Einstein and the Lorentz-Poincaré Theory of Relativity

Abstract

The title of this paper has reference to the well known remark which Whittaker has made about Einstein’s Special Theory of Relativity in his book History of the Theories of Aether and Electricity. In the Chapter entitled The Relativity Theory of Poincare and Lorentz’ he writes as follows: “In the autumn of the same year… Einstein published a paper which set forth the relativity theory of Poincare and Lorentz with some amplifications, and which attracted much attention… In this paper Einstein gave the modifications which must now be introduced into the for-mulae for aberration and the Doppler effect.”¹ The question with which I am concerned in this paper is whether from a strictly empirical point of view Whittaker’s assessment is correct. I shall argue that the physical content of both of Einstein’s postulates the Postulate of Relativity and the Postulate — of the Constancy of the Velocity of Light — was in fact already known to Lorentz and Poincar6, and that the significance of Einstein’s theory vis-à vis Lorentz’s lies purely in its conceptual-epistemological content. Furthermore, we argue that Einstein’s theory is derivable from Lorentz’s by the addition of these purely conceptual innovations. On the other hand it is, of course, precisely because of its conceptual innovations that Einstein’s theory has been the subject of much philosophical interest.