The European Physical Journal H最新文献

Heinrich Rubens (Wiesbaden, 1865, Berlin, 1922) was the first scientist to study the large gap between the conventional infrared range and the electrical wave regime, better known today as the terahertz gap. To this end, he produced numerous original instruments and was almost single-handedly responsible for all research on this region up to the 1920s. His research, motivated by Hertz’s demonstration of the electromagnetic theory of light, led him to contribute seminal works on blackbody radiation and interferometric spectroscopy that have been almost forgotten in modern expositions of these topics. On occasion of the centenary of his death, this work aims to critically assess his legacy, as well as to revitalize this important figure for a newer generation of spectroscopists.

In the early 1930’s, Fermi wrote two papers in which he introduced the concepts of “scattering length” and “pseudopotential.” Since that time, these terms have become universally associated with low energy scattering phenomena. Even though the two papers are very different—one in atomic physics, the other in neutron physics—a simple figure underlies both. The figure appears many times in Fermi’s work. We review how the two papers came about and briefly discuss modern developments of the work that Fermi initiated with these two remarkable papers.

A longstanding problem in natural science and later in physics was the understanding of the existence of ferromagnetism and its disappearance under heating to high temperatures. Although a qualitative description was possible by the Curie–Weiss theory, it was obvious that a microscopic model was necessary to explain the tendency of the elementary magnetons to prefer parallel ordering at low temperatures. Such a model was proposed in 1922 by Schottky within the old Bohr–Sommerfeld quantum mechanics and claimed to explain the high values of the Curie temperatures of certain ferromagnets. Based on this idea Ising formulated a new model for ferromagnetism in solids. Simultaneously the old quantum mechanics was replaced by new concepts of Heisenberg and Schrödinger and the discovery of spin. Thus Schottky’s idea was outperformed and finally replaced in 1928 by Heisenberg exchange interaction. This led to a reformulation of Ising’s model by Pauli at the Solvay conference in 1930. Nevertheless one might consider Schottky’s idea as a forerunner of this development explaining and asserting that the main point is the Coulomb energy leading to the essential interaction of neighboring elementary magnets.

The main focus is on the Hamilton–Jacobi techniques in classical general relativity that were pursued by Peter Bergmann and Arthur Komar in the 1960s and 1970s. They placed special emphasis on the ability to construct the factor group of canonical transformations, where the four-dimensional diffeomorphism phase space transformations were factored out. Equivalence classes were identified by a set of phase space functions that were invariant under the action of the four-dimensional diffeomorphism group. This is contrasted and compared with approaches of Paul Weiss, Julian Schwinger, Richard Arnowitt, Stanley Deser, Charles Misner, Karel Kuchař—and especially the geometrodynamical program of John Wheeler and Bryce DeWitt where diffeomorphism symmetry is replaced by a notion of multifingered time. The origins of all of these approaches are traced to Elie Cartan’s invariant integral formulation of classical dynamics. A related correspondence concerning the thin sandwich dispute is also documented.

Gullstrand’s and Oseen’s papers on the Gullstrand–Painlevé coordinates are translated from German into English, and their significance and their connection with Einstein’s Nobel prize are commented upon.

We reconstruct the genesis of the CPT theorem in quantum field theory from the first proofs of the spin-statistics theorem in 1939/1940 to the discovery of parity violation in 1957. Centrally, we highlight that the original motivation for pursuing the CPT theorem lay primarily in the attempt to identify the correct formulation of time reversal in relativistic quantum field theories.

The present year 2021 celebrates the 75th anniversary of the nuclear magnetic resonance method (NMR), which has had an immense importance for several branches of physics, chemistry and biology. The splitting of resonances and the shifts in their positions are seemingly inexhaustible sources of information for organic chemistry and biology. It was first introduced for the study of nuclear spins and their associated magnetic properties and when it was observed that resonance lines were broadened by the action of fluctuating local magnetic fields it was first seen as a limitation for the exact determination of nuclear properties. However, it was soon realized that the broadening contained important information on the dynamics of atoms, molecules or cooperative spin systems surrounding the nuclei and spin perturbations became a well-developed tool for investigation of internal dynamics in liquids and solids, over time-ranges from seconds down to femtoseconds. The present article is an attempt to review this latter line of development and to pick out a series of examples of internal dynamics in different physical systems published over the past 75 years. Examples include motions of particles in solids, magnetic resonance imaging (MRI), critical phenomena around phase transitions, functioning of biomolecules and recent applications to spintronics and quantum computing. Other spin-based spectroscopies followed in the tracks of NMR with use of electron spins (in electron spin resonance ESR also called electron paramagnetic resonance EPR, and ferromagnetic resonance, FMR), excited nuclear states (by observation of perturbations in angular correlation of gamma-rays, PAC) and later also muon spins (muon spin relaxation, MuSR), from which other examples are selected.

At the turn of the 1980s and 1990s, on the eve of the great leap in scale from the resonant bars to the long-baseline interferometers LIGO and Virgo, the four European groups then engaged in the field of interferometric gravitational wave detection in Germany, UK, France and Italy tried to set up a common strategy, with the aim of establishing a network of three long-based antennas in Europe. The paper analyzes the main causes of the failure of those early plans. An attempt is made to outline the parallels and differences with the current times, on the eve of the new leap of scale toward the third generation of gravitational wave interferometers, while the negotiations for the European-born project Einstein Telescope are taking place.