Translation
On a Heuristic Point of View Concerning the Generation and Transformation of Light
Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt
Between the theoretical conceptions that physicists have formed of gases and other ponderable bodies and Maxwell’s theory of electromagnetic processes in so-called empty space there is a profound formal difference. For while we regard the state of a body as completely determined by the positions and velocities of a very large, but nevertheless finite, number of atoms and electrons, we make use of continuous spatial functions to determine the electromagnetic state of a space, so that a finite number of quantities is thus not to be regarded as sufficient for the complete specification of the electromagnetic state of a space. According to Maxwell’s theory, in all purely electromagnetic phenomena, and so also in light, the energy is to be conceived as a continuous function of space, whereas the energy of a ponderable body, according to the present conception of physicists, is to be represented as a sum extended over the atoms and electrons. The energy of a ponderable body cannot break up into arbitrarily many, arbitrarily small parts, whereas the energy of a ray of light emitted from a point source of light, according to Maxwell’s theory (or, more generally, according to any undulatory theory) of light, distributes itself continuously over an ever-increasing volume.
The undulatory theory of light, which operates with continuous functions of space, has proved itself excellently in the representation of purely optical phenomena and will probably never be replaced by another theory. It should be kept in mind, however, that optical observations refer to time averages and not to instantaneous values, and it is quite conceivable, despite the complete confirmation of the theory of diffraction, reflection, refraction, dispersion, etc. by experiment, that the theory of light that operates with continuous functions of space leads to contradictions with experience when it is applied to the phenomena of the generation and transformation of light.
It seems to me, in fact, that the observations of “black radiation”, photoluminescence, the production of cathode rays by ultraviolet light and other groups of phenomena concerning the generation or transformation of light appear more readily understandable on the assumption that the energy of light is distributed discontinuously in space. According to the assumption to be considered here, in the propagation of a ray of light issuing from a point the energy is not distributed continuously over ever larger spaces, but consists of a finite number of energy quanta localized at points in space, which move without dividing and can be absorbed and generated only as wholes.
In what follows I shall communicate the train of thought and cite the facts that led me onto this path, in the hope that the point of view to be set forth may prove useful to some investigators in their researches.
Bern, 17 March 1905.
(Received 18 March 1905.)