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The material of this volume is organized in four parts, with separate introductions, which roughly follow the proceedings of the workshop. The overlap of these research areas is a recent feature which we would like to introduce here.
Gravity is unique because it acts universally on all interactions in Nature. For this reason it is also of fundamental relevance for the issues discussed in this volume - Decoherence, Information, Complexity, Entropy. Decoherence – the irreversible emergence of classical properties for a quantum system due to the interaction with its environment – can only be understood if a special initial condition...
A new approach to the dynamics of the universe based on work by Ó Murchadha, Foster, Anderson and the author is presented. The only kinematics presupposed is the spatial geometry needed to define configuration spaces in purely relational terms. A new formulation of the relativity principle based on Poincaré’s analysis of the problem of absolute and relative motion (Mach’s principle) is given. The...
Hamiltonian mechanics of field theory can be formulated in a generally covariant and background independent manner over a finite dimensional extended configuration space. I study the physical symplectic structure of the theory in this framework. This structure can be defined over a space G of three-dimensional surfaces without boundary, in the extended configuration space. These surfaces provide a...
A brief introduction to the decoherent histories approach to quantum theory is given, with emphasis on its role in the discussion of the emergence of classicality from quantum theory. Some applications are discussed, including quantum-classical couplings, the relationship of the histories approach to quantum state diffusion, and the application of the histories approach to situations involving time...
Black holes emit thermal radiation (Hawking effect). If after black-hole evaporation nothing else were left, an arbitrary initial state would evolve into a thermal state (‘information-loss problem’). Here it is argued that the whole evolution is unitary and that the thermal nature of Hawking radiation emerges solely through decoherence – the irreversible interaction with further degrees of freedom...
Evidence on the violation of Lorentz symmetry arises from the observation of cosmic rays with energies beyond the GZK cutoff, EGZK ≃ 4 × 1019eV, from the apparent transparency of the Universe to the propagation of high energy gamma radiation, and from the stability of pions in air showers. These three paradoxes can be explained through deformations of the...
Can the spatial distance between two identical particles be explained in terms of the extent that one can be distinguished from the other? Is the geometry of space a macroscopic manifestation of an underlying microscopic statistical structure? Is geometrodynamics derivable from general principles of inductive inference? Tentative answers are suggested by a model of geometrodynamics based on the statistical...
The question raised in the title is old, as old as quantum theory itself. An answer has not been given. Leading physicists of the .rst “quantum century” have taken a stand on the mostly philosophical issues which were surrounding it before. Can the uncomfortable unfamiliarity of quantum mechanics be overcome or is it here to stay?
Time-arrow s=±, intrinsic to a concrete physical system, is associated with the direction of information loss Δ I displayed by the random evolution of the given system. When the information loss tends to zero the intrinsic time-arrow becomes uncertain. We propose the heuristic relationship 1/[1+exp(-sΔI) for the probability of the intrinsic time-arrow. The main parts of the present work are trying...
We set up a forward–backward path integral for a point particle in a bath of photons and gravitons and derive from it a master equation for the density matrix which describes electromagnetic and gravitational dissipation. The associated Langevin equations are discussed.
We review some aspects of the quantization of the damped harmonic oscillator. We derive the exact action for a damped mechanical system in the frame of the path integral formulation of the quantum Brownian motion problem developed by Schwinger and by Feynman and Vernon. The doubling of the phase space degrees of freedom for dissipative systems and thermal field theories is discussed and the doubled...
We argue that the quantized non-Abelian gauge theory can be obtained as the infrared limit of the corresponding classical gauge theory in a higher dimension. We show how the transformation from classical to quantum field theory emerges, and relate Planck’s constant to quantities defined in the underlying classical gauge theory.
Quantum correlations can be naturally formulated in a classical statistical system of infinitely many degrees of freedom. This realizes the underlying non-commutative structure in a classical statistical setting. We argue that the quantum correlations offer a more robust description with respect to the precise definition of observables.
We study classical Hamiltonian systems in which the intrinsic proper time evolution parameter is related through a probability distribution to the physical time, which is assumed to be discrete. This is motivated by the “timeless” reparametrization invariant model of a relativistic particle with two compactified extra-dimensions. In this example, discrete physical time is constructed based...
The physics of open quantum systems encompasses a vast array of phenomena ranging from subnuclear to cosmological scales. Nevertheless, in this thematic kaleidoscope, there are a few central problems, whose generality makes them relevant at almost any scale. In this brief review I shall concentrate on some of these problems, guided by and concentrating on those more intimately related to the contributions...
Decoherence is the process by which quantum systems interact and become correlated with their external environments; quantum trajectories are a powerful technique by which decohering systems can be resolved into stochastic evolutions, conditioned on different possible “measurements” of the environment. By calling on recently-developed tools from quantum information theory, we can analyze simplified...
We present an introduction to coined quantum walks on regular graphs, which have been developed in the past few years as an alternative to quantum Fourier transforms for underpinning algorithms for quantum computation. We then describe our results on the effects of decoherence on these quantum walks on a line, cycle and hypercube. We find high sensitivity to decoherence, increasing with the number...
This paper discusses work developed in recent years, in the domain of quantum optics, which has led to a better understanding of the classical limit of quantum mechanics. New techniques have been proposed, and experimentally demonstrated, for characterizing and monitoring in real time the quantum state of an electromagnetic field in a cavity. They allow the investigation of the dynamics of the decoherence...
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