Twice the speed of light.

[exchemist]

@ c , it's mass is the equivalent of its energy divided by c^2

What does E = Mc^2 mean?
https://www.pbs.org/wgbh/nova/einstein/lrk-hand-emc2expl.html

You are using an incomplete equation. E=mc2 is the simplified equation for objects at rest relative to the observer. Obviously this is inapplicable to photons.

The full version you should be using is E2=(mc2)2 + p2c2*. Since m=0 for photons, this reduces toE=pc.

So stop trying to apply E=mc2 to photons. It’s wrong and will give you misleading ideas.

* I can’t do superscripts on the device I am using. Please read E2 as E squared etc.

 

[Write4U]

We know that in physical objects it's the mass of the object that is responsive to gravity.

What then is the property of energy that makes it responsive to gravity? Energetic mass?

From quora; Arinloye Sam Adebisi
B.Sc Earth Science & Earth Physics, Federal University of Technology Akure (2013)
Answered January 26, 2017

Mass; first of all what is mass? Mass is a measure of inertia i.e a measure of an object’s resistance to an effort trying to move it. It can be described as the degree of sluggishness a body displays in response to an action attempting to change the position of the body.

Matter occupies space and not mass, what we call mass is more or less a trapped energy and an occupation of space is not essentially a property that suits the description of energy. Meanwhile, when we look at mass as energy (light energy maybe) and view it from the point of view of photons while keeping in mind the particle nature of light, I feel it is safe to conclude that mass is affected by gravity because everything does.

https://www.quora.com/Mass-has-two-...ted-by-gravity-and-occupies-space-Is-it-right

 

[Janus58]

We know that in physical objects it's the mass of the object that is responsive to gravity.

What then is the property of energy that makes it responsive to gravity? Energetic mass?

Why is it so hard for you to just accept that the umbrella that covers those things that affect gravity has expended to include energy? There simply is no reason that you have to cram the word "mass" in there somehow.

 

[Write4U]

Why is it so hard for you to just accept that the umbrella that covers those things that affect gravity has expended to include energy? There simply is no reason that you have to cram the word "mass" in there somehow.

OK, I accept that. But then what is it in energy that responds to gravitation? It is a legitimate question.

 

[Ssssssss]

OK, I accept that. But then what is it in energy that responds to gravitation? It is a legitimate question.

But then what is it in mass that responds to gravitation? It is a legitimate question

 

[Ssssssss]

We know that in physical objects it's the mass of the object that is responsive to gravity.

No we don't we know that the stress energy is the source of gravity and all objects are affected by it full stop. In GR there is no aspect of an object that makes it responsive to gravity all objects must be because otherwise that would allow for something that didn't respond to gravity and then we couldn't use a geometric model.

 

[Ssssssss]

I know that. I was looking for a reference about Bohm's work that said that it "assigned an inherent potential that a zero value particle @ c
acquires mass, whereas the potential of a collapsing wave function @ c, converts energy into mass, however small" which is what you said and none of the excerpts you provided say and I was looking for it because Bohm's work was as far as I know non relativistic and therefore says nothing about photons and was only much later extended by others to cover QFT concepts like photons and I don't think that later work is likely to say anything of the sort anyway.

Still waiting for this reference Write4U.

 

[Ssssssss]

"virtual mass".

Please define this term.

 

[Write4U]

But then what is it in mass that responds to gravitation? It is a legitimate question

Mass has a value. Zero mass has no value. Can a thing without value be subject to gravitation?

 

[Ssssssss]

Mass has a value. Zero mass has no value. Can a thing without value be subject to gravitation?

Energy has a value. So has height and width and electric charge and many other things so if value is the only requirement for a thing to be subject to gravitation then almost anything should be. Or to put it another way you are doing your usual thing of trying to deflect a question you can't answer.

 

[Write4U]

Please define this term.

Something with a value that responds to gravity.

Abstract

The behavior of a photon is strange. It possesses both wave nature and particle nature. Some experiments show both behaviors of photons can exist simultaneously, while some other experiment state that both properties do not co-exists simultaneously.

According to electromagnetic theory, the rest mass of photon in free space is zero and also photon has non-zero rest mass, as well as wavelength-dependent.

The very recent experiment revealed its non-zero value as 10-54kg. Even experimental results concluded that within matter (dispersive) the photon shows its

imaginary rest mass.

https://www.sciencedirect.com/science/article/pii/S2211379719330943#

I am not talking about photons flying around. I am talking about what occurs when a photon hits a physical surface and with what kind of non-zero value.

 

[Write4U]

Energy has a value. So has height and width and electric charge and many other things so if value is the only requirement for a thing to be subject to gravitation then almost anything should be.

Do you believe there are things that are not subject to gravity? Can you cite an example?

Or to put it another way you are doing your usual thing of trying to deflect a question you can't answer.

Not at all. I am boring in on the pertinent questions why light is responsive to gravitation if it has no value that can be acted upon. You are deflecting because you cannot explain what you posit. At least I am asking the question. So far I have not received a satisfactory answer except repetition of the same claim.

I am waiting for your response, because you are the one making claims without supporting science.
OTOH, I have produced supporting articles from reliable sources for my probing propositions.

Just picked up a new term for me. "Radiation pressure" Can anyone explain how that occurs?

 

[Ssssssss]

Something with a value that responds to gravity.

So it's a circularly defined term with no connection to reality I see.

I am talking about what occurs when a photon hits a physical surface and with what kind of non-zero value.

So what? Light in media travels at less than c and there it has mass as I've already said.

 

[Ssssssss]

Do you believe there are things that are not subject to gravity?

Of course not but you seemed to be claiming that a nonzero value of something was all that was required for a gravitational effect and a zero value of something was all that was required for no gravitational effects so I was just pointing out the absurdity of that.

I am boring in on the pertinent questions why light is responsive to gravitation if it has no value that can be acted upon.

But the point of a geometric theory is that everything obeys the geometry it doesn't need a "value that can be acted on" because how can something not obey the laws of geometry? You are trying to make light fit into a Newtonian model of forces between masses and it won't work.

I am waiting for your response, because you are the one making claims without supporting science.

You haven't asked for a source so far. See chapter 4 of Sean Carroll's lecture notes (https://www.preposterousuniverse.com/grnotes/) particularly equation 4.9 and the discussion between there and equation 4.22.

 

[Write4U]

W4U said; Something with a value that responds to gravity.

So it's a circularly defined term with no connection to reality I see.

So what? Light in media travels at less than c and there it has mass as I've already said.

You did?!
Oops,........ I must have missed it. Can you reference post#?

On second thought, does that explain light in a vacuum being affected by gravitation?

So far what I have is that everything is subject to gravitation, even if its value is zero.
To me, that sound dubious. Haven't seen a paper on it yet, but I'll check out Sean Carroll.

 

[Ssssssss]

You did?!
Oops,........ I must have missed it. Can you reference post#?

http://www.sciforums.com/posts/3682376/

On second thought, does that explain light in a vacuum being affected by gravitation?

No. See my last post.

 

[Write4U]

From Sean Carroll

Lecture Notes on General Relativity

Gravitation
...

The WEP states that the “inertial mass” and “gravitational mass” of any object are equal. To see what this means, think about Newton’s Second Law. This relates the force exerted on an object to the acceleration it undergoes, setting them proportional to each other with the constant of proportionality being the inertial mass mi: f = mia .

.....

After the advent of special relativity, the concept of mass lost some of its uniqueness, as it became clear that mass was simply a manifestation of energy and momentum (E = mc2 and all that).

....

This means that not only must gravity couple to rest mass universally, but to all forms of energy and momentum — which is practically the claim of the EEP.

....

Sometimes a distinction is drawn between “gravitational laws of physics” and “nongravitational laws of physics,” and the EEP is defined to apply only to the latter. Then one defines the “Strong Equivalence Principle” (SEP) to include all of the laws of physics, gravitational and otherwise. I don’t find this a particularly useful distinction, and won’t belabor it. For our purposes, the EEP (or simply “the principle of equivalence”) includes all of the laws of physics

...

It is the EEP which implies (or at least suggests) that we should attribute the action of gravity to the curvature of spacetime.

Gravitation due only to space-time curvature regardless of mass. Now we're getting somewhere.

Remember that in special relativity a prominent role is played by inertial frames — while it was not possible to single out some frame of reference as uniquely “at rest”, it was possible to single out a family of frames which were “unaccelerated” (inertial). The acceleration of a charged particle in an electromagnetic field was therefore uniquely defined with respect to these frames. The EEP, on the other hand, implies that gravity is inescapable — there is no such thing as a “gravitationally neutral object” with respect to which we can measure the acceleration due to gravity. It follows that “the acceleration due to gravity” is not something which can be reliably defined, and therefore is of little use.

https://preposterousuniverse.com/wp-content/uploads/grnotes-four.pdf

Still confusing. I just picked up these tid-bits from a cursory reading. I'll need more time to absorb the formal language.

I like Sean Carroll! Thanks for the link.

 

[Write4U]

http://www.sciforums.com/posts/3682376/

↑ On second thought, does that explain light in a vacuum being affected by gravitation?

No. See my last post

OK, we have mass of a photon with zero rest-mass when traveling at less than c in a medium. But traveling @ c in a vacuum the photon does not have mass? This is still confusing. Maybe reading Carroll I'll get a better perspective.

 

[Ssssssss]

OK, we have mass of a photon with zero rest-mass when traveling at less than c in a medium.

No we don't.

This is still confusing.

No it isn't. \(m=\sqrt{|p^\mu p_\mu|}\) as I said. If \(p\) is null \(m\) is 0. If \(p\) is not null \(m\) is not 0. Light does not travel at c in media so its \(p\) is not null. In vacuum it is.

 

[Write4U]

No we don't.

No it isn't. \(m=\sqrt{|p^\mu p_\mu|}\) as I said. If \(p\) is null \(m\) is 0. If \(p\) is not null \(m\) is not 0. Light does not travel at c in media so its \(p\) is not null. In vacuum it is.

And when it strikes a surface?