Photons

[Resha Caner]

Actually, my question applies to all the elementary stuff but the photon is first on my list.

Do photons have a size or is it that there is a point that serves as a center for their properties?

Is the answer the same for all the constituents? IOW, does the electron have a size or is there instead a center for its properties? And so forth. Is there any elementary particle that has a size?

 

[metherion]

I... don't know for the photon. I know that electrons, neutrons, and protons have a size. The size of an electron is 2.8 * 10^-15 meters, and is the classical relativistic radius, as opposed to based on quantum mechanics. It may actually be smaller. So, it's diameter would be about 5.6 *10^-15 meters.
10^-15 meters is called a femtometer.

Protons are... between 80 and 90 femtometers. I remember a science article a year or two ago where German scientists measured it at 84, whereas the accepted value is 88, and the margin of error on the 88 meant 84 was WAY too low. I don't know what the follow up was, or if a final agreement has been made, or what.

Neutrons, I believe are about the same size as protons.

Metherion

 

[Resha Caner]

Thanks.

 

[juvenissun]

I... don't know for the photon. I know that electrons, neutrons, and protons have a size. The size of an electron is 2.8 * 10^-15 meters, and is the classical relativistic radius, as opposed to based on quantum mechanics. It may actually be smaller. So, it's diameter would be about 5.6 *10^-15 meters.
10^-15 meters is called a femtometer.

Protons are... between 80 and 90 femtometers. I remember a science article a year or two ago where German scientists measured it at 84, whereas the accepted value is 88, and the margin of error on the 88 meant 84 was WAY too low. I don't know what the follow up was, or if a final agreement has been made, or what.

Neutrons, I believe are about the same size as protons.

Metherion

How do they measure these things?

 

[metherion]

Th electron radius is actually a calculated quantity, and doesn't take quantum mechanics into effect, so it may not be quite right, but I did say so. The formula is:
(electric charge of the electron squared) divided by (4 * pi * the mass of the electron * speed of light squared * permeability of a vacuum).

For the proton, you can see this article:
The size of the proton : Nature : Nature Publishing Group
That's a link to the abstract, of the German study which comes up with the smaller value. It states they used pulsed laser spectroscopy and some negatively charged muons to measure the Lamb shift, which is the different between the [sup]2[/sup]S[sub]1/2[/sub] and the [sup]2[/sup]P[sub]1/2[/sub] energy levels in a hydrogen atom, which has one proton and no neutron.
The previous measurement had to do with electron/proton scattering limits in hydrogen atoms.

For neutrons, my guess is either through elastic scattering or neutron capture, but I'm not sure.

Again, sorry, but I'm a chemist, not a physicist, and subatomic particles aren't of as big a concern in my field as they are for particle physics.

Metherion

EDIT: So I can't remember how to sub and superscript things. Could someone help so I can redo the lamb thing correctly?

 

[sfs]

r[sup]2[/sup], r[sub]2[/sub]: "sub" and "sup", not superscript and subscript.

 

[metherion]

Thanks sfs, I have fixed it!

Metherion

 

[juvenissun]

Th electron radius is actually a calculated quantity, and doesn't take quantum mechanics into effect, so it may not be quite right, but I did say so. The formula is:
(electric charge of the electron squared) divided by (4 * pi * the mass of the electron * speed of light squared * permeability of a vacuum).

For the proton, you can see this article:
The size of the proton : Nature : Nature Publishing Group
That's a link to the abstract, of the German study which comes up with the smaller value. It states they used pulsed laser spectroscopy and some negatively charged muons to measure the Lamb shift, which is the different between the [sup]2[/sup]S[sub]1/2[/sub] and the [sup]2[/sup]P[sub]1/2[/sub] energy levels in a hydrogen atom, which has one proton and no neutron.
The previous measurement had to do with electron/proton scattering limits in hydrogen atoms.

For neutrons, my guess is either through elastic scattering or neutron capture, but I'm not sure.

Again, sorry, but I'm a chemist, not a physicist, and subatomic particles aren't of as big a concern in my field as they are for particle physics.

Metherion

EDIT: So I can't remember how to sub and superscript things. Could someone help so I can redo the lamb thing correctly?

Is it generally true that these particles are the heavier the larger?

Does the size of these particles matter?