Relativity and the Observer

Abstract

IN Mr. Bertrand Russell's article in the new volumes of the "Encyclopædia Britannica" entitled "Relativity Philosophical Consequences," there occurs the following sentence: "The observer who is often mentioned in expositions of relativity need not be a mind, but may be a photographic plate or any kind of recording instrument." I should like to know how far Mr. Russell can claim to be in agreement with physicists on this point. For my own part it would seem to make complete nonsense of the theory. As I understand the principle of relativity, every object which can be observed, including the measuring rods and clocks which are used to observe, not excepting the retina of the observer's eye, undergoes transformation when the observer passes from one system of reference to another. If it is not so, if there be one piece of matter which can claim to be privileged, be it only a single electron, what, I ask, is the use or meaning of the principle?