Is quantum linear superposition an exact principle of nature?

TL;DR

This paper questions whether quantum linear superposition is an exact principle of nature, exploring its limitations at macroscopic scales and considering gravitational physics as a potential explanation for the absence of large-scale superpositions.

Contribution

It investigates the possibility that quantum superposition may be an approximation and examines gravitational physics as a fundamental factor limiting superposition at large scales.

Findings

Superposition confirmed for microscopic particles and collective states.

Large objects do not exhibit superposition, suggesting a fundamental limit.

Ongoing experiments test the gravitational hypothesis for superposition limits.

Abstract

The principle of linear superposition is a hallmark of quantum theory. It has been confirmed experimentally for photons, electrons, neutrons, atoms, for molecules having masses up to ten thousand amu, and also in collective states such as SQUIDs and Bose-Einstein condensates. However, the principle does not seem to hold for positions of large objects! Why for instance, a table is never found to be in two places at the same time? One possible explanation for the absence of macroscopic superpositions is that quantum theory is an approximation to a stochastic nonlinear theory. This hypothesis may have its fundamental origins in gravitational physics, and is being put to test by modern ongoing experiments on matter wave interferometry.