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Ever popped a piece of bread into a toaster, peered into the hole and watched the toaster’s heat element turn red and slowly brown that slice for you? 

Then, have you thought “how odd that everything – whether it’s wood or metal or glass – goes the same colour when heated: first red, then yellow, then white”?

Classical physics predicts the toaster’s heat element should get hotter and hotter, and emit more and more energy at higher and higher frequencies, eventually leading to your toaster unleashing x-rays and gamma rays through the kitchen, probably killing you. 

That, thankfully, does not happen. But this question, why all matter glows hot in the same way even though classical physics says it shouldn’t, captured the fascination of researchers. And its explanation lies at the heart of quantum physics.

In 1900, German physicist Max Planck came up with a reason why, proposing that light can only be emitted in discrete packets of energy – or quanta.

Basically, each quanta, or “packet”, of light at a certain frequency will deliver the same amount of energy, no matter how many packets are stacked on top of each other.

This is distinct from the classical theory of light as a wave, which suggests stacking more waves increases the energy of the overall wave.

Plank’s “Quantum Hypothesis” – later expanded by Einstein and others – has been fundamental to physics for more than a century.

It heralded an entirely new understanding of physics, influencing the field for more than a century in ways that have had profound impacts on our lives. 

It’s a quanta’s world – you’re just super positioned in it

We use a lot of technology that’s inspired by quantum physics or described by it – here are a few examples. 

Fluorescent lighting works by exciting mercury vapour into plasma which emits visible light. We’ve known for a while that if you get a vapour of atoms hot, it will release a pattern distinct to that element. Neils Bohr explained why back in the early 20th century with the first quantum model of the atom. Mercury vapour is good for lighting because its plasma creates light within the spectrum visible to the human eye. 

If your GPS has ever come to the rescue, you can thank quantum physics for it. This technology is enabled by atomic clocks, extremely consistent timekeeping devices that measure the oscillations of specific atoms. A second is more than one Mississippi, in fact it’s exactly 9,192,631,770 oscillations of the cesium-133 atom. We only understand that because of an idea in quantum science that atoms can exist in multiple states at once – it’s called quantum superposition. These clocks are so accurate they might only lose a second every few hundred million years. Even that’s not accurate enough for some – a �ʹڲ�Ʊ researcher has proposed an atomic clock that would neither lose nor gain 1/20th of a second over 14 billion ��𲹰���.��

Without clocks this accurate, GPS wouldn’t really work. There are atomic clocks in GPS satellites, and precise timing from atomic clocks allows GPS to calculate distances based on the travel time of signals. If your computer is even a microsecond off, the GPS will get your location wrong by hundreds of metres. 

Computers and smartphones – pretty well any advanced electronics – are super important to modernity, and they’re only possible because of the semiconductors inside them, which are only possible because of…

Quantum physics. 

A semiconductor is a material that works as both a conductor and an insulator – basically, it lets only some electricity pass through it. They can be designed to let precise amounts of electricity flow through them, enabling their use in a wide array of modern technologies. Because of quantum mechanics we know that electrons are both waves and particles, and that’s a key to understanding their behaviour in semiconductors. 

Coming soon:

If you’ve heard the word “quantum”, it’s likely in the context of computing. These are computers that will be able to do hugely complicated calculations current computers just can’t. Quantum computers exist but they’re not quite ready yet to roll out at scale. 

In classical computing, the smallest unit of information is a “bit”. In quantum computing, that’s replaced by a “qubit” (“quantum + bit”). A bit is binary – it’s either a 0 or a 1. A qubit can be both a 0 and a 1 simultaneously because of quantum superposition (I wonder if Schrödinger’s cat was ever aware of his famous identity crisis?),��meaning that instead of processing calculations bit by bit, a quantum computer can do it all, simultaneously. That’ll supercharge our computing power once we’ve worked out all the details. 

When we do, it’s hoped quantum computers will revolutionise all sorts of fields including drug discovery, by increasing the pace of the discovery of new treatments for cancer and Alzheimer’s. Fields like artificial intelligence and cryptography will also benefit, and scientists think quantum computing could even finally help us unlock fusion energy, providing effectively limitless clean electricity to the entire planet. 

Quantum computers could change the world in the 21st century as fundamentally as previous generations of computers did in the 20th. Just as once unimaginable technologies like smartwatches are now commonplace, quantum advancements are likely to push humanity’s boundaries even further.