The Brownian motion of small particles interacting with a field at a finite temperature is a well-known and well-understood phenomenon. At zero temperature, even though the thermal fluctuations are absent, quantum fields still possess vacuum fluctuations. It is then interesting to ask whether a small particle that is interacting with a quantum field will exhibit Brownian motion when the quantum field is assumed to be in the vacuum state. In this paper, we study the cases of a small charge and (...) an imperfect mirror interacting with a quantum scalar field in (1 + 1) dimensions. Treating the quantum field as a classical stochastic variable, we write down a Langevin equation for the particles. We show that the results we obtain from such an approach agree with the results obtained from the fluctuation-dissipation theorem. Unlike the finite temperature case, there exists no special frame of reference at zero temperature and hence it is essential that the particles do not break Lorentz invariance. We find that that the scalar charge breaks Lorentz invariance, whereas the imperfect mirror does not. We conclude that small particles such as the imperfect mirror will exhibit Brownian motion even in the quantum vacuum, but this effect can be so small that it may prove to be difficult to observe it experimentally. (shrink)

We present a framework for analyzing black hole backreaction from the point of view of quantum open systems using influence functional formalism. We focus on the model of a black hole described by a radially perturbed quasi-static metric and Hawking radiation by a conformally coupled massless quantum scalar field. It is shown that the closed-time-path (CTP) effective action yields a non-local dissipation term as well as a stochastic noise term in the equation of motion, the Einstein–Langevin equation. Once the (...) thermal Green's function in a Schwarzschild background becomes available to the required accuracy, the strategy described here can be applied to obtain concrete results on backreaction. We also present an alternative derivation of the CTP effective action in terms of the Bogolyubov coefficients, thus making a connection with the interpretation of the noise term as measuring the difference in particle production in alternative histories. (shrink)

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)

La parenthèse Vichy marque un tournant dans la carrière de Jean Thibaud (1901-1960). Il occupe des postes rendus vacants par la mise à l’écart de Jean Perrin et de Paul Langevin, deux figures tutélaires de la physique française aux engagements politiques incompatibles avec le nouveau régime. Ces initiatives provoquent des réactions de rejet chez les universitaires qui œuvrent pour la résistance et pointent dès lors Thibaud comme un collaborateur. Nous proposons de suivre au plus près l’itinéraire de Thibaud sous (...) l’angle d’une stratégie personnelle d’accommodement, concept que l’historien Philippe Burrin a proposé pour décrire diverses formes d’adaptation aux circonstances nées de l’Occupation et que nous entendons revisiter dans le cadre de la présente étude. (shrink)

Spontaneous transitions between bound states of an atomic system, “Lamb Shift” of energy levels and many other phenomena in real nonrelativistic quantum systems are connected within the influence of the quantum vacuum fluctuations (fundamental environment (FE)) which are impossible to consider in the limits of standard quantum-mechanical approaches. The joint system “quantum system (QS) + FE” is described in the framework of the stochastic differential equation (SDE) of Langevin-Schrödinger (L-Sch) type, and is defined on the extended space R 3 (...) ⊗ R {ξ}, where R 3 and R {ξ} are the Euclidean and functional spaces, respectively. The density matrix for single QS in FE is defined. The entropy of QS entangled with FE is defined and investigated in detail. It is proved that as a result of interaction of QS with environment there arise structures of various topologies which are a new quantum property of the system. (shrink)

La « parenthèse Vichy » marque un tournant dans la carrière de Jean Thibaud (1901-1960). Il occupe des postes rendus vacants par la mise à l’écart de Jean Perrin et de Paul Langevin, deux figures tutélaires de la physique française aux engagements politiques incompatibles avec le nouveau régime. Ces initiatives provoquent des réactions de rejet chez les universitaires qui œuvrent pour la résistance et pointent dès lors Thibaud comme un « collaborateur ». Nous proposons de suivre au plus près (...) l’itinéraire de Thibaud sous l’angle d’une stratégie personnelle d’« accommodement », concept que l’historien Philippe Burrin a proposé pour décrire diverses formes d’adaptation aux circonstances nées de l’Occupation et que nous entendons revisiter dans le cadre de la présente étude. (shrink)

Comme une sorte de retour, tout anniversaire conjugue un événement du passé au présent. Cent ans après sa parution, le livre de Bergson _Durée et simultanéité_ en constitue un exemple remarquable par les oppositions contenues et qui éclatèrent lors de la rencontre avec Einstein, le 6 avril 1922. Du côté de la philosophie, Bergson développait l’étonnement éprouvé lors du congrès de Bologne onze ans plus tôt, la présentation de Langevin annonçant le fameux « paradoxe des jumeaux » ; un (...) développement qui le fit revenir à son analyse de la physique newtonienne et de la philosophie kantienne, la multiplicité du temps vrai ou durée, distinguée en 1889 de la multiplicité spatiale et de son nombre. Or, du côté des recherches menées par les physiciens au tournant du XX ème siècle, l’article d’Einstein de 1905 opérait le retour, sur les épaules de Newton, à Galilée et à son dialogue avec Aristote. La forme dialoguée ici choisie s’efforce de réactiver le paradoxe toujours vivant que constitue le retour de Bergson à son point de départ. Bien plus qu’un livre du passé, il s’agit d’un événement qui n’a cessé de conjuguer physique et philosophie, et qui nous appelle aujourd’hui à un dialogue. (shrink)

In this essay we discuss a class of apparently metaphorical idioms, exemplified by “fine as frog's hair,” that do not afford any obvious interpretation, and appear to have originated, at least in part, in language play. We review recent trends in both play theory and metaphor theory, and show that a playful approach to language is often an important element in the use and understanding of metaphors (and idioms generally), even when metaphors can be readily interpreted by means of a (...) vehicle-to-topic mapping. Based on this evidence we call for a more deliberate inclusion of language play in metaphor theory and analysis. (shrink)

Bruno Bernardi ouvre cet imposant recueil en dégageant la difficulté inhérente à son titre : peut-on trouver dans l’œuvre de Rousseau une philosophie? Les actes du colloque sur Rousseau ayant eu lieu en juin 2012 à l’ENS de Lyon manifestent un vrai renouvellement des lectures de l’œuvre du Genevois. Dans une histoire séquencée dont l’utilité pour les jeunes chercheurs justifierait à elle seule l’existence de cet ouvrage, B. Bernardi rappelle les grands jalons de la critique du xxe siècle. Le...

Transcript of speeches by a Hindu philosopher, chiefly on Hindu philosophy and Hinduism.

In order to get out of present day discussions between determinism and free will, creationism and evolution, bios and zoē, human existence and biological life – those dead end binaries of our present day thinking into which we have manoeuvred ourselves – we need to revisit the Ancient discussions relating to the care of the soul and human existence. I will draw together these two themes from Jan Patočka’s writings by anchor-ing them in his account of Socrates who was the (...) first to emphasise the idea of human re-sponsibility not only for thinking but also for human acting in the world. I will argue that the significant common feature – the care for our own being, our existence – brings Patočka’s reflections on the care for the soul and care for our human existence together. While, according to Patočka, the notion of the care for the soul was displaced from the philosophical reflection by the modern scientific venture, the idea of human existence is, although problematic from the scientific point of view, still a part of our experience.Para librarnos de discusiones contemporáneas entre determinismo y libre albedrío, creacionismo y evolución, bios y zoē, existencia humana y vida biológica, estos binomios, callejones de salida del pensamiento de hoy en los que nos hemos metido, tenemos que volver a escuchar las discusiones de la Antigüedad sobre el cuidado del alma y la existencia humana. Voy a recuperar estos dos temas de escritos de Jan Patočka, anclándolos en su interpretación de Sócrates, el primero en poner énfasis en la idea de responsabilidad humana no solo de su pensamiento sino también de su actuar en el mundo. Argumentaré que el significativo rasgo común, esto es, el cuidado por nuestro propio ser, nuestra existencia, es lo que une las reflexiones de Patočka sobre el cuidado del alma y el cuidado de la exitencia humana. Mientras que, según Patočka, la noción del cuidado del alma ha sido desplazada de la reflexión filosófica por la empresa científica moderna, la idea de la existencia humana, a pesar de lo problemático que puede resultar desde un punto de vista científi-co, todavía forma parte de nuestra experiencia. (shrink)