Quantum Theory: A Pointer to an Independent Reality

Bunge, Mario

Bernard d’Espagnat

While philosophy of science is the study of problems of knowledge concerning science in general, there also exists - or should exist - a '' philosophy in science'' directed at finding out in what ways our actual scientific knowledge may validly contribute to the basic philosophical quest. Contrary to philosophy of science, which is a subject for philosophers, philosophy in science calls on the services of physicists. When, in its spirit, quantum theory and Bell's theorem are used as touchstones, the two main traditional philosophical approaches, realism and idealism, are found wanting. A more suitable conception seems to be an intermediate one, in which the mere postulated existence of a holistic and hardly knowable Mind-Independent Reality is found to have an explaining power. Some corrections to comments by Schins of a previous work on the same subject are incorporated.

David Hodgson

Wojciech Hubert Zurek

Abstract This chapter describes three insights into the transition from quantum to classical that are based on the recognition of the role of the environment. It starts with a minimalist derivation of preferred sets of states. This breaking of the unitary symmetry of the Hilbert space yields — without the usual tools of decoherence — quantum jumps and pointer states consistent with those obtained via einselection. Pointer states obtained this way dene events without appealing to Born's rule for probabilities, which can be now derived from envariance-symmetry of entangled quantum states. With probabilities at hand one can analyze information flows in the course of decoherence. They explain how classical reality can arise from the quantum substrate by accounting for the objective existence of the einselected states of quantum systems through the redundancy of pointer state records in their environment — through quantum Darwinism. Taken together, and in the right order, these three advances (which fit well within Everett's relative states framework, but do not require ‘many worlds’ per se) extend the existential interpretation of quantum theory.

Robert B. Griffiths

Hoofar Daneshvar, G. W. F. Drake

We present a general analytic method for evaluating the generally time-dependent pointer states of a subsystem, which are defined by their capability not to entangle with the states of another subsystem. In this way, we show how in practice the global state of the system and the environment may evolve into a diagonal state as a result of the natural evolution of the total composite system. We explore the conditions under which the pointer states of the system become independent of time; so that a preferred basis of measurement can be realized. As we show, these conditions include the so-called quantum limit of decoherence and the so-called quantum measurement limit; as well as some other specific conditions which are discussed in the paper. We relate the mathematical conditions for having time-independent pointer states to some classes of possible symmetries in the Hamiltonian of the total composite system. Indeed, our theory would serve as a generalization of the existing theory for determination of the preferred basis of measurement. By exploiting this new theory we can obtain those regimes of the parameter space for a given total Hamiltonian defining our system-environment model for which a preferred basis of measurement can be realized. Moreover, we can predict the corresponding preferred basis of measurement for each regime. We can also obtain the time-dependent pointer states of the system and the environment in most of the other regimes where the pointer states of the system are time-dependent and a preferred basis of measurement cannot be realized at all. This ability to obtain time-dependent pointer states is specifically important in decoherence studies; as pointer states correspond to those initial conditions for the state of the system and the environment for which we can have longer decoherence times.