Electron Perfectly Round to One Part in a Million Billion, Experiment Finds
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By Edwin Cartlidge of Nature magazine
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 favoritism 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.
The latest study, published today in Nature, looked for the effect of this asymmetry on the spins of electrons exposed to strong electric and magnetic fields--but found nothing. Indeed, the researchers say that any deviations from perfect roundness within electrons must measure less than a billionth of a billionth of a billionth of a centimeter across.
Similar measurements had previously used beams of atoms passing through magnetic and electric fields. But Hinds and colleagues instead used molecules, which can be more sensitive to the fields. Using a pulsed beam of ytterbium fluoride, they were able to improve on the previous best sensitivity--achieved in 2002 by Eugene Commins and colleagues at the University of California, Berkeley, who used thallium atoms--by a factor of about 1.5.
Getting better all the time
Hinds reckons that by increasing the number of molecules per pulse and reducing their speed, his group should be able to raise the sensitivity of measurement by a factor of ten "over the next few years", and, ultimately, by a factor of 100. This would be more than enough to detect the distorting effects of most modifications to the standard model, and would thus provide evidence for the existence of new, very massive particles. A non-discovery, by contrast, would send theorists back to the drawing board.
"We would pretty much rule out all current theories if we went down by a factor of 100 and saw nothing," he says. "But theorists are very creative and would probably come up with models where the electric dipole moment is smaller."
Commins agrees that the latest work opens the door to major discoveries. "In the half-century since such experiments began, this is the first time that the best upper limit on the electric dipole has been achieved using molecules," he says. "Since molecules offer much greater sensitivities than atoms, it is only a question of time before the limit is greatly improved."
David DeMille of Yale University in New Haven, Connecticut, who was a co-author on the 2002 paper with Commins and is carrying out molecular experiments of his own using thorium monoxide, agrees. "On the face of it, the actual improvement in precision in the latest work is rather small," he says. "However, this paper represents the first of what many in the field believe to be a coming wave of potentially much larger improvements, because of new experimental methods that are being developed."
This article is reproduced with permission from the magazine Nature. The article was first published on May 3, 2011.
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12 Comments
Add CommentSupersymmetry has predicted that the electron is "egg-shaped".
Reply | Report Abuse | Link to thisBrand new experiments say SUSY is wrong on this prediction.
See: http://www.nature.com/news/2011/110525/full/news.2011.321.html
Discrete Scale Relativity predicts that electrons are among the most perfectly spherical objects in the Universe.
See: http://www3.amherst.edu/~rloldershaw , "Galactic Scale Self-Similarity", Section VI.
The above-linked new electron shape research vindicates the definitive prediction of Discrete Scale Relativity, and contradicts the SUSY prediction.
Robert L. Oldershaw
http://www3.amherst.edu/~rloldershaw
Discrete Scale Relativity; Fractal Cosmology
The article states:
Reply | Report Abuse | Link to this"These fleeting [virtual 'orbital' cloud] particles pop in and out of existence, and contribute to the electron's mass and volume."
Perhaps when the virtual particles seem to be nonexistent, their energy is manifested as a wave?
The article goes on to state:
"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 favoritism for matter, but also suggests that physics does not always work the same way when time is run backwards instead of forwards."
This complex scenario would be enormously simplified if only it is considered that initial universal energy was spinning as fundamental particles were condensed from it. This would provide an initial predisposition for the creation matter rather than anti-matter without any implications for temporal symmetry.
In the vacuum energy of the current universe, the much reduced (through expansion) universal spin allows symmetrical manifestations of matter and anti-matter.
Now, isn't that easier?
"...also suggests that physics does not always work the same way when time is run backwards instead of forwards."
Reply | Report Abuse | Link to thisIt seems to me that "time" is a one way thing. Does this work not bring that notion into a more likely position?
All very interesting, some great work here!
R. Carlson
English major here: in a universe where clearly so much remains that, like the man says, we don't know we don't know, and since scientific conclusion requires exclusion of all variables if they're not part of the conclusion, how can you maintain that the incredibly tiny distortion you're looking for MUST be due to effects of the theory you're touting?
Reply | Report Abuse | Link to thisMay be electrons are not perfectly round because the interaction with ether as they move in circles or in lines shapes them, as air shapes the rain drops. It's a silly explanation, but I challenge everybody to find a more hilarating one. Salud +
Reply | Report Abuse | Link to thisWhy can't the same thing be done with photons? Are photons perfectly spherical> if so why and if not why not and how exactly? What are the increments of deviation from the perfect sphere?
Reply | Report Abuse | Link to thisWhen I suggest that photons are 'spherical' I am referring to something aside from wavelength and energy frequency. The stable shape of the photon is carried by something different from the energy level. It may be considered in terms of geometry and perhaps considered in terms of crystaline structures. As a kind of crystal photons may exhibit potential for exotic properties as a new class of pseudo 'matter'. Its clear that energy and matter are abstracted from the same 'thing' in assorted tensor relationships.
Reply | Report Abuse | Link to thisJorosay, said, "May be electrons are not perfectly round because..."etc. The general point seems reasonable; to be sure, there is a lot out there to change "perfectly round". What's striking is that IT (the electron) is so near round (given IT can in truth be out of round to any degree at all). "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. That tends to make me think IT may in fact have a volume-less presence; and, thus any "observed" volume to IT is only a "cloud of virtual particles" or some such reaction between IT and our yard stick, of whatever type etc (an error).
Reply | Report Abuse | Link to thisGiven IT is something with a real volume, then a "distorting effect" should be more likely possible, and a truly "perfect sphere" more likely impossible (after all, everything is interacting with everything, albeit in finer and finer degrees).
R. Carlson
Well, so I got out my calibrated Edmund Scientific matched set of eight electrons and measured them.
Reply | Report Abuse | Link to thisTiny little buggers, they are! Lost two under the sofa.
I put leashes on the rest.
Is this a statistical measurement? All the known physical constants to my knowledge have less certainty than a measurement akin to a hairs width to the diameter of a solar system bounded by Pluto? What mathematical breakthrough allows the triumph of precision of such magnitude to preside over accuracy on something belonging to the uncertainty principle?
Reply | Report Abuse | Link to thisA definition of "virtual particle" would be nice. After all, virtual means seems like but really isn't. So essentially it occasionally seems like there are additional particles near the electron when there actually are not any there.
Reply | Report Abuse | Link to thisPersonally I interpret this in much the same way as "dark matter/energy" - the math is off so a placeholder is used to indicate the missing variable until we figure out what we missed. Thanks to whomsoever first used the term placeholder to describe dark matter/energy.
WAVE GOODBYE
Reply | Report Abuse | Link to this-- James Ph. Kotsybar
An electron, so perfectly round
it could spin without wobble or sound,
was measured carefully
at fixed velocity,
but its position couldn’t be found.