Why do photons have no rest mass and cannot have a charge?

[Nikaro]

Why photon exist without rest mass and why it can never have a charge. Plz reply.

 

[malawi_glenn]

Why photon exist without rest mass and why it can never have a charge. Plz reply.

well physics tend not to answer all "why" questions, we can only move them to a different level.

i) the photon moves at the speed of light, only massless (i.e. 0 rest mass) can do so

ii) The gauge symmetry group of electromagnetism is U(1), which is abelian, thus the photon has not charge.

Then you can ask why it moves at the speed of light and why EM has U(1) gauge symmetry group and so on.

 

[nicksauce]

There are however "photons" with charge and mass, the W- and W+ bosons. (Roughly speaking of course)

 

[Nikaro]

Please explain it simple i can't under stand above reply

 

[malawi_glenn]

and I don't understand what part of them you did not grasp or at what level you currently are at. What is "simple" is relative...

 

[Bob_for_short]

Why photon exist without rest mass and why it can never have a charge. Plz reply.

Photon is a wave, it travels. In vacuum it travels fast (v=c), in a transparent medium (glass, water) it travels slower, with v<c, so there is an accompanying reference frame where it looks as a standing wave. Despite that it still have energy ћω. You can assign some mass to it, if you like.

Photon carries energy-momentum. It can transfer part of them to another particle or system. Photons strongly interacts with charged particles: roughly speaking, photon is an electric wave. Photon practically does not interact with another photon in vacuum. It is due to the principle of superposition of electric fields, if you like. Electric fields make only sense when they appear in the particle equation motion as external forces.

Bob_for_short.

 

[prysdieheer]

I was wondering the same thing.
::::::::::::::::::::::::::::::::

In Love
Prys die Heer!

 

[Count Iblis]

http://arxiv.org/abs/hep-ph/0505250

http://arxiv.org/abs/hep-ph/0602036

 

[Nikaro]

Thanks everybody.

 

[RedX]

Keeping with the theme of particle physics, the question should really be why other particles have mass (and why they have the value of the mass that they have), rather than why doesn't the photon have mass. 0 is easy to understand.

Mass is related to the spontaneous symmetry breaking of a scalar Higgs. The photon gains no mass as it is the gauge field corresponding to a direction in field space where symmetry is not broken from the electroweak phase transition. For more information there is plenty of material on the web about the Higgs mechanism.

 

[Count Iblis]

Keeping with the theme of particle physics, the question should really be why other particles have mass (and why they have the value of the mass that they have), rather than why doesn't the photon have mass. 0 is easy to understand.

Mass is related to the spontaneous symmetry breaking of a scalar Higgs. The photon gains no mass as it is the gauge field corresponding to a direction in field space where symmetry is not broken from the electroweak phase transition. For more information there is plenty of material on the web about the Higgs mechanism.

The photon could still be massive if it couples to another scalar and gains mass that way:

http://arxiv.org/abs/hep-ph/0306245

If the photon has a small mass that is generated by such a Higgs mechanism, then it turns out that the very sharp upper bounds on the photon mass that depend on the vector potential of the galactic magnetic field, are not valid.

 

[RedX]

The photon could still be massive if it couples to another scalar and gains mass that way:

http://arxiv.org/abs/hep-ph/0306245

If the photon has a small mass that is generated by such a Higgs mechanism, then it turns out that the very sharp upper bounds on the photon mass that depend on the vector potential of the galactic magnetic field, are not valid.

So I assume this other scalar would develop a vacuum expectation value that will be a different value than usual one, i.e., the one whose ground state is U(1) charge invariant and gives mass to the Standard Model. But if this happens, then don't you lose conservation of charge, since your theory will lose U(1) charge invariance?

 

[samalkhaiat]

i) the photon moves at the speed of light, only massless (i.e. 0 rest mass) can do so

Maxwell's equations do admit massive solutions "propagating" with the speed of light! however, these solutions are trivial. They are not observable, because one can always gauge them away.


regards

sam

 

[Count Iblis]

So I assume this other scalar would develop a vacuum expectation value that will be a different value than usual one, i.e., the one whose ground state is U(1) charge invariant and gives mass to the Standard Model. But if this happens, then don't you lose conservation of charge, since your theory will lose U(1) charge invariance?

Actually, the article assumes that the ordinary Higgs mechanism would generate the photon mass. Anyway, you still have a conserved current, even in Proca theory, as the article explains.

 

[darkwood]

The Photon is an electro-magnetic wave and thus should be viewed as pure energy to understand it better, this will give insight into the no mass question, different particles are in simple a combination of a set mass ratio to their energy at ground state. The absorbsion of a photon in a particle will raise its energy state and then subsequently releases the exact energy out as a duplicate photon, this happens almost instantaneously but a fragment of time is used thus the speed of light through air liquid and solids becomes increasingly slower.

 

[malawi_glenn]

The Photon is an electro-magnetic wave and thus should be viewed as pure energy to understand it better, this will give insight into the no mass question, different particles are in simple a combination of a set mass ratio to their energy at ground state. The absorbsion of a photon in a particle will raise its energy state and then subsequently releases the exact energy out as a duplicate photon, this happens almost instantaneously but a fragment of time is used thus the speed of light through air liquid and solids becomes increasingly slower.

ohh Define pure energy please

 

[Sidnv]

Are photons made of quarks?

 

[malawi_glenn]

Are photons made of quarks?

no they are made of air

 

[nicksauce]

Quarks have mass. Photons don't have mass.
Quarks have electric charge. Photons don't have electric charge.
Quarks interact strongly. Photons don't interact strongly.
Quarks interact weakly. Photons don't interact weakly.

So no, photons are not made of quarks.

 

[Sidnv]

Thanks.
So photons aren't really particles in the traditional sense are they?. Their particle nature is just a reflection of the quantization of their energy.

 

[malawi_glenn]

Thanks.
So photons aren't really particles in the traditional sense are they?. Their particle nature is just a reflection of the quantization of their energy.

define "traditional particle" ...

 

[Sidnv]

I guess i can't really give an exact definition. I would say that traditional meant non zero rest mass but that's hardly a traditional definition.

 

[malawi_glenn]

I guess i can't really give an exact definition. I would say that traditional meant non zero rest mass but that's hardly a traditional definition.

Then why using home-made defition of things when writing in a physics forums where we are trying to discuss current accepted physics (see forum rules) ?

 

[Sidnv]

I apologise. I was just curious and I'm new to this.

 

[malawi_glenn]

it's ok, see also the term "pure energy" invented by darkwood in this thread.

 

[fleem]

Energy has mass.
Charge has energy, so charge has mass.
Charge is something that still exists while it is at rest, so charge has rest mass.
Since the photon has no rest mass, it can't carry a charge (because if it carried a charge it would have rest mass).

(Note that a confined photon in a mirrored box gives that box rest mass. We call that mass contribution the photon's "relativistic mass". But that mass is strictly caused by the photon's kinetic energy--the photon has no rest mass)

 

[Vanadium 50]

Energy has mass.
Charge has energy, so charge has mass.
Charge is something that still exists while it is at rest, so charge has rest mass.
Since the photon has no rest mass, it can't carry a charge (because if it carried a charge it would have rest mass).

That's simply not true.

If it were true, photons would carry no kinds of charges at all. But they carry something called weak hypercharge.

 

[malawi_glenn]

charge "has" energy is wrong also..

 

[gonegahgah]

The Photon is an electro-magnetic wave and thus should be viewed as pure energy to understand it better, this will give insight into the no mass question, different particles are in simple a combination of a set mass ratio to their energy at ground state. The absorbsion of a photon in a particle will raise its energy state and then subsequently releases the exact energy out as a duplicate photon, this happens almost instantaneously but a fragment of time is used thus the speed of light through air liquid and solids becomes increasingly slower.

My understanding was that - light traveling @ <c through materials due to photon absorption/re-emission - was not the accepted explanation.
I saw someone say this same explanation without comment another time so I'm starting to wonder if I got that wrong too?
I thought it was due to other factors? Was it something to do with space-time or was it magnetic interaction? I can't remember? Or is absorption/re-emission it?

 

[Vanadium 50]

charge "has" energy is wrong also..

It's all jumbled up, I'm afraid.

 

[malawi_glenn]

My understanding was that - light traveling @ <c through materials due to photon absorption/re-emission - was not the accepted explanation.
I saw someone say this same explanation without comment another time so I'm starting to wonder if I got that wrong too?
I thought it was due to other factors? Was it something to do with space-time or was it magnetic interaction? I can't remember? Or is absorption/re-emission it?

The speed of light is determined by the permittivity and permeability of a material.

 

[gonegahgah]

Thanks malawi. Hopefully that will put the 'absorption/re-emission' idea to rest.