We Have No Idea: A Guide to the Unknown Universe

by Jorge Cham

Quarks are unlike leptons in that they feel the strong nuclear force and they have weird fractional electric charges (+2/3 and −1/3). If you mix the up and down quarks in just the right way, you can make protons (two ups and a down quark, with charge = 2/3 + 2/3 − 1/3 = +1) and neutrons (one up and two down quarks, with charge = 2/3 − 1/3 − 1/3 = 0). That’s extremely important (and lucky) because the charge of the electron just happens to be −1. If the quarks had any more (or less) charge, then the charge of protons wouldn’t precisely balance the negative charge of the electron and you couldn’t form stable neutral atoms. Without those perfect −1/3 and +2/3 charges, we wouldn’t be here. There would be no chemistry, no biology, and no life. This is actually fascinating (or creepy, depending on your level of paranoia) because, according to our current theory, particles can have any charges whatsoever; the theory works just as well with any charge value, and the fact that they balance perfectly is, as far as we know, a huge and lucky coincidence.