The European Physical Journal H最新文献

In the mid-1950s, Andrzej Trautman published a series of papers connected with his dissertation work written under Leopold Infeld. In these, he drew upon the slow motion approximation developed by Infeld, the general covariance-based strong conservation laws enunciated by Bergmann and Goldberg, the Riemann tensor attributes explored by Goldberg and related geodesic deviation exploited by Pirani, the permissible metric discontinuities identified by Lichnerowicz, O’Brien and Synge, and finally Petrov’s classification of vacuum spacetimes. With several significant additions he produced a comprehensive overview of the state of research in equations of motion and gravitational waves that was presented in a widely cited series of lectures at King’s College, London, in 1958. Fundamental new contributions were the formulation of boundary conditions representing outgoing gravitational radiation, the deduction of its Petrov type, a covariant expression for null wave fronts, and a derivation of the correct mass loss formula due to radiation emission. Ivor Robinson, who attended Trautman’s London lectures, had already in 1956 developed a bi-vector based technique that had resulted in his rediscovery of exact plane gravitational wave solutions of Einstein’s equations. He was the first to characterize shear-free null geodesic congruences. He and Trautman soon developed a long-term collaboration whose initial fruits were the Robinson–Trautman metric, examples of which were exact spherical gravitational waves.

We re-examine a common narrative that experimental errors by Walther Bothe in 1941 led Germany to abandon graphite as a reactor moderator during World War II. Using document-based nuclear archaeology, we first show that both American and German scientists used an incorrect carbon scattering cross section, thereby undermining the accuracy of all wartime data, including their conclusions on carbon’s absorption. Moreover, we argue that the availability of exceptionally pure petroleum coke in the United States, rather than any academic breakthrough, decisively enabled their production of nuclear-grade graphite. In contrast, Bothe’s Siemens electrographite had more boron contamination than any graphites considered in Fermi’s experiments, rendering it genuinely impractical as a moderator. By reframing the decision to eschew graphite as a deliberate decision rather than a mere experimental oversight, we believe the German decision was a rational consequence of material constraints and wartime priorities.

I showed in my recent EPJH paper that Peierls’ approximation for small fission reproduces neither the correct fission rate nor the correct diffusion coefficient. But Peierls’ result can be presented in a way that is superficially closer to Perrin’s correct result. Perrin’s paper motivated Peierls in the first place. Peierls did not reproduce Perrin’s reaction–diffusion equation to zeroth order, but rather only diffusion to lowest order. Perrin’s rate term allowing for non-fission neutron absorption appears to first order, but then only at the expense of an incorrect diffusion coefficient. As a byproduct of this analysis, we discover the reason for Peierls’ introduction of his strange second length scale, which otherwise would seem to have been obtained by a hat trick.

No particle or signal carrying information can travel at a speed exceeding that of light in vacuum. Although this has for a long time been accepted as a law of nature, prior to Einstein’s 1905 theory of special relativity the possibility of superluminal motion of electrons was widely discussed by Arnold Sommerfeld and other physicists. Besides, it is not obvious that special relativity rules out such motion under all circumstances. From approximately 1965 to 1985, the hypothesis of tachyons moving faster than light was seriously entertained by a minority of physicists. This paper reviews the early history concerning faster-than-light signals and pays particular attention to the ideas proposed in the 1920s by the little-known Ukrainian physicist Lev Strum (Shtrum). As he pointed out in a paper of 1923, within the framework of relativity it is possible for a signal to move superluminally without violating the law of causality. Part of this article is devoted to the personal and scientific biography of the undeservedly neglected Strum, whose career was heavily—and eventually fatally—influenced by the political situation in Stalin’s Soviet Union. Remarkably, to the limited extent that Strum is known today, it is as a literary figure in a novel and not as a real person.

After 25 years, this oral history interview with Nicola Cabibbo, recorded in July 2000, is being made available to an international audience. In the interview Cabibbo describes his early years as a student at the Sapienza University of Rome in the 1950s and his collaboration with Raoul Gatto in the pioneering work that launched (e^+e^-) physics in the early 1960s. The knowledge gained in those years through the systematic application of SU(3) symmetry to particle physics prepared the ground for his greatest achievement: the formulation of the mechanism responsible for quark mixing, which paved the way for the unification of the electromagnetic and weak interactions. Cabibbo’s significant influence on the revival of theoretical physics in Italy and his inspiring contribution to the development of a Roman school are also testified, together with his wide interests and lively curiosity which led him to promote the realization of a series of parallel supercomputers for numerical simulations of quantum field theory (the APE line). His extraordinary dedication, rigor and vision in promoting Italian scientific and technological development as President of the National Institute for Nuclear Physics (INFN) and other scientific institutions form a relevant and meaningful part of the narrative, which also includes significant recollections of his role as President of the Pontifical Academy of Sciences. Prominently mentioned are: Guido Altarelli, Edoardo Amaldi, Gilberto Bernardini, Francesco Calogero, Marcello Conversi, Ugo Fano, Enrico Fermi, Bruno Ferretti, Raoul Gatto, Murray Gell-Mann, Makoto Kobayashi, Luciano Maiani, Guido Martinelli, Toshihide Maskawa, Giorgio Parisi, Roberto Petronzio, Giuliano Preparata, Giorgio Salvini, Massimo Testa, Bruno Touschek.

This work is aimed at studying the rangefinder by J.G. Hofmann preserved in the Deutsches Museum. Following the Winterthur model, the analysis will start by the study of the scientific device and its features. Some aspects of the life of J.G. Hofmann will be then reconstructed, and the details obtained will be used to provide a dating of the object and an explanation of its use. Finally, a possible scenario will be presented and discussed, outlining how the rangefinder likely came to Munich and, specifically, to the Deutsches Museum, as an attempt to reconstruct the life of the device.

This contribution aims to highlight the profoundly human aspects of Alessandro Serpieri’s personality, as emerge from the testimonies related to the teaching he practiced for his students and from his scientific writings; and to underline above all the particularities of his scientific vision in which an integral catholic faith permeates a very clear rationalist approach, thus preventing him from slipping towards past Enlightenment extremisms or towards the looming positivist materialism. From this point of view, Serpieri might be defined as an ancient rationalist, far away from the typical rationalism introduced by the Scholasticism in late Middle Ages and accepted ever since then from the Catholic Church. What emerges is the portrait of a multifaceted scientist, gifted with uncommon qualities. We will also recall some ideas, original for that time, which in the following decades and in particular in the second half of the twentieth century would find fruitful developments especially in the field of theoretical physics.

In 1947, four months before the famous Shelter Island conference, Richard Feynman wrote a lengthy letter to his former MIT classmate Theodore Welton, reporting on his efforts to develop a path integral describing the propagation of a Dirac particle. While these efforts never came to fruition, and were shortly abandoned in favor of a very different method of dealing with the electron propagator appearing in in QED, the letter is interesting both from the historical viewpoint of revealing what Feynman was thinking about during that period just before the development of QED, and for its scientific ideas. It also contains at the end some philosophical remarks, which Feynman wraps up with the comment, “Well enough for the baloney.” In this article I present a transcription of the letter along with editorial notes, and a facsimile of the original handwritten document. I also briefly comment on Feynman’s efforts and discuss their relation to some later work.

A personal recollection of early years in lattice gauge theory with a bias toward chiral symmetry and lattice fermions.