Sabina Chiriotti IFAE Thursday meeting, March 26 th 2009. Origins of the quantum theory. To know the Revolutionary impact of quantum physics one need first to look at prequantum physics:. The old quantum theory. Max Planck .
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To know the Revolutionary impact of quantum physics one need first to look at prequantum physics:
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" .
Two theorist, Niels Bohr and Max Planck, at the blackboard. first to look at prequantum physics:
By the late 1910s : first to look at prequantum physics:
 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.
 theory of matter waves
 particles can exhibit wave characteristics and vice versa, in analogy to photons.
 new way to explain the Planck radiation law.
 He treated light as if it were a gas of massless particles (now called photons).
• 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
Paul Dirac and Werner Heisemberg in Cambrige,1930.
Old faces and new at 1927 Solvay Congress first to look at prequantum physics:
Arnold Sommerfeld admitted him to his advanced seminar.

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 lifelong friendship with Wolfgang Pauli.
The breakthrough to quantum mechanics: first to look at prequantum physics:
Heisenberg set the task of finding the new
quantum mechanics:
These unfamiliar mathematics contain arrays of numbers known as “matrix”.
“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
“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
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.
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 Schrödinger’s theory, the more repulsive I find it.. What Schrödinger writes about the visualizability of his theory is not quite right, in other words it’s crap” Heisenberg, writing to Pauli, 1926
“The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa” Heisenberg, uncertainty paper, 1927
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