10-Year Study Reveals Electron Shape

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."

Comments

Units

[Nemyst]

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.

Re:Units

[Twinbee]

The 0.000...001 version maybe visually represents the amount better.

Re:Units

[mattack2]

What's wrong with calling it mysterious? The theories say there should be equal parts matter & antimatter.. There doesn't seem to be.. So it's a mystery.. Thus, as an adjective, it is mysterious.

Re:Units

[Ultra64]

Mysterious? Yes. Really.
http://en.wikipedia.org/wiki/Baryon_asymmetry

Re:Units

[blueg3]

There should be more antimatter. There's not, as far as we can see. We don't know what happened to it. Hence, mysterious.

"Fate" is a bit unfair, though, since it properly refers to the future.

Re:Units

[davester666]

Heisenberg phoned and left a message saying all these numbers just MIGHT be slightly too precise...

Under what conditions?

[blair1q]

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:Under what conditions?

[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.

Re:Under what conditions?

[SETIGuy]

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.

Re:Under what conditions?

[JonyEpsilon]

Yeah, it really is spherical in any sense that you can mean spherical. It can't have any higher order multipole moments because it only has spin 1/2. (So the Wigner-Eckart theorem tells you that all matrix elements with operators greater than spin 1/2 are necessarily zero.) Jony

Re:Under what conditions?

[AliasMarlowe]

The Heisenberg principle is just a consequence of a property of Fourier transforms that says that any signal localized in frequency space will not be localized in the original space.

It's a consequence of linear operators in general. Conceptualizing it in terms of the Fourier transform which localizes an invariant process very well in frequency and not at all in position may limit one's viewpoint. It's more informatively interpreted using time-frequency decompositions such as the Wigner distribution (or position-scale representations such as wavelet transforms), in which there is a direct trade-off between localization in frequency (or scale) and localization in time (or position).

Where the magic comes in is the relationship between momentum and position, and energy and time, operators in QM.

An even bigger magic comes from the applicability of mathematics to physics, which is an interesting philosophical issue in its own right. "How can it be that mathematics, being after all a product of human thought which is independent of experience, is so admirably appropriate to the objects of reality." - Albert Einstein.

Curious question

[gcnaddict]

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.

Re:Curious question

[gcnaddict]

My good sir, I merely asked a few questions. I made no statement indicating an expectation of multiple theories, merely a query for any in the event that any happened to exist.

As an aside, it would do you wonders to investigate new methodologies of conveying written information. Your response, most notably the capitalization, the usage of asterisks for emphasis, and the snide remark about political journalism, appeared to have a not-terribly-subtle hint of condescension. As someone who wants to learn more, this is something I most certainly do not deserve after asking a benign question.

Re:Curious question

[blair1q]

Well, having now read TFA (i do that when i'm bored and the topic is ultra-geeky like electron shape must be), it seems all they could have been measuring here is the shape of the electrical and quantum fields around the electrons in not just an atom but a molecule (of the sexily named ytterbium fluoride).

So what they've done is proved solenoidality of both; i.e., that they obey the inverse-square law to an anal-retentive degree; i.e. that force = A*1/r^(2+x) where |x| 1e-29. We only know gravity's solenoidal to about 8 significant figures, for comparison.

Interestingly, the shape of the fields around the nuclei of the atoms in the molecule ought to have played some part. I wonder if they haven't accidentally also proved that nuclei are round to a similar degree.

Re:Curious question

[lee1]

That seems to be just stupid headline writing. Nowhere in the body of the article do we encounter a scientist expressing surprise at the result.

Re:Curious question

[fermion]

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 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.

Re:Curious question

[JonyEpsilon]

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 theories of physics, usually predict a distorted electron.

Re:Curious question

[blank axolotl]

Actually, according to the paper the electron is aspheric in many theories, including the standard model (the best theory we have). From the article abstract:

The electron is predicted to be slightly aspheric, with a distortion characterized by the electric dipole moment (EDM), de. No experiment has ever detected this deviation. The standard model of particle physics predicts that de is far too small to detect, being some eleven orders of magnitude smaller than the current experimental sensitivity. However, many extensions to the standard model naturally predict much larger values of de that should be detectable. This makes the search for the electron EDM a powerful way to search for new physics and constrain the possible extensions.

Re:Curious question

[straponego]

They were hoping electrons were shaped like Pac-man. This would where the antimatter went.

Re:Curious question

[Eil]

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 experiment was over so as to not introduce bias into their final results. That's some scientific integrity right there.

Re:Curious question

[Surt]

If your father is made entirely of electrons I'd be shocked to meet him.

Re:Curious question

[jd]

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.

Re:Curious question

[Artifakt]

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 object, it would only look the same if it was rotated 720%. If you turned it around just once (360 degrees), it would look different. Some other particles have spin 1 or even 3/2, and the predicted carrier of mass itself, the Higgs boson, is predicted to be spin 2 (which means if it was a macroscopic object, you would have to rotate it only 180 degrees for it to look the same - A macroscopic object with that property might be shaped like a football or a cigar, if it was being rotated around a certain axis.). Obviously, there are no macroscopic examples of objects with classical spin less than 1, so an electron couldn't look like anything macroscopic in this model. Its shape would have to be something that can't exist in the macro world.
            A perfect sphere is spin infinite, or arguably doesn't have a spin at all, it doesn't matter how you rotate it, it still looks the same.
            Another idea was that an electron had to be an absolute point, zero size in all directions. If you go by the old Bohr atom model, Electrons orbit the nucleus like tiny planets, but physicists soon realised they had to be moving at tremendous percentages of the speed of light. So in the Bohr atom, a spherical electron would look distorted, tremendously flattened in the direction of motion. It would look almost like a pancake. This led to some problems when calculating what happens as multiple electrons orbit in shells around a single nucleus - in particular, it led to erroneous predictions about how heavier atoms than helium would emit various wavelengths of light in their spectra, and how atoms outer shells would form crystals, set the spacing between nuclei, and do a lot of other things (for examples, even how much energy it would take to fracture something or how fast two different metals weld together at a particular temperature come out different, if I remember my old physic classes),
          So that's a theory that says an electron can't be a sphere, unless (really odd idea from the 1930's) it stretches to compensate for relativistic distortion and stay a sphere when it would normally flatten. For other reasons, the Bohr atom model turned out to be inadequate and most modern physics works by treating the electron as a wave function, as in quantum mechanics, in all the cases where the Bohr model doesn't give accurate numbers for observational results.Obviously, the shape of a probabilistic wave function isn't a tiny sphere or anything else solid, more like a fuzzy shell around the nucleus.
     

Re:Curious question

[Entropius]

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 all zero. Unless you have a particular reason to suspect that you're at an inflection point, showing that B=0 strongly suggests that C, D, E, etc., are zero too for many physical systems.

It turns out that you can expand the shape of an object or the distribution of a field in something that resembles a Taylor series. The expansion terms are things called the "spherical harmonics"; you're probably most familiar with them as the shapes of the various hydrogen orbitals (s, p, d, f, etc.). It turns out that any shape (at least, any shape with a unique radius for a given latitude and longitude) can be written as a combination of these spherical harmonics. The process of calculating the coefficients corresponding to the different shapes is called a "multipole expansion" -- it's like a Taylor expansion for shapes. For something that is very nearly a sphere, this is dominated by the first few terms.

The first one of these spherical harmonics -- corresponding in a sense to the coefficient A above -- is just a perfect sphere. Its coefficient is called the "monopole moment". The second one (actually, there are three of them, corresponding to x, y, and z axes) are called "dipole moments", and they represent the leading-order deviations away from perfect sphericity. This dipole moment is what this experiment measured; they figure that if the electronic dipole moment is very nearly zero then all the higher-order moments are zero too.

Re:Curious question

[Entropius]

"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 the disturbances in these fields; in other words, you can't perfectly separate out the properties of the electron and the properties of the fields that it couples to. This is not a huge deal for electrons, since they only couple weakly to other quantum fields; the coupling constant is 1/137 (at low energy) with the photon field, and small to the Higgs field (if such a thing exists). It's a far bigger deal for quarks, where the coupling to the gluon field is large at low energy; you can't describe the properties of a quark in any meaningful way without considering how that quark affects the gluon field around it.

all that wave particle jazz

[Sebastopol]

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?

Re:all that wave particle jazz

[Daniel_Staal]

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

Re:all that wave particle jazz

[NoSig]

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.

Re:all that wave particle jazz

[iris-n]

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

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?

Re:all that wave particle jazz

[im_thatoneguy]

So, makes more sense now?

Mayyyybe...?

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 our measurements completely singularly charged and therefore has no polarity or shape?

I'm getting thrown by "Bipole Moment" since I don't know what that means but I feel like it's important to your explanation. :D

I'm imagining a magnetic field in my head. If you could create a magnet that was only positive it would be a round field pattern. But if you had a bar magnet it would form the classic figure eight of magnetic fields and therefore not be 'spherical'?
http://www.windows2universe.org/spaceweather/images/bar_magnet_correct.gif

Am I understanding you correctly?

puuurfect

[fragfoo]

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

Re:puuurfect

[blair1q]

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

Re:puuurfect

[znigelz]

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.

Re:puuurfect

[ghmh]

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.

Re:Shape?

[Warlord88]

First I studied they were particles, then I studied they are actually mixture of waves and particles. Then I studied you cannot actually pinpoint it at all, and all you can know is probability density of its existence in space. Now, I read that they are extremely round.
My mind is full of fuck.

Size of the solar system?

[Zandamesh]

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?

What about texture?

[i ate my neighbour]

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

Re:So its like a dick then?

[scififan]

Thats depends on a dick. If its yours, that sure its about same size

What's even crazier

[straponego]

...is that God did that freehand.

All the anti-matter is...

[RL78]

"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-author and head of the Centre for Cold Matter at Imperial College London, said: "The whole world is made almost entirely of normal matter, with only tiny traces of antimatter. Astronomers have looked right to the edge of the visible universe and even then they see just matter, no great stashes of antimatter. Physicists just do not know what happened to all the antimatter, but this research can help us to confirm or rule out some of the possible explanations."


Is it possible that we can't find anti-matter because it's all in one place?

Re:Shape?

[bigsexyjoe]

This experiment shows they have no wobble. I think that's pretty consistent with them being point particles, don't you?

Re:Shape?

[doublebackslash]

This is simplified, don't take this completely literally, but get this first. I'll use a car analogy.

You and several other clowns are in a clown and some of them are juggling. You are driving so you can't look at them. You can't look because you are doing a precision maneuver with several other clown cars. As part of the act they are also exchanging juggling objects with other cars. Even though you can't look at the jugglers you can sense what they are doing due to the fact that their motions and transfer of momentum are throwing you off course. It is important that you stay on course to make the jump. God help you if you hit the ramp like like the last guy did, but the kids like to see this act up close.

If the jugglers are throwing around tennis balls your course will be effected differently than if they were throwing juggling pins.

Now, back in the world of the article you've got the same thing. Atoms with electrons flying around and shared by chemical bonds. The shape of the electrons effects the shape of the molecule. More specifically the shape of the charge around the electron effects the shape.

Don't try to watch the objects being juggled, watch the clown cars try to stay in formation on their way to the jump over lion pen.

It took a long time because the measurements are so delicately precise and spurious data had to be discounted and filtered from the signal. The measurements weren't averaged but they were mercilessly filtered and subjected to analysis to take the "noise floor" down this low.

I am not a physicist. Someone correct me or clarify if I was dead wrong. Thanks!

Re:flaw?

[JonyEpsilon]

It took us ten years to build the experiment. We didn't average for ten years!

Re:Shape?

[XManticore]

You and several other clowns are in a clown

Sup dawg, I heard you like quantum physics, so I put a clown in your clown so you can juggle while you drive

Or it is irregular in shape

[Anonymous Coward]

but spinning very very very very very very very fast.

Variable shape?

[Walt Dismal]

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!"

Other subatomic particles...?

[LongearedBat]

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?

Plank

[rubycodez]

a standard Plank Length in the U.S. is 8 feet.