Whoever digs into the historical documents of the University of Heidelberg and searches for special occurrences in the history of physics at the University will quickly discover some. As in the case of the ups and downs of a sine curve, one discovers a phase of provinciality followed by a phase in which excellent research and teaching with worldwide acknowledgment has occurred. The conditions for success were (and today still are) the basic elements of a scientific culture of knowledge that Heidelberg academics subscribe to and which is fondly termed the 'Heidelberg spirit': the pursuit of a consensus in decision making as well the conscious view over the boundaries of specific scientific domains of research into others. Top performance was achieved in times in which the University understood how to use and expand on the potential offered by the scientific landscape external to it. An intelligent, well informed and skilful politics on the part of the University in filling professorial positions led to the appointments of physicists and astronomers in Heidelberg, who had obtained an excellent education and experience in European scientific centres. Furthermore, it offered them a solid research environment, a collegial, if elite, working atmosphere and sufficient academic freedom to be able to develop as scientists. If one reads personal documents of great Heidelberg scientists, such as those of Gustav Kirchhoff, Hermann von Helmholtz, Robert Bunsen, Johannes Jensen or Otto Haxel, to mention but a few, one notices that all of them speak of a Heidelberg scientific community that is held closely together in particular by an enthusiasm to present their scientific work to colleagues in their own and in other fields and to solve problems in this way in fruitful interaction.
Did (and does) the key to success thus lie in a 'we' feeling? The history of physics in Heidelberg can be traced back to the 14th century. In those early days, physics formed a part of the teaching duties accorded to the Faculty of Arts, in which students prepared themselves for studies in theology, law or medicine. Physics as such was not at this stage considered to lead to an independent occupation. The content of the course work in physics then included such things as the writings of Aristoteles, which were adopted in the 13th century by Albertus Magnus in the context of the Christian world view. Aristotelian physics was considered to encompass the basic principles of earthly movement and was thus considered appropriate for a description of both qualitative and quantitative changes in state that occur in nature.
The first lectures in physics in Heidelberg, in the Aristotelian sense, were held by Heimannus Wunnenberg, the second rector of the University, in 1387. In 1531, the members of the Faculty of Arts commenced discussions as to how to secure the continuity of teaching in physics, which culminated in the establishment of a separate chair of physics. This was further facilitated by a reorganisation of the University, which took place at that time, and in which Philipp Melanchthon played an important role. As a result of this, it was possible to appoint a physics professor 1556. Teaching in physics was however interrupted by the violence that broke out in general during the thirty year war.
The University was re-established in 1662 and the chair in physics was then occupied by Johannes Leuneschloss. Leuneschloss was strongly influenced by the latest insights in architecture, that he had gained during his travels to Holland and England. He thus moved the focus of physics from the current Aristotelian, speculative orientation, which had been reintroduced by the Jesuits as the official viewpoint in the physics programme in 1697 to a firmer basis.
Little by little, the Jesuits universities themselves established experimental physics in their institutions; in Heidelberg, this occurred during the reign of the prince-elect Karl Theodor. This was evidenced by the establishment of a chair for experimental and mathematical physics, which was occupied by the Jesuit Christian Mayer in 1752. Mayer held this position until 1774 and performed research in particular in the fields of astronomy and cartography. For his investigations of the movement of binary stars, he was elected into the scientific associations in London, Philadelphia, Bologna, Mannheim and Göttingen. The fact that he had a high reputation and was in addition the court astronomer of Karl Theodor was however not sufficient to prevent the Department of Philosophy of the University from treating experimental and mathematical physics as disjunct subjects, as was the case from 1784. Mathematical branches of physics, such as statics, optics and hydraulics were declared to be part of mathematics, while physics was reserved for 'descriptions of nature'. This however did not reduce the prestige accorded to physics by the public on the threshold of moving from the 18th to the 19th century.
Following the Jesuit professors C. Mayer, J. Schwab and J. Schmitt, Karl Wilhelm Gottlob Kastner and Jakob Friedrich Fries were appointed, who in their lectures primarily imparted knowledge with chemical, mineralogical and meteorological content as well as on natural philosophy, thus following the trends that were current in universities during the age of enlightenment. Kastner and Fries both authored text books on physical science, in which the knowledge of their time is summarised. In 1817 the separation of the chair of chemistry from the chair of physics earmarked the start of a new orientation. The sheer volume of information that had been accumulated under the generic name 'physics - the science of all nature', could no longer be systematically filed under this one name. The methodological and contentual distribution of the natural sciences into its subsciences physics, chemistry, biology, mineralogy etc. was now reflected in the continued establishment of separate chairs as well as of teaching courses in all of these fields.
Phillipp von Jolly then set new accents in Heidelberg. Jolly, the son of an industrialist, had spent time in the Berlin laboratory of Gustav Magnus while studying physics and thereafter in mechanical workshops as well as workshops for glass blowing. He was thus inspired by experiment and missed the fact that this was not available in Heidelberg. In 1846, he used the opportunity while negotiating the terms of his chair at the University to complain to the Baden Minister of Culture that both a laboratory as well as scientific instruments were lacking. Jolly then initiated the construction of a new building for science (the 'Friedrichsbau'). In addition, he introduced the concept of physics practicals which he financed partly through the local government, and partly from his private funds.
In 1854, Jolly's successor was appointed. As it turned out, this person was exceptional: Gustav Robert Kirchhoff. Kirchhoff was a former student of Franz Neumann in Königsberg, and had an excellent schooling in mathematical physics. He however also had gained experience in experimental physics in Berlin under the auspices of Gustav Magnus. In constructing the solution to the problem of the electrical conductivity of a disc, he demonstrated his creativity as a physicist; the documentation of this contains in part the so-called 'Kirchhoff laws', which universally describe the physical laws governing the flow of electrical current in circuits.
Heidelberg offered Kirchhoff favourable working conditions - the administration in the local government was interested in the sciences; in addition he received the highest salary among the scientists of his time! - furthermore, he had loyal and inspiring scientific friends and a scientific constellation that was to aid and support him in a productive period lasting 20 years.
In Heidelberg, in 1859, Kirchhoff, together with Robert Bunsen, discovered spectra using gas burners and they developed the techniques of spectral analysis, which later proved to be the key for understanding the construction of atoms. Here Kirchhoff discovered that the emission and absorption observed was independent of the properties of the substance itself. Here again, he first defined the concept of a black body, and here he discovered that electrical waves travel in a wire with the speed of light, here he analysed the spectrum of the sun.
His concept of physics lectures shaped university physics teaching until the 1920s. In 1869, he and the mathematician Leo Königsberger founded the Heidelberg Mathematical-Physical Seminar, a new way of imparting interdisciplinary knowledge.
When Kirchhoff was appointed to Berlin in 1875, what the Göttingen physicist Wilhelm Weber euphorically foresaw in his expert opinion in favor of Kirchhoff's appointment to Heidelberg had come true, namely that Kirchhoff would transform Heidelberg into a center of natural science because of his interdisciplinary approach. In fact, Kirchhoff and his friends succeeded in this and even more, the step from a teaching professorship to a professorship that claimed and fulfilled the claim to combine teaching and research in the Humboldtian sense. Kirchhoff's successor in the Heidelberg physics chair was Georg Quincke. Quincke held the chair for 32 years; his term of office included the separation of the Faculty of Natural Sciences and Mathematics from the Faculty of Philosophy, which was brought about by a state ministerial decision in 1890 and institutionally underscored the change in the importance of natural sciences and mathematics in the canon of academic subjects that had long since taken place.
Quincke, who is still remembered today by the name Quincke's Tube, made a name for himself in particular as the discoverer of diaphragm currents, but also as a convincing university teacher of experimental physics. Among the listeners of his physics lectures were Max Wolf and Phillip Lenard.
The University of Heidelberg owes the new building of the Baden State Observatory on the Königsstuhl to Max Wolf. Inaugurated in 1898, it became the center of two institutes, the already existing astronomical institute and the astrophysical institute led by Max Wolf with the trend-setting focus on astrophotography, which Max Wolf founded. Philipp Lenard, who was awarded the Nobel Prize in 1905 for his work on cathode radiation, decided to return to Heidelberg after working as an assistant to Heinrich Hertz in Bonn and as a professor in Kiel. In 1907, he returned to Heidelberg as a full professor of physics and as Quincke's successor. It is also thanks to his high reputation as a physicist that a separate university building for physics was erected in 1912, the Physics Institute on Philosophenweg. However, Lenard's work at the Heidelberg Faculty of Natural Sciences and Mathematics was not very successful. He was very skeptical of theoretical approaches, including Einstein's theory of relativity, and as he grew older he rigorously rejected them. His fundamental anti-Semitic attitude overlaid his scientific ethos; he not only denied Jewish colleagues professional respect, but also physically excluded them from events. Emeritus in 1931, Philipp Lenard had become the authoritative inventor of so-called German physics.
The nuclear physicist Walther Bothe, a student of Max Planck, Ernest Rutherford and Hans Geiger, was appointed as Philipp Lenard's successor in 1932. Influenced by international physics, Walther Bothe could not bear the confrontation with so-called German physics. In 1934, he left the Institute of Physics and took over the leadership of the physics department of the Kaiser Wilhelm Institute for Medical Research, which was to become the nucleus of a new scientific beginning under his leadership after 1945. It is thanks to Walther Bothe's (ideology-free) appointment policy that Heidelberg physics regained world fame in the middle of the century. He engaged Wolfgang Gentner, who as a fellow with the Curies at the Sorbonne and as a guest of Otto Hahn and Fritz Straßmann, the discoverers of nuclear fission, learned the latest results of nuclear physics and from 1935 worked with them in Heidelberg on the nuclear photoelectric effect. Together with Bothe, Gentner also built the first German cyclotron at what was then the Kaiser Wilhelm Institute in Heidelberg, which was completed in 1944. In 1948, he again appointed Johannes Jensen as director of the Heidelberg Institute of Physics. He established the Institute of Theoretical Physics and created the theory of the shell model of atomic nuclei, which was awarded the Nobel Prize in 1963, nine years after Walther Bothe. The appointments of the atomic physicist Hans Kopfermann and the nuclear physicist Otto Haxel were also due to Walther Bothe's commitment. In terms of personnel policy, this set the course for an extremely successful collaboration and for a division of Heidelberg physics into sub-areas of theoretical and experimental physics, which, institutionalized by additionally acquired professorships, were and are further developed in independent institutes. The Faculty of Physics and Astronomy of the University of Heidelberg is itself a child of this fanning out of the fields of knowledge; it was established in 1970 alongside the Faculties of Mathematics, Chemistry, Pharmacy, Geosciences and Biology from the Faculty of Natural Sciences and Mathematics. Today, it unites the Institute of Physics, the Kirchhoff Institute of Physics, the Institute of Environmental Physics, the Institute of Theoretical Physics, and the Heidelberg Center for Astronomy. Close links exist with the neighboring Max Planck Institutes and astronomical scientific institutions and with centers of medical-biological research (ZMBH; DKFZ; EMBL). Joint projects in physics research and physics education, as well as concerns for efficient resource management, are currently tightening the bond between the institutes. A visible sign of this development is the establishment of the Kirchhoff Institute for Physics at the turn of the millennium from the merger of the Institutes for Applied Physics and for High Energy Physics. The key to success: interdisciplinary cooperation? In retrospect: probably not alone. The will to reach a consensus in favor of science, the integration and subordination of individual and group interests in the dynamics of natural science, and being guided by factual intentions also had an inspiring effect.
