Does Quantum Gravity Happen at the Planck Scale?

TL;DR

This paper critically examines the common belief that quantum gravity occurs at the Planck scale, finding that current evidence and arguments do not conclusively support this claim.

Contribution

The paper provides a critical survey of five arguments for quantum gravity at the Planck scale and shows that none of them are conclusive.

Findings

None of the five arguments convincingly establish quantum gravity at the Planck scale.

The nonrenormalisability argument is the most persuasive but relies on unwarranted assumptions.

Current theories do not definitively predict quantum gravity at the Planck scale.

Abstract

The claim that at the so-called Planck scale our current physics breaks down and a new theory of quantum gravity is required is ubiquitous, but the evidence is shakier than the confidence of those assertions warrants. In this paper, I survey five arguments in favour of this claim - based on dimensional analysis, quantum black holes, generalised uncertainty principles, the nonrenormalisability of quantum gravity, and theories beyond the standard model - but find that none of them succeeds. The argument from nonrenormalisability is the most convincing, yet it requires the unwarranted assumption that the same constant of action occurs in every quantum field theory. Therefore, our theories don't (yet) predict that quantum gravity happens at the Planck scale.