An electron is a tiny, negatively charged particle that whizzes round the atomic nucleus. That’s been clear since its discovery by the British physicist J. J. Thomson in 1897. But 30 years later, his son George made a discovery. Sending electrons through a thin film of metal, he found that they created an interference pattern – just as if they were waves, not particles. Like his father, George won a Nobel Prize for his work, but this ‘wave-particle duality’ – shown by all particles, including photons of light – still provokes arguments.

There are two schools of thought. One: particles change their nature depending on what happens to them. In some experiments, they become wave-like, in others particle-like. Two: they’re weird things that always have a mix of both wave- and particle-like traits, but only reveal their wave-like aspects in some experiments, and their particle-like aspects in others.

So which is it? In 2012, two teams of researchers – one in France, the other in England – independently published the outcome of experiments capable of deciding between the two possibilities. Put simply, they let photons enter a device that would reveal their wave-like or particle-like nature – but the researchers could switch which of the photons’ traits were probed.

The results were consistent with the weirdest possibility: that they are both waves and particles all the time, and don’t just change from being one to the other depending on what’s done to them. Mindboggling – which is why many theorists suggest not thinking of electrons, photons and the like in everyday terms. Ultimately, they’re members of the quantum world, and unlike anything familiar.

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Robert is a science writer and visiting professor of science at Aston University.