Electrons are almost perfect spheres, and the fact that they are could help answer questions such as why antimatter is rare.

Scientists at Imperial College London made the most accurate measurement yet of the shape of the electron, in an experiment that took 10 years to complete. The data suggest the electron differs from being perfectly round by a length that is so small it is a billion trillionth of a nanometer. That is so near perfect that an electron would have to be the size of the solar system before you could see the difference.

The physicists from the college's Centre for Cold Matter studied the electrons inside molecules of ytterbium fluoride. Using a laser, they made careful measurements of the motion of these electrons. If the electrons were not perfectly round then their motion would exhibit a distinctive wobble, distorting the shape of the molecule. The researchers saw no wobbles.

The researchers are now planning to measure the electron's shape even more closely. The results of this work are important in the study of antimatter, an elusive substance that behaves in the same way as ordinary matter, except that it has an opposite electrical charge. For example, the antimatter version of the negatively charged electron is the positively charged anti-electron (also known as a positron). Understanding the shape of the electron could help researchers understand how positrons behave and how antimatter and matter might differ.

The shape of electrons - and other particles - matters because current theories struggle to explain why there is matter in the universe, but very little anti-matter. Most models predict that at the beginning of time, there would have been about equal amounts of both. But since matter and antimatter annihilate each other when they touch, that would mean that there wouldn't be anything at all in the universe except photons. If matter and anti-matter behave differently, then it might explain why one dominates the universe. Antimatter does occur, but it is created in very small amounts.

Astronomers have looked right to the edge of the visible universe and even then they see just matter, no great stashes of antimatter. Physicists just do not know what happened to all the antimatter, but this research can help us to confirm or rule out some of the possible explanations, said Professor Edward Hinds, research co-author and head of the Centre for Cold Matter, in a statement.