The statistics employed by <!g>quantum mechanics come in two varieties, both strikingly non-classical. (Technically the following results are part of relativistic quantum mechanics.) Particles such as protons and <!g>electrons obey <!g>Fermi-<!g>Dirac statistics and thus the Pauli exclusion principle. These lead to the impenetrability of matter and its ‘space-filling’ character, as well as such chemical properties as valency and color. Particles such as <!g>photons and <!g>gravitons obey Bose-<!g>Einstein statistics and carry the fundamental forces in nature, such as <!g>electromagnetism and gravity. See the discussion in Russell, "Quantum Physics."