This just in: http://www.nature.com/news/2010/100707/full/news.2010.337.html

The proton seems to be 0.00000000000003 millimetres smaller than researchers previously thought, according to work published in today’s issue of Nature.

The difference is so infinitesimal that it might defy belief that anyone, even physicists, would care. But the new measurements could mean that there is a gap in existing theories of quantum mechanics. “It’s a very serious discrepancy,” says Ingo Sick, a physicist at the University of Basel in Switzerland, who has tried to reconcile the finding with four decades of previous measurements. “There is really something seriously wrong someplace.”

What are the implications?

But, Carlson says, “the first thing is to go through the existing calculations with a fine-toothed comb”. It could be that an error was made, or that approximations made in existing quantum calculation simply aren’t good enough. “Right now, I’d put my money on some other correction,” he says. “It’s also where my research time will be going over the next month.”