[HN Gopher] The electron is so round that it's ruling out potent...
___________________________________________________________________
The electron is so round that it's ruling out potential new
particles
Author : martincmartin
Score : 122 points
Date : 2023-04-11 11:40 UTC (4 days ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| noncoml wrote:
| Explain like I'm five follow up question: is this electron able
| to exist in infinite places in space or only in predetermined
| slots?
|
| I.e. does space consists of pixels?
| DoubleFree wrote:
| Space is not quantized, so yes, the electron has infinite
| possible locations. There are, however, places the electron
| cannot be, depending on its energy. See, the electron's energy
| is quantized, meaning it can only have a predetermined set of
| values (see atoms' electron shells). The energy determines the
| wave function and the wave function squared is the probability
| distribution for the electron's location. This wave function
| has roots, indicating where the electron cannot be.
| tachyon5 wrote:
| It's interesting to consider the parallels between the electron's
| roundness and the cosmic microwave background (CMB) radiation's
| uniformity. Both seem to defy our expectations of asymmetry, with
| the electron's shape ruling out new particles and the CMB's
| uniformity challenging our understanding of the early universe.
| As we explore these seemingly unrelated phenomena, perhaps there
| lies a deep, underlying connection that could unite our
| understanding of the microcosm and the macrocosm, offering a
| fresh perspective on the laws governing our universe.
| nuccy wrote:
| For the CMB we predict (or rather invent) "inflation" - a rapid
| expansion of the space-time to preserve uniformity of early
| Universe [1]. Inflation lasted for
| 0.00000000000000000000000000000001s but the size of the
| Universe increased by 10^30 times.
|
| 1.
| https://www.esa.int/Science_Exploration/Space_Science/Planck...
|
| Edit: I wanted to come up with an analogy of increasing some
| object to the size of Earth (as it is the biggest object we can
| experience in real life). Though 10^30 times is so
| mindbogglingly large that we don't really have any sense of
| that small sizes at all. The object would have to be smaller
| than an electron by a trillion times (10^12).
| p1esk wrote:
| Can someone explain what an electron is? I remember from my high
| school physics that electrons are "point-like" particles, which
| are "elementary" (not built out of any smaller particles). And
| electron clouds are like all possible or probable trajectories of
| how electrons move around an atom's nucleus. Or something like
| that, it was many years ago. Then what is a "cloud of negative
| charge"?
| notfish wrote:
| My model for understanding phenomena where quantum effects
| matter is this: if you think of the universe like a big sheet
| of something stretchy, an electron/proton/particle is just a
| knot tied in the sheet. Outside of some small region local to
| the knot the sheet looks flat.
| scotty79 wrote:
| There is an "electron field" everywhere. Electron is a
| persistent, energetic disturbance of this field that can travel
| and interact through electroweak force. It's most convenient
| mathematical description is as if it was a "cloud" of
| probability of all of it's charge and mass being concentrated
| at a single point in space.
|
| If we forcefully interact with electron we can reshape this
| "cloud" to be as small as we need to at the cost of imparting
| on it random monentum through uncertainty principle.
|
| I think what they measure is that when you interact with
| electron then its electric field seems to be very spherical to
| the point that we can rule out a lot of ideas about electron
| having any internal substructure that might cause the field to
| be a little bumpy.
| p1esk wrote:
| This cloud of probability you're talking about - is it
| different from the cloud of probabilities of electron's
| position relative to the atomic nucleus?
| scotty79 wrote:
| It's the same thing for electron that freely propagates as
| for the one bound, for example inside atom or a molecule.
| It's just that the shape is different.
|
| I think it's worth mentioning it's not exactly a
| probability understood as a theoretical chance of something
| being somewhere. This wave function is what actually is the
| physical reality. But we can't measure this reality without
| interacting with it and when we do interact multiple times
| and interpret those interactions as if they were caused by
| pointlike particle being in particular spot then we see
| that results of those interactions have distribution
| matching this "probability" "cloud" (square of a wave
| function).
| wiml wrote:
| The cloud of probable location is the magnitude of the
| electron's wavefunction, as I understand it. So they're the
| same thing, but there's extra information in there too
| beyond simply position (wavefunctions are complex-valued,
| not real-valued). Source: Dimly remembered undergrad
| physics.
| simcop2387 wrote:
| Disclaimer: I have a theoretical degree in armchair physics,
| not a real one.
|
| So that's where the fun of Quantum Mechanics and uncertainty
| comes in. Electrons are not just point-like particles, they're
| sort of both particles and waves. If you nail down exactly
| where the electron "particle" is, then you end up with it's
| momentum being less defined, meaning that you're not going to
| be able to say anything at all about where it came from, where
| it's going, or how fast. Similarly if you can nail down it's
| momentum perfectly it won't have a definition of where it is
| anymore. This isn't the Observer effect, where you making the
| measurements changes the system, but in fact that the other
| related property actually ceases to have a valid definition
| anymore (I'm not well versed enough to say it stops existing
| with any confidence but that's my understanding). This leads to
| a situation where you end up measuring a probability density of
| the property of the electron, so you get a density of it being
| "around this point +/- some amount" and with a "momentum +/-
| this amount, and sort of in this direction". This means that
| you now have a probability density of the electron where you'll
| see it's effects of the negative charge and kinetic energy and
| those are the things that describe that "cloud of negative
| charge". The main effect of this that affects things is that
| you end up with this cloud of all the electrons around an atom
| and you don't ever observe the individual electrons, just the
| shells/clouds around the atom and how they change as energy is
| inserted into the system.
|
| My layman's understanding is that essentially as you make a
| measurement/system/whatever where it's designed to see the
| position more than the momentum you'll see more point-like
| particle behavior, but never only just that (you can't ever
| nail it down to an infinite precision, if you did it'd have a
| momentum that could send it off at the speed of light as if it
| had no mass) and in the other case if you could measure
| infinite precision on the momentum you'd end up measuring the
| electron as if it was "everywhere" in the universe all at once,
| which is just as nonsensical of a result as the first one.
| marcosdumay wrote:
| > I'm not well versed enough to say it stops existing
|
| That's a small detail, but no, it's not that the particle
| "stops existing". It's that we can't describe the momentum
| and position of something with indefinite detail with
| mathematics that is still coherent. The data type we have for
| describing things can not go there (on the QM language, of
| course).
|
| And the surprising thing is that QM predicts our experiments
| with as much detail as we can experiment with. So, we have
| this language that can't describe something with known
| position and speed, and as far as anybody is concerned, it's
| perfectly correct.
| siver_john wrote:
| Not bad for an armchair physicist. Disclaimer, my
| undergraduate degree was in physics but I'm not a quantum
| expert by any measure and my graduate work took me closer to
| statistical mechanics.
|
| So for the simplest explanation for you and the parent is
| that as you said electrons are both particles and waves,
| there are experiments that we can demonstrate for that. But
| if you're thinking of the electron cloud then that exists
| partially because you aren't measuring the electron.
| Basically this particle(s)/wave(s) orbiting the atom can
| exist in a lot of different configurations at once determined
| by it's energy (which is influenced by its/they position and
| how fast it is/they are moving). For educational purposes we
| often treat them more exclusively as a particle (early
| electrodynamics) or a wave (early quantum) depending on what
| field we are talking about.
|
| Of course there is greater definition I can give to what it
| is if we want to start talking about what protons and
| neutrons are made of and most of that is what occurs at the
| LHC. (But I'm heavily out of my depth in high energy particle
| physics).
|
| The measurement uncertainty applies to some other properties
| as well basically your uncertainty in the electron's position
| (sigma_x) and uncertainty in the electron's momentum
| (sigma_p) are bound by sigma_p * sigma_x >= hbar/2
|
| hbar is the reduced planck constant and sigma are statistical
| variance, but that condition must always hold so as sigma_x
| goes to 0 (you are more certain about the potential) sigma_p
| must get larger to compensate so you are less certain about
| the momentum. This measurement collapses the waveform and
| until enough time passes for the system to "normalize" the
| momentum will continue to be uncertain, after that you can
| measure the momentum but the position could be different too.
| criddell wrote:
| What does it mean though to say an electron is a particle?
| Isn't a particle an excitation of a quantum field? What does
| it mean to talk about the shape of a field?
| superposeur wrote:
| Yes an electron is a "quantized vibration" of a quantum
| field (the electron field). The vibration is quantized in
| the sense that you can only turn on the amplitude of
| vibration in discrete clicks, not in a continuous way. Two
| clicks would be two electrons.
|
| Such a quantized vibration has all the properties of a
| particle: it has a certain mass, it has a certain momentum,
| it has a certain angular momentum, and when you look at it
| in another frame of reference, all these quantities
| transform just as would a particle's. And, when you
| "perform a position measurement" it shows up as a single
| dot. If you don't do a position measurement it spends most
| of its time quantum superposition of states of definite
| position; hence the "cloud" aspect.
| [deleted]
| m3kw9 wrote:
| "Imagine an electron as a spherical cloud of negative charge"
| sorry man, you lost me on the very first sentence
| eitau_1 wrote:
| Some argue that metaphor is more fundamental to science than
| math.
| Waterluvian wrote:
| Fine. Oblate spheroidal cloud with a Lakitu in it*
|
| There's many abstractions. None of them are right. They're
| useful for different things. You cannot reject the simpler ones
| because you have adopted a still wrong but more complex one.
| MengerSponge wrote:
| All models are wrong, but some are useful.
| asplake wrote:
| Imagine a spherical cow, then make it really, really tiny
| revolvingocelot wrote:
| I find this result satisfying. Of course an electron is as a
| Platonic solid, that's very sensible. God does not play dice --
| God plays with marbles.
| klyrs wrote:
| Hot take, a marble is a D1.
| andygeorge wrote:
| *D-infinity
| [deleted]
| martincmartin wrote:
| _The experiments are now so sensitive that if an electron were
| the size of Earth, they could detect a bump on the North Pole the
| height of a single sugar molecule._
|
| _This new bound is sensitive to energies above roughly 10^13
| electron-volts -- more than an order of magnitude beyond what the
| LHC can currently test._
|
| Wow.
| ralferoo wrote:
| The next sentence after the first part you quoted: "The latest
| results are in: The electron is rounder than that."
|
| Which would be great if the Earth was actually perfectly round,
| but we've known for over three centuries that it's not. I'm
| sure the science the article is reporting on is fine, but it
| definitely sounds like the author of the article is out of
| their depth.
| butterNaN wrote:
| It's trying to put a size comparison so that our human minds
| can picture the scale. Earth is just a placeholder in this
| example. The author is inviting you to picture the the _size_
| of the planet. They could 've just written the sizes in terms
| of 10^x , however that is not as human-friendly to envison.
|
| There is no need to be unkind towards the author here, maybe
| your point is that they could have done a better job at
| presenting the scale for the reader? How would _you_ write
| it?
| WJW wrote:
| I know you're getting at the whole "oblate spheroid" shape
| thing, but I'm pretty sure people have known it wasn't
| perfectly round for way longer than that. You only need to
| look out a window to see hills and mountains after all
| (unless you live in the Netherlands ofc).
|
| Fun fact: the actual shape of the Earth is neither a sphere
| nor an ellipsoid but a "geoid", literally something "shaped
| like the earth".
| LadyCailin wrote:
| That's not what it's saying. It's saying, if you blew up the
| electron to the size of the earth, and sprinkled a sugar
| grain on it, then the _electron_ is rounder than that.
| kevin_thibedeau wrote:
| Definitely should have used spherical cows.
| wkat4242 wrote:
| Yeah how do they manage to get that kind of accuracy. Mind
| boggling.
| rightbyte wrote:
| Statistics, right? It is not "one" measurement?
| moron4hire wrote:
| That's precision, not accuracy.
| klausnrooster wrote:
| My (mis-?) understanding of the Central Limit Theorem is
| that the average of >30 measurements increases the
| accuracy.
| https://en.wikipedia.org/wiki/Central_limit_theorem
| moron4hire wrote:
| No, that's increasing the precision, not accuracy. Many
| imprecise measurements can be averaged to a more precise
| measurement.
|
| Say we had a perfect ruler to measure the length of
| something. It's absolutely precise and accurate. All
| measurements from it return the exact, same value, and
| preternaturally we know it's the "correct" value.
|
| Now say some bandit comes in while we're not looking and
| adds a small chunck of diamond to the end of the ruler
| without telling us. Our ruler is still precise, but no
| longer accurate. If we take many measurements with it,
| they always come back with the same value. Averaging
| those values does not improve the accuracy at all.
|
| Alternatively, say the bandit starts randomly changing
| the temperature of the room we are in. Thermal expansion
| is constantly changing the length of the ruler. The
| average length of the ruler is still the same, so it's
| still accurate, but it's no longer precise. We could
| average the measurements we take with it and get a more
| precise measurement.
|
| What the central limit theorem says is that the averages
| of our measurements will be normally distributed, even if
| the change in temperature is not.
| kelseyfrog wrote:
| This really doesn't make much sense in the context of the
| measurement which is bounding the value(0) with 90%
| confidence[1].
|
| 1. https://arxiv.org/pdf/2212.11841.pdf
| lifeisstillgood wrote:
| hang on - what?
|
| Yes it is precise ... to 17 decimal places or whatever. But
| it is also I believe accurate? I mean are they wrong and
| the electron is as bumpy as my chin on a weekend?
| delecti wrote:
| It's not that the experiment is not accurate, "accuracy"
| is simply not the aspect of the measurement being
| discussed. The sentence "That's precision, not accuracy."
| should be read to mean "we are discussing precision, we
| are not discussing accuracy" rather than "it's precise,
| but inaccurate".
| kgwgk wrote:
| When they say "they could detect a bump on the North Pole
| the height of a single sugar molecule" is not about the
| accuracy of the measurement?
|
| If my measurement device always measures 42 it may by
| hyper-precise - but it won't helping me to detect a bump
| on the North Pole the height of a single sugar molecule
| nor anything else.
| hansvm wrote:
| But the thing being concluded is that it's not very
| bumpy, and for that conclusion to hold water the data
| needs to be both accurate and precise within some very
| small bound. Spitting out precise measures of electron
| bumpiness isn't very hard without that accuracy. Right
| this second I used the "gut feeling" measurement device
| to conclude that the electron is round within 1024 bits
| of precision, and yet the authors have a publication and
| I don't. Is their conclusion over-blown?
| AnimalMuppet wrote:
| I don't think so. They're not measuring the radius to
| precision 10^-31 cm. They're measuring the _differences_
| in radius against zero, and they know the value of zero
| to infinite precision.
| hansvm wrote:
| Sure, but it's precisely that difference which they claim
| to be measuring. Why does it matter that they don't also
| know some other value (the radius) to high accuracy? It's
| kind of like how a balance can measure the difference in
| force to high accuracy (and precision), but that doesn't
| mean we know anywhere near that much about the masses on
| the balance, and...it doesn't have to; you can just state
| that you know some delta accurately and not have to
| explain why that means some auxiliary measurement is
| probably precise.
| moron4hire wrote:
| Say I devised a test of the smoothness of steel ball
| bearings. Maybe it'd be something like rolling the
| bearing around on a soft substrate and then checking the
| substrate for scratches. That test would be precise (I'd
| know the maximum bound on the size of imperfections in
| the bearing) but not accurate (it wouldn't tell me
| anything about the absolute radius of the bearing or the
| location of the imperfections).
|
| The point is, with the information given, we haven't been
| told anything about the accuracy of the test. Maybe it
| is. Maybe it isn't. That's just blank information. We've
| only been told the precision.
| Wowfunhappy wrote:
| But I feel like in this context, we're discussing both.
| Mezzie wrote:
| Precision and accuracy are slightly different
| mathematical concepts, as demonstrated by this image [0]:
|
| [0]: https://wp.stolaf.edu/it/files/2017/06/precsionvsacc
| uracy_cr...
| rektide wrote:
| To be honest accuracy Vs precision has always kind of
| makes sense to be but also not.
|
| If something is extremely accurate, it will also be
| extremely precise by necessity, it seems like? The
| difference between low precision but high & low
| accuracies is that points are closer to center. If you
| keep getting closer to center, more accurate, don't you
| necessarily get more precise too?
|
| Precise has always felt like a shitty alternate of
| accuracy. It's accuracy but with drift, accuracy to not
| the right place. But if you're accurate, you're both.
|
| Am I missing something? And, here specifically, if this
| is a case of very high precision but lower accuracy, can
| someone explain what the drift from center is about?
| Isn't a radius a radius? Where is the drift off center in
| these measures?
| alexpetralia wrote:
| I wrote about precision here if you are interested. You
| first need precision before you can start even talking
| about accuracy (otherwise there is no "center").
|
| https://alexpetralia.com/2023/01/31/what-does-it-mean-
| for-da...
| hansvm wrote:
| Something is accurate in this sense if the "true" value
| (ignoring any philosophical implications thereof) is
| contained in the error bounds of the measurement. What
| you're noting is that a high accuracy measurement will,
| upon application of statistics, allow you to derive a new
| measure which is both high-accuracy and high-precision,
| regardless of the low precision of any inputs. Not all
| things being described with accuracy and precision are
| the result of processing large amounts of data though.
| moron4hire wrote:
| I don't like the lower left quadrant of that diagram,
| because it's not clear that it's not centered on the
| target. It would have been more clear if the cluster was
| smaller so it could be moved to not be centered on the
| target.
|
| Accurate but imprecise means we can throw more and more
| shells down range and eventually hit the target.
| Inaccurate and imprecise means we may never hit the
| target. Inaccurate but precise also means we may never
| hit the target, but if we could introduce a second,
| different measurement that _was_ accurate, we could
| compensate.
| [deleted]
| PezzaDev wrote:
| No. Precision and Accuracy have very specific definitions
| in the world of science and engineering.
| https://en.m.wikipedia.org/wiki/Accuracy_and_precision
| jvanderbot wrote:
| So, when one uses statistics to rule out deviations below
| 1E-17 radians (or whatever), you're all saying that's not
| accuracy, it's precision.
|
| I'm also surprised, since IIRC precision is a measure of
| variance from a set of measurements, and accuracy is a
| measure of deviation of a value from true.
|
| The statistical aggregation to get an estimate should (I
| think?) increase both the accuracy of that estimate (it
| will converge to the true value) and it's precision (the
| spread of subsequent estimates with more measurements
| converges to zero or some noise floor).
|
| Here we're measuring something like eccentricity, which
| has a value and error bars. And the claim is we have
| eccentricity zero with precision high enough to rule out
| deviations below 1E-17 radians. So yeah, precision seems
| to be the better of the two, but accuracy matters.
|
| Either way, this is insanely pedantic.
| zmgsabst wrote:
| Consider the case where there's a configuration error --
| say, a cable not properly seated.
|
| You can have results that are highly precise, but due to
| cable issue, not baselined correctly and therefore
| systemically inaccurate. Eg, faster than light neutrinos.
|
| https://en.m.wikipedia.org/wiki/Faster-than-
| light_neutrino_a...
|
| I think people get confused because they forget that
| systemic bias can impact precise measurements: if your
| system is wrong, you'll precisely come to the wrong
| conclusion.
| jvanderbot wrote:
| You're talking about a specific measurement, not a
| derived measurement from statistical analysis, though,
| right? Is there an instrument? If not, we're not talking
| about precision or accuracy, we're talking about variance
| about the mean, and the mean is assumed to move towards
| true.
|
| In that case, the assumption is zero mean error b/c
| systemic errors average out, so the accuracy is the mean
| minus true, and the precision is established by the
| Cramer rao lower bound, and estimated my the posterior
| variance about the mean. My point is that calling it
| anything but a statistical certainty (e.g. confidence
| interval) is just jargon.
| zmgsabst wrote:
| You can't derive the correct value if all your
| measurements are (eg) +1ns due to inaccurate path length
| in your model.
|
| Your collection of measurements will converge, just as if
| you had built the device you intended to -- but they'll
| converge to the wrong value, because you're measuring the
| time incorrectly every measurement, and so averaging that
| out doesn't do anything.
|
| Your test is precise but inaccurate.
|
| The whole context of this is about a specific instrument
| measuring electron properties -- or in my example, timing
| neutrino flights. So... yes, we're talking about
| precision and accuracy.
| alexpetralia wrote:
| Yes, exactly: bias + imprecision = inaccuracy.
| [deleted]
| georgyo wrote:
| I can say Pi = 3 and be accurate but not precise.
|
| I can say Pi = 3.0000004 and be precise but not accurate.
|
| But that's not where the confusion comes from. It comes
| from measuring equipment.
|
| Example, if I have a scale that is sensitive enough to
| give several decimals of precision, it is very difficult
| to calibrate it so it is accurate.
|
| Anyone who owns a gram scale knows you basically have to
| recalibrate it after every measurement. It will gladly
| give you many decimals of precision that is just wrong.
| hansvm wrote:
| And for today's rant, you can also say Pi = 3 and be
| precise. Significant figures are a common shorthand for
| in-band signaling of error, but they're not the only tool
| and are really only useful insofar as they're pretty easy
| to do mental math with and relatively well known.
| [deleted]
| shagie wrote:
| On the subject of scales calibration and really small
| wights:
|
| Veritasium - How To Measure The Tiniest Forces In The
| Universe https://youtu.be/pXoZQsZP2PY (it gets into
| measuring piconewtons and femtonetwons)
| wkat4242 wrote:
| What's the point in measuring it with high precision if
| it's not accurate?
| ilyt wrote:
| Sometimes you're interested in delta of change, not
| absolute value itself. So absolute accuracy might be
| "wrong" but as long as it is consistently wrong (within
| duration of measurements you need to make) it doesn't
| matter all that much.
| moron4hire wrote:
| My understanding is that a highly spherical electron
| implies the electron has no sub component parts. Knowing
| the exact radius of the electron doesn't change that,
| it's knowing there is no variance in the radius that is
| important.
|
| And again, I was only commenting on what was being
| commented on here. I don't know if the experiment was
| also highly accurate. But people here were commenting on
| the precision and calling it accuracy.
| MattPalmer1086 wrote:
| Precision is about how tightly clustered your
| measurements are.
|
| Accuracy is about how well those measurements reflect
| reality.
|
| If you are just trying to see how smooth a ball is by
| measuring the diameter many times at different points,
| then a high precision can tell you that, even if the
| actual diameter is different to your measurement.
|
| You don't care about the actual diameter, you care about
| the variation in it.
| [deleted]
| JumpCrisscross wrote:
| It reminds me of Aristotelian physics' perfect aetherial
| heavenly bodies. Ironinic they were on the terrestrial sphere
| in the end.
| gattr wrote:
| Average Earth diameter = 2*6371 km ([1]). Size of glucose
| molecule [?] 9 A ([2]). Ratio = 7.06*1017.
|
| [1] https://en.wikipedia.org/wiki/Earth_radius
|
| [2] https://sphweb.bumc.bu.edu/otlt/mph-
| modules/ph/ph709_basicce...
| [deleted]
| mike_hock wrote:
| But they said they could detect a bump on the *North Pole*
| the size of a sugar molecule, so the diameter at the poles is
| relevant. Also, maybe "sugar molecule" means sucrose, not
| glucose.
| MarcoZavala wrote:
| [dead]
| comboy wrote:
| electron size: 10^-14
|
| planck length: 10^-35
|
| 10^-14 * 10^17 = 10^-31
|
| (in case somebody wondered just as I did)
| fractalb wrote:
| > 10^-14 * 10^17 = 10^-31 It's actually 10^3
| 1024core wrote:
| Typo: you forgot the "-" before the 17 in 10^17
| A_D_E_P_T wrote:
| Not even close. The diameter of the electron is under
| 10^-18 meters -- that's a sort of experimental upper bound
| derived from collision experiments -- but it may well be
| much smaller than that. Some estimates for the diameter of
| the electron approach the Planck length -- and some, which
| are no less credible, are well under the Planck length,
| e.g. at 10^-80m.
|
| In physics, the electron is usually described as a point
| with no size at all. Thus, for practical intents and
| purposes, it exists but is infinitely small. (Which sort of
| reflects the notion that human physics is an idealization
| of the natural world.)
|
| The Planck length isn't a hard physical limit for size.
| It's where direct measurement starts running into
| insurmountable barriers.
| wrycoder wrote:
| Well, 1E-18 / 1E17 is 1E-35, interestingly enough.
| AnimalMuppet wrote:
| 10^-14 / 10^17.
|
| Or 10^-14 * 10^-17.
|
| Minor nit to an interesting parent.
| [deleted]
| lagadu wrote:
| I struggle with understanding that size comparison, given that
| the size of the electron is unknown: we only have a maximum
| size that's based on the accuracy of the measurements, no lower
| bound.
| scotty79 wrote:
| I think it's supposed to relate the variation of the shape of
| electric field around electron not the size of the electron
| which is a pointlike particle.
| jethkl wrote:
| _The Standard Model predicts a vanishingly tiny EDM for the
| electron -- nearly a million times smaller than what current
| techniques can probe._
|
| This is a big achievement, but a lot more work in this direction
| remains.
| flimflamflem wrote:
| [flagged]
| vehemenz wrote:
| It's tangential, but I don't know how physicists understand the
| "why is there something rather than nothing?" question. At best,
| it's quantification without a predicate. At worst, it's
| metaphysical gobbledygook of the same variety that physicists
| constantly deride philosphers for.
| vaidhy wrote:
| But the answer to "why" is always gobbledygook. We try to
| answer how there is something instead of nothing. I do not
| think anyone can answer why it is flooding in Florida now. Many
| can answer the how, multiple levels deep.
|
| 'Why" is trying to assign a higher order causality and that is
| religion.
|
| But, if you are using "why" as a way to probe into inner
| workings, here is one possible hypothesis -
| https://www.youtube.com/watch?v=3SxowRIc20M&t=761s
| carrozo wrote:
| This was beautiful thank you.
| inportb wrote:
| If an electron were the size of Earth... did its mass increase or
| did its density decrease?
|
| Would it be a black hole with a planet-sized event horizon?
|
| What would happen to a sugar molecule on the north pole of a
| planet-sized electron with infinitesimal density?
| sdfghswe wrote:
| > If an electron were the size of Earth, the experiment could
| detect a bump the size of a sugar molecule.
|
| Makes sense, as the electrostatic force is about 10^36 times
| stronger than the gravitational force.
| kortex wrote:
| This leads me to the logical question about EDM of protons and
| neutrons. The electron and neutron are mentioned, but nothing for
| proton EDM. What's up with that?
|
| Also apparently the EDM for the neutron has yet to be detected,
| despite it being a composite particle. Our sensitivity is about
| five orders of magnitude away from the predicted value.
|
| https://en.m.wikipedia.org/wiki/Electron_electric_dipole_mom...
|
| https://en.m.wikipedia.org/wiki/Neutron_electric_dipole_mome...
|
| Also of note, here's a pEDM experiment with a 50m radius (the
| eEDM experiment is lab scale).
|
| https://aip.scitation.org/doi/10.1063/1.4967465
| vihren wrote:
| I'm working on the search for the EDM of the muon. Essentially
| it's much harder to search for the proton EDM than the neutron
| EDM. All EDM searches rely on a strong electric field applied
| to the particles. Because neutrons are neutral they are easily
| stored in some volume for a long time. You cannot so easily
| store protons because the moment you apply some E-field you
| start accelerating them. That's why you need to build a large
| storage ring with magnetic/electric focusing and so on. This
| brings numerous challenges that you don't have for the neutron.
| This, combined with the fact that we don't expect much
| different novel physics for the proton that won't be seen in
| the neutron has led to the focus on the neutron EDM, while the
| proton was left behind.
|
| The usual quote is that for the proton we can reach
| sensitivities up to 10^-29 (around three orders of magnitude
| lower than the current nEDM limit), but thats only the
| statistical sensitivity. The systematic effects that would
| spoil that come much earlier and this limit is close to science
| fiction at this point. For example, if you have a magnetic
| field in the order of attotesla in the region of the storage
| ring it will dominate the measurement.
|
| Would be happy to answer more edm questions :)
| brookst wrote:
| Whatever happened to Skrillex?
| kortex wrote:
| Thank you, this is why I love HN!
|
| Ah, that makes sense! I thought neutrons were hard to store
| because they were neutral and go right through things, but I
| guess cold neutrons can be stored (at least until they decay
| into protons).
|
| Is it expected that pEDM ~= nEDM, since they are uud and udd?
| MengerSponge wrote:
| EDM experiments are sensitive to electric field strength and
| observation time.
|
| For electrons, you can get much higher fields inside a
| molecule.
|
| For neutrons, you either need a very cleverly designed crystal
| or a bottle with ultracold neutrons. The crystal lets you get
| huge fields and huge particle counts, but relatively short
| observation times. Ultracold neutrons let you have long
| observation times (100-300 seconds) but lower fields and much
| lower particle counts.
|
| Protons are probably the hardest of the lot. They need external
| fields, but they're charged so you can't just bottle them.
| You're stuck with a holding ring, and needing to make all those
| v x E corrections.
| tonymillion wrote:
| It's simple. Antimatter goes the other direction in time.
|
| Just as you can go forwards and backwards in the X dimension.
| Matter can only go in one direction through time, antimatter the
| other.
|
| So at the point of the Big Bang matter went on its direction
| through time saying buh-bye to antimatter that went in the
| opposite direction.
|
| Note: I didn't say forward and backwards because from their
| perspective we are the ones who went in the opposite direction.
|
| This accounts for the lack of antimatter, the "missing mass" of
| the universe and why time travel (other than into the future for
| us) is impossible as the only way you could go in the opposite
| direction (the past) would be to convert yourself to antimatter
| which would be very very bad.
|
| This also doesn't mean there is an antimatter earth somewhere out
| there (in the other time direction so we'd never know anyway)
| because at the point of the Big Bang an entire series of events /
| interactions would have occurred. There's no interacting link
| between the two times (t+1 vs t-1)
|
| Figure out the maths for yourself...
| mrkeen wrote:
| Physicists are able to produce small quantities of matter and
| antimatter, which then annihilate each other, releasing energy.
| It was a big deal when they were able to trap the antimatter so
| that it didn't do this.
|
| If the two particles travelled different directions in time,
| how would they meet?
| tonymillion wrote:
| The matter particle already existed we annihilated it with an
| antiparticle, that released m _(c_ c) energy from which 50%
| of it was released as energy (the matter part) and 50%
| created the anti-particle that came into existence when we
| created it.
|
| From out point of view it all makes sense:
|
| Create anti-particle
|
| Smash it into equivalent particle
|
| Energy released
|
| ???
|
| Profit
|
| From the anti-patter point of view:
|
| Profit
|
| ???
|
| Energy coalesced into antiparticle
|
| Particle unsmashes
|
| Particle stops existing.
|
| I'm mr meseeks look at me!
| dragonwriter wrote:
| > Physicists are able to produce small quantities of matter
| and antimatter, which then annihilate each other, releasing
| energy. [...] If the two particles travelled different
| directions in time, how would they meet?
|
| The anti-matter would travel backwards in time from the event
| we see as the "mutual annihilation" to the event we see as
| the "creation of paired particles", while the matter would
| travel the other direction. Simple.
|
| When they _don't_ meet is a little trickier to explain, but
| its still the anti-particle coming back from somewhere in the
| future (possibly where it coincided with a different matter
| particule coming forward in time) and coinciding with the
| particle at the point we consider the "creation" point, and
| the same vice versa with the matter particle.
|
| I'm not saying it's _right_ , I'm saying that's how you
| explain them "meeting" in the "anti-matter goes back in time"
| framework.
| shagie wrote:
| (I give absolutely no credence to the root of this comment
| tree...)
|
| There was an idea posed a bit ago known as the "one electron
| universe" ( https://en.wikipedia.org/wiki/One-
| electron_universe )
|
| > The one-electron universe postulate, proposed by
| theoretical physicist John Wheeler in a telephone call to
| Richard Feynman in the spring of 1940, is the hypothesis that
| all electrons and positrons are actually manifestations of a
| single entity moving backwards and forwards in time.
| According to Feynman:
|
| > > I received a telephone call one day at the graduate
| college at Princeton from Professor Wheeler, in which he
| said, "Feynman, I know why all electrons have the same charge
| and the same mass" "Why?" "Because, they are all the same
| electron!"
|
| > ...
|
| > Feynman was struck by Wheeler's insight that antiparticles
| could be represented by reversed world lines, and credits
| this to Wheeler, saying in his Nobel speech:
|
| > > I did not take the idea that all the electrons were the
| same one from [Wheeler] as seriously as I took the
| observation that positrons could simply be represented as
| electrons going from the future to the past in a back section
| of their world lines. That, I stole!
|
| > Feynman later proposed this interpretation of the positron
| as an electron moving backward in time in his 1949 paper "The
| Theory of Positrons". ...
|
| ---
|
| PBS Space Time : The One-Electron Universe
| https://youtu.be/9dqtW9MslFk (highly recommended)
|
| The idea has mathematical utility, but not any practical.
| tonymillion wrote:
| My only difference to that is that the positrons and
| electrons went in opposite directions on the time axis from
| the initial big bang event. I love the idea of a single
| electron being the scan line of the universe (to make an
| analogy to CRTs)
|
| Assume you take the normal x,y,z we "know" from reality and
| separate them out into 3 distinct 1 dimensional lines.
|
| Add another 1d line for time.
|
| We can see you can't simultaneously move both "forwards"
| and "backwards" on any of these lines.
|
| Postulate: for time, matter (from our point of view) can
| only move in a singular direction from t=0 onwards (we'll
| call this positive), antimatter can only move in the
| opposite from t=0 (negative).
|
| And, unless there is momentum in any of the spatial
| dimensions the particles travel on the t axis at C. I.e v=C
| on the t axis for matter And v=-C for antimatter.
|
| Second Postulate: the cumulative velocity of all particles
| must equal the speed of light
|
| Any momentum in the spatial (x,y,z) dimensions subtracts
| from t: explains time dilation (as an adjunct)
|
| v(t) = C-(v(x)+v(y)+v(z)) (very very simplified for this)
|
| Finally matter / antimatter annihilation is the equivalent
| v _v, as is the case for any direct impact of two masses of
| equal mass and velocity. Giving us e=m(c_ c), in a general
| sense without all the pesky gravitational warping of space
| and time.
|
| Btw: I'm not a particle physicist (can you tell) but I did
| have this thought while developing code for a physics
| engine in a simulation game I was briefly involved in, so
| far I've not invested heavily in all the mathematics, but
| since I've just retired I might actually do so.
| akomtu wrote:
| Electrons don't need to move backwards in time to become
| positrons. Rather, I think, that one uber-electron
| peacefully exists on its natural multidimensional manifold,
| and it's us, who declare one axis to be "time", create the
| dihotomy of that electron sometimes aligning with the
| timeline and sometimes against it. If we chose 2
| coordinates as time, the same uber-electron would create a
| whole host of ekectron-like particles, depending on how
| it's aligning with the two timelike directions.
| ThinkBeat wrote:
| I do not understand this. May someone help me with an ELI16?
|
| An electron is a cloud that is contained with a perfectly round
| sphere. Does cloud mean a thing that contains a particle that
| travels very fast in a perfect sphere?
|
| What does cloud entail in this instance? If we have determined
| that an electronic cannot be made up of other particles then
| there should only be one particle in the cloud? Or is the
| particle a gas / cloud?
|
| I thought that the general consensus was that the precise
| location of an electron was impossible (?) to fully predict? If
| you can't predict where an electron is with a high degree of
| certainty How can you measure it ?
|
| This might be outdated, or just my brain pulling tricks on me
| again.
| dave333 wrote:
| I think the measurements don't say anything about the size or
| how the electron is distributed in the probability distribution
| other than that it's spherically symmetric to a very small
| tolerance. It's interesting that there is another model of the
| electron orbit in atoms that is a spinning fluid shell of
| charge with an exact radius. See
| https://brilliantlightpower.com/theory-overview/
| ThinkBeat wrote:
| > I think the measurements don't say anything about the size
| or how the electron is distributed in the probability
| distribution
|
| I fully admit i dont understand most of what I hear about
| particle physics anymore A lot seems non intuitive with the
| (dumb) model I have in my head. (That doesn't say much about
| tis accuracy)
|
| If you are to make such extremely detailed measurements of
| anything you need to be able to observe it over time? (Though
| how much time varies a lot)
|
| Presumably, a constantly moving electron whose location
| cannot established is a difficult thing measure?
| ineptech wrote:
| The old "is" strikes again. An electron is definitely not a
| cloud, nor a particle nor a wave, we don't know what the hell
| it is and stopped trying to describe it in those terms many
| years ago. Instead, we limit ourselves to trying to come up
| with models that accurately predict how they behave, and call
| the models useful when they predict the right answers to
| experiments. "All models are wrong but some are useful", as the
| saying goes.
|
| Like all subatomic particles, electrons don't seem to have a
| discrete location; when we try to measure their location, we
| get different results each time, as you said. However, these
| apparently-random results follow a predictable pattern, so we
| describe it using an equation predicting where it is most
| likely to be found (the Schrodinger wave equation). For
| electrons in some stable states, that area is roughly
| spherical, meaning that there is some point where it is most
| likely to be found, a fuzzy area near that point where it is
| fairly likely to be found, and a distance from that point past
| which it is very unlikely to be found. We can therefore model
| the electron as being a tiny discrete thing that whizzes around
| in a roughly spherical area, which is the "cloud" in this
| article.
|
| All that "can be modeled as" stuff is unwieldy, so people say
| the electron "is" a spherical cloud when they mean that
| modeling it as a spherical cloud is useful for understanding
| the matter at hand. What this article is describing is an
| attempt to measure whether that spherical region is perfectly
| spherical. If it weren't - meaning, if the electron was
| slightly more likely to be found on one side of the sphere than
| the other, then it would have an electrical dipole moment,
| which is what they were trying to find.
| ineptech wrote:
| Fake edit: this is why it's helpful when discussing quantum
| mechanics to banish "is" from your vocabulary. For example,
| the debate over whether an electron "is" a particle or "is" a
| wave is much more tractable when you switch to debating
| whether it behaves like a particle or a wave in some
| situation. In college, I found this very similar to how it is
| useful when learning relativity to avoid the word
| "simultaneously".
| perardi wrote:
| Yeah, I am not used to seeing the term "cloud" for a single
| electron.
|
| Is that a common term in physics for _a single electron_? I am
| very much used to seeing that phrase as the probability space
| for electrons in orbitals in an atom.
|
| https://en.wikipedia.org/wiki/Atomic_orbital
|
| In this article I take it to mean "any point particle has a
| non-zero physical radius, but because quantum mechanics shows
| everything has a measure of uncertainty, the possibility of the
| charge within that non-zero space is an amorphous cloud". But
| still a weird lexical overlap with the high school physics
| electron cloud meaning of things.
| drdeca wrote:
| Consider the case where the atom in question is hydrogen,
| with just one electron orbiting it.
|
| I would still think the word "cloud" would be used?
| LegitShady wrote:
| The electron has no known internal structure. As far as we know
| its a fundamental particle and isn't made up of other things,
| the way protons or neutrons are made up of quarks held together
| by gluons.
|
| An electron's location is subject to all sorts of rules. The
| Heisenberg uncertainty principle says that the more we know
| about a particles momentum (mass*velocity), the less we know
| about its position, and vice versa. This is not a matter of the
| observer effect (measurement upsetting one of these values), as
| some people state, but something fundamental due to the
| wavefunction nature of matter. The location of a subatomic
| particle is determined by its wavefunction (Squared) - where
| the wavefunction is big you have a high probability of finding
| a particle, and where it is small you have a small probability
| to find a particle. the wavefunction is a probability density
| function - the probability of finding a given particle at a
| given place in a given time.
|
| The next important idea is that subatomic particles can be
| considered both particles and waves, and thus have a
| wavelength. High momentum particles (high energy) have a short
| wavelength, low momentum (low energy) particles have long
| wavelengths. Waves are disturbances spread out in space, and we
| can identify the distance between two peaks (the wavelength),
| but then we wouldn't know anything about its position - it
| could be in lots of places.
|
| To localize a wave you add together lots of waves (into a
| localized wavepacket) until the resulting wave gives you areas
| where you are likely to find a particle where those added waves
| overlap in crests, and areas where you are unlikely to find the
| particle where those added waves overlap in troughs. This is a
| tradeoff, though - you are still subject to the heisenberg
| uncertainty principle so the more you know about the location,
| the less you know about the momentum. Thus the electrons, which
| move very quickly, and are interchangeable with one another
| being identical to each other, appear to exist as a cloud of
| probabilistic locations. They aren't themselves a cloud, rather
| their position is always uncertain until directly measured to a
| high degree of certainty.
|
| Now you may say "but we know electrons live in orbitals around
| atoms - how can we know that if we can't know their precise
| positions". This is because electrons obey the pauli exclusion
| principle, which states that two or more particles with half
| integer spin (fermions of which the electron is one, which have
| antisymmetric wave functions) cannot have the same set of four
| quantum numbers -
|
| n (the shell number or general region for value of energy of
| the electron),
|
| l (orbital angular momentum/the shape of the orbital),
|
| m sub l (the magnetic orientation of the orbital), and
|
| m sub s (quantum spin, which for fermions can be +/- 1/2). (the
| minus is what makes fermions antisymmetric)
|
| This principle is why electrons are more likely to be found in
| some places around an atom described as shells, and thus why
| electrons exist in discrete locations around an atom and why
| atoms and chemistry exist. The reason for the pauli exclusion
| principle is also wave related - I'll link a video below:
|
| https://www.youtube.com/watch?v=Zlp2GQ3OLeE
|
| This was a pretty surface level explanation - we didn't even
| get into the dirac equation (which is where the existence of
| antimatter was first derived) or spinor theory! but I think its
| good enough to have some understanding of why the fundamental
| wave nature of subatomic particles leads to uncertainty in
| their location, which means they appear to live in a cloud
| around atoms.
| dogma1138 wrote:
| So the TLDR is that the electric dipole moment of electron seem
| to match the one predicted by the Standard Model at least as far
| as our current measurement capability goes and as we get more and
| more accurate measurements the wiggle room shrinks so the
| likelihood that the EDM predicted by the SM is correct increases
| which lowers the likelihood of post SM physics?
| zmgsabst wrote:
| I think more accurate to say: "Lowers the probability of
| particular models"
|
| We still have open questions the standard model doesn't answer
| -- like what's up with gravity? ...why didn't we have equal
| parts antimatter? ...does braiding have wider implications than
| anyons? Etc.
| MengerSponge wrote:
| Yes and no. First off, "the sm is correct" isn't how to think
| about this. Newtonian mechanics is "correct" for airplane
| flight, or even to calculate rocket trajectories. It's a low
| order approximant of relatavistic mechanics, though. It's
| incomplete, and you need to add higher order effects to
| correctly describe the orbit of Mercury, for example.
|
| The SM is incomplete. Among many other things, it dramatically
| misses the amount of matter generated during the big bang (by
| about 10^7). To read about the generation of matter over
| antimatter, check out the Sakharov criteria. (Sakharov was also
| an interesting dude, but that's for another day.)
| Matter/antimatter asymmetry is coupled to symmetry violating
| processes, which also inevitably generate nonzero EDMs.
|
| The SM includes a bit of this asymmetry, which is why it
| predicts an eEDM at all. The SM's prediction is so small that
| any detection _has_ to come from beyond SM sources.
| dogma1138 wrote:
| That was what I wanted to raise, SM doesn't have an allowance
| for Dark Matter, and also doesn't not have an explanation for
| the matter anti matter asymmetry so the article was quite
| confusing.
| MengerSponge wrote:
| The SM _does_ have a bit of matter /antimatter asymmetry,
| as this asymmetry was first observed in the 60's by Cronin
| and Fitch (1980 Nobel).
|
| It's just not a big enough asymmetry to account for all
| this matter we see.
| elashri wrote:
| By now, there is a concessions among the particle physics
| community that SM is incomplete. The same way that we all
| agree that Newtonian mechanics is incomplete and doesn't
| describe anything on atomic/quantum level so we don't use
| it or talk about Newton mechanics when we are in this
| scale. The same thing happens here, people mostly talk
| about SM for what it predict and have an answer for not
| what it lacks (again because it is obviously incomplete).
| dogma1138 wrote:
| Hence my confusion with the title and the article at
| large. We know we need new particles if for nothing else
| than to explain dark matter (unless we will come with a
| non-MOND non-matter theory that fits current observations
| and hopefully is compatible with other well tested
| theories too).
|
| We also have "known" for a while that the standard model
| is incomplete but so far actual physics beyond it has
| been eluding us.
|
| That was to me missing in this article.
| shonenknifefan1 wrote:
| preprint is here: https://arxiv.org/abs/2212.11841
| cperciva wrote:
| Can someone tell me what version of "shape" we're talking about
| here? I thought electrons were point charges.
| JonyEpsilon wrote:
| I think it's the usual meaning of shape, it's just perhaps that
| we don't typically think about what that really means. [I was
| an author of the Imperial study mentioned in the article, and I
| had some long arguments with my collaborators about whether it
| was right to describe our measurement as the "shape of the
| electron", so I feel compelled to defend the point!]
|
| If I pick something up on my desk and feel what shape it is,
| what I'm really doing is mapping out the interaction between
| the density of electrons in the object under test and those in
| my fingers. I might infer that the electrons of the object are
| distributed in a spherically symmetric way (it's round), or
| perhaps something more complex (all the other less symmetric
| shapes).
|
| So shape in the context of the electron shape measurements
| means how it interacts electromagnetically. If it interacted
| perfectly spherically symmetrically, I think it would be
| reasonable to say it was round. If it interacted in a more
| complex way (as in, you could grab it and rotate it, because it
| has some non-spherically symmetric interactions) then it's not
| round. Interestingly, the electromagnetic interactions of an
| electron are extremely tightly constrained by it having only
| 1/2 unit of spin. You can expand any field around a point in
| terms of spherical harmonics, and you can show the with spin
| 1/2, the electron can only interact in the manner of the first
| two spherical harmonics - monopole and dipole. So it can be
| round (monopole), or round + a more negative and less negative
| end (dipole). Nothing more complicated than that. (Assuming you
| believe quantum mechanics. The Wigner-Eckart theorem is the
| thing to look up if you're interested.)
|
| These measurements, then are measuring the dipolar component of
| the electron's electromagnetic interaction. The only way in
| which it could be not round.
|
| As to the point charge thing: well, that's like your opinion
| man :-) Which is to say, the electron is what the electron is,
| and it cares not how humans decide to describe it! These
| experiments are fine examples of a long tradition of measuring
| and observing to make sure our theoretical descriptions are
| actually faithful to reality.
|
| You might be tempted so say that if one of these measurements
| discovered that the electron was not round, then maybe that
| would be evidence for the electron being not a point particle.
| It's complicated though ... and you'd find many physicists
| would start arguing with you if you did say that, because the
| current description of the electron - while being a point
| particle in a certain sense - is already pretty complicated
| (basically, because of interactions between all of the
| different quantum fields) and many people would say it's
| already not point-like. Many wouldn't though. Maybe the point
| here it's quite tricky to be precise about these things without
| just doing it properly with maths!
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