Environment as a witness: Selective proliferation of information and emergence of objectivity in a quantum universe

Abstract

We study the role of the information deposited in the environment of an open quantum system in course of the decoherence process. Redundant spreading of information -the fact that some observables of the system can be independently "read-off" from many distinct fragments of the environment -is investigated as the key to effective objectivity, the essential ingredient of "classical reality". This focus on the environment as a communication channel through which observers learn about physical systems underscores importance of quantum Darwinism -selective proliferation of information about "the fittest states" chosen by the dynamics of decoherence at the expense of their superpositions -as redundancy imposes the existence of preferred observables. We demonstrate that the only observables that can leave multiple imprints in the environment are the familiar pointer observables singled out by environment-induced superselection (einselection) for their predictability. Many independent observers monitoring the environment will therefore agree on properties of the system as they can only learn about preferred observables. In this operational sense, the selective spreading of information leads to appearance of an objective "classical reality" from within quantum substrate.

Quantum Mechanics, Spacetime Locality, and Gravity

“…While not all the aspects of the dynamics described above are fully proven, the basic picture is strongly supported by recent progress on understanding the quantum-to-classical transition (e.g. [21][22][23][24]27]). What are the implications of this in calculating physical probabilities in Eq.…”

“…(13)-the classical state basis is selected as a dynamical consequence of spacetime locality. While this is yet to be proven in the general case, analyses of simple quantum mechanical systems [21][22][23][24] strongly suggest that to be the case. The property of Eq.…”

“…(21) The argument given above, however, is not by itself sufficient to explain selection of the measurement basis, because the same analysis applies to any (not necessarily classical state) basis z = dx r zx x satisfying dx r zx r z x = δ(z − z ). The selection happens because "amplification" occurs (only) in a particular basis (called quantum Darwinism) [21][22][23][24]. Schematically, we can write as |ψ x (0) → |ψ x (t) ≡ |x |X |X · · · , where the last expression implies that the same classical information, i.e.…”

“…In the standard treatment of these problems, the openness of a system is emphasized [21][22][23][24]27]. Here we ask if the openness is really necessary at the fundamental level to account for these features.…”

“…We argue that spacetime locality-a special property of the time evolution operator-plays a crucial role in the evolution of a state. It leads to "amplification" of classical information [21][22][23][24] in a single component of the multiverse state. Schematically,…”