Size of a proton? Really small

But physicists can't agree on one number

By Marissa Cevallos, 11:51 AM December 17, 2010

There are three possibilities: Either physicists have made a mistake in their calculations, protons are playing a terrible practical joke on physicists, or — a really long shot — the quantum theory describing charged particles is wrong.

This month scientists in Germany reported measuring the size of the proton by scattering electrons off it, an experiment they’ve done before. But the diameter they found is decidedly different from other recent measurements using energy shifts in hydrogen, ...

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