It would be quite a ghostly experience to see our world through the eyes of a migratory bird. Something about their visual system allows them to ‘see’ our planet’s magnetic field, a clever trick of quantum physics and biochemistry that helps them navigate great distances.
Now, for the very first time, scientists at the University of Tokyo have directly observed a key response that is believed to be behind the talents of birds and many other creatures to sense the direction of the planet’s poles.
Importantly, this is evidence that quantum physics directly affects a biochemical response in a cell – something we’ve long thought about but haven’t seen in action before.
Using a custom microscope sensitive to faint flashes of light, the team looked at a culture of human cells with a special light-sensitive material that dynamically responded to changes in a magnetic field.
The fluorescence of a cell decreases when a magnetic field passes over it. (Ikeya and Woodward, CC BY)
The change the researchers observed in the lab is consistent with what would be expected if a wayward quantum effect was responsible for the lighting response.
“We have not changed or added these cells,” says biophysicist Jonathan Woodward.
“We think we have extremely strong evidence that we have observed a purely quantum mechanical process that affects chemical activity at the cellular level.”
So how can cells, especially human cells, respond to magnetic fields?
While several hypotheses exist, many researchers believe the power is due to a unique quantum response involving photoreceptors called cryptochromes.
Cyrptochromes are found in the cells of many types and are involved in the regulation of circadian rhythms. In species of migratory birds, dogs and other species, they have been linked to the mysterious ability to sense magnetic fields.
While most of us cannot see magnetic fields, our own cells certainly contain cryptochromes. And there is some evidence that, although unconscious, humans are actually still able to detect Earth’s magnetism.
To see the reaction in cyrptochromes in action, the researchers bathed a culture of human cells containing cryptochromes in blue light, causing them to fluoresce weakly. While they were glowing, the team repeatedly swept magnetic fields of different frequencies across the cells.
They found that every time the magnetic file went over the cells, their fluorescence dropped about 3.5 percent – enough to show an immediate response.
So how can a magnetic field affect a photoreceptor?
It all boils down to something called spin – an innate property of electrons.
We already know that spin is significantly affected by magnetic fields. Arrange electrons properly around an atom and gather enough of them together in one place, and the resulting mass of material can be displaced using nothing but a weak magnetic field like the one surrounding our planet.
This is all well and good if you want to make a needle for a navigation compass. But with no obvious signs of magnetically sensitive chunks of material in pigeon skulls, physicists had to think smaller.
In 1975, a researcher at the Max Planck Institute named Klaus Schulten developed a theory of how magnetic fields can influence chemical reactions.
It involved something called a radical couple.
A garden variety radical is an electron in the outer shell of an atom that is not a partner of a second electron.
Sometimes these bachelor electrons can adopt a wingman in another atom to form a radical pair. The two remain unpaired, but thanks to a shared history, they are considered entwined, which in quantum terms means their spins will eerily match no matter how far apart they are.
Since this correlation cannot be explained by persistent physical connections, it is purely a quantum activity, something even Albert Einstein considered “ghostly.”
In the bustle of a living cell, their entanglement will be fleeting. But even these short correlating spins should last just long enough to make a subtle difference in the way their respective parent atoms behave.
In this experiment, as the magnetic field passed across the cells, the corresponding dip in fluorescence suggests that the generation of radical pairs was affected.
An interesting consequence of the research could be how even weak magnetic fields can indirectly influence other biological processes. While the evidence that magnetism affects human health is weak, experiments similar to this one may turn out to be another avenue for research.
“The nice thing about this research is to see that the relationship between the spins of two individual electrons can have a big effect on biology,” says Woodward.
Of course, birds are not the only animal that relies on our magnetosphere for their direction. Types of fish, worms, insects and even some mammals are predisposed to it. We humans can even be cognitively affected by the Earth’s weak magnetic field.
The evolution of this ability could have yielded some vastly different actions based on different physics.
Having evidence that at least one of them connects the strangeness of the quantum world to the behavior of a living being is enough to force us to wonder what other bits of biology spring from the eerie depths of fundamental physics.
This research is published in PNAS.