One Hundred Years of Quantum
Physics
Daniel Kleppner and Roman
Jackiw* |

An informed list of the most profound scientific developments
of the 20th century is likely to include general relativity, quantum mechanics,
big bang cosmology, the unraveling of the genetic code, evolutionary biology,
and perhaps a few other topics of the reader's choice. Among these, quantum
mechanics is unique because of its profoundly radical quality. Quantum
mechanics forced physicists to reshape their ideas of reality, to rethink
the nature of things at the deepest level, and to revise their concepts
of position and speed, as well as their notions of cause and effect.
Further Reading
B. Bederson, Ed., More Things in Heaven and Earth: A Celebration
of Physics at the Millennium (Springer Verlag, New York, 1999).
J. S. Bell, Speakable and Unspeakable in Quantum Mechanics: Collected
Papers on Quantum Mechanics (reprint edition) (Cambridge University Press,
Cambridge, 1989).
L. M. Brown, A. Pais, B. Pippard, Eds., Twentieth Century Physics
(Institute of Physics, Philadelphia 1995).
D. Cassidy, Uncertainty: The Life and Science of Werner Heisenberg
(W. H. Freeman, New York, 1993).
A. Einstein, Born-Einstein Letters, trans. Irene Born (Macmillan,
London, 1971).
H. Kragh, Dirac: A Scientific Biography (Cambridge University Press,
Cambridge, 1990).
W. Moore, Schrödinger: Life and Thought (Cambridge University
Press, Cambridge, 1989).
A. Pais, Inward Bound: Of Matter and Forces in the Physical World
(Oxford University Press, Oxford, 1986).
A. Pais, Niels Bohr's Times: In Physics, Philosophy, and Polity
(Oxford University Press, Oxford, 1991).
Daniel Kleppner
is Lester Wolf Professor of Physics and Acting Director of the Research
Laboratory of Electronics at the Massachusetts Institute of Technology.
His research interests include atomic physics, quantum optics, ultraprecise
spectroscopy, and Bose-Einstein condensation.
Roman Jackiw
is Jerrold Jacharias Professor of Physics at MIT. His research interests
include applying quantum field theory to physical problems, theoretical
particle physics, and the search for unexpected, subtle effects that may
apply to particle, condensed matter, and gravitational physics.
Volume 289, Number 5481, Issue of 11 Aug 2000, pp. 893-898. Copyright © 2000 by The
American Association for the Advancement of Science. |

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 |