Discussion on the theory of relativity

Mr. J. H. Jeans: During the last century, two great dominating principles of physics emerged—the Conservation of Energy and the Second Law of Thermodynamics. The present century has already added a third member to this list, the principle of Relativity, which we are to discuss to-day. The three principles have in common that they do not explain how or why events happen; they merely limit the types of events which can happen. Thus the principle of Conservation of Energy shows that water cannot flow uphill; the Second Law of Thermodynamics shows that heat cannot flow from a cold body to a hot; the principle of Relativity shows that a planet cannot describe a perfect ellipse about the sun as focus. But it would be as unreasonable to expect the principle of Relativity to explain why a planet describes an orbit or how a ray of light is propagated as it would to propound the same questions to the principle of Conservation of Energy or the Second Law of Thermodynamics. All three principles deal with events, and not with the mechanism of events. The main interest of the new theory, however, is not merely that it discloses a new universal principle; it is rather that it discloses a new universe. Our former belief that the foundations of science had been laid for all time has been shattered; we now find that the land on which we had built was largely a mirage. New and mysterious continents appear for science to explore, but it is not for the theory of Relativity to explore them. The methods of that theory are destructive rather than constructive, and, when the theory predicts a positive result, it is invariably for the same reason, namely, that a process of exhaustion shows that any other result would be impossible.