Researchers have developed, for the first time, a method to efficiently produce long-lived “positronium” – a bound state between a positron and an electron – in a magnetic field. This is the first step towards measuring the difference in weight, if any, between matter and antimatter.

The positron is the antimatter version of the electron. It has identical mass to an electron, but a positive charge. If a positron and electron encounter each other, they annihilate to produce two gamma rays.

If it’s found that antimatter and matter don’t behave in the same way gravitationally, it would be a surprise result to the physics world. There is currently an assumption that matter and antimatter are exactly the same – other than a few properties like charge.

This assumption leads to the expectation that they should both have been created in equal amounts in the Big Bang. But we do not see much antimatter in the universe, so physicists are searching for differences between matter and antimatter to explain this.