These folks claim it does.
But I thought the electron didn’t have a “shape”? That it was a point in space with no structure or dimensions? 
That’s what you get for going to a Faux News. I saw an article on the subjectlinked from MSN and it explained carefully that it wasn’t the shape of the electron, but the shape of an electron’s interaction with electric fields. I don’t even know if that is accurate either, but it’s certainly less misleading than your cite.
It is round within 0.000000000000000000000000001 cm??? How could they possibly measure something to that level of uncertainty? Something doesn’t smell right here.
I just heard an interview with one of the study authors on the Nature podcast, and even there he was going on about electrons as perfectly round spheres. I think he briefly mentioned magnetic and electrical dipole moments, but only in passing. So it appears that in this case you can’t blame the ridiculous oversimplification on reporters.
As to the precision, basically the study found that they could not measure any electrical dipole moment at all, so if it exists it must smaller than the minimum possibly detectable by their apparatus.
An electron is not really something one can meaningfully attribute a property such as ‘round’ to. Instead, what’s being measured here is the electron’s (electric) dipole moment, which is something that measures charge distribution – for instance, two charges q and -q separated by a distance d have a dipole moment P = qd. Dipole moments therefore have units of chargelength. For a perfectly spherical, uniform charge distribution, the dipole moment vanishes – so when they say ‘the electron is spherical’ to whatever accuracy, they really mean ‘the electron’s dipole moment vanishes’ to the stated accuracy, so that it behaves like a spherical charge distribution.
Why is this interesting? Well, different theories predict different dipole moments for the electron; the vanilla standard model of particle physics predicts a very small one, while certain extensions, such as supersymmetry, predict relatively larger ones. I’m not sure what, if anything, has been ruled out by the new measurement – essentially, this is a result of the form ‘no new physics up to such-and-such an accuracy’. Within the standard model, a nonvanishing electron dipole moment leads to the breaking of parity invariance, which roughly means that particles and their antiparticles behave differently under certain circumstances – this is thought, for instance, to account for the fact that, while both matter and antimatter should have been created in equal magnitude, the universe appears to consist mostly of matter.
As for how this is measured, well, a dipole moment couples to an electric field, which means that an electron with dipole moment will have a slightly different reaction to an applied electric field than an electron without one; presumably they tried to detect that in some way (I haven’t had a look at the paper).
Interestingly, experiments of this kind are one of the few ways to probe new microphysics that don’t involve building huge particle accelerators – indeed, if they had found evidence of a dipole moment consistent with supersymmetry, they might have stolen a bit of the LHC’s thunder (and even so, of course, it’s an impressive result – as I said, I haven’t looked at any figures, but it might be that the conclusion is that supersymmetry, if it exists, will be much harder to detect at the LHC than previously thought).
You’re right. I forgot that reporters shouldn’t know anything, can’t ask questions, and should report anything they think they heard as fact.
Heh, fair enough.
At least in the podcast interview I heard, though, the interviewer was asking fairly detailed and insightful questions, which the interviewee answered with “BLAH BLAH ELECTRONS ARE SUPER ROUND BLAH”. And this is for an audience of scientists and particularly interested laymen.
So a good deal of the blame belongs to a scientist who doesn’t want to bother explaining what a dipole moment is and instead tells a lame story about shape.
Can the electric or magnetic dipole moment (or is it a tripole moment) of a proton or neutron be measured? And can we confirm it looks like it’s made up of three components? Or are the quarks “whizzing around too fast”* for this to be done?
*Layperson’s term for the uncertainty of location inherent in the wave function.
It’s all waves anyway…
The magnetic moments (one generally omits the ‘dipole’, there not being – as far as is currently known – magnetic monopoles) of the elementary particles are well known, and in the special case of the electron, the agreement of its value with theory constitutes the oft-quoted ‘most accurately verified prediction of physics’. And indeed, the fact that the neutron possesses a magnetic moment at all is taken as evidence for its compositeness (though it’s not so much the case that it ‘looks like’ something made out of three quarks, but rather that, since it is neutral, and magnetic moments are produced by moving charges, there must be ‘something’ there on a more fundamental level). (Also, just for completeness, there’s no such thing as a ‘tripole moment’, the next multipole is the quadrupole.)
As for electric dipole moments, I think that in all cases, all that’s known is an upper bound, but no definite value.
HEY!!!:mad:
As my old advisor used to put it, “We know that magnetic monopoles exist. But there might be a very small number of them, such as zero”.
nm.
Could somebody elaborate in delicious eloquent doperspeak what the implications of this ‘roundness’ are? Does this have any significance other than poking a few tiny holes in esoteric theories? Is this a WOW GROUND BREAKING EVENT IN PHYSICS?
Or is this more of a “oh hey there’s probably a dipole still but it’s smaller than we thought neat huh! grant money plz” kind of thing?
The converse of this would be that the neutrino, which is a fundamental particle, must have exactly zero magnetic moment. Is that generally accepted?
Quoth Interconnected Series of Tubes:
The roundness was expected. If they had detected a non-roundness, that would have been much more significant, as it’d have supported various extensions to the standard model of particle physics, which as of yet have little evidence for them. And those theories in turn predict the existence of various as-yet undiscovered fundamental particles, some of which would probably be stable, and which might explain dark matter, or have other practical implications.
Quoth ZenBeam:
At least, all measurements of it have been consistent with zero. It’s a lot harder to do experiments with neutrinos than with electrons, though.
No, if the neutrino is a massive Dirac particle(*), it has a magnetic moment. It would be in the ballpark of 19 or 20 orders-of-magnitude less than the electron’s magnetic moment, and about 10 orders-of-magnitude less than the current experimental sensitivity to detect it.
(*) A Dirac particle is one that has a distinct antiparticle. Neutrinos may be Dirac particles or they may be Majorana particles (which are their own antiparticles). In the latter case (or if neutrinos were massless, which they aren’t), then they would not have a magnetic moment.
Huh, this is the first I’ve heard that a massive Dirac neutrino would have a magnetic dipole. I presume it’s aligned coaxially with the spin? And is it aligned or antialigned?
It would have to be aligned, as you surmise, but I’m not actually sure which of the two possible orientations it would have. I flipped through a few books and articles, but I didn’t get anywhere, as they all deal only with the magnitude of the moment, either when calculating it or when discussing the experimental signatures.