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10-Year Study Reveals Electron Shape 370

lee1 writes "In a 10 year long experiment, scientists at Imperial College have made the most precise measurement so far of the shape of the electron. It's round. So round, in fact, that if the electron were enlarged to the size of the solar system, its shape would diverge from a perfect sphere less than the width of a human hair. The experiment continues in the search for even greater precision. There are implications for understanding processes in the early universe, namely the mysterious fate of the antimatter."
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10-Year Study Reveals Electron Shape

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  • by Nemyst ( 1383049 ) on Wednesday May 25, 2011 @07:34PM (#36245588) Homepage

    I know the site is probably trying to be approachable, but what's wrong with saying 1e-29 m instead of this absurd measurement of 0.000000000000000000000000001 cm? This is getting close to the Planck length; no matter what you compare it to, it won't be a length you can intuitively grasp.

  • by blair1q ( 305137 ) on Wednesday May 25, 2011 @07:36PM (#36245608) Journal

    Is it always round, even when it's tunnelling through a potential wall?

    And I assume that by "round" they mean that every level curve of the probability amplitude has constant radius.

    And, uh, what did they do about that Heisenberg thing? If you can't tell where the electron is relative to your frame of reference, how is the electron supposed to tell where a certain constant on its level curve is relative to its own frame of reference?

    • Re: (Score:2, Informative)

      by Anonymous Coward

      And, uh, what did they do about that Heisenberg thing? If you can't tell where the electron is relative to your frame of reference, how is the electron supposed to tell where a certain constant on its level curve is relative to its own frame of reference?

      The measurement was indirect --- they didn't observe the electron but instead observed the lack of any distortion in the shape of the molecule. I guess this observation does not require them to pin point the position of the electron.

    • by SETIGuy ( 33768 ) on Wednesday May 25, 2011 @08:56PM (#36246314) Homepage

      Is it always round, even when it's tunnelling through a potential wall?

      I think that the way they are translating the physics into English is awful. I'm not sure I fully understand their method, but I'll try to restate. What they actually found was that they electric dipole moment of the electron was very small. It it were not that small, they would have seen changes in the wave function. From there they go to stating that if the electron can be modelled as a charge distribution or a charged object, that object would be spherically symmetric with dipolar radial deviations of less than that very small number. But more precisely, the wave function of an electron behaves as if it represents a particle that has a electric dipole moment less than 1.05E-27 ecm.

      If course you couldn't actually make measurements to determine whether that dipole moment is a property of a physical shape of the electron or is an intrinsic property. Nothing we have can probe those size scales, and if you could you'd have particle antiparticle pairs popping up everywhere from the energy of the collisions. You might even create a new universe at those energies. Everything we've done so far suggests that the electron has no structure, but that's on much larger scales/lower energies.

      • by quax ( 19371 )

        Thanks for clearing this up.

        I have a master of physics but skimming through the article I could not make heads or tail of what these guys actually measured.

        Extrapolating from the dipole moment to the headline that the electron is perfectly spherical is just cringe-worthy.

    • by jd ( 1658 )

      So long as you don't know how fast it is moving, knowing where it is is fine. The exact rule is that the product of the level of uncertainty of the variables is a constant, not that the variables have to be unknown.

  • Curious question (Score:5, Interesting)

    by gcnaddict ( 841664 ) on Wednesday May 25, 2011 @07:37PM (#36245618)
    What other possible shapes were theorized for an electron? What are these theories based on? What difference would an egg-shaped electron make in the grand scheme of things?

    I know why we should care, but I wouldn't mind knowing what theories exist to justify different shapes.
    • [talking out of my ass here, IANA physicist]

      You'd expect an atom to be mostly spherical right? Well if you measure the radius of an atom, you'll find that it can fluctuate. Knowing by how much the radius of an atom fluctuates might, for example, give you an idea of the angular momentum or kinetic energy of its constituent particles. I presume that the size and shape of the electron could fluctuate in similar ways and might give an indication of what physics governs its mechanical properties.

      What I'm getting

    • What they mean is that they have tested the symmetry of the electron and found it to be equivalent in all directions, like a sphere. The hair's-width thing is just an analogy to describe the degree to which that symmetry has been tested; the electron does not have an intrinsic size or shape. If there were any detectable asymmetry, that would imply that the electron and positron are not perfect opposites, and may explain why there is so little antimatter in the universe.
    • Well they tested it's "shape" by seeing electrons have any wobble. They apparently found no wobble. Meaning that they are either little spheres, or IMHO more likely they have no wobble because they have no size. There are good reasons to think they fundamental indivisible particles already; because of the uncertainty principle the constituents of such a small particle would have to have a lot momentum.
      • by jd ( 1658 )

        Since electrons have mass, they can't be indivisible. They have, at the very least, to be divisible into a Higgs boson and whatever is left over.

        • "Divisible" is a funny term. If you mean that in quantum field theory there is a vertex between an electron line and a Higgs, sure. But this doesn't mean that you can split an electron into a Higgs and "something else", any more than it means you can split an electron into an electron and a bunch of photons.

          What it *does* mean is that every electron disturbs both the photon field and the Higgs field around it, and that by necessity some of the properties of what we call "electron" are actually related to th

    • Re:Curious question (Score:5, Informative)

      by fermion ( 181285 ) on Wednesday May 25, 2011 @08:38PM (#36246164) Homepage Journal
      From what I can tell ia this has to do with Standard Model which predicts equal quantity of matter and anti-matter in the universe. As far as can be determined, there is an asymmetry that is hard to explain. One way to explain this asymmetry in the quantity of matter is if there was a physical asymmetry between the electron and positron. The asymmetry would not exist in the particles themselve, but in the virtual particles surrounding them.

      These virtual particles are tiny compared to atomic matter and exist for short amount of time, such a short amount of time thier very existence is below the uncertainty thresholds. They are a consequence of the fundamental uncertainty in position and momentum. They are created out of the vacuum.

      So the question the experiment attempts to answer is does the electron behave like an object that reacts symmetrically in all dimensions, or is there so aberration, that is, is it not a perfect sphere. To a very high accuracy the paper claims that it is a sphere.

      However that is not the full story. The paper is based on the idea that the aspherical shape would be larger than the standard model predicts. Adjusted models predicts a larger aspherical aberration. Since this experiment did not detect large aberrations, these other models, extensions of the Standard Model seem to be less than accurate. Form what I read, the standard model predictions are orders of magnitude lower than current sensitivity [nature.com] so it remains unclear if the electron acts like a sphere or something that is almost like a sphere.

      What this experiment does is provide a novel and fascinating method to probe subatomic particles, as well as establish an upper limit on how big the abberation could be. Good science.

    • Good questions! This is actually one of the central motivations for measuring this is. The standard model of particle physics predicts that the electron will be round. But most physicists think that the standard model isn't the full story. The interesting thing is most of the proposed extensions/replacements to the standard model predict that the electron will be somewhat distorted. To give a concrete example, supersymmetric theories, which are viewed by many as the most promising avenue for extending our
    • by straponego ( 521991 ) on Wednesday May 25, 2011 @09:05PM (#36246380)
      They were hoping electrons were shaped like Pac-man. This would where the antimatter went.
    • An ellipsoid (shape of the Earth) could have been another possible shape for an electron I suppose. The earth bulges due to gravity and centrifugal forces from it's spin. An electron spins too, but if it's a near perfect sphere then this spin doesn't appear to have any effect on its shape, nor does gravity... as far as we can tell so far I guess. Interesting.
    • by Eil ( 82413 )

      One of the researchers was interviewed on NPR and he said that a round electron throws an unknown variable into a lot of unproven theories. Many scientists were apparently hoping for a significantly elliptical shape in order to make their calculations work out. (Sorry I can't provide a better description. I'm only regurgitating what I heard on the radio.)

      One interesting bit is that they had been collecting data for over 10 years, but the researchers prevented themselves from looking at it before the experim

    • When the term 'spin' was first coined for sub-atomic particles, it was chosen because it was thought to have some similarities to macro-scale situations. (this was 1925, by about 1928 when Paul Dirac used it, people were already arguing about whether 'spin' really had to correspond to anything physical about the particles shape. Still 'spin' behaves like a form of angular momentum in at least some ways.).
      The spin of an electron is 1/2. By that, if it was a macroscopic obj

    • Forgive me if this explanation includes some stuff you already know -- I have no idea what your background is.


      Are you familiar with Taylor (or Maclaurin) series? The idea is that any (well-behaved) function can be written as a polynomial of the form A + Bx + Cx^2 + Dx^3 + Ex^4 + ... ad infinitum, and that when x is close to zero, this expansion is dominated by the first few terms. If you want to see if a given function is a constant, one way to do it is to show that the coefficients B, C, D, etc., are al

  • by Sebastopol ( 189276 ) on Wednesday May 25, 2011 @07:42PM (#36245680) Homepage

    So.... it's a sphere when it is a particle?

    For years, I've been trying to un-brainwash myself out of the early models of the electron as a little ball whirring around a nucleus, and convert to the probabilistic electron cloud model, as well as the wave/particle hybrid nature.

    My head is about to explode. Can someone who is a physicist please chime in?

    • by Daniel_Staal ( 609844 ) <DStaal@usa.net> on Wednesday May 25, 2011 @07:46PM (#36245716)

      Your head exploding is a perfectly normal reaction to trying to comprehend modern physics. Carry on.

      • At what speed would it explode?

        Are there maths that describe the pressure of metaphysical forces on matter?

        • At what speed would it explode?

          To what degree is it spherical?

          Remember, TMI equals width times girth divided by the angle ...

      • by iris-n ( 1276146 ) on Thursday May 26, 2011 @12:35AM (#36247470)

        No it's not. Your head exploding is a perfectly normal reaction to trying to comprehend the piece of shit that passes as scientific journalism nowadays. I'm a physicist and after reading the article I still had no idea about what the researches discovered. At least Science Daily had the original reference so I could look up. Even more appalling is BBC's coverage: http://www.bbc.co.uk/news/science-environment-13545453 [bbc.co.uk]

        They both only said "lasers" about what the group actually measured. As if the measurement technique were as relevant as what they were actually measuring. Even laymen like OP see that there's something weird about saying the electron has a shape and is a sphere. Of course, this makes absolutely no sense. This talk about sphere is a semiclassical analogue that someone in the 20's once thought that could be true and was quickly disproved. What they measured was the electron's electric dipole moment. What is that?

        Imagine a small bar magnet, with south and north poles. This is what we call a magnetic dipole. The strength of the magnet (measured in a standard way) is what we call magnetic dipole moment. Now imagine that instead of south and north poles, we have negative and positive electric charges. This is an electrical dipole, and it's strength is likewise the electrical dipole moment.

        Now the beauty of the electron is that despite not being a small bar magnet, it still displays a strong magnetic dipole moment, which we call spin. Originally people thought that it could be explained by postulating a structure on the electron (an electric charged spinning sphere gives rise to a magnetic dipole moment, hence the name spin), but quickly we found out that it couldn't be so. We have no explanation for it, it is what it is, just a property of the electron.

        But what the electric dipole moment? The electron is a single charge, so it can't be an actual electrical dipole. But despite this, the Standard Model predicts that it has a very small electric dipole moment, too small to be measurable. But Supersymmetry predicts that it is quite larger, and even measurable, and these folks' measurement showed that Supersymmetry's prediction is probably wrong.

        Ok, but why did they call it measuring the roundness? Analogously with the spinning sphere model for the magnetic dipole moment, a distorted sphere gives rise to an electric dipole moment. But calling it measuring the roundness makes as much sense as saying that when we measure the magnetic dipole moment (spin) we are measuring the speed with which the electron spins about itself.

        So, makes more sense now?

        • So, makes more sense now?


          So if something has a north/south polarity in magnetism we say it has a strong "Magnetic Dipole Moment"? Or more simply I would using my non-physicist vocabulary say it has a distinct Magnetic Polarity. Magnetic Moment = Amount of polarity?

          So even though the electron obviously has an average electric charge some theories think it might actually be the product of a slightly + in addition to being mostly - field?

          But this study found that there isn't any duality to the charge; it's to the best of

    • by NoSig ( 1919688 ) on Wednesday May 25, 2011 @08:28PM (#36246088)
      It is neither a particle nor a wave, so there is no "when it is a particle/when it is a wave". Instead, it is something whose behavior is like that of a particle in some ways and like that of a wave in other ways, but it is never actually a wave or a particle. It is its own thing - the analogies to waves and particles are just there to aid understanding, they are not accurate descriptions. I imagine that what is meant is that the density of the probability field (or whatever the correct term is) decreases uniformly in all directions with distance - no direction is favored over another.
    • The electron cloud model is the more correct one.

      They are using 'spherical' somewhat metaphorically.. what they are actually measuring here is the electron dipole moment. A particle with a nonzero dipole moment causes an asymmetric electric force: A water molecule, for example, has a large dipole moment, so you feel a different electric force when you are near the negative oxygen vs when you are near the positive hydrogen.

      So, if the electron has a nonzero dipole moment, it means it is a bit asymmetric in it

  • puuurfect (Score:5, Insightful)

    by fragfoo ( 2018548 ) on Wednesday May 25, 2011 @07:45PM (#36245708)
    Maybe its shape is indeed a perfect sphere and the "width of a human hair" is just a measurement error. How more precise they want to get, until its shape diverges a human hair from a perfect sphere when enlarged to the size of the galaxy? Is there an end to measurement errors? Am i making any sense? I think not, its late at night :x
    • by blair1q ( 305137 )

      It will no longer be possible to measure the error, when you are bald.

    • Maybe there is something interesting to be learned about that 'measurement error'...

    • Re:puuurfect (Score:5, Informative)

      by znigelz ( 2005916 ) on Wednesday May 25, 2011 @09:34PM (#36246556)

      No matter how high of an order you go for an approximation, there will always be a truncation error. That is the problem with using infinite series to represent physical models.

    • by ghmh ( 73679 )

      Well, I came here to post the same thing. According to the third paragraph, the measurements were made:

      "Using a very precise laser"

      Then you ask about how they measured the lasers preciseness and how did they build the laser. You keep investigating and pretty soon after that the turtles (unfairly) end up getting blamed for everything.

  • What is the radius of the solar system anyway? Furthest planet (40 AU)? Furthest comet orbit (50000 AU)?

    But more importantly, how much digits of pi would you need to describe this sphere accurately?

    • Furthest planet (40 AU)

      Last I checked, the furthest planet is only 30 AU out.

      Or are you one of those heathens who hold with the sacrilegious notion that Pluto is a planet?

  • 10^-27cm (the spherical error in the article) is 10^-29m. The upper bound on the electron's radius is 10^-22m (Wikipedia). The solar system is roughly 1.5*10^13m in radius (Wolfram Alpha), so 3*10^13m in diameter. If you'd inflate the electron to the size of the solar system, scaling by 3*10^35, the spherical error would be 3*10^6m, which is more than twice the diameter of Earth, according to my calculations.

  • by i ate my neighbour ( 1756816 ) on Wednesday May 25, 2011 @07:56PM (#36245814)

    Is there a tiny ( - )sign on its surface?

  • The numbers in the article don't work for me.....

    Electron radius (wikipedia): 10^-22 meters
    Article's claim of error-from-round: 10^-29 meters
    Relative error: 10^7, or 0.1 parts per million

    "Radius of solar system" randomly chosen as Eris's avg orbit fo 68AU (wikipedia): 1.017 * 10^13 meters
    Relative error scaled to size of solar system: ~1.017 * 10^6 meters, or ~1017km

    Now I don't know about you, but my hair isn't exactly 1000km thick, eh?

    Avg thickness of human hair (answers.com): 0.1mm, or 10^-4 meters
    Ratio by

  • ..that sub-electronic particles either do no exist, or they have no* mass. Otherwise the electronic equator would be at least a teensy* bit fatter, due to its spin.

    *no and teensy are both about one over infinity. Plus or minus a tad.

    • In the current model, electron has no deeper structure - it's truly fundamental, alongside photon, quarks etc.

    • At the quantum level, is "spin" really spin (as in angular displacement over time), or is it like the term "color" or "charm", just a term to denote an aspect of quantum weirdness? Quantum spin is always up or down. It's never clockwise or counter-clockwise.
  • At last, the flat-electron rabble can finally give it a rest.
  • How, exactly, do you define the concept of "shape" for something like an electron?

    I mean, for a macroscopic object, our "common sense" definition of shape is the boundary at which an outside interaction would feel resistance - if you poke it, that's where you feel the counterforce (weak as it may be). This is actually caused by molecules interacting between each other, but at that point already the concept of "poking" something is kinda hazy, since you already get all that quantum mumbo jumbo strong enough

    • The (differential) cross section [wikipedia.org] of an atomic or subatomic particle is well defined and quite close to our idea of 'shape'. It tells you how a test particle being shot a the target 'bounces' off the target. For classical objects it reduces to our intuitive picture (ie, if you are shooting at a sphere, you know how your bullet bounces) but it applies to fuzzy particles too. Unfortunately the wikipedia pages on it are not very detailed and miss a lot. Also check out the 'scattering cross section' and 'rutherf

      • Right, that's what I mean. With macroscopic objects, the interaction is either there or it's not. Here, we're rather talking about probabilities - you can't have two particles occupying exactly the same spot, but aside from that you just need to try longer (or shoot harder) to get more "overlap".

        But that's not really shape in any common sense, and calling that "round" is quite a stretch. I understand what they mean - that probability of interaction decreases uniformly on all directions from the center - and

        • Two other things are important that I forgot to note:

          1. They are not measuring the 'shape' of the electron at all.. they are measuring its electron dipole moment. They are using the word 'spherical' metaphorically to mean 'symmetric' or 'with zero dipole'. So my comment about cross section, while answering your question, is actually irrelevant to the study.

          2. Assuming zero electroc dipole (so the electron's electric field is symmetric) the electron actually has an infinite cross section, so in this case th

    • A better description than shape of electron, is distribution of charge. Which is exactly what they are measuring. If the charge density were not uniformly spherical (or point charge) then there would be some "shape".
  • by straponego ( 521991 ) on Wednesday May 25, 2011 @08:37PM (#36246156)
    ...is that God did that freehand.
  • "Imperial's Centre for Cold Matter aims to explain this lack of antimatter by searching for tiny differences between the behaviour of matter and antimatter that no-one has yet observed. Had the researchers found that electrons are not round it would have provided proof that the behaviour of antimatter and matter differ more than physicists previously thought. This, they say, could explain how all the antimatter disappeared from the universe, leaving only ordinary matter. Professor Edward Hinds, research co
  • This is incredible! Sure they might be almost spherical, but the shape is slightly off! This small difference could have profound theoretical implications. First it means that an electron has volume, second it means they might have an inner structure to create that shape. Very interesting indeed. Might lead to new physics.
  • If an electron is just a wave I might have expected it to be more, well, wavy.

    Or is this "shape" representing a distribution of its possible locations?

  • From what part of a human, exactly? And would this hair be blond, perchance?

  • by Anonymous Coward

    but spinning very very very very very very very fast.

  • An electron's shape includes the path that it takes through the "electron cloud". And that path has to date never been plotted with any accuracy, only its overall probability densities in spacetime. It's a fractal (since time's dimension is not an integer), and so it depends in part on the size and shape of whatever measures it.

  • The size of the solar system? Lets do away with unrealistic measurements... Compare it to something we can all understand like the library of congress.
  • I've always imagined that elementary particles must be point-like, without any actual volume. Does this study contradict that notion?

    It just seems to me that it wouldn't make sense for electrons to have a volume, because that would imply some kind of structure. Nobody ever seemed to suggest that photons actually have a "shape", other than a point.
  • by Walt Dismal ( 534799 ) on Thursday May 26, 2011 @12:27AM (#36247434)
    I was under the impression that an electron is not a hard constant sized object but is a wave constrained to fit the boundaries of the quantum mechanical environment around it. Though variable, also cannot be compressed into infinite density either. I also thought, from chemistry, that the electron 'fits' into the various orbital states but that it's not a tiny sphere 'bouncing around' inside them but indeed a wave constrained within the orbital shapes. I would think an unconstrained wave in three dimensions is obviously symmetrical and hence spherical, but always morphs shape under the influence of any outside charge. So what really was measured here? Grandpa in the movie Moonstruck: "I'm so confused!"
  • by LongearedBat ( 1665481 ) on Thursday May 26, 2011 @01:19AM (#36247630)

    It would be interesting to know how the quarks that make up neutrons and protons behave. Do they cluster like a bag of bags of marbles (separate clusters), or cluster like a single bag of marbles (single cluster), or superimpose (one blob, probably spherical). Do these clusters stretch, especially in covalent bonds?

    Do we perhaps already know?

The intelligence of any discussion diminishes with the square of the number of participants. -- Adam Walinsky