Pulsar Test of a Variation of the Speed of Light with Frequency

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Science  14 Nov 1969:
Vol. 166, Issue 3907, pp. 879-881
DOI: 10.1126/science.166.3907.879


The sharply defined optical and radio pulses from pulsars make possible a test of the variation of the speed of light with frequency, and of the possible existence of a photon mass. The data indicate that the mass of a real photon is less than 10-44 gram. Detection of extragalactic pulsars could allow a substantial improvement of this limit.

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