7 ms·

New Measurement Deepens Proton Puzzle

101 points by retupmoc01 10y ago

jlebar 10y ago
Hats off to Quanta Magazine for their consistently excellent science reporting. They manage to convey why this is interesting without sensationalizing "zomg new force".
- ISL 10y ago
  Indeed. They've done a great job on so many articles. The technically-trained reporter with whom I chatted regarding an article on my field appeared to have dedicated at least a month to developing a strong understanding of the problems at hand. Most short-form science reporters seem to at most a couple of days on a story.
  - semi-extrinsic 10y ago
    This was very well written indeed. From the author's biography, she has "co-authored several academic papers in nonlinear optics". I can certainly understand how writers who lack similar years of physics background and experience in reading and writing papers would do a significantly worse job of describing the results of a new study.
- corndoge 10y ago
  I don't know. A couple paragraphs betrayed minimal understanding of the topic at hand and there were various grammatical errors...it feels more like relatively well-written clickbait.
  - mindcrime 10y ago
    For FSM's sake, is there anything that somebody around here won't refer to as "clickbait"? HN should implement an auto-filter to reject any comment containing the term.
  - sjcsjc 10y ago
    "... various grammatical errors ..." Please expand on this. I found "comprised of"[0] and "to actually measure"[1]. Cardinal grammatical sins indeed. IMHO, this article had an unusually high standard of grammar by today's standards. [0] https://en.wikipedia.org/wiki/Comprised_of https://en.wikipedia.org/wiki/Comprised_of [1] https://en.wikipedia.org/wiki/Split_infinitive https://en.wikipedia.org/wiki/Split_infinitive
    - raverbashing 10y ago
      I think you're right about 0, 1 even your link agrees is not really a problem
      - sjcsjc 10y ago
        Hmm. My cardinal sins statement was sarcasm. On reflection, that may be unclear.
- sevenless 10y ago
  I love how Quanta's writers manage to bring incredibly abstruse science to about the cusp of understanding for the layman. It's particularly noticeable considering how dumbed-down so much science writing for newspapers and magazines like New Scientist has become. Another particularly good example: https://www.quantamagazine.org/20130917-a-jewel-at-the-heart-of-quantum-physics/ https://www.quantamagazine.org/20130917-a-jewel-at-the-heart...
  - sevenless 10y ago
    Natalie Wolchover deserves credit for both these articles, I should say.
ISL 10y ago
Paper here: http://science.sciencemag.org/content/353/6300/669 http://science.sciencemag.org/content/353/6300/669 Just reading the journal article now, but if I've interpreted the Quanta article correctly, this is an important development. The proton radius puzzle has resisted resolution for long enough to be regarded as a long-standing problem. Pohl's proton measurement is widely respected (indeed, there's a known calibration line between the expected and observed values, so it's hard for it to be incorrect), but nobody has a way to solve the problem.
AnimalMuppet 10y ago
Great article. One minor nit, though: If there is a new force, there is no requirement that the electron not interact with it - only that the electron interact less than the muon. And a direction to pursue: What if you use a tau, rather than a muon? Or can't you do the experiment, because the tau decays so quickly?
- ISL 10y ago
  The latter. The tau's lifetime is 10^-13 s. The muon lifetime is 10^-6 s, and the experiment is already hard.
  - asmithmd1 10y ago
    They are doing an experiment that compares a material that lasts a millionth of a second to a material that lasts indefinitely and get a 5% difference. I am going to have to go with experimental error as more likely than new fundamental force.
    - deleted 10y ago
      [deleted]
    - bonzini 10y ago
      If only you could estimate the error...
      - aaron695 10y ago
        But you can't. Because if you knew the error than you'd know you are wrong. I think you are thinking of statistical significance perhaps?
lostmsu 10y ago
Can't quantum physics on its own predict proton radius?
- gus_massa 10y ago
  Quantum Physics is a very wide term. To calculate the size of a proton you must consider also all the details about the particles and the forces about the particles. In particular how strong is the strong force between the quarks inside the proton (and the gluons inside the proton). (To use a very bad analogy, you can use Classic Newtonian Mechanics to predict the maximal speed of a car, but you must consider the details of the car, like the size, weight, the size and position of the gears in the transmission, ...)
- akiselev 10y ago
  Any such prediction would be bound by the least precise constant involved in the calculation. This experiment is truly pushing the boundaries of distance measurement (to the tens of femtometers) so I doubt the rest of our measurements of universal constants are anywhere near precise enough to pull it off. If we could measure all of those constants as precisely as, say, LIGO can measure optical interference spread over many kilometers then it would be possible, but if we could do that we'd probably have already measured the proton's size to within femtometers.
- lordnacho 10y ago
  Predictions mean nothing without measurement.
adrianratnapala 10y ago
I'm no particle expert, but I am a little skeptical about the interpretation of these experiments. They are interested in the spatial spread of charge in a proton (or deuteron). And they call this the "size" of the proton. Good. And they reason the more spread out it is, the smaller its effective charge in the electromagnetic interacton between it and some bound particle (electron, muon). Good. So they reason that spectroscopy on that particle can tell them about that spatial charge spread. But that's assumes that the only force involved is electromagnetic. Any additional short-range interaction between the two particles can shift that specturm. And we expect those shifts to be larger for the muon just because it overlaps more with the proton even if (a) the proton's size is unchanged and (b) the interaction strength with the elecron (at a given distance) is just as strong. Now if there is no extra ineraction, then their methods do measure the proton size. But then they have to explain why it changes -- which would require an extra interaction.
andrewflnr 10y ago
Wait, how are they getting a gas of muonic deuterium to begin with? Muons have a really short half-life. Can they generate muons, combine them with deuterons, and lase them before the muons decay?
- dnautics 10y ago
  femtosecond lasers are a thing. that's well within the half life of a muon.
- sevenless 10y ago
  Muons have a half life of 2.2 microseconds. That's really quite a long time in atomic physics.
  - arethuza 10y ago
    That's 220 shakes - a long time when it comes to a weapon detonation: https://en.wikipedia.org/wiki/Shake_(unit) https://en.wikipedia.org/wiki/Shake_(unit)
atemerev 10y ago
We need some more excitement from physics, urgently. Higgs boson, while exciting, was just a confirmation of long-standing theory. Holographic universe hypothesis is almost discredited (thanks to Holometer experiment), and we are back to square one. Not anymore, I hope. Changing fundamental properties of matter with muon rays — now that's something! We are back at sci-fi territory. (And probably it will turn out to be just another boring experimental error. Sigh.)
- deleted 10y ago
  [deleted]
- mikhailfranco 10y ago
  Firstly, the Holometer is either inadequate [0] or discredited [1], take your pick. Hogan invents a theory, then invents the apparatus that 'tests' it, but there is no way a couple of 40m interferometers are probing the Planck scale. The paper [2] quotes 10^-18 m for a single interferometer, and implies 10^-23 m for both, which is about 12 orders of magnitude above the Planck scale. Secondly, quantized space-time is a slightly separate issue from the Holographic Principle [3], you can have discreteness without holography, but there has been huge theoretical progress in these subjects in the last 5-10 years and a revolution is underway - see ER=EPR and all that [4], if you need more physics excitement. [0] http://www.sciencemag.org/news/2015/12/controversial-experiment-sees-no-evidence-universe-hologram http://www.sciencemag.org/news/2015/12/controversial-experim... [1] http://backreaction.blogspot.com/2015/12/what-fermilabs-holometer-experiment.html http://backreaction.blogspot.com/2015/12/what-fermilabs-holo... [2] http://arxiv.org/abs/1512.01216 http://arxiv.org/abs/1512.01216 [3] http://en.wikipedia.org/wiki/Holographic_principle http://en.wikipedia.org/wiki/Holographic_principle [4] http://www.nature.com/news/the-quantum-source-of-space-time-1.18797 http://www.nature.com/news/the-quantum-source-of-space-time-...

101 points by retupmoc01 10y ago

Hats off to Quanta Magazine for their consistently excellent science reporting. They manage to convey why this is interesting without sensationalizing "zomg new force".

ISL 10y ago
Indeed. They've done a great job on so many articles. The technically-trained reporter with whom I chatted regarding an article on my field appeared to have dedicated at least a month to developing a strong understanding of the problems at hand. Most short-form science reporters seem to at most a couple of days on a story.
- semi-extrinsic 10y ago
  This was very well written indeed. From the author's biography, she has "co-authored several academic papers in nonlinear optics". I can certainly understand how writers who lack similar years of physics background and experience in reading and writing papers would do a significantly worse job of describing the results of a new study.
corndoge 10y ago
I don't know. A couple paragraphs betrayed minimal understanding of the topic at hand and there were various grammatical errors...it feels more like relatively well-written clickbait.
- mindcrime 10y ago
  For FSM's sake, is there anything that somebody around here won't refer to as "clickbait"? HN should implement an auto-filter to reject any comment containing the term.
- sjcsjc 10y ago
  "... various grammatical errors ..." Please expand on this. I found "comprised of"[0] and "to actually measure"[1]. Cardinal grammatical sins indeed. IMHO, this article had an unusually high standard of grammar by today's standards. [0] https://en.wikipedia.org/wiki/Comprised_of https://en.wikipedia.org/wiki/Comprised_of [1] https://en.wikipedia.org/wiki/Split_infinitive https://en.wikipedia.org/wiki/Split_infinitive
  - raverbashing 10y ago
    I think you're right about 0, 1 even your link agrees is not really a problem
    - sjcsjc 10y ago
      Hmm. My cardinal sins statement was sarcasm. On reflection, that may be unclear.
sevenless 10y ago
I love how Quanta's writers manage to bring incredibly abstruse science to about the cusp of understanding for the layman. It's particularly noticeable considering how dumbed-down so much science writing for newspapers and magazines like New Scientist has become. Another particularly good example: https://www.quantamagazine.org/20130917-a-jewel-at-the-heart-of-quantum-physics/ https://www.quantamagazine.org/20130917-a-jewel-at-the-heart...
- sevenless 10y ago
  Natalie Wolchover deserves credit for both these articles, I should say.

ISL 10y ago

Paper here: http://science.sciencemag.org/content/353/6300/669 http://science.sciencemag.org/content/353/6300/669 Just reading the journal article now, but if I've interpreted the Quanta article correctly, this is an important development. The proton radius puzzle has resisted resolution for long enough to be regarded as a long-standing problem. Pohl's proton measurement is widely respected (indeed, there's a known calibration line between the expected and observed values, so it's hard for it to be incorrect), but nobody has a way to solve the problem.

AnimalMuppet 10y ago

Great article. One minor nit, though: If there is a new force, there is no requirement that the electron not interact with it - only that the electron interact less than the muon. And a direction to pursue: What if you use a tau, rather than a muon? Or can't you do the experiment, because the tau decays so quickly?

ISL 10y ago
The latter. The tau's lifetime is 10^-13 s. The muon lifetime is 10^-6 s, and the experiment is already hard.
- asmithmd1 10y ago
  They are doing an experiment that compares a material that lasts a millionth of a second to a material that lasts indefinitely and get a 5% difference. I am going to have to go with experimental error as more likely than new fundamental force.
  - deleted 10y ago
    [deleted]
  - bonzini 10y ago
    If only you could estimate the error...
    - aaron695 10y ago
      But you can't. Because if you knew the error than you'd know you are wrong. I think you are thinking of statistical significance perhaps?

lostmsu 10y ago

Can't quantum physics on its own predict proton radius?

gus_massa 10y ago
Quantum Physics is a very wide term. To calculate the size of a proton you must consider also all the details about the particles and the forces about the particles. In particular how strong is the strong force between the quarks inside the proton (and the gluons inside the proton). (To use a very bad analogy, you can use Classic Newtonian Mechanics to predict the maximal speed of a car, but you must consider the details of the car, like the size, weight, the size and position of the gears in the transmission, ...)
akiselev 10y ago
Any such prediction would be bound by the least precise constant involved in the calculation. This experiment is truly pushing the boundaries of distance measurement (to the tens of femtometers) so I doubt the rest of our measurements of universal constants are anywhere near precise enough to pull it off. If we could measure all of those constants as precisely as, say, LIGO can measure optical interference spread over many kilometers then it would be possible, but if we could do that we'd probably have already measured the proton's size to within femtometers.
lordnacho 10y ago
Predictions mean nothing without measurement.

adrianratnapala 10y ago

I'm no particle expert, but I am a little skeptical about the interpretation of these experiments. They are interested in the spatial spread of charge in a proton (or deuteron). And they call this the "size" of the proton. Good. And they reason the more spread out it is, the smaller its effective charge in the electromagnetic interacton between it and some bound particle (electron, muon). Good. So they reason that spectroscopy on that particle can tell them about that spatial charge spread. But that's assumes that the only force involved is electromagnetic. Any additional short-range interaction between the two particles can shift that specturm. And we expect those shifts to be larger for the muon just because it overlaps more with the proton even if (a) the proton's size is unchanged and (b) the interaction strength with the elecron (at a given distance) is just as strong. Now if there is no extra ineraction, then their methods do measure the proton size. But then they have to explain why it changes -- which would require an extra interaction.

andrewflnr 10y ago

Wait, how are they getting a gas of muonic deuterium to begin with? Muons have a really short half-life. Can they generate muons, combine them with deuterons, and lase them before the muons decay?

dnautics 10y ago
femtosecond lasers are a thing. that's well within the half life of a muon.
sevenless 10y ago
Muons have a half life of 2.2 microseconds. That's really quite a long time in atomic physics.
- arethuza 10y ago
  That's 220 shakes - a long time when it comes to a weapon detonation: https://en.wikipedia.org/wiki/Shake_(unit) https://en.wikipedia.org/wiki/Shake_(unit)

atemerev 10y ago

We need some more excitement from physics, urgently. Higgs boson, while exciting, was just a confirmation of long-standing theory. Holographic universe hypothesis is almost discredited (thanks to Holometer experiment), and we are back to square one. Not anymore, I hope. Changing fundamental properties of matter with muon rays — now that's something! We are back at sci-fi territory. (And probably it will turn out to be just another boring experimental error. Sigh.)

deleted 10y ago
[deleted]
mikhailfranco 10y ago
Firstly, the Holometer is either inadequate [0] or discredited [1], take your pick. Hogan invents a theory, then invents the apparatus that 'tests' it, but there is no way a couple of 40m interferometers are probing the Planck scale. The paper [2] quotes 10^-18 m for a single interferometer, and implies 10^-23 m for both, which is about 12 orders of magnitude above the Planck scale. Secondly, quantized space-time is a slightly separate issue from the Holographic Principle [3], you can have discreteness without holography, but there has been huge theoretical progress in these subjects in the last 5-10 years and a revolution is underway - see ER=EPR and all that [4], if you need more physics excitement. [0] http://www.sciencemag.org/news/2015/12/controversial-experiment-sees-no-evidence-universe-hologram http://www.sciencemag.org/news/2015/12/controversial-experim... [1] http://backreaction.blogspot.com/2015/12/what-fermilabs-holometer-experiment.html http://backreaction.blogspot.com/2015/12/what-fermilabs-holo... [2] http://arxiv.org/abs/1512.01216 http://arxiv.org/abs/1512.01216 [3] http://en.wikipedia.org/wiki/Holographic_principle http://en.wikipedia.org/wiki/Holographic_principle [4] http://www.nature.com/news/the-quantum-source-of-space-time-1.18797 http://www.nature.com/news/the-quantum-source-of-space-time-...