
Artist’s impression of an alien world with alien cities. Credit: NASA/Jay Freidlander
What’s all this buzz about quantum? Maybe you’ve heard it in science class or maybe in a sci-fi movie! No matter where you’ve come across it, you probably know it’s a bit strange, maybe confusing but also possibly an important part of the future. And all these things are true!
Physics is about using numbers to predict how things will move and interact. Just by going about your day, you have a sense of how balls will bounce or even how the Earth orbits the Sun. This kind of physics is called “classical”.
Quantum physics looks at the tiniest particles. At these scales our familiar classical physics breaks down and new effects pop up instead. These strange quantum effects tell us more about how nature works… and could help us invent new, powerful technologies – like quantum computers.
We think everyone can get their head around quantum, so we created a contest for adults to explain their favourite quantum effect using everyday language. Our expert judges picked the top 5 entries and this story from Ciaran O’Hare is one of them. Here he talks about “decoherence”, how gazillions of bizarre, quantum particles working together make such a regular, predictable world.
As a human being, you probably think you’re pretty unique, with your personality, hobbies, favourite foods, and so on. But if I were an alien observing Earth from afar and zoomed in on you, I might still be able to figure out all of those unique characteristics by studying your life.

2025 is the International Year of Quantum Science and Technology! Credit: UNESCO
But what if I didn’t watch carefully enough? What if I zoomed out and lost track of you in the crowd? After all, I’m an alien, human beings look much the same to me. Rather than trying to understand individuals and all their strange idiosyncrasies, it might be simpler to study entire cities instead. If I watched all the little people wake up at 9am, rush about for a few hours, and then settle down at night, things would seem regular and predictable. A much easier system to study.
This idea is very important in quantum mechanics. Unique characteristics of small quantum components disappear once those components join a collective. We call this ‘decoherence’. It’s why phenomena that only happen in the quantum world—like particles being in two states at once, or passing through walls—seem so strange.
Our bodies are entire civilisations made of gazillions of tiny quantum components all interacting with each other. We are like the alien observing the daily cycle of a city. Decoherence is why our everyday “classical” world seems regular and predictable, but when we isolate and carefully study extremely small quantum things, we discover they behave in surprising and counterintuitive ways.
Did you know that the United Nations has declared 2025 as the International Year of Quantum Science and Technology? To celebrate, the Australian Institute of Physics, Cosmos and Double Helix Extra put on the Quantum Explained Challenge. We will be sharing more of the top entries from the Challenge this year. Stay tuned!
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