The European Physical Journal H最新文献

Richard P. Feynman’s work on gravitation, as can be inferred from several published and unpublished sources, is reviewed. Feynman was involved with this subject at least from late 1954 to the late 1960s, giving several pivotal contributions to it. Even though he published only three papers, much more material is available, beginning with the records of his many interventions at the Chapel Hill conference in 1957, which are here analyzed in detail, and show that he had already considerably developed his ideas on gravity. In addition, he expressed deep thoughts about fundamental issues in quantum mechanics which were suggested by the problem of quantum gravity, such as superpositions of the wave functions of macroscopic objects and the role of the observer. Feynman also lectured on gravity several times. Besides the famous lectures given at Caltech in 1962–1963, he extensively discussed this subject in a series of lectures delivered at the Hughes Aircraft Company in 1966–1967, whose focus was on astronomy and astrophysics. All this material allows to reconstruct a detailed picture of Feynman’s ideas on gravity and of their evolution until the late sixties. According to him, gravity, like electromagnetism, has quantum foundations, therefore general relativity has to be regarded as the classical limit of an underlying quantum theory; this quantum theory should be investigated by computing physical processes, as if they were experimentally accessible. The same attitude is shown with respect to gravitational waves, as is evident also from an unpublished letter addressed to Victor F. Weisskopf. In addition, an original approach to gravity, which closely mimics (and probably was inspired by) the derivation of the Maxwell equations given by Feynman in that period, is sketched in the unpublished Hughes lectures.

This article recalls three papers published by Fred Hoyle and Jayant V. Narlikar consecutively in 1966 in Proceedings of the Royal Society, London. These papers were largely overlooked at the time but a look back today more than fifty years later shows how relevant they might be even today. Fred Hoyle, one of the most imaginative astrophysicists of the twentieth century, gives examples of how his mind functioned running far ahead of the conventional views of the time.

In 1969, Roger Penrose proposed a mechanism to extract rotational energy from a Kerr black hole. With this, he inspired two lines of investigation in the years after. On the one side, the Penrose process, as it became known, allowed a comparison between black-hole mechanics and thermodynamics. On the other, it opened a path to a quantum description of those objects. This paper provides a novel take on the events that led to the rise of the thermodynamic theory of black holes, taking as a starting point the Penrose process. It studies the evolution of the research conducted independently by Western and Soviet physicists on the topic, culminating in Stephen Hawking’s groundbreaking discovery that black holes should radiate.

The present paper is a companion of two translated articles by Alfred Clebsch, titled “On a general transformation of the hydrodynamical equations” and “On the integration of the hydrodynamical equations” (https://doi.org/10.1140/epjh/s13129-021-00015-8, https://doi.org/10.1140/epjh/s13129-021-00016-7). The originals were published in the “Journal für die reine and angewandte Mathematik” (1857 and 1859). Here we provide a detailed critical reading of these articles, which analyzes methods, and results of Clebsch. In the first place, we try to elucidate the algebraic calculus used by Clebsch in several parts of the two articles that we believe to be the most significant ones. We also provide some proofs that Clebsch did not find necessary to explain, in particular concerning the variational principles stated in his two articles and the use of the method of Jacobi’s Last Multiplier. When possible, we reformulate the original expressions by Clebsch in the language of vector analysis, which should be more familiar to the reader. The connections of the results and methods by Clebsch with his scientific context, in particular with the works of Carl Jacobi, are briefly discussed. We emphasize how the representations of the velocity vector field conceived by Clebsch in his two articles, allow for a variational formulation of hydrodynamics equations in the steady and unsteady case. In particular, we stress that what is nowadays known as the “Clebsch variables”, permit to give a canonical Hamiltonian formulation of the equations of fluid mechanics. We also list a number of further developments of the theory initiated by Clebsch, which had an impact on presently active areas of research, within such fields as hydrodynamics and plasma physics.

One of the major accomplishments of the late nineteenth-century applied physics was, as it is well known, the development of wireless telegraphy by Guglielmo Marconi, future Nobel laureate. In this paper, we will explore what scientific debt, if any, Marconi had toward another Italian physicist, internationally well known for his research on electromagnetic waves: Augusto Righi. This question will be pursued through a close analysis of Marconi’s first patent, of Righi’s scientific correspondence and of the specialized and popular press of the time. At the end of this analysis, which includes a brief survey of Marconi and Righi’s activity as senators of the Kingdom of Italy, we will better appreciate what Marconi took from contemporary scientists, what specific contributions he is responsible for and, ultimately, what Marconi and Righi thought of each other.