Quantum physics

YOUR CHEAT SHEET TO THE SPOOKY SIDE OF THE UNIVERSE

Written by Colin Stuart

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1  THE QUANTUM WORLD IS LUMPY

The quantum world has a lot in common with shoes. You can’t just go to a shop and pick out trainers that are an exact match for your feet. Instead you’re forced to choose between pairs that come in predetermined sizes.

The subatomic world is similar. Albert Einstein won a Nobel Prize for proving that energy is quantised. Just as you can only buy shoes in multiples of half a size, so energy only comes in multiples of the same ‘quanta’ – hence the name quantum physics.

The quanta here is the Planck constant, named after Max Planck, the godfather of quantum physics. He was trying to solve a problem with our understanding of hot objects like the Sun. Our best theories couldn’t match the observations of the energy they kick out. By proposing that energy is quantised, he was able to bring theory neatly into line with experiment.

2  SOMETHING CAN BE BOTH WAVE AND PARTICLE

J. J. Thomson won the Nobel Prize in 1906 for his discovery that electrons are particles. Yet his son George won the Nobel Prize in 1937 for showing that electrons are waves. Who was right? The answer is both of them. This so-called wave-particle duality is a cornerstone of quantum physics.

It applies to light as well as electrons. Sometimes it pays to think about light as an electromagnetic wave, but at other times it’s more useful to picture it in the form of particles called photons.