
New Measurement Deepens Proton Puzzle - retupmoc01
https://www.quantamagazine.org/20160811-new-measurement-deepens-proton-radius-puzzle/
======
jlebar
Hats off to Quanta Magazine for their consistently excellent science
reporting. They manage to convey why this is interesting without
sensationalizing "zomg new force".

~~~
corndoge
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.

~~~
sjcsjc
"... 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
I think you're right about 0, 1 even your link agrees is not really a problem

~~~
sjcsjc
Hmm. My cardinal sins statement was sarcasm. On reflection, that may be
unclear.

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ISL
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.

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adrianratnapala
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.

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atemerev
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.)

~~~
mikhailfranco
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-
experim...](http://www.sciencemag.org/news/2015/12/controversial-experiment-
sees-no-evidence-universe-hologram)

[1] [http://backreaction.blogspot.com/2015/12/what-fermilabs-
holo...](http://backreaction.blogspot.com/2015/12/what-fermilabs-holometer-
experiment.html)

[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-...](http://www.nature.com/news/the-quantum-source-of-space-time-1.18797)

------
AnimalMuppet
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
The latter. The tau's lifetime is 10^-13 s. The muon lifetime is 10^-6 s, and
the experiment is already hard.

~~~
asmithmd1
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.

~~~
bonzini
If only you could estimate the error...

~~~
aaron695
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?

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andrewflnr
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?

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sevenless
Muons have a half life of 2.2 microseconds. That's really quite a long time in
atomic physics.

~~~
arethuza
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_\(unit\))

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

~~~
akiselev
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.

