MeV, GeV, TeV

Money has dollars, thousands, and millions; you do not buy a house in single dollars. The electronvolt is likewise too small to be handy for most of particle physics, so physicists pile on the usual metric prefixes to get bigger and bigger units. The three you meet constantly are MeV, GeV, and TeV — each a thousand times the one before — and learning their rough sizes is like learning to read a price tag in this field.

The ladder is simple: one MeV (megaelectronvolt) is a million eV, one GeV (gigaelectronvolt) is a billion eV (a thousand MeV), and one TeV (teraelectronvolt) is a trillion eV (a thousand GeV). Each rung has a natural home. MeV is the scale of nuclear physics and the lighter particles: an electron's mass is about 0.5 MeV, a typical nuclear decay releases a few MeV. GeV is the scale of the proton (about 0.94 GeV) and most of the everyday particle zoo. TeV is the frontier of today's largest accelerators: the Large Hadron Collider smashes protons together at energies of several TeV.

These units matter because in particle physics energy and mass are the same currency, so a collider's energy reach directly sets which particles it can create. To make a particle of a given mass, you need at least that much energy available in the collision — this is why discovering the 125 GeV Higgs boson required a TeV-scale machine, and why proposing the next discovery usually means proposing a higher-energy collider. A small honesty note: a collider's headline energy (say 13 TeV) is the total of the two beams, but only a fraction is usefully available in any single proton-on-proton smash, because protons are composite and the real collision is between their quarks and gluons.