Magnetovision: Birds' seventh sense revealed: Electrons normally dance round a molecule in pairs, but light can break this happy tango by shunting an electron from one molecule to another. The result is a pair of radicals - molecules with a solo electron. Electrons have a quantum property called spin, and in a radical pair the spins of the two unpaired electrons are linked; they either spin together or in opposite directions. The angle of a magnetic field can affect the flipping of the electrons from one of these spin states to the other, and in doing so, it can affect the outcome or the speed of chemical reactions involving the radical pair.
Schulten came up with the idea that radical pairs might help to explain magnetoreception back in 1978. His first paper on it was rejected by Science with a note that read, "A less bold scientist might have designated this idea to the waste paper basket." Instead, Schulten published his idea in an obscure journal and kept on refining it.