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General Relativity 50 Years a unified theory of gravitation and electromagnetism General Relativity were not successful and general relativity occupied (and still occupies) a position which is rather cut off 50 years old from other physical theories. In the last decade, special attention has been paid ^ A. Capella to two problems: gravitational radiation and the quan­ tization of the gravitational field. General relativity Theory Division postulates the existence of gravitational waves, but it In May 1916, 'The Foundations of General has not so far been possible to detect them. The Relativity Theory' by Albert Einstein was reasons for this failure seem to be, on the one hand, published in 'Annalen der Physik'. Fifty years the extremely low energy carried by the waves and, later, this major contribution to scientific thought on the other, the difficulties inherent in the construction still has a rather isolated position with respect of an emitter of gravitational waves. At present, one to the main-stream of scientific theory. (In cont­ can do no more than try to detect gravitational rast, the Special Theory of Relativity is one of the radiation coming from the interstellar regions. With cornerstones of sub-nuclear physics.) To mark regard to quantization of the gravitational field, the anniversary of the publication of Einstein's although considerable progress has been made, it is still paper a theoretician from CERN discusses the very limited and it can be said that no coherent quan­ theory and its present status. tization of general relativity theory exists at present. The difficulties arise both from the curvature of The great originality of general relativity theory rests space-time and from the identification of field and in replacing the flat space-time of special relativity geometry which is the basis of Einstein's theory. These by a Riemannian space-time with non-zero curvature. reasons, together with the weakness of the gravitational Moreover, in this theory the idea of force is abandoned, interactions, help to explain why gravitation has so far the motion of mass being determined by the geometrical played almost no part in elementary particle physics. curvature of space-time. This curvature, in its turn, is determined by all the masses in the universe, by It can therefore be said that, although general means of non-linear equations (Einstein's equations). relativity is universally accepted as the macroscopic When the curvature of space-time is small (which theory of gravitation, its validity as a microscopic corresponds to a weak gravitational field) and the theory (after quantization) has not yet been established. velocities involved are also small in comparison with Consequently, the possibility that it will one day the velocity of light, Enstein's equations become equi­ provide a bridge between physics on the macroscopic valent, to a first approximation, to the Poisson and the microscopic scale, remains no more than a hope. equations of Newtonian mechanics. Several months after the publication of Einstein's Votre work on general relativity, Schwarzschild succeeded in rigorously solving Einstein's equations for the case in maison de confiance pour which the mass creating the field has spherical sym­ metry. This solution was applied to the study of the Photocopies — Appareils d'eclairage et dispositif de developpement - Papiers motions of the planets in the gravitational field of the pour photographies - Installations pour la sun and gave striking confirmation of general relativity photocopie. theory. According to Einstein's theory, a planet does not describe a fixed ellipse (as is the case in Newtonian Heliographie — Appareils d'eclairage et mechanics when the effects produced by the other machines a developper - Nouveaute: H£LIOMATIC, machine a heliographier planets are not considered), but an ellipse whose avec VARILUX permettant de faire varier perihelion advances by a certain angle with each la puissance d'eclairage - Papiers pour revolution. This angle was measured, and the result developpements a sec et semi-humides. agreed very well with the predictions of the theory. Bureau-Offset — Machines-offset et Shortly afterwards, two other effects predicted by plaques-offset presensibilisees OZASOL. the theory of general relativity, were confirmed by Dessins — Machines a dessiner JENNY experiment: the bending of light-rays in the vicinity of et combinaison de dessins - Papiers a a mass and the red-shift of spectral lines in the presence dessin (papiers pour dessins de details), of a gravitational field. The latter prediction, moreover, listes de pieces, papiers transparents (a received further confirmation following the discovery calquer), papier pour croquis. of the Mossbauer effect. Meubles pour serrer les plans — «Sys- teme a suspension, a soulevement et a Since then, great progress has been made in the abaissement». development of general relativity theory (Cauchy's problem for Einstein's equations, the study of the Installations de reproduction pour helio- equations of motion, the discovery of new solutions, graphies, impression de -plans, photo­ etc.), but it has not received any further confirmation copies, travaux de photographie tech- nique, reductions, agrandissements, tra­ by observation or experiment. Certain problems ffic vaux de developpement de microfilms. concerning the physical interpretation of the theory (the definition of energy and momentum, interpretation of co-ordinates, etc.) are still far from reaching a satis­ OZALID ZURICH factory solution. Furthermore, Einstein's attempts to Seefeldstrasse 94 - T6I. (051) 24 47 57 develop, from the point of view of general relativity, 92 .
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