Quantum Tunnelling: When the Impossible Becomes Possible | Physics Explained for Beginners

Here's how I visualise Quantum Tunnelling (or Quantum Tunneling if you're American).

Hey everyone! I'm back after a lengthy hiatus! I had a dodgy computer that meant that I couldn't really create or upload anything, but I'm back up and running now!

In this video I wanted to talk to you about Quantum Tunnelling - a phenomenon that is another one of those "wtf quantum mechanics" ideas. The easiest way to learn about this phenomenon (in my opinion_ is to consider the behaviour of an electron when it encounters a potential barrier. If we use classical physics to analyse the behaviour of this electron, we see that if the electron has less energy than the peak of the barrier, then it cannot "overcome" the barrier. However if it has more energy than the peak of the barrier, then it can get to the other side. A nice analogy is to imagine a ball trying to roll up a hill - we need to provide it with enough energy for it to get to the top of the hill and roll over to the other side. However, this analogy has limitations which is why I don't like to use it too often.

So that is how an electron should behave when it encounters a potential barrier under the rules of classical physics. However, we like to do things in a much more quantum manner on this channel. As it turns out, when analysing our system with quantum mechanics, we need to consider the wave function of the electron. This is essentially linked to the probability distribution of the electron - it gives us information about how likely we are to find the electron in certain locations in space. However the wave function is known as a wave function for a reason - it behaves like a wave!

When we solve the Schrodinger equation (the grand equation of quantum mechanics) for a system consisting of an electron encountering a potential barrier that looks like a step, and the electron has less energy than the top of the step barrier, then we find that the wave function of the electron is actually non-zero on the other side of the barrier! This means that despite not having "enough energy" (at least according to classical physics), our electron can still be found on the other side of the potential barrier!

Within the potential barrier itself, the wave function displays some interesting behaviour - it looks like an exponentially decaying evanescent wave. Evanescent waves are actually very classical, we've known for ages that electromagnetic waves (for example) can display evanescent behaviour. However, the reason our study is quantum, is because objects we originally believed to be particles (i.e. electrons) can actually behave like waves through their wave functions!

Quantum tunnelling has a few useful applications - it is how we explain a large chunk of radioactivity, for example. The principle of quantum tunnelling is also very important in building a Scanning Tunnelling Microscope (something which I described in detail in a video on Higgsino Physics' channel - go check it out).

With all that being said, it's great to be back! If you want to follow what I get up to on a more day-to-day basis, follow me on Instagram @parthvlogs