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Asked by strangeness to Arttu, Ceri, James_M, Monica, Philip on 14 Jun 2011.
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Philip Dolan answered on 14 Jun 2011:
Yeah, I was reading on the BBC news the other day.
They’ve been doing an experiment at Imperial College over the last 10 years (at least) which allows them to pin down that an electron is indeed very spherical. If you were to expand an electron to be the size of the solar system, it’s surface will vary less than the width of a human hair from being perfectly spherical. And that’s just an upper bound, so it could be more spherical than that.
I’d be tempted to say that it is a perfect sphere from that experiment.
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Arttu Rajantie answered on 14 Jun 2011:
The electron does not have a surface so when physicists talk about how spherical it is they mean specifically its electric dipole moment (EDM). The EDM can be measured by looking at the behaviour of the electron in an electric field. In a classical object it measures how electric charges are distributed, and it is zero if the charge distribution is spherically symmetric. In the standard model of particle physics, electrons have zero EDM, but some other theories predict slight deviations from this.
In that recent experiment, the physicists were able to increase their sensitivity but the result was still zero, so it is still consistent with a fully spherical electron.
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James M Monk answered on 14 Jun 2011:
yes, Arttu is right – it is the shape of the electric field of the electron that was measured to be spherical.
When I read those reports in the news I didn’t understand what they were about for a moment – we normally hear about the electric dipole moment, not how “spherical” the electron is
Comments
strangeness commented on :
Ooh thank you, all those answers are fascinating! I was a little confused when I read the report at first as it sounded as if the electron had actually been found to be (very slightly) non-spherical, but now it makes sense. 🙂
Do you know how exactly the experiment would be carried out, and how the equipment would work?