• The existence and stability of atoms relies heavily on the fact that neutrons are slightly more massive than protons. The experimentally determined masses differ by only around 0.14 percent. A slightly smaller or larger value of the mass difference would have led to a dramatically different universe, with too many neutrons, not enough hydrogen, or too few heavier elements.
  • The tiny mass difference is the reason why free neutrons decay on average after around ten minutes, while protons — the unchanging building blocks of matter — remain stable for a practically unlimited period. Simulations on supercomputers confirmed that most of the mass of the proton and neutron results from the energy carried by their quark constituents in accordance with Einstein’s formula E=mc2.
  • The results of this work open the door to a new generation of simulations that will be used to determine the properties of quarks, gluons, and nuclear particles.

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