Eur. Phys. J. Plus (2024) 139: 628
https://doi.org/10.1140/epjp/s13360-024-05351-4

Regular Article

Interpretation of quantum theory in a cosmological perspective

¹ Dipartimento Di Fisica dell’Università Di Milano, Milan, Italy
² I.N.F.N., Sezione Di Milano, Milan, Italy

^a giovanni.prosperi@mi.infn.it

Received: 18 November 2023
Accepted: 9 June 2024
Published online: 19 July 2024

Abstract

We reconsider the problem of the interpretation of the quantum theory (QT) in the perspective of the entire universe and of the Bohr's idea that the classical language is the language of our experience and QT acquires a meaning only with a reference to it. We distinguish a classical or macroscopic state, and a quantum or microscopic one that is perceived only through the modifications that it induces in the first. The macroscopic state is specified by a set of variables, a classical energy–momentum tensor and conserved currents, which are supposed to have always a well-defined value. The microscopic state and dynamics are expressed by the usual QT formalism. For the macroscopic variables, a basic distribution of probability is postulated in terms of quantum operators and a statistical operator, what replace the usual probability rule of QT. For the universe, a variance of the ΛCDM model with $\mathrm{\Omega }=1$ is assumed, one inflaton, a Goldstone type potential, initial time at $t=-\infty$, expectation values of all fundamental fields vanishing for $t\to -\infty$. The scalar fluctuations in the cosmic microwave background is correctly explained, but the absence of the tensor fluctuations remains not understood. This seems to suggest that gravity is a pure classical phenomenon what perhaps could be accommodated in our framework.