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Quantum Mechanics

Light Quanta and Photon Evidence

The light-quanta chapter traces how the photon concept emerged from evidence, not from a single slogan. The photoelectric effect motivated Einstein’s light-quantum hypothesis. Compton scattering later strengthened the case that light quanta carry momentum. The fully modern photon belongs to quantum electrodynamics, but the experimental pressure begins here.

Current Pages

Section titled “Current Pages”
  • Photoelectric Effect explains frequency thresholds, stopping potentials, and Einstein’s energy relation.
  • Einstein’s Light Quantum Hypothesis separates Einstein’s proposal from Planck’s oscillator quantization and explains why it was historically radical.
  • Millikan’s Photoelectric Measurements shows how precision stopping-potential data confirmed Einstein’s linear energy-frequency relation while interpretation remained contested.
  • Compton Scattering explains the X-ray wavelength shift and why it strengthened the photon momentum concept.
  • Photon Momentum connects E=hνE=h\nu, p=h/λp=h/\lambda, radiation pressure, and Compton scattering.
  • Early Photon Debates explains why the photon concept remained contested and how later evidence narrowed the alternatives.
  • From Light Quanta to Photons bridges historical light-quanta evidence to modern photon states and field quantization.

Historical Boundary

Section titled “Historical Boundary”

This chapter should not overstate what the early evidence proved. Photoelectric data supported quantized light-matter energy transfer. Compton scattering supported photon-like momentum transfer. The bridge page points toward quantum optics and quantum electrodynamics, but the detailed field theory belongs to the QFT bridge material.

Section titled “Cross-Links”

References

Section titled “References”
  • A. Einstein, “Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt,” Annalen der Physik 322, 132-148 (1905), DOI: 10.1002/andp.19053220607.
  • R. A. Millikan, “A Direct Photoelectric Determination of Planck’s h,” Physical Review 7, 355-388 (1916), DOI: 10.1103/PhysRev.7.355.
  • A. H. Compton, “A Quantum Theory of the Scattering of X-rays by Light Elements,” Physical Review 21, 483-502 (1923), DOI: 10.1103/PhysRev.21.483.
  • G. N. Lewis, “The Conservation of Photons,” Nature 118, 874-875 (1926).
  • Nobel Prize Outreach, Albert Einstein Facts.