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At least 163 records · Page 9Linked to original sources
arXiv2012

Emergence of time in quantum gravity: is time necessarily flowing ?

We discuss the emergence of time in quantum gravity, and ask whether time is always "something that flows"'. We first recall that this is indeed the case in both relativity and quantum mechanics, although in very different manners: time flows geometrically in relativity (i.e. as a flow of proper time in the four dimensional space-time), time flows abstractly in quantum mechanics (i.e. as a flow in the space of observables of the system). We then ask the same question in quantum gravity, in the light of the thermal time hypothesis of Connes and Rovelli. The latter proposes to answer the question of time in quantum gravity (or at least one of its many aspects), by postulating that time is a state dependent notion. This means that one is able to make a notion of time-as-an-abstract-flow - that we call the thermal time - emerge from the knowledge of both: 1) the algebra of observables of the physical system under investigation, 2) a state of thermal equilibrium of this system. Formally, this thermal time is similar to the abstract flow of time in quantum mechanics, but we show in various examples that it may have a concrete implementation either as a geometrical flow, or as a geometrical flow combined with a non-geometric action. This indicates that in quantum gravity, time may well still be "something that flows" at some abstract algebraic level, but this does not necessarily imply that time is always and only "something that flows" at the geometric level.

gr-qc↗
arXiv2018

Early publications about nonzero cosmological constant

In 2011 the Nobel Prize in Physics was awarded for the 1998 discovery of the nonzero cosmological constant. This discovery is very important and surely worth to receive the Nobel Prize. However, years earlier several papers had been published (Paal, Horvath, & Lukacs 1992; Holba et al. 1992, Holba et al. 1994) about a very similar discovery from observational data.

astro-ph.CO↗
arXiv2019

A conjecture concerning determinism, reduction, and measurement in quantum mechanics

Determinism is established in quantum mechanics by tracing the probabilities in the Born rules back to the absolute (overall) phase constants of the wave functions and recognizing these phase constants as pseudorandom numbers. The reduction process (collapse) is independent of measurement. It occurs when two wavepackets overlap in ordinary space and satisfy a certain criterion, which depends on the phase constants of both wavepackets. Reduction means contraction of the wavepackets to the place of overlap. The measurement apparatus fans out the incoming wavepacket into spatially separated eigenpackets of the chosen observable. When one of these eigenpackets together with a wavepacket located in the apparatus satisfy the criterion, the reduction associates the place of contraction with an eigenvalue of the observable. The theory is nonlocal and contextual.

quant-ph↗
arXiv2012

The Universe, the Cold War, and Dialectical Materialism

Ideological considerations have always influenced science, but rarely as directly and massively as in the Soviet Union during the early Cold War period. Cosmology was among the sciences that became heavily politicized and forced to conform to the doctrines of Marxism-Leninism. This field of science developed entirely differently in the Communist countries than in the West, in large measure because of political pressure. Certain cosmological models, in particular of the big bang type, were declared pseudo-scientific and idealistic because they implied a cosmic creation, a concept which was taken to be religious. The result of the ideological pressure was not an independent Soviet cosmology, but that astronomers and physicists abandoned cosmological research in the Western sense. Only in the 1960s did this situation change, and cosmology in the Soviet Union began to flourish. The paper examines the relationship between science and political ideology in the case of the Soviet Union from about 1947 to 1963, and it also relates this case to the later one in the People's Republic of China.

physics.hist-ph↗
arXiv2014

Gauge Theory of Gravity and Spacetime

The advent of general relativity settled it once and for all that a theory of spacetime is inextricably linked to the theory of gravity. From the point of view of the gauge principle of Weyl and Yang-Mills-Utiyama, it became manifest around the 1960s (Sciama--Kibble) that gravity is closely related to the Poincare group acting in Minkowski space. The gauging of this external group induces a Riemann-Cartan geometry on spacetime. If one generalizes the gauge group of gravity, one finds still more involved spacetime geometries. If one specializes it to the translation group, one finds a specific Riemann-Cartan geometry with teleparallelism (Weitzenbock geometry).

gr-qc↗
arXiv2012

A Long View of Particle Physics

2011 marked the hundredth anniversary both of the famous Solvay conferences, and of the Geiger-Marsden experiment that launched the modern understanding of subatomic structure. I was asked to survey the status and prospects of particle physics for the anniversary Solvay conference, with appropriate perspective. This is my attempt.

hep-th↗
arXiv2012

Do we have a Theory of Early Universe Cosmology?

The inflationary scenario has become the paradigm of early universe cosmology, and - in conjuction with ideas from superstring theory - has led to speculations about an "inflationary multiverse". From a point of view of phenomenology, the inflationary universe scenario has been very successful. However, the scenario suffers from some conceptual problems, and thus it does not (yet) have the status of a solid theory. There are alternative ideas for the evolution of the very early universe which do not involve inflation but which agree with most current cosmological observations as well as inflation does. In this lecture I will outline the conceptual problems of inflation and introduce two alternative pictures - the "matter bounce" and "string gas cosmology", the latter being a realization of the "emergent universe" scenario based on some key principles of superstring theory. I will demonstrate that these two alternative pictures lead to the same predictions for the power spectrum of the observed large-scale structure and for the angular power spectrum of cosmic microwave background anisotropies as the inflationary scenario, and I will mention predictions for future observations with which the three scenarios can be observationally teased apart.

astro-ph.CO↗
arXiv2013

In defence of non-ontic accounts of quantum states

The paper discusses objections against non-hidden variable versions of the epistemic conception of quantum states - the view that quantum states do not describe the properties of quantum systems but reflect, in some way to be specified, the epistemic conditions of agents assigning them. In the first half of the paper, the main motivation for the epistemic conception of quantum states is sketched, and a version of it is outlined, which combines ideas from an earlier study of it [Friederich 2011] with elements of Richard Healey's recent pragmatist interpretation of quantum theory [Healey 2012]. In the second half, various objections against epistemic accounts of quantum states are discussed in detail, which are based on criticisms found in the literature. Possible answers by the version outlined here are compared with answers from the quantum Bayesian point of view, which is at present the most discussed version of the epistemic conception of quantum states.

quant-ph↗
arXiv2013

Epistemological-Scientific Realism and the Onto-Relationship of Inferentially Justified and Non-Inferentially Justified Beliefs

The traditional concept of knowledge is a justified true belief. The bulk of contemporary epistemology has focused primarily on that task of justification. Truth seems to be a quite obvious criterion-does the belief in question correspond to reality? My contention is that the aspect of ontology is far too separated from epistemology. This onto-relationship between reality and beliefs require the epistemic method of epistemological realism. This is not to diminish the task of justification. I will then discuss the role of inference from the onto-relationships of free invention and discovery and whether it is best suited for a foundationalist or coherentist model within a theistic context.

physics.hist-ph↗
arXiv2012

Geometry and Astronomy: Pre-Einstein Speculations of Non-Euclidean Space

The recognition that physical space (or space-time) is curved is a product of the general theory of relativity, such as dramatically shown by the 1919 solar eclipse measurements. However, the mathematical possibility of non-Euclidean geometries was recognized by Gauss more than a century earlier, and during the nineteenth century mathematicians developed the pioneering ideas of Gauss, Lobachevsky, Bolyai and Riemann into an elaborate branch of generalized geometry. Did the unimaginative physicists and astronomers ignore the new geometries? Were they considered to be of mathematical interest only until Einstein entered the scene? This paper examines in detail the attempts in the period from about 1830 to 1910 to establish links between non-Euclidean geometry and the physical and astronomical sciences, including attempts to find observational evidence for curved space. Although there were but few contributors to "non-Euclidean astronomy," there were more than usually supposed. The paper looks in particular on a work of 1872 in which the Leipzig physicist K. F. Zoellner argued that the universe is closed in accordance with Riemann's geometry.

physics.hist-ph↗
arXiv2012

Notes on the page proof and publication of "Schallausbreitung in teilweise dissoziierten Gasen" by A. Einstein

Recently, the page-proof, with corrections, of Einstein's 1920 publication on the "Propagation of Sound in Partly Dissociated Gases" was discovered in Leiden. The last two pages of the proof are crossed out and replaced by a sheet in Einstein's handwriting. In these notes, I briefly address the following two questions: A) Concerning the page proof, what is the difference between the contents of the crossed-out pages and the new page? B) Concerning the publication, are Eqs. (18,21,22) correct?

physics.hist-ph↗
arXiv2012

Lomonosov's Discovery of Venus Atmosphere in 1761: English Translation of Original Publication with Commentaries

Key figure of Russian Enlightenment, polymath Mikhail Vasilievich Lomonosov (1711-1765) had discovered atmosphere of Venus during its transit over the Sun's disc in 1761. This paper contains the first full English translation of his report (originally published in Russian in July of 1761 and in German in August of the same year), commentaries and extensive bibliography.

physics.hist-ph↗
arXiv2014

Characterizing Entropy in Statistical Physics and in Quantum Information Theory

A new axiomatic characterization with a minimum of conditions for entropy as a function on the set of states in quantum mechanics is presented. Traditionally unspoken assumptions are unveiled and replaced by proven consequences of the axioms. First the Boltzmann-Planck formula is derived. Building on this formula, using the Law of Large Numbers - a basic theorem of probability theory - the von Neumann formula is deduced. Axioms used in older theories on the foundations are now derived facts.

math-ph↗
arXiv2012

Psychophysical Interpretation of Quantum theory

It is shown that the formalism of quantum theory naturally incorporates the psychophysical parallelism and thereby interprets itself, if the subjective aspects are taken as equal partners alongside the objective aspects as determinants of Reality as a Whole. The inevitable interplay of the subject (observer) and the object (observed) in making up Reality is brought out succinctly through a comprehensive psychophysical interpretation which includes in its bosom the truths of many of the major interpretations proposed so far as essential ingredients. At the heart of this novel approach lies the interpretation of the complex conjugate quantities such as the conjugate wave function Ψ*(r, t), the bra vector <Ψ|, and the adjoint operator A† etc. as representing the subjective counterparts of the corresponding objective aspects represented by the wave function Ψ(r, t), the ket vector |Ψ>, and the observable A etc. respectively. This brings out the psycho-physical parallelism lying hidden in the quantum mechanical formalism in a quite straightforward manner. The measurement process is shown to be a two-step process comprising objective interaction through the retarded waves and subjective observation leading to rise of knowledge through the advanced waves.

quant-ph↗
arXiv2012

The fate of presentism in modern physics

There has been a recent spate of essays defending presentism, the view in the metaphysics of time according to which all and only present events or entities exist. What is particularly striking about this resurgence is that it takes place on the background of the significant pressure exerted on the position by the relativity of simultaneity asserted in special relativity, and yet in several cases invokes modern physics for support. I classify the presentist arguments into a two by two matrix depending on whether they take a compatibilist or incompatibilist stance with respect to both special relativity in particular and modern physics in general. I then review and evaluate what I take to be some of the most forceful and intriguing presentist arguments turning on modern physics. Although nothing of what I will say eventuates its categorical demise, I hope to show that whatever presentism remains compatible with empirical facts and our best physics is metaphysically repugnant.

physics.hist-ph↗
arXiv2012

Time in quantum gravity

Quantum gravity--the marriage of quantum physics with general relativity--is bound to contain deep and important lessons for the nature of physical time. Some of these lessons shall be canvassed here, particularly as they arise from quantum general relativity and string theory and related approaches. Of particular interest is the question of which of the intuitive aspects of time will turn out to be fundamental, and which 'emergent' in some sense.

physics.hist-ph↗