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Soyuz T-15
Soyuz T-15 (Russian: Союз T-15, Union T-15) was a crewed mission to the Mir and Salyut 7 space stations and was part of the Soyuz programme. It marked the final flight of the Soyuz-T spacecraft, the third generation Soyuz spacecraft, which had been in service for seven years from 1979 to 1986. This mission marked the first time that a spacecraft visited, and docked with, two space stations in the same mission.
  • 520
  • 17 Oct 2022
Topic Review
Lieb-Robinson Bounds
The Lieb-Robinson bound is a theoretical upper limit on the speed at which information can propagate in non-relativistic quantum systems. It demonstrates that information cannot travel instantaneously in quantum theory, even when the relativity limits of the speed of light are ignored. The existence of such a finite speed was discovered mathematically by Elliott H. Lieb and Derek W. Robinson (de) in 1972. It turns the locality properties of physical systems into the existence of, and upper bound for this speed. The bound is now known as the Lieb-Robinson bound and the speed is known as the Lieb-Robinson velocity. This velocity is always finite but not universal, depending on the details of the system under consideration. For finite-range, e.g. nearest-neighbor, interactions, this velocity is a constant independent of the distance travelled. In long-range interacting systems, this velocity remains finite, but it can increase with the distance travelled. In the study of quantum systems such as quantum optics, quantum information theory, atomic physics, and condensed matter physics, it is important to know that there is a finite speed with which information can propagate. The theory of relativity shows that no information, or anything else for that matter, can travel faster than the speed of light. When non-relativistic mechanics is considered, however, (Newton's equations of motion or Schrödinger's equation of quantum mechanics) it had been thought that there is then no limitation to the speed of propagation of information. This is not so for certain kinds of quantum systems of atoms arranged in a lattice, often called quantum spin systems. This is important conceptually and practically, because it means that, for short periods of time, distant parts of a system act independently. One of the practical applications of Lieb-Robinson bounds is quantum computing. Current proposals to construct quantum computers built out of atomic-like units mostly rely on the existence of this finite speed of propagation to protect against too rapid dispersal of information. 
  • 520
  • 20 Oct 2022
Topic Review Peer Reviewed
Development of the Concept of Space up to Newton
The concept of space, ubiquitous among all humans from birth, has changed profoundly in the course of the history of Western civilization, the only one to be considered here. An important contribution to this change was the theoretical elaborations of the philosophers of nature and mathematicians, started in Ancient Greece. Here, the process is considered up to Newton, when the concept of space for physicists, who then replaced the traditional philosophers of nature, took on a connotation that remained substantially undisputed for two centuries—that of absolute space. 
  • 523
  • 18 Oct 2022
Biography
Reimar Lüst
Reimar Lüst (German: [ˈʁaɪmaʁ ˈlyːst]; 25 March 1923 – 31 March 2020)[1] was a German astrophysicist. He worked in European space science from its beginning, as the scientific director of the European Space Research Organisation (ESRO) from 1962 and as Director General of the European Space Agency (ESA) from 1984 until 1990. Lüst taught internationally and influenced German politics a
  • 519
  • 29 Dec 2022
Topic Review
Testing General Relativity with Gravitational Waves
The detections of gravitational-wave (GW) signals from compact binary coalescence by ground-based detectors have opened up the era of GW astronomy. These observations provide opportunities to test Einstein’s general theory of relativity at the strong-field regime. 
  • 518
  • 18 Jan 2022
Biography
Nima Arkani-Hamed
Nima Arkani-Hamed (Persian: نیما ارکانی حامد‎; born April 5, 1972) is an Iranian-American-Canadian[1][2] theoretical physicist, with interests in high-energy physics, quantum field theory, string theory, cosmology and collider physics. Arkani-Hamed is a member of the permanent faculty at the Institute for Advanced Study in Princeton, New Jersey.[3] He is also director of The Cent
  • 518
  • 01 Dec 2022
Topic Review
Simulation Argument (Coding Planck Units)
Coding Planck units for deep universe (Programmer God) Simulation Hypothesis models The deep universe simulation hypothesis or simulation argument is the argument that the universe in its entirety, down to the smallest detail, could be an artificial simulation, such as a computer simulation. A deep universe simulation begins with the big bang and is programmed by an external intelligence (external to the universe), this intelligence by definition a Programmer God in the creator of the universe context. In Big Bang cosmology, the Planck epoch or Planck era is the earliest stage of the Big Bang, where cosmic time was equal to Planck time. Thus for a deep universe simulation, Planck time can be used as the reference for the simulation clock-rate, with the simulation operating at or below the Planck scale, and with the Planck units as (top-level) candidates for the base (mass, length, time, charge) units.
  • 517
  • 22 Nov 2022
Topic Review
Free Entropy
A thermodynamic free entropy is an entropic thermodynamic potential analogous to the free energy. Also known as a Massieu, Planck, or Massieu–Planck potentials (or functions), or (rarely) free information. In statistical mechanics, free entropies frequently appear as the logarithm of a partition function. The Onsager reciprocal relations in particular, are developed in terms of entropic potentials. In mathematics, free entropy means something quite different: it is a generalization of entropy defined in the subject of free probability. A free entropy is generated by a Legendre transformation of the entropy. The different potentials correspond to different constraints to which the system may be subjected.
  • 517
  • 04 Nov 2022
Topic Review
Jet Flavour Tagging
Jet Flavour Tagging briefly describes the main algorithms used to reconstruct heavy-flavour jets. Jet Substructure and Deep Tagging focuses on the identification of heavy-particle decay in boosted jets. These so-called tagger algorithms have a relevant role in physics studies since they allow researchers to successfully reconstruct and identify the particles that caused the jet and, in some cases, allow analyses that would otherwise be unfeasible.
  • 516
  • 09 Nov 2022
Topic Review
Isotopes of Osmium
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 516
  • 27 Oct 2022
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