Faster-Than-Light Neutrinos Do It Again!

[Huram Abi]

Photons have zero rest mass, so they are massless particles. They do have momentum, however.

Photons don't rest.

 

[acropolis]

Photons don't rest.

Yes, so they always have momentum, but as 'mass' is defined for particles as the mass at rest, photon are defined to be a massless particle. If they did have a rest mass there would need to be changes made to Coulomb's law, among other tweaks to physics. If you prefer to think of them as having mass since they always have momentum, that is OK, but know that they are not defined as having mass as far as physics is concerned currently.

 

[Huram Abi]

photon mass - Google Scholar

 

[Naraoia]

photon mass - Google Scholar

I don't think the "mass" in mass attenuation coefficient refers to the photon's mass.

 

[Huram Abi]

I didn't mean the first article. Just a jumping off point for where one might look for information regarding photons having mass as far as physics is concerned currently.

 

[acropolis]

The wiki page on photons does a decent job of explaining it. Photons being massless agrees with current theory and evidence. What might be confusing is that 'massless' is a defined rather specifically for a particle, so a massless particle can still transmit momentum and other things normally associated with massive objects.

 

[Huram Abi]

Considering that photons are never at rest, I don't find the rest mass at all useful in this discussion.

The invarient mass suggests that, infintesimally, photons do have mass.

 

[pgp_protector]

What happens to a photon when it hits the Electron.
I know that it "knocks" the Electron into a "Higher" Orbit, but is the Photon converted 100% into energy or what?

 

[Huram Abi]

Counter-intuitively, the photon is 100% energy.

Some forms of energy have mass.

 

[Naraoia]

I didn't mean the first article. Just a jumping off point for where one might look for information regarding photons having mass as far as physics is concerned currently.

Pretty much the entire first page appeared to be about mass attenuation coefficients.

 

[sfs]

Considering that photons are never at rest, I don't find the rest mass at all useful in this discussion.

Physicists feel otherwise. "Rest mass" is the name for a quantity that can be calculated for any particle, at rest or not, massless or massive.

The invarient mass suggests that, infintesimally, photons do have mass.

What invariant mass suggests that? "Invariant mass" is just another name for the rest mass.

 

[acropolis]

Considering that photons are never at rest, I don't find the rest mass at all useful in this discussion.

The invarient mass suggests that, infintesimally, photons do have mass.

Regardless of the utility in this discussion, photons do not have rest mass, and so are massless particles.

 

[razeontherock]

.

Light not being able to escape the gravitational pull of a blackhole should be the first indication that photons have mass.

Never thought of that. Is this valid?

 

[razeontherock]

photon mass - Google Scholar

Ok, can somebody translate this into English?

Rev. Mod. Phys. 43, 277 (1971): Terrestrial and Extraterrestrial Limits on The Photon Mass

It's a short little page. Is it saying photons actually do have mass?

 

[sfs]

Never thought of that. Is this valid?

Not if General Relativity is correct. In GR it is the stress-energy tensor that is the source of gravitation, not the mass (which is not trivially defined in GR, as I understand it).

 

[sfs]

Ok, can somebody translate this into English?

Rev. Mod. Phys. 43, 277 (1971): Terrestrial and Extraterrestrial Limits on The Photon Mass

It's a short little page. Is it saying photons actually do have mass?

No. It's discussing upper limits on the photon mass. In other words, experiments show that the photon mass must be less than some (really small) quantity. Experiments can't show that the mass is exactly zero; all they can do is show that there is no deviation from the results you'd expect if it were exactly zero, and so that the mass must be either zero or very close to it.

 

[razeontherock]

HA - so there is some unknown element to this! (Not that it matters) Now I have to go read up on stress-energy tensor

 

[Doveaman]

So what are peoples opinions here?

Did the Neutrinos exceed the speed of light?

Scientists said they did, and scientists said they didn't.

Both positions are most likely to be true since both positions are supported by science.

 

[acropolis]

Until the results are corroborated by groups outside of OPERA there isn't much reason to take the experiment seriously.

 

[razeontherock]

IOW, the fat lady hasn't sung yet? (haha)