Optical Records and Relativity

Abstract

PROF. LLOYD MORGAN, in his interesting and most original and suggestive article, “Optical Records and Relativity” (NATURE, October 18, p. 577), sums up his argument in sixteen questions. These raise a variety of problems, but are all directed to the conclusion that we may accept the physics of relativity and yet find that the scientific creed of classical mechanics stands in no need of revision. The crux of his whole position appears to me to lie in the answer to his question 6, which he expects to be affirmative, but which must in my view be emphatically negative. The question is: “May we, on the basal principle of relativity, give primacy in reality to either set of events [optical records and their distant source-events], since each is acknowledged as physically real in the same sense?” Surely the answer is that the source-events are, in the theory of relativity, four-dimensional, while the optical records in any aspect of them are only two-dimensional, and the latter cannot therefore have primacy. To say that it is indifferent which we regard as primary, because both are real in the same physical meaning, is like saying that because the map of a country is physically real in the same meaning as the country of which it is the map, we may therefore give primacy either to the country or to the map?