One of the main goals of modern theoretical physics is to find a common framework that explains all of the fundamental forces of nature: gravity; the strong force that binds quarks into protons and neutrons; and the forces of the electroweak theory (which encompasses electromagnetism on macroscopic scales, and the 'weak' and hypercharge forces on subnuclear scales). On page 56 of this issue, Toms1 reports results that could be significant for finding such a framework. The author describes a mathematical analysis of the behaviour of gravity at ultrashort distances and of how this most familiar of forces affects 'Abelian gauge' theories, which, notably, include the theory of electromagnetism and that of the hypercharge force.
Relevant to Toms's study1 is the fact that coupling constants — parameters that are used to characterize the strength of forces — are actually not constant but vary with the distance scale of the physical process in which they are measured. This phenomenon is both well established experimentally and predicted by current theories, and is known as 'running coupling constants'.
The author's results have implications for what might be the next revolution in fundamental physics, a hint of which is found by extrapolating the experimentally established 'running' of the coupling constants down to distance scales much shorter than can be accessed experimentally. Within the successful standard model of particle physics, we can make such an extrapolation for the running of the coupling constant of the hypercharge force (αY) — which is described by an Abelian gauge theory of the type studied by Toms1 — and for that of the strong (αS) and weak (αW) forces, which are described by non-Abelian gauge theories. The results are shown semi-quantitatively in Figure 1, together with a cruder estimate of the effective coupling constant of gravity (αG).
