Origins of the quantum theory

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Origins of the quantum theory

• Sabina Chiriotti
• IFAE Thursday meeting, March 26th 2009

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The old quantum theory
To know the Revolutionary impact of quantum
physics one need first to look at pre-quantum
physics
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Max Planck

• 1900 Max Plank introduced the concept of energy
  radiated in discrete quanta.
• Found ? relationship between the radiation
  emited by a blackbody and its temperature.
• Eh? quanta of energy is proportional to the
  frequency with which the blackbody radiate

assuming that energies of the vibrating
electrons that radiate the light are quantized ?
obtain an expression that agreed with experiment.
he recognized that the theory was physically
absurd, he described as "an act of desperation" .
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Albert Einstein

• The photoelectric effect
• Not explained by Maxwell's theory since the rate
  of electrons not depended on the intensity of
  light, but in the frequency.
• 1905 Einstein applied the idea of Plank's
  constant to the problem of the photoelectric
  effect ? light consists of individual quantum
  particles, which later came to be called photons
  (1926).
• Electrons are released from certain materials
  only when particular frequencies are reached
  corresponding to multiples of Plank's constant
  .

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Niels Bohr

• 1913 Bohr quantized energy ? explain how
  electrons orbit a nucleus.
• Electrons orbit with momenta, and energies
  quantized.
• Electrons do not loose energy as they orbit the
  nucleus, only change their energy by "jumping"
  between the stationary states emitting light
  whose wavelength depends on the energy
  difference.
• Explained the Rydberg formula (1888), which
  correctly modeled the light emission spectra of
  atomic hydrogen
• Although Bohr's theory was full of
  contradictions, it provided a quantitative
  description of the spectrum of the hydrogen atom

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Two theorist, Niels Bohr and Max Planck, at the
blackboard.
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By the late 1910s

• 1916 Arnold Sommerfeld
• - To account for the Zeeman effect (1896)
  atomic absorption or emission spectral lines
  change when the light is first shinned through a
  magnetic field,
• - he suggested elliptical orbits in atoms
  in addition to spherical orbits.
• In 1924, Louis de Broglie
• - theory of matter waves
• - particles can exhibit wave
  characteristics and vice versa, in analogy to
  photons.
• 1924, another precursor Satyendra N. Bose
• - new way to explain the Planck radiation law.
• - He treated light as if it were a gas of
  massless particles (now called photons).

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Scientific revolution 1925 to January 1928

• Wolfang Pauli the exclusion principle
• Werner Heisemberg, with Max Born and Pascual
  Jordan,
• - discovered matrix mechanics ?first
  version of quantum mechanics.
• Erwin Schrödinger
• - invented wave mechanics, a second form
  of quantum mechanics in which the state of a
  system is described by a wave function,
• Electrons were shown to obey a new type of
  statistical law, Fermi- Dirac statistics
• Heisenberg Uncertainty Principle.
• Dirac contributions to quantum mechanics
  and quantum electrodynamics

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Many physicists have also contributed to the
quantum theory

• Max Planck Light quanta
• Einstein photon photoelectric
• Louis de Broglie Matter waves
• Erwin Schrödinger waves equations
• Max Born probability waves
• Heisenberg uncertainty
• Paul Dirac Spin electron equation
• Niels Bohr Copenhagen
• Feynman Quantum-electrodynamics
• John Bell EPR Inequality locality
• David Bohm Pilot wave (de Broglie)
• ...

Paul Dirac and Werner Heisemberg in Cambrige,1930.
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The first Solvay Congress in 1911 assembled the
pioneers of quantum theory.
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Old faces and new at 1927 Solvay Congress
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Scientific revolution Heisenberg the
uncertainty principle
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Werner Karl Heisenberg Brief chronology

• 1901 - 5Dec He was born in Würzburg, Germany
• 1914 Outbreak of World War I.
• 1920 he entered at the University of Munich
• ? Arnold Sommerfeld admitted
  him to his advanced seminar.
• 1925. 29 June Receipt of Heisenberg's paper
  providing breakthrough to quantum mechanics
• 1927. 23 Mar. Receipt of Heisenberg's paper on
  the uncertainty principle.
• 1932. 7 June Receipt of his first paper on the
  neutron-proton model of nuclei.
• 1933 .11 Dec. Heisenberg receives Nobel Prize for
  Physics (for 1932).
• 1976. 1 Feb. Dies because of cancer at his home
  in Munich.

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Influences

• Studied with three of the worlds leading atomic
  theorists Sommerfeld, Max Born and Niels Bohr.
• In 3 of the worlds leading centres for
  theoretical atomic physics Munich, Göttingen and
  Copenhagen.
• -

Max Born
From Sommerfeld I learn optimism, from the
Göttigen people mathematics and from Bohr
physics Heisemberg
Arnold Sommerfeld (left) and Niels Bohr
Wolfgang Pauli
- In Munich he began a life-long friendship with
Wolfgang Pauli.
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During 1920

• Heisenbergs travels and teachers during help him
  to become one of the leading physicists of his
  time.
• Goal fortune of entering in the world atomic
  physics just in the right moment for
  breakthrough.
• Found that properties of the atoms predicted from
  the calculations did not agree with existing
  experimental data.
• The old quantum theory, worked well in simple
  cases, but experimental and theoretical study was
  revealing many problems ? crisis in quantum
  theory.
• The old quantum theory had failed but Heisenberg
  and his colleagues saw exactly where it failed.

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Quantum mechanics 1925-1927

• The leading theory of the atom when Heisenberg
  entered at University was quantum theory of Bohr.
• Although it had been highly successful, three
  areas of research indicated that this theory was
  inadequate
• light emitted and absorbed by atoms
• the predicted properties of atoms and molecules
• The nature of light, did it act like waves or
  like a stream of particles?
• 1924 physicists were agreed old quantum theory
  had to be replaced by quantum mechanics.

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The breakthrough to quantum mechanics

• Heisenberg set the task of finding the new
• quantum mechanics
• Since the electron orbits in atoms could not be
  observed, he tried to develop a quantum mechanics
  without them.
• By 1925 he had an answer, but the mathematics was
  so unfamiliar that he was not sure if it made any
  sense.
• ? These unfamiliar mathematics contain arrays of
  numbers known as matrix.
• Born sent Heisenbergs paper off for publication.

All of my meagre efforts go toward killing off
and suitably replacing the concept of the orbital
path which cannot observe Heisemberg, letter to
Pauli 1925
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The first page of Heisenberg's break-through
paper on quantum mechanics, published in the
Zeitschrift für Physik, 33 (1925),
The present paper seeks to establish a basis for
theoretical quantum mechanics founded exclusively
upon relationships between quantities which in
principle are observable. Heisemberg, summary
abstract of his first paper on quantum mechanics
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The wave-function formulation
1926 Erwin Schrödinger proposed another quantum
mechanics, wave mechanics. Appealed to many
physicists because it seemed to do everything
that matrix mechanics could do but much more
easily and seemingly without giving up the
visualization of orbits within the atom.
I knew of Heisemberg theory, of course, but I
felt discouraged, not to say repelled, by the
methods of transcendental algebra, which appeared
difficult to me, and by the lack of
visualizability.- Schrödinger in 1926.

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The Uncertainty Principle
1926 The rout to uncertainty relations lies in
a debate between alternative versions of quantum
mechanics - Heisenberg and his closest
colleagues who espoused the matrix
form of quantum mechanics - Schrödinger and
his colleagues who espoused the new
wave mechanics .
May 1926, Matrix mechanics and wave mechanics,
apparently incompatible ? proof that gave
equivalent results.

The more I think about the physical portion of
Schrödingers theory, the more repulsive I find
it.. What Schrödinger writes about the
visualizability of his theory is not quite right,
in other words its crap Heisenberg, writing to
Pauli, 1926
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• In 1927 the intensive work led to Heisenbergs
  uncertainty principle and the Copenhagen
  Interpretation
• The more precisely the position is determined,
  the less precisely the momentum is known in this
  instant, and vice versa Heisenberg, uncertainty
  paper, 1927
• After that, Born presented a statistical
  interpretation of the wave function, Jordan in
  Göttingen and Dirac in Cambridge, created unified
  equations known as transformation theory. The
  basis of what is now regarded as quantum
  mechanics.
• The uncertainty principle was not accepted by
  everyone. Its most outspoken opponent was
  Einstein.

.
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Conclusion

• The history of Quantum mechanics its not easy,
  many events pass simultaneously ? difficult
  period.
• Quantum mechanics was created to describe an
  abstract atomic world far removed from daily
  experience, its impact on our daily lives has
  become very important.
• Spectacular advances in chemistry, biology, and
  medicine
• Quantum information
• The creation of quantum physics has transformed
  our world, bringing with it all the benefitsand
  the risksof a scientific revolution.

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Bibliography

• http//www.aip.org/history/heisenberg/p08.htm
• http//www.4physics.com/phy_demo/QM_Article/articl
  e.html
• http//www.vcpc.univie.ac.at/ian/hotlist/qc/qm.sh
  tml
• http//www.slac.stanford.edu/pubs/beamline/30/2/30
  -2-carson.pdf