Question: Could you please explain some quantum physics? I know a bit about it but not much.

Struan Simpson answered on 15 Mar 2020:

Sure! It’s a very big topic and I won’t go into any of the underlying maths, but I’ll try to cover some of the basics.

Towards the end of the 1800s, scientists began to realise that the models of physics they had so far been using (otherwise known as “classical physics”) seemed to result in logical inconsistencies and impossible experimental outcomes. In particular, they couldn’t use classical physics to describe the behaviour of things on the atomic and subatomic scales.

To solve this problem, they created a new form of physics called “quantum mechanics”. There are a few important differences between quantum mechanics and classical physics! For example, quantum mechanics introduced the idea that energy exists in finite amounts. To understand what this means, imagine you’ve got a penny. Let’s say I come along, and ask you if I can have half a penny, or 0.5p. For you, this is impossible – you can either give me 0p, or 1p, not 0.5p! The same is true of energy, except instead of a penny, it can exist as a single “quantum”. You can then add these up to get two, three, four (and so on) “quanta”, but you can’t get one and a half quanta!

Another example of how quantum mechanics is different is the famous concept of “wave-particle duality”. This is just a fancy way of saying that subatomic particles like electrons can behave as both particles, and waves. Well so what, you might ask? This turns out to be essential if we want to understand quantum mechanics as it explains quite a lot of strange things that happen on a subatomic scale.

Strange things like what? Well, take quantum “tunnelling” for example. Because subatomic particles like electrons or protons can behave as waves as well as particles, it means they can get to places they shouldn’t be able to. It’s sort of like if I asked you to get to the other side of a wall, and instead of climbing over it or walking around it, you just phased right through it and appeared on the other side! For subatomic particles, these walls aren’t physical walls – instead, they’re walls of energy. Obviously if you or I tried to walk through a solid wall, we’d look a bit stupid, but this is an everyday occurrence for subatomic particles!

That’s just a brief overview, but hopefully it’s given you a bit more info! It’s difficult to find a good introduction on the subject, but the Wikipedia article below is fairly readable. If you have any more questions, feel free to ask!

https://en.wikipedia.org/wiki/Introduction_to_quantum_mechanics