Note 102 — Chapter XXXI · THE SEPARATION OF SPACE-TIME INTO SPACE AND TIME IN A GRAVITATIONAL FIELD

The Einstein effect is due to a veritable decrease in the frequency of vibration of the atom situated nearer the sun, and this retardation is caused by the increasing departure from unity of the potential , tending as it does towards zero as we approach the sun. It would be totally incorrect to ascribe it to a slowing down in the motion of a ray of light travelling away from the sun in a radial direction, owing to the retarding effect of the sun’s gravitational pull. The gravitational pull has nothing to do with the Einstein effect; and as a matter of fact, calculation shows that a ray of light travelling away from the sun would gradually increase in speed till it attained its invariant speed at infinity, as though it were repelled, not attracted by the sun. But over and above these results of calculation, it can be seen immediately that a modification in the speed of light would be incapable of explaining the existence of the Einstein effect. In all cases we are bound to receive the successive vibrations with the same frequency as they are emitted by the atom; for otherwise there would be a gradual accumulation or depletion of light waves travelling along the fixed distance separating us from the atom. Hence any verification of the Einstein effect could be ascribed only to a real modification in the frequency of the atom’s vibrations.