About 150 million kilometres away from us, there is a huge sphere of hot plasma, which we call the Sun. Just like any other star, the Sun makes its energy by colliding lighter atomic nuclei to form a heavier element. This process, called nuclear fusion, is crucial for the existence of every single star in the universe.
However, there is a problem. The colliding nuclei are all positively charged, which means that they repel each other electrically. How do the nuclei fuse, then? There is another force – the strong nuclear force – which brings them together, but only when they are really close to each other to begin with. Therefore, the nuclei must have a huge energy (and thus velocity) in order to approach each other to the point where the attractive nuclear strong force surpasses the repulsive electrical force for nuclear fusion to occur. But when the temperature of the Sun was ascertained by its spectrum, it came to light that it does not even remotely reach the values necessary for nuclear fusion. In other words, the Sun simply should not shine whatsoever. This conclusion is obviously wrong – the Sun evidently shines, for which we owe to a peculiar phenomenon of quantum physics – quantum tunnelling.
Quantum tunnelling is a phenomenon wherein particles or even whole atoms have a certain probability of surpassing a barrier, even though they do not have enough energy to surpass it, which is unambiguously against the principles of classical physics. This phenomenon may not seem that peculiar at first sight, but the opposite is true. It would probably be quite strange if a person who run up against a wall appeared on the other side of the wall or even inside the wall. However incredible it may sound, this is essentially what happens to objects from the microworld during quantum tunnelling.
Quantum tunnelling can be explained using the principle of quantum superposition and the uncertainty principle. How? According to classical physics, the Sun does not have the sufficient temperature for atomic nuclei to approach each other enough for fusion to occur. However, the principle of quantum superposition states that the nuclei can be in more places at once (due to their wave nature), so there is a certain probability of them approaching enough and fusing. According to the Heisenberg uncertainty principle, on the other hand, there is always some uncertainty regarding the momentum of an object, so from time to time, one or both nuclei obtain an immense velocity (momentum) and fuse.
Quantum tunnelling is one of a few phenomena of quantum mechanics whose consequences we can hugely feel in the macroworld as well. The structure of our own bodies, for instance, is determined by the DNA molecule. However, it has been theorised that protons within this molecule can experience quantum tunnelling and therefore change our genetic makeup! These random genetic mutations caused by quantum tunnelling may even be linked to the existence of cancer, but more research is needed. Tunnelling also occurs during radioactive decay or in flash discs.
Keishinrei 