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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

#51

Post by yyyk »

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…

"One of the biggest problems in physics right now is that there are no experiments (except possibly this one) whose results are at odds with the Standard Model."

What about Neutrino masses? Or the Muon 'anomalous' magnetic moment?

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

#52

Post by analog31 »

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?

In addition to the many good answers here, I'd add that whatever parameter represents "diameter" for a proton, probably also represents the classical diameter of something macroscopic like a billiard ball if carried to that extreme.

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

#53

Post by gbear605 »

willis936 wrote: post #12
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.

I wonder if there is a Future Circular Collider that could help expand the standard model into this regime.

There unfortunately isn't, at least not at a scale that's feasible right now. [0]

[0]: http://backreaction.blogspot.com/2019/03/nonsense-arguments-...

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

#54

Post by doubleunplussed »

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?

Other answers are either overcomplicated or imprecise: the proton's radius is defined as the RMS radius of its charge distribution. It's the same idea as describing the size of a probability distribution by its standard deviation.

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

#55

Post by colechristensen »

pavel_lishin wrote: post #2

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

There is a certain philosophical dissatisfaction with the standard model and it just keeps getting confirmed over and over, nobody can seem to find any significant new physics because possible discrepancies keep getting eliminated one by one. Hope dies is maybe a bit florid, but it's a bit real if you don't take it too seriously.

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

#56

Post by chasd00 »

DoctorOetker wrote: post #37
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?

Consider a perfectly spherical earth, and a vertical tunnel perforating it through the center, with an elevator in the tunnel. suppose you are halfway towards the center, coming from the surface, and you pause the elevator. How strong will the gravitational field be? Can we pretend all of Earth's mass is concentrated in the center? No, let's see why. Consider a perfectly spherical hollow shell of mass, and an observe…

forgive my ignorance, but don't you have to assume uniform density in both cases? It seems to me the person in the earth elevator halfway down would feel more gravity toward the center of the earth because there's actually more mass due to the higher density. In a similar way, the proton would have higher mass toward the center because of the higher wave amplitude.

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

#58

Post by asdfman123 »

pavel_lishin wrote: post #2

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

The world runs on clicks now, and you have to make headlines sound at least a little outrageous to keep up.

I mean, I clicked because I thought, "Hope dies? I'm sure that's an exaggeration..."

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

#59

Post by DoctorOetker »

chasd00 wrote: post #56
DoctorOetker wrote: post #37

Earlier quoted context omitted.

Consider a perfectly spherical earth, and a vertical tunnel perforating it through the center, with an elevator in the tunnel. suppose you are halfway towards the center, coming from the surface, and you pause the elevator. How strong will the gravitational field be? Can we pretend all of Earth's mass is concentrated in the center? No, let's see why. Consider a perfectly spherical hollow shell of mass, and an observe…

forgive my ignorance, but don't you have to assume uniform density in both cases? It seems to me the person in the earth elevator halfway down would feel more gravity toward the center of the earth because there's actually more mass due to the higher density. In a similar way, the proton would have higher mass toward the center because of the higher wave amplitude.

correct, it does assume uniform density, if it didnt, you could say the density was zero throughout the sphere except for a small spherical region, and it would be trivially false then

I was illustrating how in principle radii can be derived in a phenomenological sense.

I didn't read the actual papers by the experimenters of the proton radius determination, but it would probably require a modification of the Hamiltonian for the hydrogen atom, since usually one treats the nuclei as point particles.

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

#60

Post by willis936 »

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…

Does the magnitude of the field wave drop at some fixed shape (like an exponential)?

Is the wavelength fixed? Is it in meters?

Is it the field of a proton made up of multiple frequencies/modes?

Is a proton’s influence on fields extend to all space or is there a point (within the hubble sphere) at which a proton does not influence fields at all?

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