The Equivalence Principle and The Cosmological Constant Problem

TL;DR

This paper argues that the equivalence principle can help address the cosmological constant problem by suggesting that ultra-violet modes do not contribute to vacuum energy in a freely-falling frame, potentially resolving the discrepancy.

Contribution

It introduces a semi-classical gravity perspective where the equivalence principle limits vacuum energy contributions, offering a novel approach to the cosmological constant problem.

Findings

Ultra-violet modes do not contribute to the effective energy-momentum tensor in a freely-falling frame.

Normal ordering removes vacuum self-energy on Minkowski background, consistent with the equivalence principle.

The approach provides a potential resolution to the cosmological constant problem.

Abstract

In this essay I point out that, in the context of semi-classical gravity, the equivalence principle can mitigate the cosmological constant problem. On a Minkowski space-time background with the usual $\mathbb{R}^4$ topology, the vacuum self-energy is removed by normal ordering; this is allowed because it is not observable; I argue that, in a freely-falling frame of reference, the same must hold true, up to contributions from modes whose wavelength is of the order of the background radius of curvature. Thus, the equivalence principle implies that ultra-violet modes do not contribute to the effective energy-momentum tensor.