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At least 343 records · Page 19Linked to original sources
arXiv2013

Cultural Astronomy and Archaeoastronomy: an Italian Experience

A brief review is given of some recent positive developments regarding the reception of archaeoastronomy by the archaeological institutions in Italy. Discussions and problems that are currently going on in this field are also mentioned, such as the separation of the scientific and humanistic disciplines (i.e. the two cultures problem). Suggestions based on contemporary philosophy are also reported. Finally, sky-gazing is proposed as the place where the two cultures could meet, since, taking Plato into account, sky-gazing could be considered the mom of the human knowledge, and of the scientific and humanistic disciplines.

physics.hist-ph↗
arXiv2013

Non-local common cause explanations for EPR

The paper argues that a causal explanation of the correlated outcomes of EPR-type experiments is desirable and possible. It shows how Bohmian mechanics and the GRW mass density theory offer such an explanation in terms of a non-local common cause.

quant-ph↗
arXiv2014

Marcel Grossmann and his contribution to the general theory of relativity

This article reviews the biography of the Swiss mathematician Marcel Grossmann (1878-1936) and his contributions to the emergence of the general theory of relativity. The first part is his biography, while the second part reviews his collaboration with Einstein in Zurich which resulted in the Einstein-Grossmann theory of 1913. This theory is a precursor version of the final theory of general relativity with all the ingredients of that theory except for the correct gravitational field equations. Their collaboration is analyzed in some detail with a focus on the question of exactly what role Grossmann played in it.

physics.hist-ph↗
arXiv2013

In memory of M. I. Polikarpov

This obituary is devoted to M. I. Polikarpov (28.12.1952 - 18.07.2013), our teacher, our colleague, our friend. We recollect some facts of his biography and stages of his scientific career, and make a brief review of some of his most known scientific works. We conclude with some messages of condolence which were received from his colleagues and friends after his sudden death.

physics.hist-ph↗
arXiv2013

Time in Fundamental Physics

The first three sections of this article contain a broad brush summary of the profound changes in the notion of time in fundamental physics that were brought about by three revolutions: the foundations of mechanics distilled by Newton in his Principia, the discovery of special relativity by Einstein and its reformulation by Minkowski, and, finally, the fusion of geometry and gravity in Einstein's general relativity. The fourth section discusses two aspects of yet another deep revision that waits in the wings as we attempt to unify general relativity with quantum physics.

physics.hist-ph↗
arXiv2017

The flow of time in the theory of relativity

Dennis Dieks advanced the view that the idea of flow of time is implemented in the theory of relativity. The 'flow' results from the successive happening/becoming of events along the time-like worldline of a material system. This leads to a view of now as local to each worldline. Each past event of the worldline has occurred once as a nowpoint, and we take there to be an ever-changing present now-point 'marking' the unfolding of a physical system. In Dieks' approach there is no preferred worldline and only along each worldline is there a Newtonian-like linear order between successive now-points. We have a flow of time per worldline. Also there is no global temporal order of the now-points of different worldlines. There is, as much, what Dieks calls a partial order. However Dieks needs for a consistency reason to impose a limitation on the assignment of the now-points along different worldlines. In this work it is made the claim that Dieks' consistency requirement is, in fact, inbuilt in the theory as a spatial relation between physical systems and processes. Furthermore, in this work we will consider (very) particular cases of assignments of now-points restricted by this spatial relation, in which the now-points taken to be simultaneous are not relative to the adopted inertial reference frame.

physics.hist-ph↗
arXiv2014

Kenneth Geddes Wilson

A look back at Kenneth Wilson's contributions to theoretical physics, with some reminiscences of the professor I encountered at Cornell during the 1980s.

physics.hist-ph↗
arXiv2013

Nero's "solar" kingship and the architecture of Domus Aurea

The Domus Aurea, Nero's last "palace" constructed in the very heart of ancient Rome, is a true masterpiece of Roman architecture. We explore here symbolic aspects of the emperor's project, analysing the archaeoastronomy of the best preserved part of the Domus, the Esquiline Wing. In particular, we study the so-called Octagonal Room, the huge vaulted room which is in many respects a predecessor of the Pantheon. The project of the room turns out to be connected with astronomy, as will be that of the Hadrian's Pantheon 60 years later. Indeed, the divinization and "solarisation" of the emperor placed at the equinoxes as a point of balance in the heavens are shown to be explicitly referred to in the rigorous orientation of the plan and in the peculiar geometry of the design of the dome.

physics.hist-ph↗
arXiv2014

Photon: New light on an old name

After G. N. Lewis (1875-1946) proposed the term "photon" in 1926, many physicists adopted it as a more apt name for Einstein's light quantum. However, Lewis' photon was a concept of a very different kind, something few physicists knew or cared about. It turns out that Lewis' name was not quite the neologism that it has usually been assumed to be. The same name was proposed or used earlier, apparently independently, by at least four scientists. Three of the four early proposals were related to physiology or visual perception, and only one to quantum physics. Priority belongs to the American physicist and psychologist L. T. Troland (1889-1932), who coined the word in 1916, and five years later it was independently introduced by the Irish physicist J. Joly (1857-1933). Then in 1925 a French physiologist, Rene Wurmser (1890-1993), wrote about the photon, and in July 1926 his compatriot, the physicist F. Wolfers (ca. 1890-1971), did the same in the context of optical physics. None of the four pre-Lewis versions of "photon" was well known and they were soon forgotten.

physics.hist-ph↗
arXiv2014

The Giza "written" landscape and the double project of King Khufu

In recent years, different scientific disciplines, from Physics to Egyptology, from Geology to Archaeoastronomy, evidenced a series of clues pointing to the possibility that the original project of the pyramid complex of Khufu at Giza included also the project of the second pyramid complex at the same site, that of Khafra. The aim of the present paper is to discuss this issue in a systematic fashion and to explore its consequences on the way the ancient Egyptians conceived and built monuments and entire landscapes during the Old Kingdom.

physics.hist-ph↗
arXiv2014

Gödel, Tarski, Turing and the conundrum of free will

The problem of defining and locating free will (FW) in physics is studied. On basis of logical paradoxes, we argue that FW has a meta-theoretic character, like the concept of truth in Tarski's undefinability theorem. Free will exists relative to a base theory if there is freedom to deviate from the deterministic or indeterministic dynamics in the theory, with the deviations caused by parameters (representing will) in the meta-theory. By contrast, determinism and indeterminism do not require meta-theoretic considerations in their formalization, making FW a fundamentally new causal primitive. FW exists relative to the meta-theory if there is freedom for deviation, due to higher-order causes. Absolute free will, which corresponds to our intuitive introspective notion of free will, exists if this meta-theoretic hierarchy is infinite. We argue that this hierarchy corresponds to higher levels of uncomputability. In other words, at any finitely high order in the hierarchy, there are uncomputable deviations from the law at that order. Applied to the human condition, the hierarchy corresponds to deeper levels of the subconscious or unconscious mind. Possible ramifications of our model for physics, neuroscience and artificial intelligence (AI) are briefly considered.

physics.hist-ph↗
arXiv2014

N.C. Rana: The Life of a `Comet' in the Astrophysical World

Narayan Chandra Rana, a person with extraordinary potential from a remote village of Bengal, India, came into the limelight of the international scientific world through his exceptional talent, zeal and courage. In his very short life-span, he excelled not only into various branches of astrophysics, but also took a leading role in science popularization, text book writing etc. In this paper, life and works of that budding scientist of India have been discussed from multifarious viewpoints.

physics.hist-ph↗
arXiv2014

Partitions and Objective Indefiniteness in Quantum Mechanics

Classical physics and quantum physics suggest two meta-physical types of reality: the classical notion of a objectively definite reality with properties "all the way down," and the quantum notion of an objectively indefinite type of reality. The problem of interpreting quantum mechanics (QM) is essentially the problem of making sense out of an objectively indefinite reality. These two types of reality can be respectively associated with the two mathematical concepts of subsets and quotient sets (or partitions) which are category-theoretically dual to one another and which are developed in two mathematical logics, the usual Boolean logic of subsets and the more recent logic of partitions. Our sense-making strategy is "follow the math" by showing how the logic and mathematics of set partitions can be transported in a natural way to Hilbert spaces where it yields the mathematical machinery of QM--which shows that the mathematical framework of QM is a type of logical system over the complex numbers. And then we show how the machinery of QM can be transported the other way down to the set-like vector spaces over Z_2 showing how the classical logical finite probability calculus (in a "non-commutative" version) is a type of "quantum mechanics" over Z_2, i.e., over sets. In this way, we try to make sense out of objective indefiniteness and thus to interpret quantum mechanics.

quant-ph↗
arXiv2014

The relevance of ontological commitments

In this introductory note, I describe my particular view of the notion of ontological commitments as honest and pragmatic working hypotheses that assume the existence (out there) of certain entities represented by the symbols in our theory. I argue that this is not naive, in the sense that it does not entail the belief that the hypotheses could ever be proved to be true (or false), but it is nevertheless justified by the success and predictive power of the theory that contains the concepts assumed to exist. I also claim that the ontological commitments one holds (even if tacitly so) have a great influence on what kind of science is produced, how it is used, and how it is understood. Not only I justify this claim, but I also propose a sketch of a possible falsification of it. As a natural conclusion, I defend the importance of identifying, clarifying and making explicit one's ontological commitments if fruitful scientific discussions are to be had. Finally, I compare my point of view with that of some philosophers and scientists who have put forward similar notions.

physics.hist-ph↗
arXiv2014

Einstein's first gravitational field equation 101 years latter

We review and strengthen the arguments given by Einstein to derive his first gravitational field equation for static fields and show that, although it was ultimately rejected, it follows from General Relativity (GR) for negligible pressure. Using this equation and considerations folowing directly from the equivalence principle (EP), we show how Schwarzschild metric and other vacum metrics can be obtained immediately. With this results and some basic principles, we obtain the metric in the general spherically symmetric case and the corresponding hydrostatic equilibrium equation. For this metrics we obtain the motion equations in a simple and exact manner that clearly shows the three sources of difference (implied by various aspects of the EP) with respect to the Newtonian case and use them to study the classical tests of GR. We comment on the origin of the problems of Einstein first theory of gravity and discuss how, by removing it the theory could be made consistent and extended to include rotations, we also comments on various conceptual issues of GR as the origin of the gravitational effect of pressure.

gr-qc↗