[jeffreyH (OP)]

That I am very unsure of. BTW Alan I hope you don't agree with JD that photons can be accelerated and decelerated??

I wa quite explicit in pointing out that the speed of a photon is invariable. However it can gain or lose kinetic energy, or be deflected,  in a gravitational field.

Thanks. Point taken.

[jeffreyH (OP)]

I can find nothing sensible online about the active gravitational mass of photons. The gist is that it is a naive classical view and it is the tensor formulation that is needed. Isn't that missing the point?

[guest4091]

Isn't the pointing away from the sun of the tail of a comet the effect of solar radiation, i.e. light momentum?

[jeffreyH (OP)]

In the case of E = m(wf)^2 when frequency is zero then wavelength is infinite. So that at the event horizon the equation breaks down. Except that zero point energy should still be present. I am wondering if the addition of such a term can rescue the situation. This would mean that mass never vanishes. Even though it may be greatly reduced. If the reduction reaches a critical value at the horizon then free quarks within the confinement of the horizon are entirely feasible.

[jeffreyH (OP)]

Will this have a bearing on the vacuum catastrophe?

[JohnDuffield]

The photon should not generate a gravitational field.

It does. Any concentration of energy has a gravitational effect.   

]Since it has no inertial mass.

It does have an inertial mass, which is equivalent to its active gravitational mass. Google it. But as I said, these terms are really measures of energy rather than mass per se. The photon has no rest mass. 

In which case the Higgs field may indirectly cause the gravitational field by donating mass.

It doesn't. See Gian Guidice's Zeptospace Odyssey where he says the Higgs field is reponssible for only 1% of the mass of matter.

[jeffreyH (OP)]

In which case the Higgs field may indirectly cause the gravitational field by donating mass.

It doesn't. See Gian Guidice's Zeptospace Odyssey where he says the Higgs field is reponssible for only 1% of the mass of matter.

That is a bold and sweeping statement. Can you justify it in your own words? Since by inference you profess to understand it. Will I get a reply?

[JohnDuffield]

That is a bold and sweeping statement. Can you justify it in your own words?

It isn't a bold and sweeping statement, it's just physics. Gian Francesco Guidice is a respected CERN physicist with over a hundred papers to his name.

Since by inference you profess to understand it. Will I get a reply?

Why don't you start a thread asking some question or making some proposal, and I'll tell you what I can.

[jeffreyH (OP)]

That is a bold and sweeping statement. Can you justify it in your own words?

It isn't a bold and sweeping statement, it's just physics. Gian Francesco Guidice is a respected CERN physicist with over a hundred papers to his name.

Since by inference you profess to understand it. Will I get a reply?

Why don't you start a thread asking some question or making some proposal, and I'll tell you what I can.

In other words you can't.

[jeffreyH (OP)]

John if you are just going to pick out snippets of what I have posted out of context just to make a point it is a futile exercise. I had moved on but you didn't even notice. How much attention are you actually paying?

[yor_on]

It's weird. Inertia: the tendency of a body to maintain its state of rest or uniform motion unless acted upon by an external force. You can say that a photon has a tendency to 'propagate' in a geodesic (the 'easiest path' sort of), and that it takes a force, as in a mirrors constituents, to change that propagations direction, that should relate to inertia possibly. You can also argue it from waves and perfect elastic scattering in where 'no energy' is lost though? I prefer to think of it as losing energy myself, no matter if it is waves or 'photons'. Here's an alternative definition https://physics.stackexchange.com/questions/255340/does-a-box-containing-photons-have-more-inertia-than-an-empty-box

[jeffreyH (OP)]

That is a very thought provoking thread yor_on.

[zx16]

If a "photon" is an actual particle, and it's travelling at the speed of light, why hasn't it got any mass?

[yor_on]

Is it?

If so, define a particle.

[PmbPhy]

Jeff asked the following questions which I’d like to respond to:

Re – Ok so does the photon have a gravitational field?

Yes. But there’s a caveat to that which is that photons properly belong to quantum mechanics whereas GR is a classical theory. To properly address your question would require a theory of quantum gravity which does not yet exist in a complete finished theory. However you could easily ask the similar question of the gravitational field of a pulse of an electromagnetic wave and the answer to that is worked out in its entirety in Tolman’s GR text.

Re – Is the active gravitational mass constant or variable?

Variable. A photon travels in space so the gravitational field at a point in space must change in time as the photon moves through space.

Re – Since the energy relates to frequency I would assume variable.
It’s not as easy as that. The frequency of a photon does not have the same exact meaning as the frequency of an EM wave.

I wa quite explicit in pointing out that the speed of a photon is invariable. However it can gain or lose kinetic energy, or be deflected,  in a gravitational field.

The speed of a photons does indeed change as it moves through a gravitational field from regions of different gravitational potentials. This is a direct consequence of gravitational time dilation. This was in fact one of the first results that Einstein showed when he invented GR in 1907 and its just as true today as it was then. If you read Shapiros papers in which he reports the experimental results of what is now referred to as the Shapiro delay you’ll in fact see him state this fact and that it’s the cause of the results of his experiments. I'm sure those papers are available online if you'd like to read them for yourself.

I can find nothing sensible online about the active gravitational mass of photons. The gist is that it is a naive classical view and it is the tensor formulation that is needed. Isn't that missing the point?

Exactly. But what are you so worried about photons and taking your focus off of classical radiation/EM waves? After all they’re in essence composed of photons.

Isn't the pointing away from the sun of the tail of a comet the effect of solar radiation, i.e. light momentum?

Yes. Quite so.

In the case of E = m(wf)^2 …

Where did you get such an expression? It doesn’t look like anything that I’ve ever seen before. Please define those variables for me. Thanks.

If a "photon" is an actual particle, and it's travelling at the speed of light, why hasn't it got any mass?

It does. It has inertial mass, aka relativistic mass. You’re doing what most non-experts are doing and confusing two of the definitions of mass, i.e. inertial mass and proper mass (aka “rest mass”).

[jeffreyH (OP)]

Pete the w = photon wavelength and the f photon frequency since I can't easily put greek symbols. I take your point about classical radiation.