Equivalence Principle in Classical and Quantum Gravity

TL;DR

This paper reviews different forms of the equivalence principle in classical and quantum physics, emphasizing that only the strong form is fundamentally extendable to quantum gravity, while others are only approximately valid.

Contribution

It provides a comprehensive overview of the equivalence principle's various forms and argues that the strong equivalence principle is the only one suitable for generalization to quantum gravity.

Findings

Only the strong equivalence principle can be fundamentally extended to quantum gravity.

Other flavors of the equivalence principle are only approximately valid at the classical level.

The paper contrasts the validity of the equivalence principle in mechanics and field theory.

Abstract

We give a general overview of various flavors of the equivalence principle in classical and quantum physics, with special emphasis on the so-called weak equivalence principle, and contrast its validity in mechanics versus field theory. We also discuss its generalisation to a theory of quantum gravity. Our analysis suggests that only the strong equivalence principle can be considered fundamental enough to be generalised to a quantum gravity context, since all other flavors of equivalence principle hold only approximately already at the classical level.