Olimpia Lombardi

The Self-Induced Approach to Decoherence in Cosmology

In this paper we will present the self-induced approach to decoherence, which does not require the interaction between the system and the environment: decoherence in closed quantum systems is possible. This fact has relevant consequences in cosmology, where the aim is to explain the emergence of classicality in the universe conceived as a closed (noninteracting) quantum system. In particular, we will show that the self-induced approach may be used for describing the evolution of a closed quantum universe, whose classical behavior arises as a result of decoherence.

Self‐Induced Decoherence and the Classical Limit of Quantum Mechanics

In this paper we argue that the emergence of the classical world from the underlying quantum reality involves two elements: self‐induced decoherence and macroscopicity. Self‐induced decoherence does not require the openness of the system and its interaction with the environment: a single closed system can decohere when its Hamiltonian has continuous spectrum. We show that, if the system is macroscopic enough, after self‐induced decoherence it can be described as an ensemble of classical distributions weighted by their corresponding probabilities. We also argue that classicality is an emergent property that arises when the behavior of the system is described from an observational perspective.

Decoherence time in self-induced decoherence

A general method for obtaining the decoherence time in self-induced decoherence is presented. In particular, it is shown that such a time can be computed from the poles of the resolvent or of the initial conditions in the complex extension of the Hamiltonians spectrum. Several decoherence times are estimated:

The Cosmological origin of time asymmetry

{10}^{\ensuremath{-}13}\char21{}{10}^{\ensuremath{-}15}\phantom{\rule{0.3em}{0ex}}\mathrm{s}

The Global Arrow of Time as a Geometrical Property of the Universe

for microscopic systems, and

The Arrow of Time: From Universe Time-Asymmetry to Local Irreversible Processes

{10}^{\ensuremath{-}37}\char21{}{10}^{\ensuremath{-}39}\phantom{\rule{0.3em}{0ex}}\mathrm{s}

A general theoretical framework for decoherence in open and closed systems

for macroscopic bodies. For the particular case of a thermal bath, the order of magnitude of our results agrees with that obtained by the einselection (environment-induced decoherence) approach.

Suppression of decoherence in a generalization of the spin-bath model

In this paper, we address the problem of the arrow of time from a cosmological point of view, rejecting the traditional entropic approach that defines the future direction of time as the direction of the entropy increase: from our perspective, the arrow of time has a global origin and it is an intrinsic, geometrical feature of spacetime. Time orientability and the existence of a cosmic time are necessary conditions for defining an arrow of time, which is manifested globally as the time asymmetry of the universe as a whole, and locally as a time-asymmetric energy flux. We also consider arrows of time of different origins (quantum, electromagnetic, thermodynamic, etc) showing that they can be non-conventionally defined only if the geometrical arrow is previously defined.

A General Conceptual Framework for Decoherence in Closed and Open Systems

Traditional discussions about the arrow of time in general involve the concept of entropy. In the cosmological context, the direction past-to-future is usually related to the direction of the gradient of the entropy function of the universe. But the definition of the entropy of the universe is a very controversial matter. Moreover, thermodynamics is a phenomenological theory. Geometrical properties of space-time provide a more fundamental and less controversial way of defining an arrow of time for the universe as a whole. We will call the arrow defined only on the basis of the geometrical properties of space-time, independently of any entropic considerations, “the global arrow of time.” In this paper we will argue that: (i) if certain conditions are satisfied, it is possible to define a global arrow of time for the universe as a whole, and (ii) the standard models of contemporary cosmology satisfy these conditions.

Partial Traces in Decoherence and in Interpretation: What Do Reduced States Refer to?

Abstract In several previous papers we have argued for a global and non-entropic approach to the problem of the arrow of time, according to which the “arrow” is only a metaphorical way of expressing the geometrical time-asymmetry of the universe. We have also shown that, under definite conditions, this global time-asymmetry can be transferred to local contexts as an energy flow that points to the same temporal direction all over the spacetime. The aim of this paper is to complete the global and non-entropic program by showing that our approach is able to account for irreversible local phenomena, which have been traditionally considered as the physical origin of the arrow of time.