The Issue of Choosing Nothing: What Determines the Low Energy Vacuum State of Nature?

TL;DR

This paper explores how the low-energy vacuum state of the universe may be determined by fundamental principles combining quantum theory and general relativity, using a toy model to illustrate the concept.

Contribution

It proposes that the vacuum state is a relic from fundamental theories, derived through a hierarchy of approximations, and demonstrates this with a simple toy model.

Findings

Wave function of the universe influences vacuum selection

Vacuum state determines the concept of particles at low energies

Potential link to a quantum mechanical version of Mach's principle

Abstract

Starting from an (unknown) quantum gravitational model, one can invoke a sequence of approximations to progressively arrive at quantum field theory (QFT) in curved spacetime, QFT in flat spacetime, nonrelativistic quantum mechanics and newtonian mechanics. The more exact theory can put restrictions on the range of possibilities allowed for the approximate theory which are not derivable from the latter - an example being the symmetry restrictions on the wave function for a pair of electrons. We argue that the choice of vacuum state at low energies could be such a `relic' arising from combining the principles of quantum theory and general relativity, and demonstrate this result in a simple toy model. Our analysis suggests that the wave function of the universe, when it describes the large volume limit of the universe, dynamically selects a vacuum state for matter fields - which in turn defines the concept of particle in the low energy limit. The result also has the potential for providing a concrete quantum mechanical version of Mach's principle.