What does a proton look like?


by stonehaven
Tags: proton
Vince Summers
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#37
Jan18-10, 03:39 PM
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Quote Quote by Hurkyl View Post
I wanted to object to this. The electron doesn't look like a point particle revolving around the nucleous: it's smeared out across its entire orbital! It really is stationary in the sense that it doesn't change over time. (Sort of like a stationary current)
Actually, electrons are not smeared out at all. This is a misconception. They are actual particles. The smearing out refers to the probability of the location.
Bob S
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#38
Jan18-10, 04:13 PM
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What does a proton look like? Jerry Friedman, Henry Kendall, and Richard Taylor participated in experiments (under Robert Hofstadter) at the Mark III electron accelerator (~ 300 MeV) at Stanford to measure the form factor of the proton in the late 1950's.
The electron accelerator at SLAC (~ 20 GeV, Stanford) was built in part to make better proton form factor measurements, because the momentum transfer would be much higher. But when they did the experiment, the proton "broke" apart ~1970).
Here is Jerry Friedman's 1990 Nobel Prize Lecture:
http://nobelprize.virtual.museum/nob...an-lecture.pdf

Bob S
Vince Summers
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#39
Jan18-10, 04:18 PM
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Quote Quote by samalkhaiat View Post
It is not possible to see the atom. Heisenberg uncertainty principle does not let you take a picture.


regards

sam
Now I'm a chemist, and not a physicist -- but I believe this isn't right. Not too far off, but not right.
Bob S
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#40
Jan18-10, 04:36 PM
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Quote Quote by samalkhaiat View Post
It is not possible to see the atom. Heisenberg uncertainty principle does not let you take a picture.
Δp Δx ≥ h-bar/2

If Δp > ~300 MeV/c

then Δx < ~1 fermi

So momentum transfers over ~300 MeV/c can "see" structure inside the proton (radius ~ 0.8 fermi).

Bob S
mssmatthelhc
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#41
Jan19-10, 02:42 AM
P: 3
What ANYTHING "looks like" is really a function of its Compton wavelength.I mean,the ratio of "h-bar/momentum".That's as good as it gets.Start by calculating,say,the Compton wavelength of the Earth for example,then,work yer way "down" to smaller and smaller critters.The attempts to give a "familiar structure" to leptons/hadrons tormented the minds of some very bright people and it led nowhere.Read-up on Heisenberg's "gamma ray microscope",read Feynman Chapter 37-38 Lectures Vol.1.Get a feel for the limits of how far "mental pictures" can go before they are,...,worthless.
mssmatthelhc
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#42
Jan19-10, 02:55 AM
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I just read Bob S about the Mark III and the Stanford experiments of Hofstadter.They were beutiful experiments,and Hofstedter richly deserved the 1961 Nobel.Annual Reviews contains his take,as well as an early volume from the old Benjamin-Cummings "Frontiers In Physics" series.These experiments proved beyond a reasonable doubt that nucleons are NOT point-particles,as leptons continue to be.Nope.Hadrons have a "structure",they are ALL "resonances",as far as I am concerned(though not with the same intent as Chew and the "bootstrap" gang,...,)Keep studying,....
cragar
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#43
Mar2-10, 10:07 PM
P: 2,454
If single particles cannot emit light , then where does the light come from in a neutron star.
I know a neutron star has electrons and other particles in it but i don't think it has atoms of molecules in it .
bapowell
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#44
Mar3-10, 02:30 PM
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Quote Quote by cragar View Post
If single particles cannot emit light
But single particles can emit light.
cragar
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#45
Mar3-10, 07:08 PM
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Quote Quote by bapowell View Post
But single particles can emit light.
ok thats what i thought that makes sense.
Dmitry67
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#46
Mar4-10, 05:37 AM
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I always imagine protons as red balls, and neutrons as yellow balls. Electrons are blue of course.


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