Joos’ “theoretical Physics”

This book presents a perspective on the history of theoretical physics over the past two hundreds years. It comprises essays on the history of pre-Maxwellian electrodynamics, of Maxwell's and Hertz's field theories, and of the present century's relativity and quantum physics. A common thread across the essays is the search for and the exploration of themes that influenced significant con­ ceptual changes in the great movement of ideas and experiments which heralded the emergence of theoretical physics (hereafter: TP). The fun. damental change involved the recognition of the scien­ tific validity of theoretical physics. In the second half of the nine­ teenth century, it was not easy for many physicists to understand the nature and scope of theoretical physics and of its adept, the theoreti­ cal physicist. A physicist like Ludwig Boltzmann, one of the eminent contributors to the new discipline, confessed in 1895 that, "even the formulation of this concept [of a theoretical physicist] is not entirely without difficulty". 1 Although science had always been divided into theory and experiment, it was only in physics that theoretical work developed into a major research and teaching specialty in its own right. 2 It is true that theoretical physics was mainly a creation of tum­ of-the century German physics, where it received full institutional recognition, but it is also undeniable that outstanding physicists in other European countries, namely, Ampere, Fourier, and Maxwell, also had an important part in its creation.

This book presents a perspective on the history of theoretical physics over the past two hundreds years. It comprises essays on the history of pre-Maxwellian electrodynamics, of Maxwell's and Hertz's field theories, and of the present century's relativity and quantum physics. A common thread across the essays is the search for and the exploration of themes that influenced significant con­ ceptual changes in the great movement of ideas and experiments which heralded the emergence of theoretical physics (hereafter: TP). The fun. damental change involved the recognition of the scien­ tific validity of theoretical physics. In the second half of the nine­ teenth century, it was not easy for many physicists to understand the nature and scope of theoretical physics and of its adept, the theoreti­ cal physicist. A physicist like Ludwig Boltzmann, one of the eminent contributors to the new discipline, confessed in 1895 that, "even the formulation of this concept [of a theoretical physicist] is not entirely without difficulty". 1 Although science had always been divided into theory and experiment, it was only in physics that theoretical work developed into a major research and teaching specialty in its own right. 2 It is true that theoretical physics was mainly a creation of tum­ of-the century German physics, where it received full institutional recognition, but it is also undeniable that outstanding physicists in other European countries, namely, Ampere, Fourier, and Maxwell, also had an important part in its creation.

This concise treatment embraces, in four parts, all the main aspects of theoretical physics. Recent topics such as holography and quantum cryptography are included. The book summarizes what a graduate student, physicist working in industry, or a physics teacher should master during his or her degree course. It will also be useful for deepening one’s insight and it adds new dimensions to understanding of these elemental concepts.

The interaction between geometry and theoretical physics has often been very fruitful. A highlight in this century was Einstein's creation of the theory of general relativity. Equally impressive was the recognition, starting from the work of Yang and Mills and culminating in the Weinberg-Salam theory of the electroweak interaction and quantum chromodynamics, that the fundamental interactions of elementary particles are governed by gauge fields, which in ma­ thematical terms are connections in principal fibre bundles. Theoretical physi­ cists became increasingly aware of the fact that the use of modern mathematical methods may be necessary in the treatment of problems of physical interest. Since some of these topics are covered at most summarily in the usual curricu­ lum, there is a need for extra-curricular efforts to provide an opportunity for learning these techniques and their physical applications. In this context we arranged a meeting at the Physikzentrum Bad Ronnef 12-16 February 1990 on the subject "Geometry and Theoretical Physics", in the series of physics schools organized by the German Physical Society. The participants were graduate students from German universities and research institutes. Since the meeting occurred only a short time after freedom of travel between East and West Germany became a reality, this was for many from the East the first opportunity to attend a scientific meeting in the West, and for many from the West the first chance to become personally acquainted with colleagues from the East.

The interaction between geometry and theoretical physics has often been very fruitful. A highlight in this century was Einstein's creation of the theory of general relativity. Equally impressive was the recognition, starting from the work of Yang and Mills and culminating in the Weinberg-Salam theory of the electroweak interaction and quantum chromodynamics, that the fundamental interactions of elementary particles are governed by gauge fields, which in ma­ thematical terms are connections in principal fibre bundles. Theoretical physi­ cists became increasingly aware of the fact that the use of modern mathematical methods may be necessary in the treatment of problems of physical interest. Since some of these topics are covered at most summarily in the usual curricu­ lum, there is a need for extra-curricular efforts to provide an opportunity for learning these techniques and their physical applications. In this context we arranged a meeting at the Physikzentrum Bad Ronnef 12-16 February 1990 on the subject "Geometry and Theoretical Physics", in the series of physics schools organized by the German Physical Society. The participants were graduate students from German universities and research institutes. Since the meeting occurred only a short time after freedom of travel between East and West Germany became a reality, this was for many from the East the first opportunity to attend a scientific meeting in the West, and for many from the West the first chance to become personally acquainted with colleagues from the East.

The recent most impressive developments in theoretical physics, i.e. gauge and string theories with their far- reaching relations to basic concepts of present day mathematics brought a renewed and intense exchange between mathematicians and physicists. In a way the past few years might be compared to the great period of the mid-twenties with its really decisive mathematical contributions to the foundations of both quantum theory as well as general relativity .. Among others, this far-reaching exchange led H.Weyl in 1929 to the formulation of his (second) gauge principle (concerning the phase of the quantum mechanical wave function) which led, in turn (through the most natural generalization by C.N.Yang and R.Mills in 1954) to present day gauge theory which brought, first of all, a real breakthrough with respect to a theoretical inter- pretation of an enormous realm of data in modern particle physics. It led, in fact, to the well-known unification of electromagnetism with weak interactions (Weinberg-Salam theory) and, at the same time, to a most natural unifica- tion of particle and nuclear physics through QCD which deals with the basic quark-gluon structure of heavy matter, e.g. hadrons.

The recent most impressive developments in theoretical physics, i.e. gauge and string theories with their far- reaching relations to basic concepts of present day mathematics brought a renewed and intense exchange between mathematicians and physicists. In a way the past few years might be compared to the great period of the mid-twenties with its really decisive mathematical contributions to the foundations of both quantum theory as well as general relativity .. Among others, this far-reaching exchange led H.Weyl in 1929 to the formulation of his (second) gauge principle (concerning the phase of the quantum mechanical wave function) which led, in turn (through the most natural generalization by C.N.Yang and R.Mills in 1954) to present day gauge theory which brought, first of all, a real breakthrough with respect to a theoretical inter- pretation of an enormous realm of data in modern particle physics. It led, in fact, to the well-known unification of electromagnetism with weak interactions (Weinberg-Salam theory) and, at the same time, to a most natural unifica- tion of particle and nuclear physics through QCD which deals with the basic quark-gluon structure of heavy matter, e.g. hadrons.

HISTORICAL PRELUDE Ettore Majorana's fame solidly rests on testimonies like the following, from the evocative pen of Giuseppe Cocconi. At the request of Edoardo Amaldi, he wrote from CERN (July 18, 1965): "In January 1938, after having just graduated, I was invited, essen­ tially by you, to come to the Institute of Physics at the University in Rome for six months as a teaching assistant, and once I was there I would have the good fortune of joining Fermi, Bernardini (who had been given a chair at Camerino a few months earlier) and Ageno (he, too, a new graduate), in the research of the products of disintegration of /-L "mesons" (at that time called mesotrons or yukons), which are produced by cosmic rays [ . . . ] "It was actually while I was staying with Fermi in the small laboratory on the second floor, absorbed in our work, with Fermi working with a piece of Wilson's chamber (which would help to reveal mesons at the end of their range) on a lathe and me constructing a jalopy for the illumination of the chamber, using the flash produced by the explosion of an aluminum ribbon short circuited on a battery, that Ettore Majorana came in search of Fermi. I was introduced to him and we exchanged few words. A dark face. And that was it.