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Phoenix666 writes:

New Scientist:

[...] In addition to the 9 percent of the proton's mass that comes from quarks' heft, 32 percent comes from the energy of the quarks zipping around inside the proton, Liu and colleagues found. (That's because energy and mass are two sides of the same coin, thanks to Einstein's famous equation, E=mc2.) Other occupants of the proton, massless particles called gluons that help hold quarks together, contribute another 36 percent via their energy.

The remaining 23 percent arises due to quantum effects that occur when quarks and gluons interact in complicated ways within the proton. Those interactions cause QCD to flout a principle called scale invariance. In scale invariant theories, stretching or shrinking space and time makes no difference to the theories' results. Massive particles provide the theory with a scale, so when QCD defies scale invariance, protons also gain mass.

The results of the study aren't surprising, says theoretical physicist Andreas Kronfeld of Fermilab in Batavia, Ill. Scientists have long suspected that the proton's mass was made up in this way. But, he says, "this kind of calculation replaces a belief with scientific knowledge."

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