Shinjini Bandopadhyay, Amity University Kolkata
Migratory birds fly thousands of miles each year between their breeding and wintering grounds. Their astonishing sense of direction coupled with remarkable navigation abilities are believed to be guided by a highly sensitive and precise biological ‘magnetic compass’.
The Avian Magnetic Compass
The compass which allows birds to navigate is a biophysical sensory mechanism that relies on magnetically sensitive light-dependent chemical reactions. These reactions occur in a specific protein known as cytochrome inside the bird’s eye. Cytochrome is responsible for maintaining circadian rhythm and sensing magnetic fields. It has been strongly hypothesized that quantum biology is responsible for generating prolonged spin coherences inside cryptochromes to help execute avian understanding and interpretation of the earth’s magnetic field for a successful migration. Migrating birds use a combination of environmental cues to migrate from one point to the other, including the sun, stars, landmarks, and most importantly, the Earth’s magnetic field.
Quantum Entanglement and Spin Coherence
Spin coherence is a property of radical pairs that have been formed photochemically in cryptochrome proteins of the retina. The main phenomenon behind this, inside the magnetic compass, is called quantum entanglement.
When a particle of light (photon) strikes a bird’s cryptochrome, its energy disturbs the molecules within the protein. This disturbance throws a pair of the molecule into an unstable state. This unstable state being extremely fragile is affected by even the subtle energetic pulses of Earth’s magnetic field.
The energy from that photon specifically perturbs the electrons within cryptochrome molecules. If an electron is knocked out of position (for example: exiting one molecule and joining another), a radical pair gets created. A radical pair is a duo of molecules where each has an odd number of electrons.
This type of radical pair is special because both radicals were generated at the same time, and hence the fates of the two molecules are now linked together. This locks them into a delicate relationship which is known as quantum entanglement.
The consequences of quantum entanglement are remarkable. Even after the entangled molecules are physically separated, the molecules are completely in sync and the change in properties of one molecule instantaneously alters its partner in the same manner. The two participating molecules in an entangled pair are always described together.
The entangled, radical pair state is generally a precarious, transient condition. Eventually, the two molecules recover and return to their original configuration. But while the pair are still intertwined, they flip-flop back and forth between two distinct chemical states. This switching between two specific chemical states forms the foundation of avian navigation. The amount of time the radical duo spends in one chemical state versus the other is believed to affect how the bird’s eye relays information to the brain about the surrounding environment.
Effect of Magnetic Field
The role of the magnetic field is the final factor according to researchers. Scientists have hypothesized that the effect of the magnetic field biases the proportion of time that the radical pair spends in one chemical state versus the other state. Hence, the time spent in each state is controlled by the magnetic field, and the duration of the radical pair existing in one state before it switches to the other is the information that is communicated between the eye and brain.
Although the exact mechanism is still not confirmed, the most popular theory is that one of these states helps produce a specific chemical whereas the other does not. The production or absence of this chemical might influence how signals are received by the brain’s visual cortex.
To migrate efficiently over large distances, it is not sufficient simply to distinguish north from south or pole-ward from equator-ward. A directional error of more than a few degrees can be fatal. The magnetic compass appears to be the dominant source of directional information and the only compass available at night under an overcast (but not completely dark) sky. Hence migratory birds should be able to determine their flight direction with high precision using their magnetic compass. Studies indicate that migratory songbirds can detect the axis of the magnetic field lines with accuracy better than 5°.
Directional Precision of the Avian Compass
It is still scientifically ambiguous how birds achieve the very high precision with which they detect the direction of the Earth’s magnetic field. Coherent spin dynamic simulations have studied cryptochrome-based radical pairs to observe that the persistence of the radical pairs in migratory birds is marginally longer than normally seen in quantum entanglement pairs.
When the spin coherence persists for longer than a few microseconds, the generation of a sharp feature that is called ‘spike’ occurs. The spike appears from avoided crossings of the quantum mechanical spin energy levels of radicals that are fostered in cryptochromes. This may explain the navigational behavior of migratory birds.
Conclusion
In conclusion, this sophisticated and intricate phenomenon of magnetically-sensitive quantum entangled radical pairs in bird eye cytochromes is a remarkable explanation for the perfect migratory abilities of birds each year. Further research can help us better understand avian body mechanisms and the role played by quantum biology for frequently seen events of animal behavior.
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REFERENCES:
- Hiscock, H. G., Worster, S., Kattnig, D. R., Steers, C., Jin, Y., Manolopoulos, D. E., Mouritsen, H., & Hore, P. J. (2016). The quantum needle of the avian magnetic compass. Proceedings of the National Academy of Sciences of the United States of America, 113(17), 4634–4639 https://doi.org/10.1073/pnas.1600341113
- Wu KJ. (2019). A bird’s eye view of quantum entanglement. Nova Wonders. https://www.pbs.org/wgbh/nova/article/birds-quantum-entanglement/
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Well written!
Very cool science