Standard Quantum Mechanics without observers

TL;DR

This paper proposes a reformulation of standard quantum mechanics that eliminates the need for observers and measurements by constraining Wigner functions to classical regions, addressing paradoxes like Wigner's friend.

Contribution

It introduces a measurement-free formulation of quantum mechanics using phase-space Wigner functions constrained to classical regions, avoiding anthropocentric measurement assumptions.

Findings

Addresses Wigner's friend paradoxes.

Provides a phase-space based reformulation.

Discusses experimental implications.

Abstract

The Projection Postulate from Standard Quantum Mechanics relies fundamentally on measurements. But measurements implicitly suggest the existence of anthropocentric notions like measuring devices, which should rather emerge from the theory. This article proposes an alternative formulation of the Standard Quantum Mechanics, in which the Projection Postulate is replaced with a version in which measurements and observations are not assumed as fundamental. More precisely, the Wigner functions representing the quantum states on the phase space are required to be tightly constrained to regions of the classical coarse-graining of the phase space. This ensures that states are quasiclassical at the macro level. Within a coarse-graining region, the time evolution of the Wigner functions representing the quantum system is required to obey the Liouville-von Neumann equation, the phase-space equivalent of the Schr\"odinger equation. The projection is postulated to happen when the system transitions from a coarse-graining region to others, by selecting one of them according to the Born rule, but without reference to a measurements. The connection with the standard formulation of Quantum Mechanics is explained, as well as the problems that the present formulation solves, in particular the Wigner's friend type of paradoxes. Experimental consequences and open problems of the proposed formulation are discussed.