Since Chemistry is applied Physics, and Biology is applied Chemistry, of course Biology is somewhat related to Physics. Classical physics is clearly a key part of Biology, for example the Thermodynamics that dictates chemical reactions within organisms. However, Quantum Physics, which is based on the interaction of subatomic particles, doesn’t seem to have a place in an organism. Even in a single cell, there are way too many atoms for Quantum Physics to seem to have any great effect on the cell as a whole, particularly as thermodynamics, a branch of classical physics, is definitely the most noticed system – it is the random molecular jostling understood by classical physics that in large amounts gives predictable results, i.e. order from disorder. Not the realm of quantum physics yet. However, if I told you that quantum physics could well have a huge impact on the navigation of robins, how we smell, the efficiency of photosynthesis, and how enzymes work, you might either not believe me, or tell me that you don’t have a clue because you don’t know what quantum physics is, never mind understand it.
Nevertheless, I shall try to explain how robins use quantum physics to navigate, however there is so much going on at once that in Jim Al-Khalili’s book ‘Life on the Edge – the Coming of Age of Quantum Biology’ (the book where I have learnt just about everything I know not just of Quantum Biology but of Quantum Physics in general), it takes just about half of the book to finish explaining any one phenomenon, as there is so much other Physics, Chemistry, and Biology to explain at once.
The European Robin migrates to southern Europe for the winter. The majority of migrating birds who use techniques such as using the sun and the stars to help them, or previously seen landmarks, however this robin is believed to use quantum physics to navigate – it has an “inclination compass”, so it can differentiate between the pole and the equator, however it is unable to differentiate between North and South. This is because the robins’ internal compass measures the angle of the magnetic field line, so at the equator the magnetic field line is nearly parallel to the ground, whereas at the poles the field line is pretty much vertical. However, how exactly the robin does this is nsomewhat unknown, as the Earth’s magnetic field is far too weak for an animal to detect as we would know it, so this is where quantum physics comes in.
But what is Quantum Physics? This is where it is clear that it is much easier to explain this whole process in a book, rather than in a single blog post. Quantum physics is a fairly modern strand of Physics which deals with the “spooky” world inside atoms, where the laws of Classical Physics no longer apply. The Quantum world deals with completely counter-intuitive ideas, for example the Entanglement theory states that two entangled electrons will ‘communicate’ with each other in such a way that if something happens to one atom, instantaneously the other will react, meaning that this message is sent faster than the speed of light, which according to classical physics, is impossible. There is also wave-particle duality, and the famous ‘Schrodinger’s Cat’ which shows that the mere act of measurement erases the quantum properties, along with many other equally confusing concepts of Quantum Physics. Anyway, after this extremely brief and probably confusing summary of quantum physics, I shall attempt to explain how exactly the robin does navigate.
The robin’s compass is located in its eyes, and photons from light provide the majority of the energy for the reaction. This can be visualised as a hill – the photons provide the energy to bring a ball up to the top of the hill, so only the slightest push is required to make the ball fall one of two ways down the hill. Then, when a photon enters the robin’s eye, it creates an entangled pair of electrons. Each electron can have one of two possible polarisation states, ie spin one way or the other, however before you force the electron to ‘choose’ by measuring it, it is neither one nor the other, it is both simultaneously. When you force it to choose a polarisation state, the other electron in the pair instantaneously chooses a polarisation state too. Depending on how the pair has been entangled, the two electrons might always spin parallel, or always anti-parallel. Depending on the inclination of the magnetic field lines, the pair of electrons might be more likely to be entangled a certain way. It is unclear exactly which way round, but it could be that at the pole the electrons are more likely to be entangled so that when measured the spins are parallel, whereas at the equator they are entangled to spin anti-parallel. Because photons have already done the majority of the work of “climbing the energy hill”, only the slightest push is required to cause the eye to produce one of two sets of chemicals which will then guide the bird as to where to go. The key to this discovery was the discovery of cryptochrome in animal eyes, which is a protein that was known to potentially generate radical pairs which are the pairs of ‘left over’ electrons that can spin either parallel of anti-parallel, and are affected by even weak magnetic fields.
Although I have (attempted) to explain how the European Robin uses Quantum Physics to navigate, showing that Quantum Physics has a huge effect on biological organisms which were assumed to be way to large, and hot for Quantum Physics to be noticeable. In Jim Al-Khalili’s book, various other situations are explained where Quantum Physics has an effect on organisms, and he argues that our lack of understanding of quantum physics is why we have not been able create life from entirely artificial materials. I would definitely recommend this book, and also his two part series ‘The Secrets of Quantum Physics’ if you are interested in any of the sciences, as both the book and the documentary take you from the absolute basics to the mind boggling theories.
Why is there a fault line, an edge, between the world that we see and the world that physicists know really exists beneath its surface?