How Do Birds Find Their Way Home?
Birds must be geniuses because they use quantum mechanics to navigate
How do the birds find their way home? Decades of studies with frosted lenses, magnetic coils or scent deprivation show they use pretty much every clue available. The most difficult one for us to comprehend may be the earth’s magnetic field. Birds see it, but what it looks like to them, nobody knows. Work by Roswitha and Wolfgang Wiltschko in Germany, among others, suggests that this sense relies on quantum mechanics—that is, birds detect something happening in the eye at a subatomic level. Light striking the retina seems to stimulate chemical reactions that produce pairs of molecules with electrons that are “entangled,” meaning they share certain quantum properties. One of those properties, called “spin,” is affected by a magnetic field. That effect could tell the bird which way is north.
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One study into cryptochromes attempted to illustrate how the magnetic field might look to a bird flying at altitude. This data, from the Theoretical and Computational Biophysics group at the University of Illinois shows how magnetic field data is overlaid and changed by what the scholars called a “magnetic filter function.”
But the question remains — how does a bird, fruit fly, or other creature sense the weak, low-level magnetic field on Earth? That’s where things get a bit odd. According to the theory, cryptochrome forms a pair of radicals (molecules with a single unpaired electron) when exposed to blue light (in fruit flies) or the Earth’s magnetic field in birds. As weak as the Earth’s magnetic field is, it’s powerful enough to influence the spin state of the unpaired electrons, and it’s thought that the by doing so, it impacts the chemical reactions the cryptochrome causes.