has wavelike properties, also consists of discrete, quantized bundles of
energy, which are later called photons.
1911
Ernest Rutherford proposes the nuclear model
of the atom.
1913
Niels Bohr proposes his planetary model of
the atom, along with the concept of stationary energy states, and accounts
for the spectrum of hydrogen.
1914
James Franck and Gustav Hertz confirm the existence
of stationary states through an electron scattering experiment. |

1923
Arthur Compton observes that x-rays behave
like miniature billiard balls in their interactions with electrons, thereby
providing further evidence for the particle nature of light.
1923
Louis de Broglie generalizes wave-particle
duality by suggesting that particles of matter are also wavelike.
1924
Satyendra Nath Bose and Albert
Einstein find a new way to count quantum particles, later called
Bose- Einstein statistics, and they predict that extremely cold atoms should
condense into a single quantum state, later known as a Bose-Einstein condensate.
1925
Wolfgang Pauli enunciates the exclusion principle.
1925
Werner Heisenberg, Max Born, and Pascual Jordan
develop matrix mechanics, the first version of quantum mechanics, and make
an initial step toward quantum field theory.
1926
Erwin Schrödinger develops a second description
of quantum physics, called wave mechanics. It includes what becomes one
of the most famous formulae of science, which is later known as the Schrödinger
equation.
1926
Enrico Fermi and Paul A. M. Dirac find that
quantum mechanics requires a second way to count particles, Fermi-Dirac
statistics, opening the way to solid state physics.
1926
Dirac publishes a seminal paper on the quantum
theory of light.
1927
Heisenberg states his Uncertainty Principle,
that it is impossible to exactly measure the position and momentum of a
particle at the same time.
1928
Dirac presents a relativistic theory of the
electron that includes the prediction of antimatter.
1932
Carl David Anderson discovers antimatter, an
antielectron called the positron.
1934
Hideki Yukawa proposes that nuclear forces
are mediated by massive particles called mesons, which are analogous to
the photon in mediating electromagnetic forces. |

1946-48
Experiments by Isidor I. Rabi, Willis Lamb, and Polykarp
Kusch reveal discrepancies in the Dirac theory.
1948
Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga
develop the first complete theory of the interaction of photons and electrons,
quantum electrodynamics, which accounts for the discrepancies in the Dirac
theory.
1957
John Bardeen, Leon Cooper, and J. Robert Schrieffer
show
that electrons can form pairs whose quantum properties allow them to travel
without resistance, providing an explanation for the zero electrical resistance
of superconductors.
1959
Yakir Aharonov and David Bohm predict that
a magnetic field affects the quantum properties of an electron in a way
that is forbidden by classical physics. The Aharonov-Bohm effect is observed
in 1960 and hints at a wealth of unexpected macroscopic effects.
1960
Building on work by Charles Townes, Arthur Schawlow,
and others, Theodore Maiman builds the first practical
laser.
1964
John S. Bell proposes an experimental test,
"Bell's inequalities," of whether quantum mechanics provides the most complete
possible description of a system.
1970s
Foundations are laid for the Standard Model of Particle
Physics, in which matter is said to be built of quarks and leptons
that interact via the four physical forces.
1982
Alain Aspect carries out an experimental test
of Bell's inequalities and confirms the completeness of quantum mechanics.
1995
Eric Cornell, Carl Wieman, and Wolfgang Ketterle
trap clouds of metallic atoms cooled to less than a millionth of a degree
above absolute zero, producing Bose-Einstein condensates, which were first
predicted 70 years earlier. This accomplishment leads to the creation of
the atom laser and superfluid gases.
For more extensive timelines of quantum physics, see two of Abraham
Pais's books: Inward Bound: Of Matter and Forces in the Physical World
and Niels Bohr's Times: In Physics, Philosophy, and Polity.
Also see timeline.aps.org/APS/index.html |