Question: What is antimatter?

Suzie Sheehy answered on 20 Mar 2011:

Great question!

Paul Dirac (one of my favourite physicists) realised in 1928 when he was looking at quantum mechanics, that all of the equations ought to work out just the same if the particles had the same mass but opposite electrical charge.

He thought this was strange, but it was a really important observation and it really is one of my favourite things in the history of science, because until then, no-one had thought about or seen anything like antimatter. It was completely, well… crazy!

But they had a lot of respect and trust in the mathematics and so within a few years started looking for anti-particles. They first found anti-electrons (called positrons) in 1932… and since then have found anti-particles for just about everything. We now don’t even blink an eye at the fact that these particles exist! It’s a great example of a theory predicting something, prompting experiments and then discovering something new and fundamental.

The strangest thing, though, is that Dirac’s equation and other theories tell us there should be equal amounts of matter and antimatter – but in the Universe, most of the time, we only see matter! This is called the matter-antimatter asymmetry and it’s a problem that we’d love to solve, where did all the antimatter go?

If there were equal amounts, it would mean that by now it would have annihilated, and none of the matter in the universe, including the Earth and us, could exist… so we have a lot to be thankful for!