How round is round?

Tom Feilden
Science correspondent, Today

Fascinating piece on the shape of the electron in Nature this week, which Pallab Ghosh explains here.

What struck me is how truly round this most basic building block of matter really is. If you want to understand the meaning of spherical, then look no further than one of the most basic building blocks of matter: the electron.

Using a very precise laser the team at Imperial College London's Centre for Cold Matter carefully measured the motion of electrons inside molecules of Ytterbium Fluoride. They were looking for the tell-tale wobble in the track of an electron that, like an unbalanced spinning top, would reveal the tiniest imperfections in its overall shape.

What they found shows that an electron departs from perfect roundness by less than 0.000000000000000000000000001 of a centimetre.

Or, to put it another - perhaps more intuitively comprehensible - way: if an electron were magnified to the size of the solar system it would appear spherical to within the width of a human hair.

And before you log off muttering darkly about angels dancing on the heads of pins and the expense of so much modern physics, the study does tell us something important about the preponderance of matter over antimatter, and throw a spanner in the workings of the Standard Model of particle physics.

Roundness, it seems, really matters.