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View Full Version : The Electron: An (Almost) Perfect Sphere



Eldritch
05-27-2011, 09:44 PM
Physicists step up the search for particle's predicted deformity — and hope to solve antimatter mystery along the way.

http://www.nature.com/news/2011/110525/images/news321-i1.0.jpg

Now that's precision measurement: the electron is a perfect sphere, give or take barely one part in a million billion.

The result comes from the latest in a long line of experiments to probe the shape of the fundamental particle that carries electrical charge. "If you imagine blowing up the electron so that it is the size of the Solar System, then it is spherical to within the width of a human hair," says physicist Edward Hinds at Imperial College London, who led the team responsible for the minuscule measurement.

But this is more than a quest for accuracy. Many physicists are intent on finding out whether the electron is actually slightly squashed, as some theories predict. If the deformity is there, further refinement of the technique that made the latest measurement should pin down the deformity in the coming decade. The discovery would show that time is fundamentally asymmetrical, and could prompt an overhaul of the 'standard model' of particle physics.

Although the electron has traditionally been considered to be an infinitesimally small point of charge, it actually drags a cloud of virtual particles around. These fleeting particles pop in and out of existence, and contribute to the electron's mass and volume. All experiments so far have revealed that this cloud is perfectly spherical, but hypothetical virtual particles predicted by extensions to the standard model would make the cloud bulge slightly along the electron's axis of spin. This bulge would make one side of the electron slightly more negatively charged than the other, creating an electric dipole similar to the north and south poles of a bar magnet.

Physicists argue that we would expect to see this electric dipole in a Universe which consists overwhelmingly of matter. Although equal quantities of matter and antimatter are thought to have been created in the Big Bang, we see almost no antimatter in today's Universe. This asymmetry not only implies a cosmic favouritism for matter, but also suggests that physics does not always work the same way when time is run backwards instead of forwards.

Be kind, rewind

Evidence of this asymmetry could be found by playing a film of a spinning, slightly squashed electron in reverse. Although the direction of the electric dipole would remain unchanged, the magnetic dipole around the electron — which depends on the direction of its spin — would flip to the opposite direction.

Full story (http://www.nature.com/news/2011/110525/full/news.2011.321.html).