Discovery shakes up standard view of atomic structure

LOS ANGELES — Physicists might have to rethink what they know about 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.

If the 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.

The standard model — which defines the structure and behavior of matter, radioactivity, electricity and just about 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.

If the standard model 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 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, 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 variety of other modern miracles.

In an editorial accompanying the report in the journal Nature, physicist Jeff Flowers of the National Physical Laboratory in Teddington, England, said 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 a problem.

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 confusion.

The Scherrer team is rechecking its calculations, as will physicists around the world. Meanwhile, the Scherrer team plans to repeat the experiment using helium atoms, which have two protons and two electrons, instead of hydrogen. That should either confirm or refute their findings.

For now, it's unclear whether the result will be confirmed as an experimental mistake or a revolution in physics. "I wouldn't bet on anything now," Mohr said. "It's not at all clear."