New limit placed on physics constant

One of physics’ most fundamental constants just got a little more constant.

Physicists have placed the strictest limit yet on how much the fine structure constant — which determines how strongly electrically charged objects interact — could change with the density of nearby matter. The team's method for measuring the constant may help scientists probe whether the value has remained constant over the lifetime of the universe.

The fine structure constant, also known as alpha, has long been both essential and confounding to physicists. It was introduced in 1916 to describe the strength of the electromagnetic force, which governs how charged objects interact and how molecules form. From there, the constant worked its way into important quantum mechanical equations. "It pops up all of the time in all of our theories," says Michael Tarbutt, an Imperial College London physicist who led the study.

However, physicists know of no fundamental