The Shrinking Proton: Particle Is Smaller Than Thought

The Shrinking Proton: Particle Is Smaller Than Thought

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How many protons can dance on the head of a pin? The answer is nowhere near as straightforward as one may think — and it might offer new insights into one of the most well-tested theories in physics. An international team of scientists recently tried to find out the actual size of a proton, one of the ingredients (along with neutrons and electrons) of the atoms that make up our bodies and the world around us.

Reporting in the journal Science, the researchers found that the particle’s radius is 0.84087 femtometers. A femtometer is a billionth of a billionth of a meter, or so small that the wavelength of gamma radiation is 100 times longer. The new measurement is about 4 percentsmaller than the currently accepted radius of 0.8768 femtometers, and that small difference presents a puzzle.

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