The European Physical Journal H最新文献

Gamma-ray astronomy has been one of the prime scientific research fields of the Max-Planck Institute for Extraterrestrial Physics (MPE) from its beginning. Over the years, the entire gamma-ray energy range accessible from space was explored. The purpose of this review article is to summarise the achievements of the gamma-ray group at MPE during the last 50+ years. This covers a substantial part of the general history of space-based gamma-ray astronomy, for which both, general review articles (e.g. Pinkau in Exp Astron 5: 157, 2009; Schönfelder in AN 323: 524, 2002; Trimble in AIP Conf Proc 304: 40, 1994) and a detailed tabular list of events and missions (Leonard and Gehrels in https://heasarc.gsfc.nasa.gov/docs/history, version 1.0.8, 2009), have been compiled. Here, we describe the gamma-ray activities at MPE from the beginning till the present, reviewing the tight interplay between new technological developments towards new instruments and scientific progress in understanding gamma-ray sources in the sky. This covers (i) the early development of instruments and their tests on half a dozen balloon flights, (ii) the involvement in the most important space missions at the time, i.e. ESA’s COS-B satellite, NASA’s Compton Gamma-ray Observatory and Fermi Space Telescope, as well as ESA’s INTEGRAL observatory, (iii) the participation in several other missions such as TD-1, Solar Maximum Mission, or Ulysses, and (iv) the complementary ground-based optical instruments OPTIMA and GROND to enhance selected science topics (pulsars, gamma-ray bursts). With the gradual running-out of institutional support since 2010, gamma-ray astrophysics as a main research field has now come to an end at MPE.

In this article, we present the second part of our historical survey on quantum Monte Carlo methods. We focus on the simulations performed at a finite temperature and based on Feynman’s path-integral formulation of quantum mechanics. We introduce the method and insist on the central role played by the description of the transition to superfluidity for Helium 4.

The paper aims at characterising and documenting a fundamental change in how phase transitions were modelled microscopically in the period 1937–1970. At first, physicists took what will be called a naturalistic approach to phase transitions such as the condensation of gases and the Curie point of ferromagnets. Here the purpose was to explain the phenomenon in question, i.e., to show that a model exhibits the same features as the phenomenon. The scope of this approach was broad, as the goal was to account for several aspects of the phenomenon. The employed model should be very realistic and close to the foundational theory, be it classical or quantum mechanics. In the 1960s, the physicists used an alternative approach that they termed a caricature approach. This approach not only required explanation in the above sense but also understanding of the physical phenomenon, i.e. insights into why the phenomenon behaves as it does. The scope was limited to certain aspects of the phenomenon, such as the behaviour near the critical point. The caricature approach used a hierarchy of models, ranging from realistic ones over more simplified models to models that were mere caricatures of the system in question. Hence, the two approaches represent very different orientations when it comes to the purpose and scope, the organisation of the resulting theories, and what models are acceptable.

This paper is devoted to two hitherto unpublished original documents by Henry Cavendish (1731–1810) which provide insight into his calculations of the deflection of light by isolated celestial bodies. Together with a transcription of these documents, we comment on their contents in the present-day language of physics. Moreover, we compare them with a paper by Johann Georg von Soldner (1776–1833) on the same subject.

A chronicle describing the historical context and the development of ideas and experiments leading to the discovery of the back-bending phenomenon in rapidly rotating atomic nuclei some 50 years ago is presented. The moment of inertia of some atomic nuclei increases anomalously at a certain rotational frequency, revealing important clues to our understanding of nuclear structure. I highlight the decisive interactions and contacts between experimentalists and theorists, which created the right environment, allowing for the revelation of an undetected phenomenon in Nature. Finally, I reflect on the key points allowing for the discovery and particularly point to the importance of systematic surveys, which in this case investigated the energy levels in heavy nuclei of a large sample of elements, as well as to the accuracy of the measurements of the ground state levels made at the time.

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.