Limites de la connaissance (Les) Ce livre dresse un panorama de la physique des années 1950 jusqu’aux découvertes les plus récentes, à travers 130 sujets, chacun traité avec la plus grande clarté sur une double page illustrée. Research EU: The Magazine of the European Research Area M. Feuer nous apprend par le détail, documents pertinents à l'appui, que la relativité surgit entretissée aux courants politiques, idéologiques, socialistes en un mot, représentés par ces dériveux. (L'élément juif est important et ...

Earlier arguments for an upper bound on entropy depend on considerations of black holes or on classical approximations for systems of noninteracting particles. Here the bounds are deduced from quantum statistical considerations only. They are also extended to incorporate interacting particles and fields (modelled by a set of harmonic oscillators).

We study the influence of the light-force exerted by two optical fields on the motion of a harmonically bound particle, modelled by a two-state system. The radiation force is calculated semiclassically in the limit of weak driving fields and strong damping by spontaneous emission. Depending on the frequency of the two laser fields and the frequency of the free oscillation in the trapping potential we calculate the energy transferred to the particle per cycle. Among various cooling/heating situations we find multistable orbits of finite size in the case of counterpropagating waves.

The radiation force on a three-level atom exerted by two laser fields is calculated semiclassically. If the system is spatially confined by a harmonic potential one or more stable orbits can be found for certain conditions (frequencies, field strengths). As a consequence, variation of the laser frequencies leads to hysteresis effects.

We have calculated 〈x2〉 and 〈v2〉 for an ion in a rf trap being cooled by a stochastic force. The results agree with earlier work (using a Fokker-Planck equation) as long as there is white noise. However, there is an appreciable reduction for both quantities, if non-Markovian processes are included.

Le probleme concerne la recherche de l'irreversibilite dans des equations du mouvement reversibles

The smallness of the Planck length alone does not explain the absence of quantum effects of gravitation. Instead, in order to become classical, spacetime has to be continuosly measured by matter. Therefore the geometry of spacetime appears classical because our universe is not empty.

The dependence of macroscopic systems upon their environment is studied under the assumption that quantum theory is universally valid. In particular scattering of photons and molecules turns out to be essential even in intergalactic space in restricting the observable properties by locally destroying the corresponding phase relations. The remaining coherence determines the ‘classical’ properties of the macroscopic systems. In this way local classical properties have their origin in the nonlocal character of quantum states.