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Physicists finally nail the proton’s size, eliminating an anomaly

quantamagazine.org

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Re: Physicists finally nail the proton’s size, eliminating an anomaly

#71

Post by charles_f »

AnthonBerg wrote: post #63
WhitneyLand wrote: post #50

Earlier quoted context omitted.

The clever thing about these kinds of jokes as when it happens in politics is, they manage to mock two groups of people such that each group reads the joke and tends to laugh because they infer it as poking fun at the other group.

We laugh even if it is rotated by 180 degrees.

Reminds me of a person on HN that was telling a joke on a specific group of people, and another person came and said "that can be laughed about", and the initial person said "actually it's about all groups of people", and the other person said "that can also be laughed about".

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#72

Post by Filligree »

Symmetry wrote: post #19
certifiedloud wrote: post #9

Earlier quoted context omitted.

Einstein's theory hasn't yet been reconciled with quantum theory. That's a good place to watch for progress.

That may require waiting to become a Kardashev III[1] civilization so we can do experiments where we know General Relativity and the Standard Model give different results. The energies required for the disagreements to show up are really insane. [1] https://en.wikipedia.org/wiki/Kardashev_scale

More or less. We can hope that something more clever would be possible, like in the novel Schild's Ladder...

Though we'd have to hope that, unlike that novel, we don't accidentally set off a vacuum collapse. That would be unfortunate.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#73

Post by ufmace »

cthalupa wrote: post #42
Sharlin wrote: post #20

Earlier quoted context omitted.

Not really sure about that. Physicists are getting really frustrated by the fact that the LHC has found exactly the missing piece that the SM predicted (the Higgs) and zero evidence of any physics beyond that, anything that would get us closer to quantum gravity. No strings, no supersymmetry, not even any hints as to the nature of dark matter. All it has done is give new lower bounds to the energy scales at which som…

>For all we know, we might need a solar system size collider to attain the required energies. We just need to observe the collisions happening at these energies - we don't necessarily need to produce them ourselves. Some physicists are starting to think about how we might be able to observe naturally occurring collisions at these energy levels rather than producing them ourselves.

AIUI, the trick with colliders isn't so much creating high-energy collisions, but creating them exactly inside gigantic detectors that can measure what happens in those collisions, as well as the collisions having a known amount of energy and contents.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#74

Post by Filligree »

nategri wrote: post #65
cthalupa wrote: post #42

Earlier quoted context omitted.

>For all we know, we might need a solar system size collider to attain the required energies. We just need to observe the collisions happening at these energies - we don't necessarily need to produce them ourselves. Some physicists are starting to think about how we might be able to observe naturally occurring collisions at these energy levels rather than producing them ourselves.

IIRC that only buys you 2-3 orders over LHC energy.

Considering this would represent a continent-sized collider... I'll take it.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#75

Post by pbhjpbhj »

blhack wrote: post #61
ur-whale wrote: post #21

I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm. Is the hydrogen atom two hard little balls of matter orbiting one another, as we were taught in primary school, or are they a probabilistic soup with various, vaguely localized extrema? If the latter, how do you even define the notion of diameter?

This is true for every physical object though. You cannot tell me with perfect certainty the width of a ball of tungsten, because the edges aren’t actually rigidly defined. In fact: it doesn’t really have an “edge” the way you might think of it geometrically. Just a boundary across which forces start interacting with each other.

Well if we're going to be pedantic why not do it properly - surely there is no force boundary, instead there is a proximity at which the forces become significant. Significance being determined according to the situation being analysed.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#77

Post by Mathnerd314 »

devb wrote: post #64
pavel_lishin wrote: post #2

What a headline. Should someone talk to the author, make sure they're doing ok?

Authors don't always have a final say on what the headline will be. Sometimes they don't have any say at all.

The original headline is much more positive: http://yfile.news.yorku.ca/2019/09/06/just-how-big-is-a-prot...

I'd say the writer has a tendency to write gloomy headlines: https://www.quantamagazine.org/famous-experiment-dooms-pilot...

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#78

Post by jpmattia »

Probably worth noting: The author writes the article as though the latest experiment "solves" the issue.

A more nuanced description (which is not exactly quantamagazine's forte) would note there is a conundrum about the proton size. The article describes a measurement that falls under "spectroscopic methods" in the wiki [1].

Why eg scattering measurements should yield a different value is not at all clear.

[1] https://en.wikipedia.org/wiki/Proton_radius_puzzle

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#79

Post by jpmattia »

ur-whale wrote: post #21

I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm. Is the hydrogen atom two hard little balls of matter orbiting one another, as we were taught in primary school, or are they a probabilistic soup with various, vaguely localized extrema? If the latter, how do you even define the notion of diameter?

> I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm.

Usually these are describing expectation values of radial positions.

For the well-understood example of the hydrogen electronic orbit, the Bohr radius is the expectation value of the radial position of the electron. The electron has a wavefunction Ψ; When you calculate the expectation value of the radius r using Ψ (= \int_0^\infinity Ψ* r Ψ dr ) you find a value of about 0.5 nm.

People will drop the subtlety of the "expectation value" and just say "the hydrogen atom has a radius of about 0.5 nm".

The issue for the proton radius that the article did not delve into: There is currently more than one way to measure the proton radius. One is scattering (pitch another particle at the proton, look at how it "bounces" off), and another is spectroscopically (look at the energy levels of the electron, deduce the proton radius from the interaction of the electron orbit and the proton.) These methods do not give the same answer.

Re: Physicists finally nail the proton’s size, eliminating an anomaly

#80

Post by jemorya »

lisper wrote: post #27
ur-whale wrote: post #21

I wish a physicist could explain here how the very notion of "diameter" has any meaning for an object whose size (IIUC) belong entirely to the quantum realm. Is the hydrogen atom two hard little balls of matter orbiting one another, as we were taught in primary school, or are they a probabilistic soup with various, vaguely localized extrema? If the latter, how do you even define the notion of diameter?

That is an excellent question! The definition is somewhat arbitrary, but still has some real physical significance. In actual fact, a proton is a field, so it doesn't have sharp boundaries. But the amplitude of the field still dies off very rapidly with distance from the center, so you can pick some arbitrary small value and say "the point at which the amplitude becomes less than this value is the radius of the proto…

There are some really good responses to lisper's post: what about 96% of the universe's mass, neutrino mass, what about gravity for that matter. (zing!)

The thing about those particular questions is that they only tell us that the standard model is incomplete. Gravity exists. The fact that it's not in the standard model doesn't necessarily mean that the model is broken, just that gravity needs to be added somehow.

What we need more of are instances where the standard model makes a precise numeric prediction and it's dead wrong. That puts a spotlight on every piece of the standard model that went into the prediction.

(Edited for the pun I didn't intend.)

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