Although the use of the geomagnetic field for directional information is well established experimentally, it is not known by which biophysical mechanism magnetoreception is achieved. The magnetic sense is maybe the last perception mechanism for which the nature of the receptors and of the underlying biophysical mechanism remain unknown. Of the many mechanisms proposed, only two have been supported by theoretical analysis and experimental evidence, namely the use of ferromagnetic material (magnetite) and a chemical detection mechanism based on the sensitivity of a class of chemical reactions - radical-pair reactions - to weak magnetic fields.

Understanding the physical basis of the radical pair mechanism is an intriguing problem that can be addressed theoretically through solving the relevant quantum mechanical equations (stochastic Liouville equation) for a given radical-pair system. Based on such calculations, we have suggested a model for a chemical compass that can explain experimental observations.

We are currently interested in testing the chemical compass hypothesis. How can one determine whether the magnetic compass of animals is based on a radical pair mechanism? Quantum physical calculations show that oscillating magnetic fields in the radio frequency (RF) range can change radical pair reactions and, thus, would disturb a compass based on such reactions. An animal should therefore show a change in its magnetic orientation behavior when it is exposed to RF fields. Together with behavioral biologists we work on designing such an earth-field magnetic resonance experiment on the basis of existing behavioral assays.