Chapter 21 — The Force That Permits Chemistry

The electromagnetic force governs the interaction between charged particles—holding electrons in atoms and enabling atoms to form chemical bonds. The strength of this force determines whether electrons bind to nuclei at all and whether atoms share electrons with each other.

If the electromagnetic force were significantly stronger, electrons would bind too tightly to atomic nuclei to participate in chemical bonds. Chemistry requires electrons to be shared or transferred between atoms. Electrons bound too tightly to their own nuclei cannot be shared. No sharing means no chemistry.

If the electromagnetic force were significantly weaker, electrons would not bind stably to nuclei at all. Atoms would not hold together. There would be no periodic table, no stable matter, no chemistry. The value that permits chemistry occupies a narrow window between two modes of sterility. Martin Rees, Astronomer Royal, includes the electromagnetic force coupling among the six numbers whose values together permit the existence of the universe as we know it.

Rees, M.J. Just Six Numbers: The Deep Forces That Shape the Universe. New York: Basic Books, 2000.

Chapter 22 — The Ratio That Makes Atoms

The proton-to-electron mass ratio is approximately 1836 to 1. This ratio is not derived from any known physical principle. It is measured. Its precise value is required for the stability of atoms and for the chemistry of molecular bonding.

Protons provide the nuclear positive charge that defines the atom. Electrons provide the outer shells that participate in bonding. The mass ratio determines orbital energy levels, the relative sizes of nuclei and electron shells, and the dynamics of chemical reactions. If the proton were significantly lighter or the electron significantly heavier, the orbital dynamics would prevent stable chemical bonds from forming.

Physicist Freeman Dyson of the Institute for Advanced Study noted that small changes in the fundamental constants—including this ratio—would produce a universe in which chemistry is impossible. The precision of this ratio, like the precision of every other constant in this section, points toward a universe whose parameters were selected rather than random.

Barrow, J.D. and Tipler, F.J. The Anthropic Cosmological Principle. Oxford: Clarendon Press, 1986. Dyson, F.J. "Energy in the Universe." Scientific American 225, no. 3 (1971): 50–59.