A proton is heavier than its parts
The quarks inside a proton account for only about one percent of its mass. The rest is the energy of the gluon field and the motion of the quarks, via E = mc².
Established2 min read
Up and down quarks have masses of only a few MeV. A proton is 938 MeV. Quantum chromodynamics binds the quarks with gluons so tightly that the binding energy, and the relentless motion inside, is the mass. Lattice calculations now reproduce the proton mass from the theory.
You are not made of heavy stuff. You are made of light stuff held in a furious equilibrium, and the equilibrium has weight. The Higgs field gives the quarks their small masses. The kilogram, almost all of it, is QCD.
Caveats
- ‘One percent’ is the current-quark mass contribution, a scheme-dependent number at the order-of-magnitude level. It is not 50 percent in any honest accounting.
Sources
- 1Dürr S. et al.. Ab Initio Determination of Light Hadron Masses. Science 322, 2008.