Development of the Quantum Theory

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Development of the Quantum Theory

• Progress was piecemeal, but accelerated once
  physicists began to accept the idea of a
  dualistic nature in light
• I was compelledto assert its unambiguous
  verification in spite of its unreasonablenessit
  seemed to violate everything we knew about the
  interference of light
• - R. Millikan, 1915

• Light is a particle
• Photoelectric effect
• Compton effect
• Pair production

• Light is a wave
• Refraction
• Interference
• Diffraction
• Polarization

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Wave-Particle Duality
Louis deBroglie (1924) - If light (waves) can be
made to manifest particle (photons) behavior, why
shouldnt particles (say, electrons) manifest
wave properties?
Unstable electron orbit
Stable electron orbit
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Wave-Particle Duality
Wavelength of a particle
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Thats a bunch of crap, Dr B!...
If this is all true, why dont we see the moon
jump between allowed orbits???
Here size matters.the size of the wavelength
that is.
Wavelength of an electron
Wavelength of the moon
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Pauli and the Exclusion Principle

• Problem with Bohr model
• WHY dont electrons all go into ground state?
• WHY do electrons fill these orbital shells?
• Pauli develops exclusion principle
• Two electrons cannot occupy the same state
• That is, shells have certain number of vacancies

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Periodic Table
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The State of Quantum Theory Circa 1925

• Still only a semblance of a consistent theory
  for one-electron atoms
• Theory in many ways was enormously successful,
  in many ways bitterly disappointing

a lamentable hodgepodge of hypotheses,
principles, theorems and computational
recipes. - Max Jammer
8
Heisenbergs Matrix Mechanics

• 1925 Heisenberg develops matrix mechanics
• Differential operators correspond to physical
  measurements
• In matrix mathematics, these operators dont
  always commute

9
Heisenbergs Uncertainty Principle

• Any two operators or quantities (whose product
  gives units of action) do not commute - that
  is,
• A x B B x A ? 0
• and cannot be simultaneously known with unlimited
  precision DADB gt h Ex Dx Dp gt h
• DE Dt gt h
• This is NOT a statement limiting experimental
  precision, but rather a fundamental
  characteristic of nature

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To measure something, you must interact with
itOn a macroscopic scale, the influence of this
interaction is negligible, but in the quantum
case it is of fundamental import Experiment
phenomena observer form one holisticnon-separa
ble systemany observation necessitates an
interference with the course of the phenomena,
and requires a final renunciation of the
classical ideal of causality and a radical
revision of our attitude towards the problem of
physical reality-Bohr
The Measurement Problem