Uitleg van nieuwe wetenschappelijke-wijsgerige visies op de natuurwetten, in het bijzonder in de thermodynamica, berustend op het belang van de instabiliteit van bestaande systemen.

[Time, the fundamental dimension of our existence, has fascinated artists, philosophers, and scientists of every culture and every century. All of us can remember a moment as a child when time became a personal reality, when we realized what a "year" was, or asked ourselves when "now" happened. Common sense says time moves forward, never backward, from cradle to grave. Nevertheless, Einstein said that time is an illusion. Nature's laws, as he and Newton defined them, describe a timeless, deterministic universe (...) within which we can make predictions with complete certainty. In effect, these great physicists contended that time is reversible and thus meaningless. (shrink)

The formulation of the second law of thermodynamics in the frame of general relativity is reconsidered in the case of an istotropic homogeneous universe. We show that there appears then a direct link between the cosmological state of the universe, as expressed in terms of conformal coordinates, and quantities such as energy density, pressure, and entropy associated with the description of nature. In the early universe there appears a kind of phase transition due to transfer of gravitational energy to matter (...) associated with the cosmological expansion if the universe starts with a non-Euclidian (space) state. As a result, we may envisage the possibility of a “cold big-bang model,” in which the universe would start at zero temperature and entropy. The temperature goes then through a maximum before entering the present area of cooling related to adiabatic expansion. (shrink)

The role of passion and more generally irrational elements in processing knowledge are discussed. This seems to be a paradox, as science by definition is beyond passion. At the same time science is the expression of a culture. This paradox is examined through the experience and work of crucial figures in physics such as Newton and Einstein. Science is a dialogue between man and nature: part of the search for the transcendental which is common to many cultural activities: art, music, (...) literature. Our time is one of expectation, anxiety, and bifurcation. Far from there being an ?end? of science, our period will see the birth of a new vision, a new science whose cornerstone encloses the arrow of time: a science that makes us and our creativity the expression of a fundamental trend in the universe. (shrink)

In recent papers the authors have discussed the dynamical properties of “large Poincaré systems” (LPS), that is, nonintegrable systems with a continuous spectrum (both classical and quantum). An interesting example of LPS is given by the Friedrichs model of field theory. As is well known, perturbation methods analytic in the coupling constant diverge because of resonant denominators. We show that this Poincaré “catastrophe” can be eliminated by a natural time ordering of the dynamical states. We obtain then a dynamical theory (...) which incorporates a privileged direction of time (and therefore the second law of thermodynamics). However, it is only in very simple situations that this time ordering can be performed in an “extended” Hilbert space. In general, we need to go to the Liouville space (superspace) and introduce a time ordering of dynamical states according to the number of particles involved in correlations. This leads then to a generalization of quantum mechanics in which the usual Heisenberg's eigenvalue problem is replaced by a complex eigenvalue problem in the Liouville space. (shrink)

"En cette fin de siècle, la question de l'avenir de la science est souvent posée. Je crois que nous sommes seulement au début de l'aventure. Nous assistons à l'émergence d'une science qui n'est plus limitée à des situations simplifiées, idéalisées, mais nous met en face de la complexité du monde réel, une science qui permet à la créativité humaine de se vivre comme l'expression singulière d'un trait fondamental de tous les niveaux de la nature. J'ai tenté de présenter cette transformation (...) conceptuelle qui implique l'ouverture d'un nouveau chapitre dans l'histoire féconde des relations entre physique et mathématique sous une forme lisible et accessible à tout lecteur intéressé par l'évolution de nos idées sur la nature. Nous ne sommes qu'au début de ce nouveau chapitre de l'histoire de notre dialogue avec la nature". (shrink)

The Norbert Wiener Memorial Gold Medal address delivered by the Nobel Laureate recipient. Considers Norbert Wiener and the idea of contingence. Refers to Wiener's book The Human Use of Human Beings and in particular to the preface entitled "The idea of a contingent universe" and to the epilogue of the book by Rosenblith. This raises the question faced by Wiener: how to reconcile a deterministic world à la Newton with the intrinsically probabilistic universe of Gibbs, the relativistic universe of Einstein (...) and the Heisenberg uncertainty principle? Notes the parallelism among the questions Wiener is asking with the ones to which the Gold Medallist has devoted most of his scientific life. Presents a different point of view, as a tribute to the visionary ideas developed by Wiener. Discusses the "new physics" and the problems facing physics today, at the end of the twentieth century. (shrink)