Expert Opinions on The Photon
Albert Einstein, 1905
"One should, however, bear in mind that optical observations refer to time averages and not to instantaneous values ... (to provide) the complete experimental verification of the theory of diffraction, reflexion, refraction, dispersion, and so on ... In fact, it seems to me that the observations on 'black-body radiation', photoluminescence, the production of cathode rays by ultraviolet light and other phenomena involving the emission or conversion of light can be better understood on the assumption that the energy of light is distributed discontinuously in space (photons)."
[It was more than 20 years before the word "photon" was proposed and came into common use.]
Max von Laue, 1906
[In a letter to Einstein] "...hence, radiation does not consist of light quanta (photons) as it says in § 6 of your first paper; rather, it is only when it is exchanging energy with matter that it behaves as if it consisted of them."
Max Planck, 1913
[Commenting on Einstein's 1905 paper explaining the photoelectric effect] " ...for instance in his hypothesis on light quanta (photons), he may have gone overboard in his speculations..."
Robert Millikan, 1916
"We are confronted, however, by the astonishing situation that these facts were correctly and exactly predicted nine(sic) years ago ... (by a) bold, not to say reckless, hypothesis of an electromagnetic light corpuscle (photon)...which flies in the face of thoroughly established facts of interference."
Niels Bohr, 1922
"The hypothesis of light quanta (photons) is not able to throw light on the nature of radiation."
Sir William Henry Bragg, 1922
"Light is waves on Mondays, Wednesdays, and Fridays; it's particles on Tuesdays, Thursdays, and Saturdays, and on Sundays, we try not to think about it!"
[There are many variants of this quote. The original version appeared in Electrons and Ether Waves, Scientific Monthly, 1922]
Gilbert Lewis, 1926
"I therefore take the liberty of proposing for this hypothetical new atom, which is not light but plays an essential part in every process of radiation, the name photon."
Arthur Compton, 1927
"We are thus confronted with the dilemma of having before us a convincing evidence that radiation consists of waves, and at the same time that it consists of corpuscles."
[ Nobel Prize lecture, p. 189]
Paul Dirac, 1930
"Each photon then interferes only with itself. Interference between two different photons never occurs."
[This statement was made long before Hanbury Brown Twiss correlations and biphoton entanglement were demonstrated.]
Albert Einstein, 1951
"All these fifty years of conscious brooding have brought me no nearer to the answer to the question, 'What are light quanta (photons)?' Nowadays every rascal thinks he knows, but he is mistaken."
Richard Feynman, 1979
"In fact, both objects (electrons and photons) behave somewhat like waves, and somewhat like particles. In order to save ourselves from inventing new words such as wavicles, we have chosen to call these objects particles."
Willis Lamb, 1995
"...there is no such thing as a photon. Only a comedy of errors and historical accidents led to its popularity among physicists and optical scientists."

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On 30 May 2021, 12:25.