Quantum vision lets birds see the magnetic field

Both the current theories are based on the reaction of cryptochromes to blue light. An incident photon creates a radical-ion pair in the bird's retina (one molecule with one too many electrons, and one too few, so both are electrically charged). Professor Hore of the University of Oxford proposes that these charged particles can be pulled apart by an applied magnetic field. While actual cryptochromes are quite hard to get hold of, a similar synthetic molecule known as a carotenoid-porphyrin-fullerene triad (or CPF for people who don't want to spend ten minutes saying its name) was examined by his team. By shining blue light on a chemical solution and applying a magnetic field, he was able to create different concentrations of radicals and ions in different parts of the solution. If birds can detect this chemical imbalance (and most of biology is just moving chemicals around), then they have their magnetic compass.