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At least 649 records · Page 36Linked to original sources

arXiv2017

Remarks to the article: New Light on the Invention of the Achromatic Telescope Objective

The article analysis was carried out within the confines of the replication project of the telescope, which was used by Mikhail Lomonosov at observation the transit of Venus in 1761. At that time he discovered the Venusian atmosphere. It is known that Lomonosov used Dollond 4.5 feet long achromatic telescope. The investigation revealed significant faults in the description of the approximation method, which most likely was used by J. Dollond & Son during manufacturing of the early achromatic lenses.

physics.hist-ph↗

arXiv2017

Spinor analysis

"Let us call the novel quantities which, in addition to the vectors and tensors, have appeared in the quantum mechanics of the spinning electron, and which in the case of the Lorentz group are quite differently transformed from tensors, as spinors for short. Is there no spinor analysis that every physicist can learn, such as tensor analysis, and with the aid of which all the possible spinors can be formed, and secondly, all the invariant equations in which spinors occur?" So Mr Ehrenfest asked me and the answer will be given below.

physics.hist-ph↗

arXiv2018

Comets, historical records and vedic literature

A verse in book I of Rigveda mentions a cosmic tree with rope-like aerial roots held up in the sky. Such an imagery might have ensued from the appearance of a comet having `tree stem' like tail, with branched out portions resembling aerial roots. Interestingly enough, a comet referred to as `heavenly tree' was seen in 162 BC, as reported by old Chinese records. Because of weak surface gravity, cometary appendages may possibly assume strange shapes depending on factors like rotation, structure and composition of the comet as well as solar wind pattern. Varahamihira and Ballala Sena listed several comets having strange forms as reported originally by ancient seers such as Parashara, Vriddha Garga, Narada and Garga. Mahabharata speaks of a mortal king Nahusha who ruled the heavens when Indra, king of gods, went into hiding. Nahusha became luminous and egoistic after absorbing radiance from gods and seers. When he kicked Agastya (southern star Canopus), the latter cursed him to become a serpent and fall from the sky. We posit arguments to surmise that this Mahabharata lore is a mythical recounting of a cometary event wherein a comet crossed Ursa Major, moved southwards with an elongated tail in the direction of Canopus and eventually went out of sight. In order to check whether such a conjecture is feasible, a preliminary list of comets (that could have or did come close to Canopus) drawn from various historical records is presented and discussed.

physics.hist-ph↗

arXiv2018

On the Incompatibility of Special Relativity and Quantum Mechanics

Some of the strategies which have been put forward in order to deal with the inconsistency between quantum mechanics and special relativity are examined. The EPR correlations are discussed as a simple example of quantum mechanical macroscopic effects with spacelike separation from their causes. It is shown that they can be used to convey information, whose reliability can be estimated by means of Bayes' theorem. Some of the current reasons advanced to deny that quantum mechanics contradicts special relativity are refuted, and an historical perspective is provided on the issue.

gr-qc↗

arXiv2017

Einstein's 1935 papers: EPR=ER?

In May of 1935, Einstein published with two co-authors the famous EPR-paper about entangled particles, which questioned the completeness of Quantum Mechanics by means of a gedankenexperiment. Only one month later, he published a work that seems unconnected to the EPR-paper at first, the so called Einstein-Rosen-paper, that presented a solution of the field equations for particles in the framework of general relativity. Both papers ask for the conception of completeness in a theory and, from a modern perspective, it is easy to believe that there is a connection between these topics. We question whether Einstein might have considered that a correlation between nonlocal features of Quantum Mechanics and the Einstein-Rosen bridge can be used to explain entanglement. We analyse this question by discussing the used conceptions of "completeness," "atomistic structure of matter," and "quantum phenomena." We discuss the historical embedding of the two works and the context to modern research. Recent approaches are presented that formulate an EPR=ER principle and claim an equivalence of the basic principles of these two papers.

physics.hist-ph↗

arXiv2018

Notwithstanding Bohr, the Reasons for QBism

Without Niels Bohr, QBism would be nothing. But QBism is not Bohr. This paper attempts to show that, despite a popular misconception, QBism is no minor tweak to Bohr's interpretation of quantum mechanics. It is something quite distinct. Along the way, we lay out three tenets of QBism in some detail: 1) The Born Rule---the foundation of what quantum theory means for QBism---is a normative statement. It is about the decision-making behavior any individual agent should strive for; it is not a descriptive "law of nature" in the usual sense. 2) All probabilities, including all quantum probabilities, are so subjective they never tell nature what to do. This includes probability-1 assignments. Quantum states thus have no "ontic hold" on the world. 3) Quantum measurement outcomes just are personal experiences for the agent gambling upon them. Particularly, quantum measurement outcomes are not, to paraphrase Bohr, instances of "irreversible amplification in devices whose design is communicable in common language suitably refined by the terminology of classical physics." Finally, an explicit comparison is given between QBism and Bohr with regard to three subjects: a) The issue of the "detached observer" as it arose in a debate between Pauli and Bohr, b) Bohr's reply to Einstein, Podolsky, and Rosen, and c) Bohr's mature notion of "quantum phenomena." At the end, we discuss how Bohr's notion of phenomena may have something to offer the philosophy of William James: A physics from which to further develop his vision of the world---call it an ontology if you will---in which "new being comes in local spots and patches."

quant-ph↗

arXiv2017

Renormalizability, fundamentality and a final theory: The role of UV-completion in the search for quantum gravity

Principles are central to physical reasoning, particularly in the search for a theory of quantum gravity (QG), where novel empirical data is lacking. One principle widely adopted in the search for QG is UV completion: the idea that a theory should (formally) hold up to all possible high energies. We argue---\textit{contra} standard scientific practice---that UV-completion is poorly-motivated as a guiding principle in theory-construction, and cannot be used as a criterion of theory-justification in the search for QG. For this, we explore the reasons for expecting, or desiring, a UV-complete theory, as well as analyse how UV completion is used, and how it should be used, in various specific approaches to QG.

physics.hist-ph↗

arXiv2017

Readings and Misreadings of J. Willard Gibbs Elementary Principles in Statistical Mechanics

J. Willard Gibbs' Elementary Principles in Statistical Mechanics was the definitive work of one of America's greatest physicists. Gibbs' book on statistical mechanics establishes the basic principles and fundamental results that have flowered into the modern field of statistical mechanics. However, at a number of points, Gibbs' teachings on statistical mechanics diverge from positions on the canonical ensemble found in more recent works, at points where seemingly there should be agreement. The objective of this paper is to note some of these points, so that Gibbs' actual positions are not misrepresented to future generations of students.

physics.hist-ph↗

arXiv2017

Cauchy Tetrahedron Argument and the Proofs of the Existence of Stress Tensor, a Comprehensive Review, Challenges, and Improvements

In 1822, Cauchy presented the idea of traction vector that contains both the normal and tangential components of the internal surface forces per unit area and gave the tetrahedron argument to prove the existence of stress tensor. These great achievements form the main part of the foundation of continuum mechanics. For about two centuries, some versions of tetrahedron argument and a few other proofs of the existence of stress tensor are presented in every text on continuum mechanics, fluid mechanics, and the relevant subjects. In this article, we show the birth, importance, and location of these Cauchy's achievements, then by presenting the formal tetrahedron argument in detail, for the first time, we extract some fundamental challenges. These conceptual challenges are related to the result of applying the conservation of linear momentum to any mass element, the order of magnitude of the surface and volume terms, the definition of traction vectors on the surfaces that pass through the same point, the approximate processes in the derivation of stress tensor, and some others. In a comprehensive review, we present the different tetrahedron arguments and the proofs of the existence of stress tensor, discuss the challenges in each one, and classify them in two general approaches. In the first approach that is followed in most texts, the traction vectors do not exactly define on the surfaces that pass through the same point, so most of the challenges hold. But in the second approach, the traction vectors are defined on the surfaces that pass exactly through the same point, therefore some of the relevant challenges are removed. We also study the improved works of Hamel and Backus, and indicate that the original work of Backus removes most of the challenges. This article shows that the foundation of continuum mechanics is not a finished subject and there are still some fundamental challenges.

physics.hist-ph↗

arXiv2017

Martin David Kruskal: a biographical memoir

Martin David Kruskal was one of the most versatile theoretical physicists of his generation and is distinguished for his enduring work in several different areas, most notably plasma physics, a memorable detour into relativity, and his pioneering work in nonlinear waves. In the latter, together with Norman Zabusky, he invented the concept of the soliton and, with others, developed its application to classes of partial differential equations of physical significance.

physics.hist-ph↗

arXiv2020

Astrometric accuracy during the past 2000 years

The great development of astrometric accuracy since the observations by Hipparchus about 150 BC was documented in 2008 in the first version of the present report. This report was updated in Høg (2017d), e.g. with recent information on the catalogues before 1800 AD. The development has often been displayed in diagrams showing the accuracy versus time. A new simplified diagram is provided in the present report as Fig.2 and in a .png file and this information will presumably be the main interest for some readers.

astro-ph.IM↗

arXiv2017

Betting on Quantum Objects

Dutch book arguments have been applied to beliefs about the outcomes of measurements of quantum systems, but not to beliefs about quantum objects prior to measurement. In this paper, we prove a quantum version of the probabilists' Dutch book theorem that applies to both sorts of beliefs: roughly, if ideal beliefs are given by vector states, all and only Born-rule probabilities avoid Dutch books. This theorem and associated results have implications for operational and realist interpretations of the logic of a Hilbert lattice. In the latter case, we show that the defenders of the eigenstate-value orthodoxy face a trilemma. Those who favor vague properties avoid the trilemma, admitting all and only those beliefs about quantum objects that avoid Dutch books.

physics.hist-ph↗

arXiv2018

Causation, Information, and Physics

This work outlines the novel application of the empirical analysis of causation, presented by Kutach, to the study of information theory and its role in physics. The central thesis of this paper is that causation and information are identical functional tools for distinguishing controllable correlations, and that this leads to a consistent view, not only of information theory, but also of statistical physics and quantum information. This approach comes without the metaphysical baggage of declaring information a fundamental ingredient in physical reality and exorcises many of the otherwise puzzling problems that arise from this view-point, particularly obviating the problem of `excess baggage' in quantum mechanics.

physics.hist-ph↗

arXiv2017

From Quantum to Classical Physics: The Role of Distinguishability

The transition from quantum to classical statistics is studied in light of Huggett's finding that the empirical data do not support the usual claim that the distinction between classical and quantum objects consists in the capacity of classical objects to carry permutable labels as opposed to quantum objects. Since permutation of the labels of classical objects counts as a distinct configuration, this feature is usually taken as signifying that classical objects are not identical while quantum objects are. Huggett's finding threatens that characterization of the distinction between classical and quantum objects. The various statistical distributions are examined, and it is found that other distinctions, corresponding to separability and distinguishability, emerge in the classical limit. The role of the chemical potential (the rate of change of the Helmholtz free energy with particle number) is found to be of crucial significance in characterizing this emergence of classicality from the quantum distributions.

quant-ph↗

arXiv2018

Theoretical High Energy Physics in Latin America from 1990 to 2012: a Statistical Study

We present a statistical overview of the publications in theoretical high energy physics (HEP), which emerged in Latin America (LA) in the period from 1990 to 2012. Our study captures the eight Latin American nations, which are dominant in this field of research: Brazil, Mexico, Argentina, Chile, Colombia, Venezuela, Uruguay and Cuba. As an intercontinental benchmark, we compare them with India, Canada, South Korea, Belgium and South Africa. We consider the productivity of research papers in specialized high-impact journals, and the corresponding numbers of citations. The goal is to document the efforts in LA to catch up with the most wealthy countries, in a field of research without direct practical benefits. The restriction to theoretical HEP excludes large international collaborations, which enables a fair evaluation of national achievements. We further investigate how these records are correlated with three socio-economic indices: the Gross Domestic Product (GDP), the Human Development Index (HDI) and the Education Index (EI). Despite some progress, there remains a backlog of LA compared to the dominant countries, which cannot be explained solely by economic deficiency. In general, a detailed correlation between the socio-economic and scientific evolution is not obvious.

physics.soc-ph↗

arXiv2017

Are black holes about information?

Information theory is increasingly invoked by physicists concerned with fundamental physics, including black hole physics. But to what extent is the application of information theory in those contexts legitimate? Using the case of black hole thermodynamics and Bekenstein's celebrated argument for the entropy of black holes, I will argue that information-theoretic notions are problematic in the present case. Bekenstein's original argument, as suggestive as it may appear, thus fails. This example is particularly pertinent to the theme of the present collection because the Bekenstein-Hawking formula for black hole entropy is widely accepted as 'empirical data' in notoriously empirically deprived quantum gravity, even though the laws of black hole thermodynamics have so far evaded empirical confirmation.

physics.hist-ph↗

arXiv2017

Remarks on the empirical accuracy of the optical superposition principle [Engl. transl. of Zh. Russk. Fiz.-Khim. Obshch., Ch. Fiz. 60(1928)555]

English translation of a Russian article from 1928. Translator's abstract: The article presents general considerations on the validity of the superposition principle for light in vacuo from out a quantum theoretic point of view. It contains a report on an optical experiment designed to detect the phenomenon of photon-photon scattering. To understand the negative result of the performed experiment, a consideration of the solar corona is undertaken in order to derive an empirical upper limit on the photon-photon scattering rate. Source details: S. I. Vavilov: Zamechaniya ob empiricheskoi tochnosti opticheskogo printsipa superpozitsii. Zhurnal Russkogo Fiziko-Khimicheskogo Obshchestva pri Leningradskom Universitete, Chast' Fizicheskaya [Journal of the Russian Physico-Chemical Society at Leningrad University, Physical Part], Vol. LX (1928) No. 6, pp. 555-563.

physics.hist-ph↗

arXiv2017

Memories of a Theoretical Physicist

While I was dealing with a brain injury and finding it difficult to work, two friends (Derek Westen, a friend of the KITP, and Steve Shenker, with whom I was recently collaborating), suggested that a new direction might be good. Steve in particular regarded me as a good writer and suggested that I try that. I quickly took to Steve's suggestion. Having only two bodies of knowledge, myself and physics, I decided to write an autobiography about my development as a theoretical physicist. This is not written for any particular audience, but just to give myself a goal. It will probably have too much physics for a nontechnical reader, and too little for a physicist, but perhaps there with be different things for each. Parts may be tedious. But it is somewhat unique, I think, a blow-by-blow history of where I started and where I got to. Probably the target audience is theoretical physicists, especially young ones, who may enjoy comparing my struggles with their own. Some disclaimers: This is based on my own memories, jogged by the arXiv and Inspire. There will surely be errors and omissions. And note the title: this is about my memories, which will be different for other people. Also, it would not be possible for me to mention all the authors whose work might intersect mine, so this should not be treated as a reference work.

physics.hist-ph↗