Magazine article Science News

Physics Constant Gets New Limit: Analysis Checks Variability of Quantum Mechanics Value

Magazine article Science News

Physics Constant Gets New Limit: Analysis Checks Variability of Quantum Mechanics Value

Article excerpt

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 may help scientists probe whether the value has remained steady over the lifetime of the universe.

The fine structure constant, also known as alpha, has 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, a physicist at Imperial College London.

But alpha may not be a true constant. Some recent theories about the origins of dark energy--the repulsive energy field that seems to pervade the universe--suggest that alpha's value might vary depending on how much matter is nearby.

To probe this possibility, Tarbutt and his team measured alpha on Earth and in interstellar space, where the density of matter is far lower. To do this, they measured the frequency of light needed to change an electron's energy in a particular way in a molecule called CH, which is composed of one carbon atom and one hydrogen atom. …

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