Scientists have suspected for a while that birds navigate their way around the world while migrating south using the Earth’s magnetic field as a guide. However, the mechanism by which this happens is not understood. New research is suggesting that birds are able to “see” the Earth’s magnetic field as if it were a pattern of colors by the method of quantum entanglement. The idea that birds have the ability to see the invisible magnetic fields all around us as different colors is fascinating to think about.
Quantum entanglement describes a phenomenon that links a pair of electrons so that either one of them “knows” what the other is doing, regardless of their distance apart. According to a paper published in an upcoming issue of Physical Review Letters, physicists at the University of Innsbruck in Austria have designed experiments testing the theory that birds use a molecule called cryptochrome, located in their eyes, to sense magnetic fields.
Prior to this experiment, researchers at the University of California, Irvine, singled out cryptochrome as a candidate for the molecule that determines how birds sense magnetic fields, as it was known that cryptochrome electrons typically come in entangled pairs. Movement between the pairs occurs when magnetic fields cause the molecules’ electrons to wobble and when sunlight knocks one of the electrons aside. The theory posits that a chemical reaction in response to the wayward electron’s altered spin lets birds see magnetic fields in color.
Physicist Hans Briegel and colleagues at the University of Innsbruck in Austria wondered if having entangled electrons in cryptochrome could make birds more sensitive to magnetic fields. The researchers calculated how strongly a pair of electrons with entangled spins should respond to a magnetic field, compared with an unentangled pair.
The results showed that entanglement can be helpful, but maybe not for birds. Briegel and colleagues ran the numbers for cryptochrome and for another molecule, pyrene, a well-studied molecule with little biological significance. For pyrene, they found that entanglement between the electrons’ spins made the particles much more sensitive to magnetic fields. But for cryptochrome, entanglement made no difference.
“This first indication says no,” Briegel says.
A disappointment, perhaps. But spinning off the theoretical work on cryptochrome, the researchers have come up with a way to test this effect in real molecules. Zapping the electron pair with short, energetic bursts of microwaves could reveal whether the electrons are entangled or not. The same calculations used for cryptochrome suggest that if electrons’ spins are entangled, their sensitivity to magnetic field shouldn’t change. If the spins are not entangled, their sensitivity should drop, Briegel says.
This technique could be used to test many different molecules. Finding that different molecules can use entanglement differently highlights the complexity of the role quantum mechanics may play in biology, Briegel says. “This is one example where you would think upon first seeing this, well, that is a proper quantum feature,” he says. “But it requires a closer look. It’s nontrivial because, as we see in our study, it depends on the molecule.”
Briegel imagines jolting individual molecules in a lab, but Ritz hopes to find a way to test quantum entanglement effects in live birds. He’s already doing the legwork to see if it’s possible, he says.
“I’m sufficiently interested in these suggestions to see whether they can be realized, to work on designing experiments,” Ritz says. “There’s a lot of promise there.”