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Protons even smaller, researchers report

LOS ANGELES – Physicists might have to rethink what they know about, well, everything.

European researchers dropped a potential bombshell on their colleagues around the world Wednesday by reporting that sophisticated new measurements indicate the radius of the proton is 4 percent smaller than previously believed.

In a world where measurements out to a dozen or more decimal places are routine, a 4 percent difference in this subatomic particle – found in every atom’s nucleus – is phenomenally large, and the finding has left theoreticians scratching their heads in wonderment and confusion.

If the startling results are confirmed, a possibility that at least some physicists think is unlikely because the calculations involved are so difficult, they could have major ramifications for the so-called standard model on which most modern physics is based.

In an editorial accompanying the report in the journal Nature, physicist Jeff Flowers of the National Physical Laboratory in Teddington, England, said that there are three possibilities: Either the experimenters have made a mistake, the calculations used in determining the size of the proton are wrong or, potentially most exciting and disturbing, the standard model has some kind of problem.

If the theory turns out to be wrong, “it would be quite revolutionary. It would mean that we know a lot less than we thought we knew,” said physicist Peter J. Mohr of the National Institute of Standards and Technology in Gaithersburg, Md., who was not involved in the research. “If it is a fundamental problem, we don’t know what the consequences are yet.”

Whatever the explanation, however, it will have far more import for physicists than for anyone else, he added. The standard model “works pretty well in most cases,” explaining lasers, telephones, magnetic resonance scanning and a host of other modern-day miracles.

The standard model, which defines the structure and behavior of matter, radioactivity, electricity – pretty much everything other than gravity – is based upon the hydrogen atom. That atom, composed of a single proton orbited by a single electron, is the most thoroughly studied atom in physics, primarily because of its simplicity. “To understand hydrogen is to understand all of physics,” said physicist Aldo Antognini of the Paul Scherrer Institute in Villigen, Switzerland, a co-author of the report.