Les observations de Galilée quant aux propriétés intensives sont un exemple de la « puissance du rationnel », et un indicateur fondamental de la réalité physique. D’un bout à l’autre de son travail, Galilée trace des chemins de l’intensif vers l’extensif, ce qui incite Leibniz à élaborer une « science des intensités », créant ainsi de nouveaux concepts liés aux sensations comme fondements de l’expérimentation. L’idée de virtualité, que Descartes voulait bannir de sa philosophie naturelle, est ainsi justifiée, le principe (...) des vitesses virtuelles ayant été anticipé par Galilée. Le fameux texte de L’Essayeur sur les qualités sensibles est un bon exemple d’une « expérience de pensée » qui implique le rejet des formes substantielles. La principale portée d’une telle expérience « mentale » n’était pas de réduire les sensations concrètes à certaines idéalités abstraites, mais d’anticiper des définitions génétiques des objets physiques, selon le modèle constitutif des mathématiques. La puissance du rationnel est une invitation à relire dans une nouvelle perspective la prose de Galilée. (shrink)

The most reliable source for a reconstruction of Galileo's progress toward a science of motion is the series of undated fragmentary notes on that subject preserved in Codex A of the Galilean manuscripts at Florence. A gathering of such fragments was published by Favaro in the National Edition of Galileo's works, following the Discorsi. The more sophisticated fragments are clearly associated with the composition of that work, and show a definite and consistent understanding of acceleration. Eliminating those, it will be (...) found that the earlier notes fall into recognizable groups. First, there are some that refer to “moment of gravity”, or to the impetus of a body along a line of descent, and are associated with the discussion of inclined planes in De motu. Second, some refer to descent along arcs and chords of circles, associated with Galileo's letter of 29 November 1602 to Guido Ubaldo. These first two groups of notes do not explicitly refer to accelerated motion, and should not be assumed to do so implicity, where such an assumption can be avoided. (shrink)

We obtained an exact solution for a uniformly accelerated Unruh–DeWitt detector interacting with a massless scalar field in (3 + 1) dimensions which enables us to study the entire evolution of the total system, from the initial transient to late-time steady state. We find that the conventional transition probability of the detector from its initial ground state to excited states, as derived from time-dependent perturbation theory over an infinitely long duration of interaction, is valid only in the transient stage and (...) is invalid for cases with proper acceleration smaller than the damping constant. We also found that, unlike in (1 + 1)D results, the (3 + 1)D uniformly accelerated Unruh– DeWitt detector in a steady state does emit a positive radiated power of quantum nature at late-times, but it is not connected to the thermal radiance experienced by the detector in the Unruh effect proper. (shrink)

We argue that purely local experiments can distinguish a stationary charged particle in a static gravitational field from an accelerated particle in (gravity-free) Minkowski space. Some common arguments to the contrary are analyzed and found to rest on a misidentification of “energy.”.

We present a stochastic theory for the nonequilibriurn dynamics of charges moving in a quantum scalar field based on the worldline influence functional and the close-time-path (CTP or in-in) coarse-grained effective action method. We summarize (1) the steps leading to a derivation of a modified Abraham-Lorentz-Dirac equation whose solutions describe a causal semiclassical theory free of runaway solutions and without pre-acceleration patholigies, and (2) the transformation to a stochastic effective action, which generates Abraham-Lorentz-Dirac-Langevin equations depicting the fluctuations of a particle’s (...) worldline around its semiclassical trajectory. We point out the misconceptions in trying to directly relate radiation reaction to vacuum fluctuations, and discuss how, in the framework that we have developed, an array of phenomena, from classical radiation and radiation reaction to the Unruh effect, are interrelated to each other as manifestations at the classical, stochastic and quantum levels. Using this method we give a derivation of the Unruh effect for the spacetime worldline coordinates of an accelerating charge. Our stochastic particle-field model, which was inspired by earlier work in cosmological backreaction, can be used as an analog to the black hole backreaction problem describing the stochastic dynamics of a black hole event horizon. (shrink)

We investigate in detail the electromagnetic fields of a uniformly accelerated charge, in order to ascertain whether such a charge does ‘emit’ radiation, especially in view of the Poynting flow computed at large distances and taken as an evidence of radiation emitted by the charge. In this context, certain important aspects of the fields need to be taken into account. First and foremost is the fact that in the case of a uniformly accelerated charge, one cannot ignore the velocity fields. (...) This then leads to other equally vital points. The net field energy turns out to be exactly the same as that of a non-accelerated charge having a uniform velocity equal to the instantaneous velocity of the uniformly accelerated charge. Further, the Poynting vector, seen with respect to the ’present’ location of the uniformly accelerated charge, during the deceleration phase, possesses everywhere a radial component pointing inward toward the charge, becoming nil when the charge becomes momentarily stationary, and during the acceleration phase, points away from the charge position. Last, but not least, when the leading spherical front of the relativistically beamed Poynting flux, advances forward at a large time t to a far-off distance \, the charge too is not lagging far behind. In fact, these relativistically beamed fields, increasingly resemble fields of a charge moving in an inertial frame with a uniform velocity \, with a convective flow of fields in that frame along with the movement of the charge. There is no other Poynting flow in the far-zones that could be termed as radiation emitted by the charge which, in turn, is fully consistent with the absence of radiation reaction and is also fully conversant with the strong principle of equivalence. (shrink)

Maxwell's equations are established for the free electromagnetic field in two-dimensional space-times. In Minkowski space they are solved under the boundary conditions set by a pair of uniformly accelerated “plates.” With the help of these solutions we determine the regularized energy-momentum tensor of the canonically quantized electromagnetic field at the position of one of the “plates.” Thereby (as a new result) we arrive at a Casimir effect in an accelerated reference frame.

Yanick Laverdière Le problème de l’accélération des mouvements naturels est un aspect de la physique médiévale qui reçoit une attention récurrente de l’historiographie depuis les travaux pionniers de Pierre Duhem. La position de Nicole Oresme à ce propos a été maintes fois survolée par les spécialistes, puis écartée des discussions au profit de théories contemporaines. L’objectif de cet article est d’approfondir la démarche mise en place par Oresme dans deux de ses commentaires sur le traité Du ciel pour résoudre la (...) question de l’accélération des mouvements naturels. S’il est vrai que le penseur français s’accorde sur plusieurs points avec la position de ses collègues parisiens, notamment à propos de la théorie de l’impetus, son approche se distingue par l’attention qu’il porte à l’accélération du mouvement plutôt qu’à la vélocité du mobile. (shrink)

We study the response of a uniformly accelerated model particle detector in a spacetime with compact spatial sections. The basic thermal character of the response re-emerges, in spite of the fact that the spacetime does not possess event horizons. Our model also permits a study of detector response to twisted field states.

Cet article aborde la question du temps dans l’institution judiciaire en prenant pour objet le contentieux familial. En considérant la dimension temporelle du règlement des conflits qui émergent lors des ruptures d’union, il met en évidence le changement radical de la vision du temps qui a touché le monde de la justice civile dans les dernières décennies. Le mouvement d’accélération qui touche l’ensemble de l’institution judiciaire se trouve redoublé dans ce champ par l’urgence qu’impose la réaction face à un (...) contentieux de masse : il s’agit de répondre sans délais aux conflits familiaux, selon des modalités adaptées aux besoins des intéressés. L’étude s’appuie sur une enquête réalisée dans cinq juridictions, en France et en Belgique. Dans ces deux pays, les dernières réformes intervenues ont eu pour projet de hâter les procédures de divorce. Dans la pratique, différentes modalités de l’accélération du traitement judiciaire sont observées. En France, le juge aux affaires familiales est un acteur central qui traite l’ensemble des ruptures de couple soumises à la justice. Les JAF font tout pour accélérer les décisions, en s’appuyant autant que faire se peut sur l’accord des parties et en cherchant à contrôler les avocats. En Belgique, l’accélération est particulièrement apparente s’agissant du procès en divorce, mais les décisions sur les effets accessoires de la séparation sont renvoyées à différentes instances ayant leur propre temporalité. Par-delà ces différences, la comparaison suggère que l’accélération du traitement du contentieux de la famille résulte de la coprésence des deux tendances majeures observées, la managérialisation de la justice et le renvoi des décisions relatives à la famille vers les intéressés eux-mêmes. L’accélération du traitement judiciaire du divorce n’est cependant pas sans conséquence : en particulier, elle rend plus apparente la disjonction du temps du procès et de celui que vivent les conjoints en rupture. (shrink)

Within Special Relativity accelerated systems can be described as those systems in which standard clock synchronism does not hold. Therefore, the ε -generalized Lorentz equations derived by Winnie are the equations governing accelerated systems. The ε -generalized equation for time is used in analyzing two cases of the clock paradox: (1) the case in which a clock travels in a straight line, stops, and returns, and (2) the case in which a clock travels with uniform velocity in a circular path. (...) The treatment of case (1) of the paradox within this generalization of the Special Theory is compared with Møller's treatment of it within the General Theory. (shrink)

We investigate a possible form of Schrödinger’s equation as it appears to moving observers. It is shown that, in this framework, accelerated motion requires fictitious potentials to be added to the original equation. The gauge invariance of the formulation is established. The example of accelerated Euclidean transformations is treated explicitly, which contain Galilean transformations as special cases. The relationship between an acceleration and a gravitational field is found to be compatible with the picture of the ‘Einstein elevator’. The physical effects (...) of an acceleration are illustrated by the problem of the uniformly-accelerated harmonic oscillator. (shrink)

A linear wave field in its Minkowski ground state is analyzed heuristically by two observers, one inertial, the other accelerating in a linear and uniform way. Relative to the accelerated observer, the zero-point oscillations of each Minkowski plane wave mode have an unusual Fourier spectrum. Its intensity is (i) the same for all plane wave modes, (ii) isotropic, and (iii) that of a thermal ambience (relative to the accelerated frame). The temperature of this ambience is given by the Davies-Unruh formula (...) kT=(ħ/2π)(g/c). The existence of this ambience is incompatible with the requirement that the laws of nature be formulated in terms of tensors. (shrink)

This paper starts from the assumption that linguistic diversity, and more generally, cultural diversity, are intrinsically good. I will look at their opposites, linguistic and cultural poverty, and the current tendencies towards the latter within the globalization process. I will also briefly explore the relationship between human rights and cultural diversity, which may be viewed as somewhat problematic, but the emphasis will be on what I consider the essential aspect of that relationship, namely, the mutually reinforcing relationship be-tween rights and (...) diversity, and between their opposites, human rights violations and cultural uniformity . In this context, the issue of legislative protection and promotion of cultural diversity will be investigated from a global perspective. Finally, I wish to assess the roles of Africa and of Africanicity with regard to these issues. (shrink)

In the framework of classical electromagnetism, a charge however accelerated with respect to an inertial frame radiates energy, in any circumstance. Regarding the energy as made of photons, the hypothesis is here introduced that the emission of a photon is only possible as a result of a change of the energy of the charge, which requires an energy-work exchange with the accelerating field. On such an hypothesis an elementary impulsive-dissipative model for the photon emission is constructed, in the framework of (...) special relativity, in which no energy radiation is emitted from a charge in a central Coulomb field uniformly describing a circular orbit. (shrink)

Une théorie physique s'appuie généralement sur un modèle physique. Un modèle habituel est formé par des corps en mouvements rectilignes uniformes. Il est tout aussi légitime de considérer un autre modèle formé par des corps en mouvements circulaires uniformes. Les conclusions concernant la simultanéité, l'écoulement du temps, obtenues à partir du premier modèle, ne semblent pas pouvoir être étendues au second.A physical theory is generally based on a physical model. One ordinary model consists of bodies in uniform rectilinear motion. It (...) is just as legitimate to consider another model consisting ofbodi.es in uniform circular motion. It seems that the conclusions on simultaneity obtained from the uniform rectilinear model cannot be extended to the uniform circular model. (shrink)

Classical electron theory with classical electromagnetic zero-point radiation (stochastic electrodynamics) is the classical theory which most closely approximates quantum electrodynamics. Indeed, in inertial frames, there is a general connection between classical field theories with classical zero-point radiation and quantum field theories. However, this connection does not extend to noninertial frames where the time parameter is not a geodesic coordinate. Quantum field theory applies the canonical quantization procedure (depending on the local time coordinate) to a mirror-walled box, and, in general, each (...) non-inertial coordinate frame has its own vacuum state. In particular, there is a distinction between the “Minkowski vacuum” for a box at rest in an inertial frame and a “Rindler vacuum” for an accelerating box which has fixed spatial coordinates in an (accelerating) Rindler frame. In complete contrast, the spectrum of random classical zero-point radiation is based upon symmetry principles of relativistic spacetime; in empty space, the correlation functions depend upon only the geodesic separations (and their coordinate derivatives) between the spacetime points. The behavior of classical zero-point radiation in a noninertial frame is found by tensor transformations and still depends only upon the geodesic separations, now expressed in the non-inertial coordinates. It makes no difference whether a box of classical zero-point radiation is gradually or suddenly set into uniform acceleration; the radiation in the interior retains the same correlation function except for small end-point (Casimir) corrections. Thus in classical theory where zero-point radiation is defined in terms of geodesic separations, there is nothing physically comparable to the quantum distinction between the Minkowski and Rindler vacuum states. It is also noted that relativistic classical systems with internal potential energy must be spatially extended and can not be point systems. The classical analysis gives no grounds for the “heating effects of acceleration through the vacuum” which appear in the literature of quantum field theory. Thus this distinction provides (in principle) an experimental test to distinguish the two theories. (shrink)

We discuss the intertwined topics of Fulling non‐uniqueness and the Unruh effect. The Fulling quantization, which is in some sense the natural one for an observer uniformly accelerated through Minkowski spacetime to adopt, is often heralded as a quantization of the Klein‐Gordon field which is both physically relevant and unitarily inequivalent to the standard Minkowski quantization. We argue that the Fulling and Minkowski quantizations do not constitute a satisfactory example of physically relevant, unitarily inequivalent quantizations, and indicate what it would (...) take to settle the open question of whether a satisfactory example exists. A popular gloss on the Unruh effect has it that an observer uniformly accelerated through the Minkowski vacuum experiences a thermal flux of Rindler quanta. Taking the Unruh effect, so glossed, to establish that the notion of particle must be relativized to a reference frame, some would use it to demote the particle concept from fundamental status. We explain why technical results do not support the popular gloss and why the attempted demotion of the particle concept is both unsuccessful and unnecessary. Fulling non‐uniqueness and the Unruh effect merit attention despite these negative verdicts because they provide excellent vehicles for illustrating key concepts of quantum field theory and for probing foundational issues of considerable philosophical interest. (shrink)

We discuss the intertwined topics of Fulling non-uniqueness and the Unruh effect. The Fulling quantization, which is in some sense the natural one for an observer uniformly accelerated through Minkowski spacetime to adopt, is often heralded as a quantization of the Klein-Gordon field which is both physically relevant and unitarily inequivalent to the standard Minkowski quantization. We argue that the Fulling and Minkowski quantizations do not constitute a satisfactory example of physically relevant, unitarily inequivalent quantizations, and indicate what it would (...) take to settle the open question of whether a satisfactory example exists. A popular gloss on the Unruh effect has it that an observer uniformly accelerated through the Minkowski vacuum experiences a thermal flux of Rindler quanta. Taking the Unruh effect, so glossed, to establish that the notion of particle must be relativized to a reference frame, some would use it to demote the particle concept from fundamental status. We explain why technical results do not support the popular gloss and why the attempted demotion of the particle concept is both unsuccessful and unnecessary. Fulling non-uniqueness and the Unruh effect merit attention despite these negative verdicts because they provide excellent vehicles for illustrating key concepts of quantum field theory and for probing foundational issues of considerable philosophical interest. (shrink)

A “frame of reference” is a standard relative to which motion and rest may be measured; any set of points or objects that are at rest relative to one another enables us, in principle, to describe the relative motions of bodies. A frame of reference is therefore a purely kinematical device, for the geometrical description of motion without regard to the masses or forces involved. A dynamical account of motion leads to the idea of an “inertial frame,” or a reference (...) frame relative to which motions have distinguished dynamical properties. For that reason an inertial frame has to be understood as a spatial reference frame together with some means of measuring time, so that uniform motions can be distinguished from accelerated motions. The laws of Newtonian dynamics provide a simple definition: an inertial frame is a reference-frame with a time-scale, relative to which the motion of a body not subject to forces is always rectilinear and uniform, accelerations are always proportional to and in the direction of applied forces, and applied forces are always met with equal and opposite reactions. It follows that, in an inertial frame, the center of mass of a system of bodies is always at rest or in uniform motion. It also follows that any other frame of reference moving uniformly relative to an inertial frame is also an inertial frame. For example, in Newtonian celestial mechanics, taking the “fixed stars” as a frame of reference, we can determine an inertial frame whose center is the center of mass of the solar system; relative to this frame, every acceleration of every planet can be accounted for as a gravitational interaction with some other planet in accord with Newton 's laws of motion. (shrink)

By a simple revision of Newton's diagram for Proposition 6 of the third edition of the Principia, one can see directly how the mathematics of uniform circular motion have been employed to solve the Kepler problem of elliptical planetary motion in Proposition 11. Newton strove initially to build his dynamics on the linear kinematics of Galileo; and, in this utilization of uniformly accelerated linear motion to solve more complicated problems, he can be seen as revolutionary. But he could not escape (...) completely from the coils of celestial circularity, and in his utilization of uniform circular motion to solve problems of elliptical motion, he can be seen as reactionary. The key to understanding Newton's mature dynamics resides in the discussion of the alternate dynamics ratio, as presented here in section six. (shrink)

Ptolemy presents only one argument for the eccentricity in his models of the superior planets, while each one of them has two eccentricities: one for center of the uniform motion, the other for the center of the constant distance. To take into account the first eccentricity, he introduces the equant point, but he provides no argument for the eccentricity of the center of the deferent. Why is the second eccentricity different from the first one? The 13 th century astronomer Quṭb (...) al-Dīn al-Shīrāzī, a member of the famous school of Marāgha, who was interested in this problem, suggests the “retrograde arcs” as the empirical origin of the second eccentricity and develops an argument to justify this conjecture. Although his argument is not without difficulty, his suggestion is in line with the suggestions made by some historians of astronomy in recent decades. Résumé Ptolémée ne donne qu'un seul argument pour expliquer dans son système l'excentricité des planètes supérieures, alors que chacune d'elles a deux excentricités: l'une par rapport au centre du mouvement uniforme, l'autre par rapport au centre de la distance constante. Pour rendre compte de la première excentricité, il introduit le point équant, mais il ne donne en revanche aucun argument pour l'excentricité par rapport au centre du cercle déférent. Or, pourquoi la seconde excentricité est-elle différente de la première? Quṭb al-Dīn al-Shīrāzī, astronome du xiii e siècle membre de l'école de Marāgha, qui s'est intéressé à cette question, a fait l'hypothèse que les “arcs de rétrogradation” constituent l'origine empirique de cette seconde excentricité. Bien que l'argument sur lequel il appuie cette hypothèse ne soit pas exempt de difficultés, sa suggestion rejoint celles faites par des historiens de l'astronomie durant les dernières décennies. (shrink)

The differential aging effect is shown to be valid in any physically reasonable extension of the special theory of relativity which includes a description of accelerating observers. Einstein's controversial assumption—the clock hypothesis—is avoided. Instead, it is sufficient to assume accessibility—that it is possible to travel from one inertial observer to another and then return to the first in a reasonable manner. Since Minkowski space-time displays this accessibility property, there must be an error in Sachs's quaternion development of general relativity. No (...) assumptions concerning measurements—proper time—of accelerating observers are necessary, nor are assumptions concerning special features of their motion—uniform acceleration. (shrink)

Although the laws of thermodynamics are well established for black hole horizons, much less has been said in the literature to support the extension of these laws to more general settings such as an asymptotic de Sitter horizon or a Rindler horizon (the event horizon of an asymptotic uniformly accelerated observer). In the present paper we review the results that have been previously established and argue that the laws of black hole thermodynamics, as well as their underlying statistical mechanical content, (...) extend quite generally to what we call here “causal horizons.” The root of this generalization is the local notion of horizon entropy density. (shrink)

The work of Newstein is now so familiar to us, thanks to Professor Stachel's efforts, that it bears only the briefest recapitulation. Sometime after 1880 but before the advent of general relativity, Newstein brooded on the equality of inertial and gravitational mass. Through an ingenious thought experiment — the Newstein elevator — he hit upon the idea of an essential unity of gravitation and inertia. This was expressed in the indistinguishability of the effects of acceleration in a uniformly accelerated..

The work of Newstein is now so familiar to us, thanks to Professor Stachel's efforts, that it bears only the briefest recapitulation. Sometime after 1880 but before the advent of general relativity, Newstein brooded on the equality of inertial and gravitational mass. Through an ingenious thought experiment — the Newstein elevator — he hit upon the idea of an essential unity of gravitation and inertia. This was expressed in the indistinguishability of the effects of acceleration in a uniformly accelerated..

Einstein's gravitational field equations in empty space outside a massive plane with infinite extension give a class of solutions describing a field with flat spacetime giving neutral, freely moving particles an acceleration. This points to the necessity of defining the concept “gravitational field” not simply by the nonvanishing of the Riemann curvature tensor, but by the nonvanishing of certain elements of the Christoffel symbols, called the physical elements, or the nonvanishing of the Riemann curvature tensor. The tidal component of a (...) gravitational field is associated with a nonvanishing Riemann tensor, while the nontidal components are associated with nonvanishing physical elements of the Christoffel symbols. Spacetime in a nontidal gravitational field is flat. Such a field may be separated into a homogeneous and a rotational component. In order to exhibit the physical significance of these components in relation to their transformation properties, coordinate transformations inside a given reference frame are discussed. The mentioned solutions of Einstein's field equations lead to a metric identical to that obtained as a result of a transformation from an inertial frame to a uniformly accelerated frame. The validity of the strong principle of equivalence in extended regions for nontidal gravitational fields is made clear. An exact calculation of the weight of an extended body in a uniform gravitational field, from a global point of view, gives the result that its weight is independent of the position of the scale on the body. (shrink)

Two problems have long been confused with each other: the gravitational redshift as discussed by the equivalence principle; and the Doppler shift observed by a detector which moves with constant proper acceleration away from a stationary source. We here distinguish these two problems and give for the first time a solution of the former which is ‘exact’ within the context of the equivalence principle in a sense discussed in the paper. The equivalence principle leads to transformations between flat spacetimes. These (...) are analyzed, and a generalized Lorentz transformation is proposed which covers transformations from inertial to uniformly accelerated frames of reference. (shrink)

With the help of syncretiсs as a new philosophical logic, the philosophy of carriers, the theory of similarity and the theory of Infinite Hierarchical Nesting of Matter, the problems of modern physics are analyzed. We consider the classical and relativistic mechanics, the special and general theories of relativity, the theory of electromagnetic and gravitational fields, of weak and strong interactions. The goal is axiomatization of these theories, building models of elementary particles and of their interactions with each other. The main (...) obtained results are: description of the electrokinetic theory of the origin of magnetic fields in cosmic bodies; calculation of metric in the uniformly accelerated reference frame; the axiomatic construction of electrodynamics, Lorentz invariant (LITG) and covariant theories of gravitation (CTG); comparing CTG with the general theory of relativity and with the results of gravitational experiments. Among other results – the analysis of the properties of ether as the medium responsible for transfer of electromagnetic and gravitational waves, and derivation of the formula for entropy in a tensor form. For students and researchers, as well as for those interested in physical and philosophical problems. (shrink)

The Thomas precession of relativity physics gives rise to important isometries in hyperbolic geometry that expose analogies with Euclidean geometry. These, in turn, suggest our bifurcation approach to hyperbolic geometry, according to which Euclidean geometry bifurcates into two mutually dual branches of hyperbolic geometry in its transition to non-Euclidean geometry. One of the two resulting branches turns out to be the standard hyperbolic geometry of Bolyai and Lobachevsky. The corresponding bifurcation of Newtonian mechanics in the transition to Einsteinian mechanics indicates (...) that there are two, mutually dual, kinds of uniform accelerations. Furthermore, while current hyperbolic geometry “does not use the notion of vector at all” (I. M. Yaglom, Geometric Transformations III, p. 135, trans. by Abe Shenitzer, Random House, New York, 1973), our bifurcation approach exposes the elusive hyperbolic vectors, that we call gyrovectors. (shrink)

We investigate how a uniformly rotating frame is defined as the rest frame of an observer rotating with constant angular velocity Ω around the z axis of an inertial frame. Assuming this frame to be a Lorentz one, we second quantize a free massless scalar field in the rotating frame and obtain that creation-annihilation operators of the field are not the same as those of an inertial frame. This leads to a new vacuum state—a rotating vacuum. After this, introducing an (...) apparatus device coupled linearly with the field, we obtain that there is a strong correlation between the number of Trocheries-Takeno particles (in a given state) obtained via canonical quantization and the response function of the rotating detector. Finally, we analyze polarization effects in circular accelerators in the proper frame of the electron, making a connection with the inertial frame point of view. (shrink)

Après avoir restitué le mouvement, en vertu duquel le philosophe expose dans Le Principe responsabilité une éthique qui s’applique à la vie et en provient, cet ouvrage justifie le tournant médical opéré par Hans Jonas dans Technik, Medizin und Ethik. Cela ouvre une réflexion en quatre temps. En premier lieu, il faut faire un diagnostic éthique du rôle de la technique au sein de la recherche scientifique. En second lieu, il faut se demander si l’accélération de nos progrès technologiques (...) ne modifie pas la signification de la médecine, ce qui requiert une interrogation sur les valeurs qui guident cette pratique. Il apparaît alors que ce sont les conditions les plus essentielles de notre être-au-monde, la naissance et la mort, qui risquent d’être altérées par l’agir technologique. Dans un troisième et quatrième moment, il faudra donc se pencher sur la manière dont la procréation médicale assistée et, plus fondamentalement encore, l’ingénierie future pourraient modifier le sens de la venue au monde des enfants. Outre la natalité, la mortalité est le second pôle qui détermine les conditions essentielles de la présence au monde de l’homme. C’est la raison pour laquelle, dans un dernier temps, l’éthique doit également se pencher sur la manière dont des techniques, apparues dans la seconde moitié du XXe siècle, peuvent bouleverser notre façon de mourir. (shrink)

Mechanisms of visual prediction based on spatial extrapolation work only for targets moving at constant speed, but do not easily accommodate accelerating or decelerating motion. We argue that mechanisms based on temporal extrapolation deal with both uniform and non-uniform motion. We provide behavioural examples from interception of falling objects and suggest possible neurophysiological substrates of time extrapolation.

La photographie, dès sa naissance, entretint des relations tout à la fois difficiles et opaques avec l’art. En France notamment, et cela jusqu’à l’aube du xxe siècle, nombre d’écrivains et artistes se liguèrent pour affirmer qu’entre les deux, seuls prévalaient des rapports de subordination de la première au second. L’intérêt et la possible reconnaissance de la photographie en tant qu’art ne se manifesta donc qu’assez tardivement, une fois marginalisées les productions du premier « pictorialisme » visant à aligner l’esthétique du (...) nouveau médium sur celle de la peinture. Au cours de la première moitié du xxe siècle, en partie grâce au surréalisme, la photographie entra progressivement dans le champ de l’art avant qu’au cours des années 1970, un emballement se produise, autorisant des légitimations rétrospectives rehaussées de justifications théoriques et esthétiques. L’entrée en scène du numérique contribua à l’accélération de ce mouvement de fusion – absorption par l’art contemporain, dont il n’est pas inutile de se demander s’il n’est pas une autre manière de soumettre la photographie à une identité rétrécie et réductrice. (shrink)

Le livre de Borkenau, „Der Übergang vom feudalen zum bürgerlichen Weltbild“ développe une nouvelle théorie de la naissance de la pensée moderne. Il s’attache à rechercher l’origine, moins de telles ou telles idées particulières que des concepts fondamentaux et des méthodes de penser de l'époque moderne. Borkenau considère avant tout la représentation mécaniste du monde telle qu'elle a été fondée dans la philosophie de Descartes et de ses successeurs comme décisive pour la pensée moderne et il élucide ses conditions sociologiques.L'étude (...) de Grossmann part du livre de Borkenau qu'il soumet à la critique et il essaye d'indiquer de manière indépendante une meilleure voie qui mène à la compréhension de la formation de la pensée bourgeoise. Ses arguments se rapportent avant tout à deux groupes de problèmes. D'après Borkenau, c'est au début du xvne siècle que la conception mécaniste du monde l'a emporté sur la philosophie qualitative qui régnait auparavant. Cette interprétation est jugée par Grossmann comme une méconnaissance de l'histoire réelle des idées et des faits. L'origine des questions fondamentales de la mécanique doit être cherchée à la Renaissance et Léonard de Vinci est un de ses créateurs. Ces théories nouvelles, dégagées en grande partie de l'étude des machines de son temps, se sont développées par différentes voies jusqu'à Galilée et Descartes, dont les doctrines ne marquent donc pas le début de la pensée mécaniste.L'autre critique fondamentale est étroitement liée à celle-ci. Elle concerne l'explication que donne Borkenau de la représentation mécaniste. Si celle- ci a pris naissance au xvne siècle, la condition essentielle de cette réalisation doit donc s’être produite à peu près à cette époque. D'après Borkenau cette condition serait la diffusion des manufactures. Avec la division de l'activité artisane en activités uniformes non qualifiées à l'intérieur de la manufacture, serait né le concept d'un travail social abstrait. La décomposition du processus de travail en mouvements simples dans la manufacture aurait rendu comparables les heures de travail. Le calcul avec du travail abstrait constituerait la base de la représentation mécaniste du monde. Grossmann montre en s'appuyant sur Marx que le plus souvent il ne saurait être question de division de travail dans les manufactures, mais que, en règle générale, des artisans qualifiés travaillaient réunis dans un même local. Ce n’est pas le calcul avec les heures de travail, mais l'évolution du machinisme qui aurait été la cause immédiate de la mécanique scientifique. Cette genèse remonte sans doute à la Renaissance et a très peu à faire avec les manufactures qui ont été finalement refoulées par l'industrie des machines.Alors que Borkenau, lorsqu'il vient à parler du conditionnement social des philosophes et des savants, remonte surtout aux batailles des partis politiques, Grossmann ne voit dans les partis qu’un facteur de l'ensemble de la situation complexe, à partir de laquelle s'explique le mouvement des idées modernes. Une théorie suffisante de l'évolution de la pensée moderne implique qu'on tienne compte de la totalité des forces sociales.Franz Borkenau's book „The Transition from Feudal to Modern Thought“ („Der Übergang vom feudalen zum bürgerlichen Weltbild“), serves as background for Grossmann's study. The objective of this book was to trace the sociological origins of the mechanistic categories of modern thought as developed in the philosophy of Descartes and his successors. In the beginning of the 17th century, according to Borkenau, mechanistic thinking triumphed over mediaeval philosophy which emphasized qualitative, not quantitative considerations. This transition from mediaeval and feudal methods of thought to modern principles is the general theme of Borkenau's book, and is traced to the social changes of this time. According to this work, the essential economic change that marked the transition from mediaeval to modern times was the destruction of the handicraft system and the organization of labor under one roof and under one management. The roots of the change in thought are to be sought here. With the dismemberment of the handicraft system and the division of labor into relatively unskilled, uniform, and therefore comparable activities, the conception of abstract homogeneous social labor arises. The division of the labor process into simple, repeated movements permits a comparison of hours of labor. Calculation with such abstract social unities, according to Borkenau, was the source from which modern mechanistic thinking in general derived its origin.Grossmann, although he considers Borkenau’s work a valuable and important contribution, does not believe that the author has achieved his purpose. First of all, he contends that the period that Borkenau describes as the period of the triumph of modern thought over mediaeval should not be placed at the beginning of the 17th century, but in the Renaissance, and that not Descartes and Hobbes but Leonardo da Vinci was the initiator of modern thought. Leonardo's theories, evolved from a study of machines, were the source of the mechanistic categories that culminated in modern thought.If Borkenau’s conception as to the historical origin of these categories is incorrect in regard to time, Grossman claims it follows that it is incorrect also in regard to the social sources to which it is ascribed. In the beginning, the factory system did not involve a division of labor into comparable homogeneous processes, but in general only united skilled handicraftsmen under one roof. The development of machinery, not the calculation with abstract hours of labor, is the immediate source of modern scientific mechanics. This goes back to the Renaissance and has relatively little to do with the original factory system that was finally superseded by the Industrial Revolution.While Borkenau, in tracing the social background of the thought of the period, relies chiefly on the conflicts and strife of political parties, Grossmann regards this as one element only in the formation of the general social situation, which in its entirety and in the interaction of its elements explains the development of modern thought. (shrink)

In publications in 1914 and 1918, Einstein claimed that his new theory of gravity somehow relativizes the rotation of a body with respect to the distant stars and the acceleration of the traveler with respect to the stay-at-home in the twin paradox. What he showed was that phenomena seen as inertial effects in a space-time coordinate system in which the non-accelerating body is at rest can be seen as a combination of inertial and gravitational effects in a space-time coordinate system (...) in which the accelerating body is at rest. Two different relativity principles play a role in these accounts: the relativity of non-uniform motion, in the weak sense that the laws of physics are the same in the two space-time coordinate systems involved; what Einstein in 1920 called the relativity of the gravitational field, the notion that there is a unified inertio-gravitational field that splits differently into inertial and gravitational components in different coordinate systems. I provide a detailed reconstruction of Einstein's rather sketchy accounts of the twins and the bucket and examine the role of these two relativity principles. I argue that we can hold on to but that is either false or trivial. (shrink)

Marquée à juste titre par le mouvement des Annales, l’historiographie française a intériorisé lidée qu’avant 1929 dominait ce que Henri Berr avait stigmatisé sous le nom d’ « histoire traditionnelle » : une histoire politique et individualiste ne tenant pas compte des déterminations collectives, sociales ou mentales. La fameuse Introduction aux études historiques de Langlois et Seignobos (1898) serait l’expression de ce «positivisme» qu’aurait initié Gabriel Monod, fondateur de la Revue historique en 1876. Cette vision traditionnelle de l’histoire de (...) la discipline est globalement remise en cause dans cet article qui montre que les années 1870-1930 sont au contraire un moment central dans l’historiographie tant au plan institutionnel qu’au plan intellectuel, qui nous intéresse surtout ici. C’est en effet dès cette époque que s’est cristallisée laspiration à faire de l’histoire une science sociale, ce qui se comprend aisément dès lors qu’on contextualise cette histoire et que l’on replace cette discipline dans l’ensemble du champ des sciences sociales. Les années 1890–1914 voient même se développer fortement une histoire économique et une histoire sociale. 1929 apparaît alors moins comme une révolution que comme une accélération dans une direction déjà marquée. (shrink)

L’œuvre de Copernic est à la fois tournée vers l’avenir par le système héliocentrique du monde qu’elle inaugure, et vers le passé par sa fidélité au principe du mouvement réel circulaire et uniforme des astres, hérité de Ptolémée, et à la conception du monde fini ayant pour limite la sphère des fixes et hiérarchisé ayant pour centre le Soleil, héritée des Pythagoriciens. Dès lors, est-elle à bon droit nommée « révolution copernicienne » selon l’expression consacrée ou bien doit-elle être (...) rigoureusement pensée comme réforme de l’astronomie ptoléméenne? La question engage la remise en chantier du concept de révolution scientifique. Celle-ci est-elle, selon son concept kuhnien, un changement de paradigme pour un groupe scientifique dans un domaine de recherche – auquel cas l’œuvre de Copernic serait une révolution scientifique en substituant au paradigme géocentrique de l’astronomie son paradigme héliocentrique? Ou bien est-elle, selon Kant qui a élaboré le premier son concept, une transformation dans la façon de penser, qui instaure une science – auquel cas cette œuvre serait bien plutôt une réforme scientifique, l’astronomie étant une science déjà instaurée dans l’Antiquité? (shrink)

It has recently been remarked that the argument for physicalism from the causal closure of the physical is incomplete. It is only effective against mental causation manifested in the action of putative mental forces that lead to acceleration of particles in the nervous system. Based on consideration of anomalous, physically unaccounted-for correlations of neural events, I argue that irreducible mental causation whose nature is at least prima facie probabilistic is conceivable. The manifestation of such causation should be accompanied by a (...) local violation of the Second Law of thermodynamics. I claim that mental causation can be viewed as the disposition of mental states to alter the state probability distribution within the nervous system, with no violation of the conservation laws. If confirmed by neurophysical research, it would indicate a kind of causal homogeneity of the world. Causation would manifest probabilistically in both quantum mechanical and psychophysical systems, and the dynamics of both would be determined by the temporal evolution of the corresponding system state function. Finally, I contend that a probabilistic account of mental causation can consistently explain the character of selectional states that ensure the uniformity of causal patterns, as well as the fact that different physical realizers of a mental property cause the same physical effects in different contexts. (shrink)

Dans cet article seront examinées les propositions cosmologiques de Gödel qui de façon apparente autorisent les boucles temporelles et les voyages à travers le temps, et surtout sa thèse selon laquelle l’objectivité du cours du temps n’est pas a priori garantie, mais elle dépend des conditions physiques dans l’univers. On ne peut « définir» la ligne du temps uniforme et mondiale par rapport à l’état moyen du mouvement de la matière, mais des cours du temps relatifs et partiels qui (...) apparaîtraient simultanés aux observateurs. Je pose la question de la possibilité des perceptions différentes du temps pour un même observateur, à savoir une perception là où le cours du temps serait un « mouvement » ordinaire et où le passé précède le présent ainsi que d’une autre perception là où ce cours du temps serait d’une certaine manière simultané. Je suis d’avis que la conscience peut avoir de nombreuses modalités de temps dont l’annihilation du cours de temps. Peut-être que le souvenir momentané des événements passés renvoie, dans notre esprit, à une telle possibilité. Or, la question de la signification de cette possibilité pour la réalité physique et l’univers même reste ouverte. (shrink)

Dans les textes inédits « Effets moraux de l’accélération de l’histoire» et « Sommes-nous libres?», Jules Vuillemin montre un visage peu connu : celui d’un observateur engagé de son époque. Il y critique des mouvements sociaux et politiques contemporains – mai 1968 et la réforme du Code pénal de 1989 – en s’appuyant sur des considérations métaphysiques et morales. Plus que des tribunes politiques, ces textes montrent que la politique n’est pas, pour Vuillemin, simple affaire d’« opinion» et que l’engagement (...) n’a de valeur que soutenu par l’argumentation. (shrink)

Dans les textes inédits « Effets moraux de l’accélération de l’histoire» (1969-1970) et « Sommes-nous libres?» (1989-1990), Jules Vuillemin montre un visage peu connu : celui d’un observateur engagé de son époque. Il y critique des mouvements sociaux et politiques contemporains – mai 1968 et la réforme du Code pénal de 1989 – en s’appuyant sur des considérations métaphysiques et morales. Plus que des tribunes politiques, ces textes montrent que la politique n’est pas, pour Vuillemin, simple affaire d’« opinion» et (...) que l’engagement n’a de valeur que soutenu par l’argumentation. (shrink)

In publications in 1914 and 1918, Einstein claimed that his new theory of gravity in some sense relativizes the rotation of a body with respect to the distant stars and the acceleration of the traveler with respect to the stay-at-home in the twin paradox. What he showed was that phenomena seen as inertial effects in a space-time coordinate system in which the non-accelerating body is at rest can be seen as a combination of inertial and gravitational effects in a space-time (...) coordinate system in which the accelerating body is at rest. Two different relativity principles play a role in these accounts: the relativity of non-uniform motion, in the weak sense that the laws of physics are the same in the two space-time coordinate systems involved; what Einstein in 1920 called the relativity of the gravitational field, the notion that there is a unified inertio-gravitational field that splits differently into inertial and gravitational components in different coordinate systems. I provide a detailed reconstruction of Einstein's rather sketchy accounts of the twins and the bucket and examine the role of these two relativity principles. I argue that we can hold on to but that is either false or trivial. (shrink)