Just how birds use the earth’s magnetic field to navigate has puzzled researchers for decades.
But in recent years, a growing body of evidence points to the possibility that a weak magnetic field can influence the outcome of a certain type of chemical reaction in bird retinas involving radical ion pairs.
The idea is that the chemical outcome of the recombination of the ion pairs depends on whether the radical electrons are in a singlet or triplet state. A magnetic field creates a bias towards the triplet state which in turn leads to a one chemical output being preferred over another.
To test the idea, various experimenters have successfully confused the navigational abilities of birds such as robins by zapping them with magnetic fields specifically designed to disrupt this reaction. Case closed.
Not quite. The problem is that the ion recombination is known to happen too quickly for the Earth’s magnetic field to have any effect. So how can this mechanism work?
The claim made today by Iannis Kominis at the University of Crete is that the quantum zeno effect explains all. This is the watched-pot-never-boils effect on the qauntum scale. It states that the act of observing a quantum system can alter its evolution in a way that maintains the state for longer than expected.
One well known example is that it is possible to slow down the rate at which molecules convert from ortho to para isomers when they are constantly involved in collisions.
Kominis says a similar thing happens in birds: the presence of a geomagnetic field extends the lifetime of the singlet-triplet mixture from which the ions recombine. This gives the magnetic field time to bias the outcome of the recombination.
Interesting idea. But what’s most impressive is that it accounts for a number of unexplained observations about avian magnetoreception, such as the heading error of about 30 degrees that often afflicts birds (Kominis says a change in heading angle causes a change in the coherence time) and that avian compasses appear sensitive to only a certain window of magnetic field strength (Kominis says the window depends on the hyperfine couplings of the atoms involved which have been selected for by evolution).
If Kominis is correct, this is extraordinary news: it means a quantum sensor determines the macroscopic behaviour of magnetic sensitive birds.
Kominis says we may well see similar effects elsewhere, and mentions that a similar mechanism might be at work in photosynthesis.
But there’s another system closer to home that is bound to come up. Kominis is careful not to mention it but the quantum consciousness people are going to be all over this like freshmen at a sorority party.
Ref: arxiv.org/abs/0804.2646: Quantum Zeno Effect Underpinning the Radical-Ion-Pair Mechanism of Avian Magnetoreception