At the heart of quantum magnetoreception is the radical-pair mechanism, which involves the formation of short-lived molecular fragments, known as radical pairs, in the eyes of birds. These radical pairs are sensitive to magnetic fields, and their spin dynamics can be influenced by Earth’s magnetic field, allowing birds to detect and use this information for navigation.
The Radical-Pair Mechanism
The radical-pair mechanism involves the creation of radical pairs in the retina of birds. These radical pairs are formed when light-sensitive molecules in the eye, called cryptochromes, absorb photons and undergo chemical reactions that split the molecules into two unpaired electrons, creating the radical pair.
Spin Dynamics and Magnetic Field Detection
The spin states of the unpaired electrons in the radical pair are sensitive to the Earth’s magnetic field. As the radical pair undergoes chemical reactions, the spin states of the electrons can be influenced by the magnetic field, leading to changes in the concentrations of the different spin states. These changes in spin state concentrations can then be detected by the bird’s visual system, providing information about the direction of the magnetic field.