Albert A. Michelsons experimentum crucis 1881 in Potsdam, Germany

This paper reviews briefly the history of the Michelson experiment, invented and performed for the first time in the Astrophysical Observatory Potsdam in 1881. The paper draws attention to the International Michelson Colloquium, held from April 27 to April 30, 1981 in Potsdam (Germany). This paper is an attempt to reconsider a scientific event organized 40 years ago, as the follow-up to Einstein’s Centenary in 1979, for Michelson’s experiment done 140 years ago. In his famous experiment in 1881 in the eastern basement of the Astrophysical Observatory Potsdam, Michelson intended to demonstrate that his interferometer was able to satisfy the task to verify the effect of the motion of the Earth on the propagation of light. It was expected that the velocity of light is composed of that of the Earth. The speed of the light should exceed the speed of the light which traverses the orbit by 30 km/s. In that case, the distance of the two images would depend on the orientation of the interferometer. The interferometer did not find any difference in the two velocities. Michelson had to conclude a so-called ‘null result’ that the propagation of light was determined by the walls, just as the propagation of sound in the air of the basement room had to relate to the walls. Michelson’s interferometer result is a paradigmatic example of a null result in physics, a result may be said to be null when it not detected by the measuring device employed. The value returned by the measuring instrumentation is ‘zero’. It is very rarely the case that an unadulterated zero result will occur since there will almost always be measurable, small interfering causes and resultant noise at play. Thus, a better description of a null result is that it is ‘zero’ plus small though annoying residual variations. Today, Michelson’s original experiment and its many repetitions are considered as a venerable well understood historical chapter for which, at least from a physical point of view, there is nothing more to refine or clarify. Though, this is not necessarily true and this was also the subject of the Michelson Colloquium and it remains the subject until today [3, 4]. From April 27 to April 30, 1981, an international colloquium in honour of the physicist and first American Nobel laureate Albert Abraham Michelson (1852-1931) and his scientific work took place in Potsdam, Germany. The occasion for this Michelson Colloquium at the Astrophysical Observatory Potsdam was the centenary of the year in which the famous Michelson experiment was performed for the first time in the Astrophysical Observatory Potsdam [1]. The Michelson Colloquium was held under the auspices of the Academy of Sciences of the GDR (Central Institute for Astrophysics); its arrangement at the Astrophysical Observatory Potsdam was sponsored by the Einstein Laboratory for Theoretical Physics, Caputh, the Physical Society of the GDR, Berlin, and the Department of Physics of the Humboldt University, Berlin. Fig. 1. Main building of the Astrophysical Observatory Potsdam. About one hundred years ago, in April 1881, Michelson performed for the first time his interferometer experiment to determine the velocity of the Earth relative to the hypothetical luminiferous aetheran experiment which entered into history of physics and astronomy. The nullresult of the experiment, rejecting the aether hypothesis of Fresnel, turned out to be fundamental for the evolution of physics, as a landmark on the way of the genesis of Einstein’s theory of relativity. The incitement for undertaking such a crucial experiment Michelson had found in ideas of J.C. Maxwell. The interferometer by which he carried out his experiment and which he later on used in various investigations in physics and astronomy, Michelson invented during a visit to Europe, beginning at the end of 1880. The device was made by the optical firm Schmidt and Haensch in Berlin and the experiment was prepared at the Physical Institute of the Friedrich Wilhelms University of Berlin (later Humboldt University), located at the Reichstagsufer and lead by Hermann von Helmholtz. However, because of the sensitivity of the instrument against vibrations, one had to look for a place of lower vibration level. The memorable experiment was finally realised in the Astrophysical Observatory Potsdam, not far from Berlin. As Michelson later mentioned, the then director of the Observatory, H.C. Vogel, was at once interested in the experiment. The whole experimental set up was placed in the basement of the east dome of the main building of the Observatory (Fig. 1). The lectures delivered at the Michelson Colloquium, with large thematic variety gathering round the Michelson experiment as the focus, especially appreciated its importance for physics and astronomy and dealt with philosophical and scientific historical aspects of the Michelson experiment. They took place during two days in a solemnly decorated room of the old city-hall of Babelsberg. On April 28, H.-J. Treder (1928-2006) opened the jubilee colloquium and Michelson exhibition by welcoming special guests and participants to the internationally organized colloquium which was understood as a natural follow-up to the Einstein Centenary celebrations held in Berlin and Potsdam in 1979 [5]. Subsequently Treder asked J. Auth (1930-2011; Humboldt University, Berlin, Germany) for delivering the opening lecture “Albert A. Michelson at the University of Berlin” [1]. By means of documents from the archive of the Humboldt University, Auth portrayed Michelson’s scientific visit to Berlin and the preparation of the experiment. In that he built upon a detailed investigation of H.J. Haubold and R.W. John “Albert A. Michelson’s aether drift experiment 1880/1881 in Berlin and Potsdam” [2, 6]. Auth also sketched the social life of that time at the University of Berlin. In great detail he devoted his attention to the theory and the physical consequences of the Michelson experiment. This general view over Michelson’s visit to Berlin was followed by the celebration lecture of Dorothy Michelson Livingston (1906-1994; New York, USA) “Michelson and Einstein, artists in science” [1]. Mrs. Michelson Livingston (Figs. 2, 3 and 8) drew a vivid picture of her famous father and analysed the characteristics of his creative activity, especially in comparison with Albert Einstein. From her memories she made the audience familiar with the great experimental physicist Albert A. Michelson, which was painting with pleasure in his spare time and was athletically active up to the old age. At that the lecturer showed slides from her private photo collection. Mrs. Michelson Livingston is the author of the outstanding Michelson biography “The Master of Light”, first published in 1973 [7]. She finished her lecture with words spoken by Einstein in appreciating Michelson on the occasion of meeting him at the California Institute of Technology, Pasadena, in January 1931, a few months before the death of Michelson: “It was you who led the physicists into new paths, and through your marvelous experimental work paved the way for the development of the theory of relativity”. Fig. 2. Dorothy Michelson Livingston opening speech of the Michelson Colloquium. The next lecturer announced was R.S. Shankland (1908-1982; Case Western Reserve University, Cleveland, Ohio, USA) “Michelson in Potsdam” [1]. It happened in Cleveland in 1887, when Michelson in cooperation with E.W. Morley repeated the aether-drift experiment with higher precision. The result confirmed the null-result of the Potsdam experiment. Shankland himself was leading engaged in the disclosure of the misinterpretation of the result announced by D.C. Miller in single carrying out a further repetition of the Michelson experiment. Shankland lucidly and concisely presented that part of Michelson’s scientific activity, which begins with his collaboration with S. Newcomb, then, in 1880, lead to the visit to Europe – stations were Paris and Berlin/Potsdam – and which included the invention of the Michelson interferometer, its construction in Berlin, the preparation of the experiment in von Helmholtz’ institute, and finally, the realization of the experiment in the Astrophysical Observatory Potsdam. At that time, H. von Helmholtz was already a famous scientist, inter alia for his contributions to physical optics and the foundation of physiological optics. His laboratory was a renown modern centre for optical research. This intensive scientific environment no doubt was an important factor in Michelson’s progress, as Shankland stated. After this lecture a short annotation given by H. Melcher (b.1927; Training College for Teachers, Erfurt, Germany) followed, concerning some special questions of the history of the aether-drift experiment and the genesis of special relativity [1, 8]. The afternoon lectures began with a joint contribution by R. Rompe (1905-1993; Physical Society, Berlin, Germany) and G. Albrecht (1930-2015; German Academy of Sciences, Berlin, Germany) “The importance of experiments for the progress in physics” [1]. Rompe pointed out, how “the nearness of an experiment to experience”, what was just existing yet in Michelson’s investigations, today threatens to fade away due to the more and more increasing complexity of the experimental proceeding in physics and the necessary inclusion of electronic data processing. He stressed the tight nexus of physical conception, mathematical theory, and experiment. So, on one hand, the experimental advance is essential for the development of physical theory, but, on the other hand, according to a remark made by Einstein to Heisenberg, designing an experiment is again decisively codetermined by the theory. The lecturers spoke about the methodical benefit one may also yet today derive from Albert A. Michelson’s, the great master of precision optics, style of working. A further part of the lecture, separately read by K. Lanius (1927-2010; Institute of High Energy