#quantum tunnelling

Mistakes happen. Especially when it comes to the replication of vast sequences of DNA inside our cells. It's a good thing too. If not for the errors in our genes we refer to as mutations, natural selection would be a no-go, and life would be dead in the water.

As crucial as mutations are to everything from disease to biodiversity, we know shockingly little about the physics of the process.

Findings from the University of Surrey in the UK have revived speculations that a primary trigger behind the chemical sleight-of-hand that spontaneously swaps one coded base for another is quantum in nature.

Specifically, a significant part of the mutation process is the displacement of a single hydrogen that glues together the genetic bases to make the 'rungs' of DNA's twisted ladder structure. This occurs through the process of tunneling, breaking bonds between the genetic bases of guanine and cytosine over time scales that permit permanent changes.

Sure! Thank you!

Quantum tunnelling:

The Sun is powered by nuclear fusion, where protons (the nuclei of hydrogen atoms) stick together to form heavier helium nuclei. Protons are positively charged, so they repel each other electrically. However, if you get protons really close together - more or less touching - a very powerful force called the strong nuclear force kicks in and holds the protons together. Picture the protons as two magnets with their north poles pointing together covered in superglue. The magnets will repel each other while they’re some distance apart, but if you can make them touch, the glue will overcome that repulsion and stick them together.

(Source)

So how do we get the protons to overcome their initial shyness and stick? One way’s to increase the pressure and squeeze them tightly together - the core of the Sun’s got pretty high pressure. We also have to increase the temperature, so the protons be moving quickly and will slam into each other at high speeds - too fast to be repelled before they have a chance to stick. The problem is that at the pressure at the core of the Sun, temperatures need to be really hot. Really hot. Hotter than the core of the Sun, in fact. And that’s a problem.

The solution comes from quantum physics, which offers a sort of “shortcut” around this problem - quantum tunnelling. In classical physics, if two protons come close together, they’re a certain distance apart, and that’s it. But in quantum physics, there’s some uncertainty in the proton’s position and momentum. We can’t say exactly where a proton is and where it’s going - we can only talk in terms of probabilities. If you hold two protons quite close together, their most likely position is some distance apart - but there’s a small chance they could be touching. 

You can also think of this in terms of wave functions. If two protons get close enough that their wave functions overlap, there’s a chance the two protons will be able to touch even though their most likely positions are quite far apart. We call this tunnelling because it’s as if there’s a barrier of electrical repulsion acting between the two protons. They could be heated to very high temperatures and “jump over the barrier,” or take the quantum shortcut and “tunnel” under the barrier and allow fusion to happen at the temperatures inside the Sun’s core.

Another example of tunnelling is radioactive decay. Protons and neutrons are held together inside the nucleus by the strong nuclear force, which holds them tightly together while they’re touching. If a clump of protons and neutrons gets too far from its neighbours, though, it can overcome that strong force and be repelled from the nucleus. Classically, they would never have enough energy to break out of the nucleus - but thanks to quantum physics, they can tunnel their way out. 

(Source 1, 2)

We should be thankful by the way that these equations only really predict sensible probabilities for quantum tunnelling on a very tiny scale. If Planck’s constant were bigger, then cars might “leak” out of garages through quantum uncertainty!

I’ll talk about virtual particles some other time if you don’t mind, Anon - if I haven’t done that post within a few days feel free to send me another ask to remind me!

In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, should not be passable due to the object not having sufficient energy to pass or surmount the barrier.

Tunnelling is a consequence of the wave nature of matter and quantum indeterminacy. The quantum wave function describes the states of a particle or other physical system and wave equations such as the Schrödinger equation describe their evolution. In a system with a short, narrow potential barrier, a small part of wavefunction can appear outside of the barrier representing a probability for tunnelling through the barrier.

Explore the Daily Current Affairs 8 October 2025, relevant for UPSC exam. Also download quick REVISION NOTES. Source: The Hindu newspaper (Page no. 1) Quantum Tunnelling Context: 2025 Nobel Prize in Physics has been awarded to John Clarke, Michel Devoret, and John Martinis for their groundbreaking work in experimental quantum physics, particularly for exploring and demonstrating quantum…

There is not a Case for 'Black Hole' Evaporation and Explosion, but Perhaps for Hawking Radiation

by Graeme Heald "There is not a Case for 'Black Hole' Evaporation and Explosion, but Perhaps for Hawking Radiation" 

Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-1 , December 2019, 

URL: https://www.ijtsrd.com/papers/ijtsrd29661.pdf  

Paper URL: https://www.ijtsrd.com/physics/astrophysics/29661/there-is-not-a-case-for-%E2%80%98black-hole%E2%80%99-evaporation-and-explosion-but-perhaps-for-hawking-radiation/graeme-heald

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