Based on New Scientist, Rachel Courtland (Jan 22) & Ed Young (Nov. 27)
The ability of some birds to navigate by means of the Earth’s magnetic field had been known for some time without the mechanism by which they achieved this being fully understood. In fact the mechanism may vary somewhat between species. Some may rely on the radical pair mechanism. With this, light excites two electrons in a molecule, and this pushes one of the electrons into another molecule. The electrons are now in different molecules but remain quantum entangled. The electrons can have either opposite or same spin, but the angle of the Earth’s magnetic field can flip the spin of the electrons. Ultimately each molecule will be aligned with the magnetic field, and this alignment could change across a bird’s retina, which might in turn allow it to sense the Earth’s magnetic field.
Initially this theory had a problem as no molecule capable of forming the radical pairs needed was known to exist in the eye. However, it then emerged that there were proteins in both plants and animals known as cryptochromes that can detect blue or blue-green light. In a 2007 study showed that one species of bird could produce a radical pair that lasted for milliseconds, which would be long enough to detect the Earth’s magnetic field.
These studies suggest that contrary to the orthodoxy based on Tegmark’s 2000 paper quantum states can survive in the noisy environment of the eye, which is defined as being part of the brain. It has been shown that a magnetic field at only one thousandth of the strength of the Earth’s magnetic field can disrupt a bird’s sense of direction, which in turn has been calculated to mean that electron spin in a radical pair can remain entangled for at least 100 microseconds. This is longer than the 80 microsecond record for entanglement in an artificial environment. It is pointed out that evolution has been able to protect quantum states to a greater degree than so far achieved by technology.Tags: avian brains, bird navigation, electron spin Posted by