CHAPTER IX
EINSTEIN OR NEWTON?
Recent discussion of Relativism at the Academy of Sciences—Traces of the privileged space of Newton—The principle of causality the basis of science—Examination of M. Painlevé’s objections—Newtonian arguments and Relativist replies—M. Painlevé’s formulæ of gravitation—Fecundity of Einstein’s theory—Two conceptions of the world—Conclusion.
What are these “special signs” by which the Newtonian conception of nature recognises that we are in touch with the privileged space which Newton called absolute space, and which seemed to him the real, intrinsic, exclusive frame of phenomena?
These signs or criteria are implicitly at the root of the development of classic science, but they for a time remained in the shades of the discussions provoked by Einstein’s theory. Leaving aside for a moment other, and perhaps less noble, cares, M. Paul Painlevé, addressing the Academy of Sciences at Paris, has with brilliant success drawn attention to the arguments, ancient yet ever robust, which constitute the strength of the Newtonian conception of the world.
Let us from this point speak of the absolute time and space of Newton and of Galileo as privileged space and privileged time, in order not to expose our flanks further to the metaphysical objections—not without justification—which the qualification “absolute” provokes.
Why is classical science, the mechanics of Galileo and Newton, founded upon privileged space and privileged time? Why do they refer all phenomena to these unique standards, and consider them adequate to reality? It is on account of the principle of causality.
The principle may be formulated thus: Identical causes produce identical effects. That means that the initial conditions of a phenomenon determine its ulterior modalities. It is briefly a statement of the determinism of phenomena, and without that science is impossible.
It is, of course, possible to be captious on the point. Conditions entirely identical with given initial conditions can never be reproduced or discovered at a different time or in a different place. There is always some circumstance that will be different; for instance, the fact that in the interval between the two experiments the Nebula in Andromeda will have come several thousand miles nearer to us. And we have no influence on the Nebula in Andromeda.
Happily—this saves the situation—distant bodies have, it seems, only a negligible influence on our experiments. That is why we can repeat them. For instance, if we to-day put a gramme of sulphuric acid in ten grammes of soda-solution (one-tenth), they will in the same period of time produce the same quantity of sulphate of sodium that they would have done a year previously in the same conditions of temperature and pressure; in spite of the fact that meantime Marshal Foch sailed for the United States.