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What is antimatter?

It’s the favoured fodder of sci-fi writers, but antimatter is no fiction; it’s real and our very existence depends upon its properties.

It’s the favoured fodder of sci-fi writers, from fuel to power interstellar spaceships to the volatile ingredient in Vatican-annihilating bombs. But antimatter is no fiction; it’s real and what’s more, our very existence depends upon its properties.

Artist’s impression of a spacecraft proposed by NASA that is powered by antimatter
Artist’s impression of a spacecraft proposed by NASA that is powered by antimatter. © NASA

The first particle of antimatter

We’ve known about antimatter for a long time. Paul Dirac, one of the greatest theorists of the 20th century, was the first to anticipate its existence when he predicted that the electron should have a partner with opposite electric charge – the anti-electron or positron – his only guide, a beautiful equation he first wrote down in 1927.

Few physicists took Dirac’s prediction seriously (including Dirac himself). But in 1932 Carl Anderson took a photograph that would turn the tide of scepticism for good. The photograph showed a faint white line crossing a cloud chamber, which he was using to study cosmic rays. Crucially, it curved in exactly the opposite way expected of an electron, providing conclusive evidence that anti-electrons were real.

Over the following years, physicists discovered that every particle had a corresponding anti-particle and just as particles clump together to make matter, antiparticles can clump to make antimatter.

But this begged a question: could there be parts of the universe made of antimatter? Perhaps with anti-stars, anti-planets, anti-little-green-men and anti-museums? The answer, as far as we can tell, appears to be a resounding no.

The LHCb cavern © CERN

Inside the the LHCb cavern.

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