How to quantize gravity and how not to quantize gravity

TL;DR

This paper argues that traditional canonical quantization of gravity is impossible and proposes a novel approach where gravity is quantized through its coupling to matter, offering a solution to the cosmological constant problem.

Contribution

It introduces a new perspective on quantizing gravity via matter coupling and demonstrates its implications for the cosmological constant problem, contrasting with standard approaches.

Findings

Canonical quantization of gravity is not feasible.

Gravity's zero-point energy is intrinsically tied to matter coupling.

This approach offers a potential solution to the cosmological constant problem.

Abstract

Taking the quantization of electromagnetism as the paradigm, we show how this procedure cannot work for Einstein gravity. However, it does work for conformal gravity, a fourth-order derivative, renormalizable theory of gravity that Bender and Mannheim have shown to be ghost free. We show that in any gravity theory gravity cannot be quantized canonically. Rather, because of an interplay between the zero-point energy of gravity and that of its matter source, gravity is quantized purely by its coupling to a quantized matter source, with gravity being intrinsically quantum mechanical. Treating the zero-point energy this way provides a solution to the cosmological constant problem. With the gravitational zero-point energy issue having been ignored in standard Einstein gravity, it is not possible to solve the cosmological constant problem in standard gravity, since without the zero-point contribution gravity does not know where the zero of energy is.