Relativity

RELATIVITY. The progress of natural science in the first quarter of the present century was especially noteworthy through the appearance of the doctrine of relativity, and its almost immediate acceptance by the scientific world in general. The need for some such theory had long been felt and was becom ing continually more urgent. As far back as 1887 Michelson and Morley, experimenting for quite another purpose, had obtained results which obstinately refused to fit into 19th-century concep tions of the general nature of the universe. Experiments in other directions soon indicated that the difficulties thus revealed were not isolated difficulties confined to one special corner of science, but extended throughout a large part of electrical and optical science. Theoretical discussions by Lorentz, Larmor and others drew attention to the serious nature and extent of the difficulties which had arisen, and pointed, although somewhat vaguely, to the direction in which a solution was likely to be found.

In 1905 a paper appeared by Albert Einstein, then professor of theoretical physics in the University of Berne, which showed, although its implications were not at first fully understood, that the difficulties revealed by the experiment of Michelson and Mor ley, as well as others which had subsequently come to light, could be removed at the expense of pouring into the melting-pot all the ideas then prevalent as to the fundamental nature and mean ing of space and time. In effect, although this again was not W. Gifford, "Miwok Moieties," U. Cal. Pub., 1916, vol. 12, 139— '94, esp. 181 seq. (1916).

H. Lowie, "The Kinship Systems of the Crow and Hidatsa," Proc. 19th Intern, Congr. Americ., 1917, 34o.

realized at the time, it went further and showed that the experi ments in question actually compelled a recasting of these ideas.

At this time gravitation held obstinately aloof from all other physical phenomena ; an ether had been devised which explained optical and electrical phenomena with fair success, but it refused to find room for the phenomenon of gravitation. In 1915 Ein stein published further papers which showed that gravitation ad mitted of a very simple explanation in terms of the new ideas as to the nature of space and time. The gravitation which was explained in this way was, however, just a shade different from the gravitation of Newton. When it was realized that the gravi tation of nature was also just a shade different from that of Newton, and it was further discovered that nature ranged herself completely with Einstein in this matter, then the acceptance of Einstein's theory was universal and complete.

While gravitation fitted quite naturally into the new scheme of nature demanded by the theory of relativity, it was found to be less easy to fit in the general phenomena of electromagnetism. The last few years have seen a great deal of discussion as to the way in which these must be joined on to Einstein's general theory of relativity and, as we shall see below, the issue is still in doubt.

General Nature of the Principle.

Science advances in two ways, by the discovery of new facts, and by the discovery of mechanisms or systems which account for the facts already known. The outstanding landmarks in the progress of science have all been of the second kind. Such, for instance, was the Copernican system of astronomy, which explained the already known motions of the planets; such was the Newtonian mechan ism (the force of gravitation) which explained the elliptic orbits of the planets and the earth's pull on terrestrial bodies; such was the Darwinian mechanism of natural selection, which explained the survival of some species and the extinction of others. Such also is the theory of relativity.

The scientist's desire to discover mechanisms or systems arises no doubt primarily from the constitution of the human mind; our intellects, unsatisfied with a mere accumulation of facts, impel us ever to search for the causes underlying the facts : V ere scire est per causes scire. But to the working scientist the discovery of a mechanism has an additional and more practical value. When he has found a mechanism which will account for certain laws, he can proceed to examine the complete set of laws which the mechanism demands. If his mechanism corresponds with suffi cient closeness to reality he may in this way be led to the dis covery of new natural laws. On the other hand, the new laws deduced from the supposed mechanism may be false. If the falsity of the new laws is not at once revealed science may for a time be led into wrong paths. When more accurate experi menting or observation discloses that the new laws are not true a recasting of ideas becomes necessary, and the branch of science concerned may experience a time of revolution followed by a period of rapid growth.