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Scientists Calculate Most Precise Measurement of Electron's Mass

Posted by samzenpus on from the step-on-the-scale dept.

sciencehabit writes "A team of physicists has produced the most precise electron mass measurement ever made. Instead of trying to measure the mass directly, the researchers bound a single electron to a bare carbon nucleus and placed the resulting atom in a uniform electromagnetic field called a Penning trap. The team's new measurement is 13 times more precise than previous efforts, with an uncertainty of just 0.03 parts per billion. The group's precise result will help physicists more accurately calculate the fine-structure constant, an important value in tests of the standard model of particle physics, which shapes our understanding of the basic building blocks of the universe."

59 comments

  1. So what's the mass then? by Anonymous Coward · · Score: 1

    TFA didn't post it, I'm curious what the actual measurement is.

    1. Re:So what's the mass then? by Anonymous Coward · · Score: 5, Informative

      They determined the electron mass compared to that of a proton, so it depends on how accurate the proton mass has been determined.

    2. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      As accurate as Avragado's constant is known. Hydrogen / L = proton + electron

    3. Re:So what's the mass then? by moschner · · Score: 0

      If I'm not mistaken, and I could be, I believe they were comparing it to the mass of a proton within the carbon nucleus they were using in the experiment.

    4. Re:So what's the mass then? by fishybell · · Score: 3, Funny

      1

      The unit is SE, for Standard Electron

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    5. Re:So what's the mass then? by davester666 · · Score: 4, Funny

      They have to run the test again. One of the researchers was looking at the electron when they took the measurement.

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    6. Re:So what's the mass then? by hcs_$reboot · · Score: 0

      9.10938291379103210491350982761553051869972813 × 10^-31 kilograms

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    7. Re:So what's the mass then? by jmv · · Score: 4, Informative

      Actually, the mass of a hydrogen atom isn't equal to the sum mass of the proton and that of the electron. There's a 13.6 eV binding energy (good 'ol E-mc^2) that needs to be taken into account. Considering that the 511 eV rest mass of the electron and the fact that we're taking about measurements that are supposed to be accurate to less than 1 part per billion, then the binding energy is pretty significant. I suspect there are other effects that also need to be taken into account.

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    8. Re:So what's the mass then? by jmv · · Score: 3, Informative

      Sorry, I meant to say 511 *keV* for the rest mass of the electron.

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      Opus: the Swiss army knife of audio codec
    9. Re:So what's the mass then? by Sockatume · · Score: 1

      This needs to be emphasised: laymen frequently don't really get just how equivalent the mass-energy equivalence is, that they're literally the same quantity. This is why sci-fi characters shouldn't (for example) convert their alien invasion fleet into energy and store it in a tiny cube and put it in their pocket; it still has all of its original mass-energy.

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      No kidding!!! What do you say at this point?
    10. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      511 *keV* for the rest mass of the electron

      Isn't that a circular definition? I mean, eV is delta kinetic energy (which depends on electron's rest mass) of electron being accelerated in electric field between two potentials that differ by one Volt.

    11. Re:So what's the mass then? by AlabamaCajun · · Score: 1

      To that effect, considering energy I would like to see results at high and a low energy states to determine if the added energy affects the weight. Photons are particles that are the energy carriers used to upstate the electron. Does this change also increase the weight electron or the atom?

    12. Re:So what's the mass then? by AlabamaCajun · · Score: 1

      LOL, 511eV, desktop particle physics?

    13. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      These days, fewer and fewer places have use of eV in the original sense to any high precision, and it gets used as some generic conversion from SI units. The precision talked about here about a thousand times finer than the measured conversion from eV to J, so you could instead just assume some set conversion to SI untils and re-interpret what the previous post was trying to say, as it still holds. Or assume that conversion is not well know and it being a good example of precision versus accuracy...

    14. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      Well seems significant if you don't actually bother to run the numbers, or consider where the denominator or numerator is of your big numbers are located. If you use the ionization energy, chemist version of binding energy, hydrogen is 1312 kjol/mol. Which works out to 1.4 * 10^-14 grams. Electron bonds are puny compared to neutron binding.

    15. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      1

      The unit is SE, for Standard Electron

      I for one salute our accurately weighed, negatively charged overlords!

    16. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      Oops. Wrong direction on kg to g 1.4*10-8. Which if there is no nasty circular dependency in the numbers sources ( yes this happens in physics too), adjusting for the binding energy in the atom, molecule and thermal would leave the accuracy well under the 10-9.

    17. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      There's a 13.6 eV binding energy (good 'ol E-mc^2) that needs to be taken into account

      I know how to calculate the energy that comes form splitting atoms using change in mass. Does this relate to this binding energy? Otherwise I have nothing and need some education because I don't see how the H nucleus is gonna split barring sub-atomics. What is this binding energy?

      Asking out of pure curiosity.

    18. Re:So what's the mass then? by Anonymous Coward · · Score: 3, Informative

      I don't know where the parent poster got that number, but that is way too many digits, even considering the new precision the recent experiment added. As in, that is nearly 3 times as many digits as the error bars in the paper would suggest. They gave the measurement in two forms, the mass of the electron in atomic mass units: m_e = 0.000548579909067(14)(9)(2), and as the ratio of the proton mass to electron mass: m_p/m_e = 1836.15267377(17).

    19. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      When I convert aliens into cubes, I only store enough information to recreate the aliens if needed. It's a bit link an mp3. It's lossy compression. The restored aliens come out close enough to the originals that only an alienphile would claim they could tell the difference, but would likely fail in a blind taste test.

    20. Re:So what's the mass then? by cellocgw · · Score: 1

      This is why sci-fi characters shouldn't (for example) convert their alien invasion fleet into energy and store it in a tiny cube and put it in their pocket; it still has all of its original mass-energy.

      Oh you silly 3-dimensioner! The tiny cube is merely the 3D representation of a portal into 9-D space where the invasion fleet is stored. The mass of the cube itself is less than 50TeV (I made that number up)

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    21. Re:So what's the mass then? by Anonymous Coward · · Score: 0

      It's binding energy of the electron's attachment to the nucleus, which is orders of magnitude smaller than most nuclear reactions. That energy isn't involved in some splitting of the hydrogen nucleus, but in just ionizing the atom.

    22. Re:So what's the mass then? by jmv · · Score: 1

      Consider this, if an electron were to transition from "really far" down to the first energy level of the hydrogen atom, then the photon emitted would have an energy of 13.6 eV, and the mass of the resulting hydrogen atom would be 13.6 eV less than the sum of the original masses.

      --
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  2. Proton Size by Anonymous Coward · · Score: 0

    Whatever happened to that story about the proton being smaller than first thought?
    Supposedly that rejiggered the standard model as well.

  3. I find myself wondering... by CrimsonAvenger · · Score: 1, Offtopic

    ...if the authors of TFA and TFS are aware that there's a difference between "precise" and "accurate".

    TFA seems to be trying to use "precise" to mean "both precise and accurate", TFS just summarizes TFA without noticing that there's a distinction to be made.

    DO remember that there IS a difference:

    3.14159 is much more precise than 3.14.

    But if the actual value is 3.141, then 3.14 is more accurate than 3.14159.

    And I'm betting that at least one /. entity is going to focus like a laser on 3.14159 being an approximation of pi, and therefore 3.141 is NOT accurate at all. Alas for that entity, I picked 3.141 as the target number purely arbitrarily, and the only relation to pi is the lemon meringue on one of my keys from dessert.

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    1. Re:I find myself wondering... by Baloroth · · Score: 5, Insightful

      I'm puzzled where you're seeing the confusion. TFA uses the term "precise" precisely (heh) as it is meant to be used: it tells you the uncertainty (known uncertainty, obviously, though you can throw in a "fudge factor" to account for unknown factors) in the measurement. It's not really possible to tell if the measurement is *accurate* except by comparing it to other measurements made by other teams, but given the higher level of precision in this experiment, that comparison is mostly useless (I'm assuming their data with error lies within the data with error of other measurements. If it didn't, that might end being much bigger news).

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    2. Re:I find myself wondering... by TrollstonButterbeans · · Score: 1

      I think it is very accurate that your comment was rated Offtopic precisely because this article isn't about the value of PI.

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    3. Re:I find myself wondering... by Workaphobia · · Score: 1

      Precision without accuracy is meaningless, hence the "significant digits" we were all taught in science class. Mentioning accuracy when bragging about precision would be redundant. Why split hairs?

      --
      Evidently, the key to understanding recursion is to begin by understanding recursion. The rest is easy.
    4. Re:I find myself wondering... by Anonymous Coward · · Score: 0

      Precision without accuracy is meaningless

      There are plenty of times when all you care about are relative measurements where certain types of systematic errors can cancel out. The lab I work in has various meters and measurement devices that are very linear and precise, but without calibration against a standard lack accuracy. Considering the calibration process can be expensive at such levels, we don't both for the meters where it doesn't matter if they are off by some proportionality constant or have some unknown offset.

      hence the "significant digits" we were all taught in science class. Mentioning accuracy when bragging about precision would be redundant.

      Some science classes cover the difference between precision and accuracy, which might have helped with you not seeing the two terms as redundant. Although sometimes that is left to the level where you don't discuss significant figures but instead work with actual error bars.

    5. Re:I find myself wondering... by oodaloop · · Score: 1

      It's just odd to hear only of precision. I can precisely tell you that the time is 9:14:12 on August 18 1912 BC. That's not even remotely accurate, but damn is it precise!

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    6. Re:I find myself wondering... by Anonymous Coward · · Score: 0

      Computer clocks can report times to the microsecond or less, but chances are your system clock is not synched with anywhere near that accuracy. But there is still a use for that precision if you only care about relative times and not about specific time stamps relative to other computers. Likewise, when the battery dies and the BIOS time resets on an older computer, the clock doesn't lose any precision and still is useful for making the computer work even if you don't bother resetting time on every boot.

  4. DOI not found. by MurukeshM · · Score: 1

    I'm getting a DOI not found for the paper from TFS, the DOI being 10.1038/nature13026.
    Does anyone know the correct identifier?

    1. Re:DOI not found. by Baloroth · · Score: 4, Informative

      DOIs can take a few hours/days or so to start working in some cases, if the results were recently announced. While Slashdot covering recent news would be surprising, it's not totally unheard of.

      --
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    2. Re:DOI not found. by Anonymous Coward · · Score: 1

      Here is a link using Nature's own DOI resolver and here is one to the final paper.

    3. Re:DOI not found. by fahrbot-bot · · Score: 4, Funny

      I'm getting a DOI not found for the paper from TFS, the DOI being 10.1038/nature13026.
      Does anyone know the correct identifier?

      So, the DOI is precise and you're asking if it's accurate? :-)

      --
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    4. Re:DOI not found. by Anonymous Coward · · Score: 0

      Obviously Slashdot just recently found Tachyons.

  5. Rough measure... by ackthpt · · Score: 5, Funny

    ...Slightly larger than a particle of commons sense, which is in such short supply these days.

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  6. FSC? by Anonymous Coward · · Score: 0, Offtopic

    So, what is the new value of the fine structure constant?

  7. It's 42 pounds. by Anonymous Coward · · Score: 0

    Oops! I mean 42.12 pounds.

  8. I have a more precise measurement. by PSXer · · Score: 1

    It is exactly 1 electron mass.

    1. Re:I have a more precise measurement. by wonkey_monkey · · Score: 2

      Is that an African electron or a European electron?

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    2. Re:I have a more precise measurement. by dltaylor · · Score: 1

      Is that rest mass (to which GP SHOULD HAVE referred), or while migrating (with, or without, coconut)?

  9. Calculate? by pahles · · Score: 2

    How do you calculate a measurement? Or is it just me, not speaking English on a daily basis, getting in the way?

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    Sig?
  10. So what if the act of binding with an atomic nucle by Anonymous Coward · · Score: 0

    Sounds crazy, but prove it ain't so.

  11. Calulate by Anonymous Coward · · Score: 0

    You can calculate a weight by measuring some other property. Say you have a cube of water at 4C and can measure the cubes dimensions. You can then calculate the weight of the water knowing at 1 gram = 1 cc. What amazes me is the number of significant digits involved (if you believe the number reported in a previous comment is correct).

  12. Can't we just change the fine structure constant? by bluefoxlucid · · Score: 2

    You'd only have to collapse the universe and then influence it at roughly the moment when it cooled down enough that photons had less mass than protons.

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  13. Re:Yep, beta still fucked by AlabamaCajun · · Score: 1

    Wet farts have more electron weight than dry ones. Can we just ask that this beta sh!t be optional so that we can get on with life. Make the new one function like the new one and let users choose a color base. I like the dark because I can read is better with out all the white page burning out my retina.

  14. Re:Yah, old slashdot is back, Black text on white! by jones_supa · · Score: 1

    Yeah, the Beta is morphing from a "complete trainwreck" to just a "garbage can". ;)

    Now, I wish the full article summaries were shown in the front page.

  15. Yeah, bad title. by DoctorNathaniel · · Score: 1

    You don't 'calculate' a measurement. Measurements often require some mathematics, but it's the incorrect verb. Calculations are theoretical.

  16. link between mass value and avogadro's constant by lkcl · · Score: 0

    well... this is puzzling. i tried converting the value reported to MeV and accidentally divided by the atomic units constant 9.109 382 91 x 10-31 instead. what i got shocked the hell out of me: 1000x avogadro's constant. according to reports here http://phys.org/news/2014-02-p... the value is 0.000548579909067 atomic mass units. if however you divide that by the atomic unit of mass reported here http://physics.nist.gov/cgi-bi...|search_for=atomic+mass+unit you get, to 6 decimal places, avogadro's constant times 1,000.

    i am... very very startled! the implications are that there is some sort of link between the mass of the electron and (if you look up the definition of 1 mole on wikipedia) the number of atoms in 12 kg of carbon. which is.... incredibly odd.

    i don't think it's a systemic error, because the original experiment's value agrees with that of other measurements that have been made of the electron's mass. what it would mean is that there appears to genuinely be a link between the mass of the electron and avogadro's constant.

    1. Re:link between mass value and avogadro's constant by Anonymous Coward · · Score: 0

      You just divided the mass of the electron in amu by the mass of the electron in kilograms, which gives you the number of amu per kilogram. It should be no surprise you get 1000 times Avogadro constant, since the definition of the amu works out to there being an Avogadro constant of amu per gram.

      In other words: m_of_anything_in_amu / m_of_same_thing_kg = conversion factor of kg to amu = 1000 * Avogardo constant.

  17. TLDR by Anonymous Coward · · Score: 0

    The answer is 0, more or less.

  18. Re:Yah, old slashdot is back, Black text on white! by Soulskill · · Score: 2

    If you switch the view to Classic using this dropdown menu, you should see full summaries rather than truncated ones.

    I'm still arguing to get it changed/fixed for the default view.

  19. Re:Yah, old slashdot is back, Black text on white! by jones_supa · · Score: 1

    Excellent, thanks!