On large scales, the universe is electrically
neutral; the number of electrons is equal to the number of protons. Since pro-
tons outmass electrons by a factor of 1836 to 1, the mass density of electrons
is only a small perturbation to the mass density of protons and neutrons.
For this reason, the component of the universe made up of ions, atoms, and
molecules is generally referred to as baryonic matter, since only the baryons
(protons and neutrons) contribute significantly to the mass density.