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arXiv2019

Quantum gravity from general relativity

Although general relativity is a predictively successful theory, it treats matter as classical rather than as quantum. For this reason, it will have to be replaced by a more fundamental quantum theory of gravity. Attempts to formulate a quantum theory of gravity suggest that such a theory may have radical consequences for the nature, and indeed the fate, of spacetime. The present article articulates what this problem of spacetime is and traces it through three approaches to quantum gravity taking general relativity as their vantage point: semi-classical gravity, causal set theory, and loop quantum gravity.

physics.hist-ph↗

arXiv2019

Lost in Math? A review of 'Lost in Math: How Beauty Leads Physics Astray', by Sabine Hossenfelder

This is a review of Hossenfelder's book, 'Lost in Math: How Beauty Leads Physics Astray'. The book gives a breezy exposition of the present situation in fundamental physics, and raises important questions: both about the content of the physics, and the way physics research is organized. I first state my main disagreements. Then, I mostly praise the book: I concentrate on Hossenfelder's discussion of supersymmetry, naturalness and the multiverse.

physics.hist-ph↗

arXiv2019

Claudius Ptolemy and Giambattista Della Porta: Two Contrasting Conceptions of Optics

We address the phenomenon of reflection in concave spherical mirror in two contrasting approaches to optics. In his Optics (ca.165) Ptolemy applied the cathetus principle as a regulative means for explaining qualitatively effects related to visual perception in concave spherical mirror. By contrast, Della Porta's study of reflection in concave spherical mirror in Bk. 17, Ch. 4 of his Magia naturalis (1589) and De refractione (1593), was based on the assumption that there is a reciprocal relation between reflection in concave spherical mirror and refraction in glass sphere. We juxtapose these two studies and draw several philosophical lessons from the comparison between these two practices with a view to throwing into relief the fundamental differences in their respective conceptions of optics.

physics.hist-ph↗

arXiv2019

The future of US-China relations: a scientific investigation

In earlier centuries kings and governments employed astrologists to help them take the best decisions. Present-day governments no longer employ astrologists but still have no clear analytical tool to replace them. Over the past two decades we have developed a methodology for the scientific investigation of recurrent historical events. It consists in two steps. (i) Identification and comparison of historical episodes driven by a common mechanism. (ii) Under the reasonable assumption that what has happened several times in the past is likely to happen again, one then derives testable predictions. This of course is nothing other than the protocol used in experimental science when exploring new phenomena. We believe such a tool can give decision makers much better insight. In the present paper we illustrate this analysis by considering challenges, that span more than a century, to US hegemony in the Pacific. The outcomes suggest that it is only through the sidelining of one of the contenders that the confrontation will end. At the time of writing (late 2018) early evidence of this confrontation is already visible at three levels. (i) Growing US concerns for domestic security that are leading to a new form of McCarthyism. (ii) Political instability due to China-US polarization in several Asian countries as well as in the countries participating in the Belt and Road Initiative. (iii) Tension and sanctions in procurement and trade.

physics.hist-ph↗

arXiv2019

Experiments made before the instituted society in confirmation of the theory of the pressures which the walls of the channel sustain due to the flowing water

This is an annotated translation from Latin of "Experimenta coram societate instituta in confirmationem theoriae pressionum quas latera canalis ab aqua tranfluente sustinet" in which Daniel Bernoulli describes six experiments conducted before the St. Petersburg Academy in 1729, in confirmation of his theory dedicated to the motion of water through ducts, which contains the developments that led to the relation between pressure and velocity in fluid flows, known as Bernoulli's principle.

physics.hist-ph↗

arXiv2019

Prehistory of Neutrino Oscillations

First ideas of neutrino masses, mixing and oscillations proposed by Bruno Pontecorvo in 1957 and later development of these ideas are considered in some details. Original ideas of the two-neutrino mixing proposed by Maki, Nakagawa and Sakata in 1962 are also discussed.

physics.hist-ph↗

arXiv2019

Indigenous use of stellar scintillation to predict weather and seasonal change

Indigenous peoples across the world observe the motions and positions of stars to develop seasonal calendars. Additionally, changing properties of stars, such as their brightness and colour, are also used for predicting weather. Combining archival studies with ethnographic fieldwork in Australia's Torres Strait, we explore the various ways Indigenous peoples utilise stellar scintillation (twinkling) as an indicator for predicting weather and seasonal change, discussing the scientific underpinnings of this knowledge. By observing subtle changes in the ways the stars twinkle, Meriam people gauge changing trade winds, approaching wet weather, and temperature changes. We then explore how the Northern Dene of Arctic North America utilise stellar scintillation to forecast weather.

physics.hist-ph↗

arXiv2019

Quantum Probability: a reliable tool for an agent or a reliable source of reality?

In this paper we attempt to analyze the concept of quantum probability within quantum computation and quantum computational logic. While the subjectivist interpretation of quantum probability explains it as a reliable predictive tool for an agent in order to compute measurement outcomes, the objectivist interpretation understands quantum probability as providing reliable information of a real state of affairs. After discussing these different viewpoints we propose a particular objectivist interpretation grounded on the idea that the Born rule provides information about an intensive realm of reality. We then turn our attention to the way in which the subjectivist interpretation of probability is presently applied within both quantum computation and quantum computational logic. Taking as a standpoint our proposed intensive account of quantum probability we discuss the possibilities and advantages it might open for the modeling and development of both quantum computation and quantum computational logic.

quant-ph↗

arXiv2019

Position Measurements and the Empirical Status of Particles in Bohmian Mechanics

The paper addresses the debate about the empirical status of particles versus wave functions in Bohmian quantum mechanics. It thereby clarifies questions and misconceptions about the role of the particles in the measurement process, the (un)reliability of position measurements ("surrealistic trajectories"), and the limited empirical access to particle positions ("absolute uncertainty"). Taking the ontological commitment of Bohmian mechanics seriously, all relevant empirical results follow from an analysis of the theory in terms of particle motions. Finally, we address the question, why particle motions rather than patterns in the wave function would be the supervenience base of conscious experience.

quant-ph↗

arXiv2019

Closing in on the Cosmos: Cosmology's Rebirth and the Rise of the Dark Matter Problem

Influenced by the renaissance of general relativity that came to pass in the 1950s, the character of cosmology fundamentally changed in the 1960s as it became a well-established empirical science. Although observations went to dominate its practice, extra-theoretical beliefs and principles reminiscent of methodological debates in the 1950s kept playing an important tacit role in cosmological considerations. Specifically, belief in cosmologies that modeled a "closed universe" based on Machian insights remained influential. The rise of the dark matter problem in the early 1970s serves to illustrate this hybrid methodological character of cosmological science.

physics.hist-ph↗

arXiv2019

Black Hole Entropy is Thermodynamic Entropy

The comparison of geometrical properties of black holes with classical thermodynamic variables reveals surprising parallels between the laws of black hole mechanics and the laws of thermodynamics. Since Hawking's discovery that black holes when coupled to quantum matter fields emit radiation at a temperature proportional to their surface gravity, the idea that black holes are genuine thermodynamic objects with a well-defined thermodynamic entropy has become more and more popular. Surprisingly, arguments that justify this assumption are both sparse and rarely convincing. Most of them rely on an information-theoretic interpretation of entropy, which in itself is a highly debated topic in the philosophy of physics. We discuss some of the pertinent arguments that aim at establishing the identity of black hole surface area (times a constant) and thermodynamic entropy and show why these arguments are not satisfactory. We then present a simple model of a Black Hole Carnot cycle to establish that black hole entropy is genuine thermodynamic entropy which does not require an information-theoretic interpretation.

physics.hist-ph↗

arXiv2019

Against the disappearance of spacetime in quantum gravity

This paper argues against the proposal to draw from current research into a physical theory of quantum gravity the ontological conclusion that spacetime or spatiotemporal relations are not fundamental. As things stand, the status of this proposal is like the one of all the other claims about radical changes in ontology that were made during the development of quantum mechanics and quantum field theory. However, none of these claims held up to scrutiny as a consequence of the physics once the theory was established and a serious discussion about its ontology had begun. Furthermore, the paper argues that if spacetime is to be recovered through a functionalist procedure in a theory that admits no fundamental spacetime, standard functionalism cannot serve as a model: all the known functional definitions are definitions in terms of a causal role for the motion of physical objects and hence presuppose spatiotemporal relations.

physics.hist-ph↗

arXiv2019

The Roman Colonia Marciana Ulpia Traiana Thamugadi (Timgad) and Trajan's Birthday

It is told that the Roman Colonia Marciana Ulpia Traiana Thamugadi, that is Timgad in Algeria, had been oriented to the sunrise on the day of Trajan's birthday, that is 18 September 100 AD. Here we use software CalSKY to investigate the sunrise azimuth and compare it to the direction of the decumanus of the Roman town.

physics.pop-ph↗

arXiv2019

Discovery goals and opportunities in high energy physics: a defense of BSM-oriented exploration over signalism

Discoveries come through exclusions, confirmations or revolutionary findings with respect to a theory canon populated by the Standard Model (SM) and beyond the SM (BSM) theories. Guaranteed discoveries are accomplished only through pursuit of BSM exclusion/confirmation, and thus require investment in the continual formation and analysis of a vibrant theory canon combined with investment in experiment with demonstrated capacity to make BSM exclusions/confirmations. Risks develop when steering away from BSM-oriented work toward its methodological rival, "signalism," which seeks to realize SM falsification or revolutionary discoveries outside the context of any BSM rationale. It is argued that such an approach leads to inscrutable exertions that reduce prospects for all discovery. The concepts are applied to the European Strategy Update, which seeks to identify future investments in forefront experiment that bring a balance of guaranteed and prospective value.

physics.hist-ph↗

arXiv2019

Bhasvati of Satananda: In the Pages of Mystery

Satanandacharya the astronomer and mathematician of 11th century was born in 1068 C.E. at Purusottamdham Puri of Odisha wrote the scripture Bhasvati in 1099 C.E.. The scripture has significant contribution to world of Astronomy and Mathematics. Satananda has adopted centisimal system for the calculation of position and motion of heavenly bodies, which is similar to present day decimal system. The treaties got the recognition of a scripture of Karana grantha. Commentaries of this work has been made by defferent persons during different time of history. Though it is found to be remade in almost once in each century and was well known all over India and abroad. Presently it is completely lost and no reference is available in ongoing works. The main aim of this paper is to outline and bring to the notice of a wider audience -- the genius of Satananda and his contribution to the world of astronomy and Mathematics.

physics.hist-ph↗

arXiv2019

The experiment paradox in physics

Modern physics is founded on two mainstays: mathematical modelling and empirical verification. These two assumptions are prerequisite for the objectivity of scientific discourse. Here we show, however, that they are contradictory, leading to the `experiment paradox'. We reveal that any experiment performed on a physical system is - by necessity - invasive and thus establishes inevitable limits to the accuracy of any mathematical model. We track its manifestations in both classical and quantum physics and show how it is overcome `in practice' via the concept of environment. We argue that the scientific pragmatism ordains two methodological principles of compressibility and stability.

physics.hist-ph↗

arXiv2019

Explore with caution: mapping the evolution of scientific interest in Physics

In the book The Essential Tension Thomas Kuhn described the conflict between tradition and innovation in scientific research --i.e., the desire to explore new promising areas, counterposed to the need to capitalize on the work done in the past. While it is true that along their careers many scientists probably felt this tension, only few works have tried to quantify it. Here, we address this question by analyzing a large-scale dataset, containing all the papers published by the American Physical Society (APS) in more than $25$ years, which allows for a better understanding of scientists' careers evolution in Physics. We employ the Physics and Astronomy Classification Scheme (PACS) present in each paper to map the scientific interests of $181,397$ authors and their evolution along the years. Our results indeed confirm the existence of the `essential tension' with scientists balancing between exploring the boundaries of their area and exploiting previous work. In particular, we found that although the majority of physicists change the topics of their research, they stay within the same broader area thus exploring with caution new scientific endeavors. Furthermore, we quantify the flows of authors moving between different subfields and pinpoint which areas are more likely to attract or donate researchers to the other ones. Overall, our results depict a very distinctive portrait of the evolution of research interests in Physics and can help in designing specific policies for the future.

physics.soc-ph↗

arXiv2019

Wigner and his many friends: A new no-go result?

In April 2016, Daniela Frauchiger and Renato Renner published an article online in which they introduce a Gedankenexperiment that led them to conclude that single-world interpretation of quantum theory cannot be self-consistent. In a new version of the paper, published in September 2018, the authors moderate their original claim by concluding that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner. The purpose of this article is to offer a careful reconstruction of the F-R argument, which allows us to show that: (i) the argument can be more clearly formulated with no reference to what subjects know or see, but rather only in terms of quantum propositions, (ii) in contrast to what some commentators suppose, the argument does not require the hypothesis of collapse to arrive to its conclusion, and (iii) the contradiction resulting from the F-R argument is inferred by making classical conjunctions between different and incompatible contexts. On the basis of this clarification, we will finally argue that the conclusion of the F-R argument is not as novel and original as its great impact might make us to suppose.

quant-ph↗