11.10. Kepler and modern physics

Abstract

Every generation writes the history of science anew, selecting with partiality the topics especially close to its own mentality, interests and views, as if projecting the difficulties and problems of the science of its period into the past. On the pages of ancient treatises, through a phraseology and archaic argumentation that seem strange to us, we unexpectedly find the outlines of familiar ideas, detect the echo of doubts worrying us, take notice of the course of reasoning which is similar to ours, and then the authors of these old volumes that seemed something like bronze statues suddenly come to life, descend from their pedestals and their ideas become close and comprehensible. In our report we want to outline the parallels between the circle of ideas that were interesting for Johann Kepler and nourished his scientific genius, and the views which considerably determine the outlook of modern physicists. In spite of the erroneous but nevertheless widely spread opinion Kepler enters the history of science not only as the discoverer of three famous laws of planetary motions. His scientific legacy is extremely rich but very complicated and contradictory. The main motive of the whole of Kepler's activity, i.e. the search for the “world harmony”, has recently gained special significance. Here in this short note we want to emphasize this point. As is known, logically irreproachable reasoning never leads to any discovery that overthrows our notions referring to the structure of the world. Only by overthrowing the circle of the customary ideas can we enlarge our knowledge of nature. In our days such a disrupture of the well-established canons was due after Niels Bohr's “mad idea”. Many topics which are quite clear and understandable for us were, in the distant epoch when Kepler lived and worked, mad ideas. Mad was the very thought of the possibility of mathematical description of nature, of the necessity of comparison of theory with experiment, of physical causes of motion, of the unity of the world, i.e. of the universal laws which govern different events both on Earth and in the sky, of the rejection of the circular motions and the substitution of them by the elliptical ones. Yet the most “mad” among Keplerian ideas was the idea of the “world harmony”. Changing and developing it brought Kepler to his most important discoveries. In it we see the forerunner of Einstein's “cosmic religious feeling”, that is the feeling of the universal objective order which underlies different phenomena. In it we trace the deepest analogue to modern views on the role of the symmetry principles in the system of the laws of Nature. Both Kepler and modern physicists impart symmetry with a two-fold function. It is symmetry that plays a part in a principle which enables them to fill the gap in reasoning and to predict and describe a phenomenon even before it is properly understood. At the same time symmetry comes forward as the final aim of the search for new laws of nature. The difference is that a modern physicist uses the symmetry principle together with other methods of knowledge and has no intention to consider them as absolute, while Kepler saw in them the highest truth, “the manifestation of the wisdom of the creation”. Nevertheless, disrespectful references to Kepler, which sometimes can be heard, as astrologer and even as a mediocre scientist who was able to achieve his outstanding results only through hard work and industry, are thoroughly erroneous. Kepler and the modern physicist have much in common in their approach to the investigation of the regularities underlying the structure of the world. In fact, the modern physicist trying to embrace a vast amount of experimental data in the compact form of a conservation law, to discover the underlying symmetry and to unite numerous conservation laws into one universal law, solves the problem which like the well-known two-body problem can be called a “Keplerian problem”.