Quantum physics is often portrayed as a strange and murky area of physics, which tells us that we cannot know precisely where particles are and how fast they are moving – and also that they are not really particles at all.
The name “quantum” comes from quantisation, because quantum physics tells us that properties of an object, like an electron, can only take on certain values and not others. It’s like when you go to the theatre or cinema: you must sit in a certain seat on a certain row, say row C. You can’t decide to sit in between rows C and D. In the same way, is it is a law of physics that an electron orbiting an atom is only allowed to have certain energy values.
But you never see this quantisation in everyday life, because the jumps between different energy levels are tiny and are just not directly visible to us. But for tiny objects, such as particles, tiny differences do matter. This is why quantum physics is only concerned with the very small. The world on this scale is very different from the one we know. It really is the case that electrons, for example, are not waves or particles – it is only when we decide to look at them that they behave as a wave or as a particle would do. We also have to do away with certainty, and move into a world where we can only predict the probability of events happening.
This is not due to any flaw in our measurements. In everyday life, we could in theory always predict exactly where a ball would land when we threw it if we made suitable measurements of how fast it was moving to begin with, at what angle, what effect the wind had, etc. For objects where quantum physics is important, i.e. very small objects, we cannot do this – events can be random and unpredictable.
You might have heard about radioactive uranium atoms used to generate nuclear power: whilst we can determine the probability that an atom undergoes radioactive decay in a certain time frame, we can’t predict when that will happen for any individual atom. If you find this upsetting, you are in the good company of Einstein.
But what you must remember is that the world quantum physics is describing is unimaginably small, so why should it behave in a way that is at all familiar to us?
Despite this remoteness, it has had a dramatic impact on both the scientific community and the world.