Finally a story about birds that doesn't involve them falling out of the sky. We know that robins, like many other animals, uses the Earth's magnetic field to navigate, but we don't know how. The answer could be quantum mechanics.

Although birds are probably the most famous magnetic navigators, the technique of sensing subtle variations in our planet's magnetic field is also used by creatures like bacteria and mole rats. But just how any of these critters manage to sense the Earth's magnetic field has long been a mystery. The leading hypothesis suggests that the field could affect small iron molecules in a bird's eyes, but new research suggests the real mechanisms might be much, much weirder.

The new model says that quantum entanglement is the key. Entanglement is when the quantum status of two particles becomes intertwined so that knowing the properties of one particle means you instantly know the properties of the other, no matter how far apart the two particles might be. (That's the short version, at any rate - here's a more detailed explanation.)

For our purposes, the exact mechanisms of quantum entanglement don't really matter. The crucial bit is that the magnetic field might disrupt the entanglement between two electrons in a light-sensitive protein inside a robin's eye. If that really is the case, it would be nothing short of amazing - in laboratory conditions, quantum entanglement has only been possible for about 80 microseconds at a time, and then only in ultra cold conditions close to absolute zero. But the research indicates robins can sustain entanglement for 100 microseconds while flying around at room temperature.

It's an amazing discovery, and here's how the scientists figured it out. Back in 2006, researchers captured twelve migrating robins and locked them in a small wooden room. They then applied small magnetic fields to the room. These fields were far too weak to have any effect on the world of classical physics - but they were still powerful enough to disrupt entangled electrons.


The results were stunning, as the robins became disoriented and flew aimlessly around the room whenever the field was turned on. At 150 nanoTesla, the field was about 300 times weaker than the Earth's magnetic field, which means the birds should never have become disoriented unless they really were using quantum entanglement to navigate. It does seem to rule out the iron molecule hypothesis, as the field would need to be 100 to 1000 times stronger for iron to be affected.

Figuring out the exact mechanisms by which robins sustain (relatively) long periods of quantum entanglement at room temperature could be a very big deal, as it could help enable practical applications like quantum computers. That's probably still a long way off, but at least the researchers have a decent idea how the robins would use entanglement to navigate.

As light enters the eye, it hits a protein called the cryptochrome, which surrounds the retina. Electrons in this protein are entangled, but light causes one part of an electron pair to get knocked out. The freed electron starts to wobble in reaction to Earth's magnetic field, but its still entangled brother also experiences these same movements and the magnetic pull from the rest of the molecule. The difference in how these two electrons move - because the free electron is no longer affected by the magnetic pull of the cryptochrome - creates patterns in the retina that the robin's brain can then interpret and use for navigation.

[via Science News]