Photons carry both energy and momentum (not energy and force) 😌

The question doesn't make sense.

A photon is nothing more and nothing less than a single particle state of the electromagnetic field. Electromagnetic fields-like all fields-exert forces on other objects; that's why it makes sense to associate energy and momentum to them, since forces change the energy and the momentum of the objects they act on (something known as Newton's second law).

The quoted text doesn't have anything to do with the question asked.

ِDear Kåre

"The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles)".

https://en.wikipedia.org/wiki/Photon

ِDear Stam

You have repeated old ideas about the photon.

The quoted text comes from old ideas.

My question is: what is different between real and virtual photons?

@ Hossein: You should not take all poetic statements you read too literary. Force carrier is a rather common expression for excitations of the fields responsible for the fundamental interactions, but energy-momentum carrier is a more correct statement (although momentum is more likely to be incomprehensible to laymen).

It doesn't make sense talking of ``old'' vs. ``new'' ideas-but of ``meaningful'' vs. ``meaningless'' statements. It's a good idea to avoid meaningless statements and to learn what are the meaningful questions-not all questions make sense.

The question about the difference between real vs. virtual photons doesn't have anything to do with the original question.

The difference is very easy to state: real photons have definite energy and momentum; virtual photons don't.

Dear Stam

When I say old ideas, that is what you say.

The electrical force transfers by virtual photons.

But when the electron is excited, it emits the energy that is transferred by real photons.

Virtual photons transmit electric and magnetic forces. Electric charges, when moving non-uniformly, emit real photons.

Indeed, these are not new statements-they're, also correct. It's the latter property that matters, not the former.

But, so what? The rules for computing physical quantities are the only things that matter, not the qualifiers attached to the particles.

It's wrong, however, to claim that virtual photons transmit forces and real photons do not. That distinction doesn't make sense. Real photons do recoil off electric charges-that was found in the photoelectric effect and the Compton effect.

Dear Stam

You provide a personal commentary.

In quantum electromagnetic, "forces between two charged particles are due to exchange of virtual photons.

“Photon mediates electromagnetic interaction” No action at a distance required!"

https://www2.ph.ed.ac.uk/~muheim/teaching/np3/lect-qed.pdf

"Virtual photons pop up when something emits a photon which is almost immediately absorbed by another particle of some kind. This relates to the uncertainty principle as such: Becuase the time of the photon's existence was so short, you really did not have a chance to measure its energy very well".

http://www.fnal.gov/pub/science/inquiring/questions/virtual_photons_1.html

This is confusing because quantum electrodynamics is incapable of explaining the electromagnetic interaction.

Because the difference between virtual and real photons is not clear.

For this reason, the physical properties between real and virtual photons should be exactly explained

This question was raised about it.

Dear Sydney Ernest Grimm

Thank you for explaining.

I have not understood your opinion, what is different between real and virtual photons really?

Best Regards

Hossein

Dear Hossein,

Interesting question, to which the various contributions highlight how much confusion there is about "photons".

From my understanding, two models are being mixed up when this is being discussed.

One model is QFT from which QED was developed, in which "virtual photons" are conceptually seen as spontaneous quantum energy fluctuations on either side of a zero point energy level that would exist everywhere in space, that establishes virtual photons as being bosons that are seen as the "force carriers" that would explain the energy levels and motion of real elementary electromagnetic particles in space.

These virtual photon do not convert to electromagnetic photons, because electromagnetic photons come into being only when electrons are stopped in their motion when being captured in various orbitals in atoms, of when jumping from a metastable far orbital to be captured by an orbital closer to a nucleus in an atom for example. The same for similar orbital shifts inside nuclei.

Electromagnetic photons can only be made of energy. For example, when an electron is captured by a proton to form a hydrogen atom, the 13.6 eV momentum energy that it accumulated during its Coulomb induced acceleration (due to the attraction between the charged electron and the oppositely charged proton) is ejected as a bremmsstrahlung "electromagnetic photon" that we can detect, and that makes up part of the "spectral signature" that we can detect of the whole range of very precise frequencies that can be related to the hydrogen atom.

This one is no "force carrier" in the QFT or QED sense, but is made exclusively of "electromagnetic energy" that moves in vacuum at c by structure until it is absorbed at some other location, transmitting its energy to another electron, for example, causing it to jump away from the orbital it is captive into, possibly completely ejecting it, if still energetic enough after having diminished in intensity as it travelled between emission point and absorption point.

Since it is "electromagnetic" in nature, its energy can only oscillate between both electric and magnetic state at the frequency related to its energy quantum.

To conclude, it would seem that "virtual photons" are "defined" as "force carrier" in QFT and QED, while "real electromagnetic photons" are observed and detected as "energy carriers" only.

Best Regards

André

Dear André

Thank you for interesting mentions.

When we apply the work-energy theorem to electromagnetism, we get significant results.

For example: in the history of mass-energy equivalence E=mc2, we saw there is a close relationship between electromagnetic force and electromagnetic energy.

"In 1904 when Fritz Hasenöhrl created a thought experiment involving heat energy in a moving cavity".

"A simple application of the “work–energy theorem,” which equates the difference in work produced by the forces to the cavity’s kinetic energy, allowed Hasenöhrl to conclude that blackbody radiation has mass m = (8⁄3) E / c2. In his second paper Hasenöhrl considered a slowly accelerating cavity already filled with radiation and got the same answer. After a communication from Abraham, however, he uncovered an algebraic error and in his third paper corrected both results to m = (4⁄3) E / c2".

"In considering the mass inherent in heat Hasenöhrl extended the previous deliberations beyond the electromagnetic field of charged objects to a broader thought experiment very similar to Einstein’s own of the following year, which gave birth to E = mc2".

https://www.scientificamerican.com/article/was-einstein-the-first-to-invent-e-mc2/

I agree with you that virtual photon that carries electromagnetic force is not same as real that carries electromagnetic energy. But according to "work-energy theorem" and relation F=-dU/dx, we can conclude negative and positive virtual photons combine and convert to a real photon.

This is the importance different between real and virtual photons. We cannot see or detect the virtual photon, same as other forces, but we can see its effect when it applies to a particle such as an electron and converts to energy.

Hossein Javadi, et, at., Generalization of the Dirac’s Equation and Sea, 2016

https://www.researchgate.net/publication/303988070_Generalization_of_the_Dirac's_Equation_and_Sea

Dear Hossein,

You wrote: "For example: in the history of mass-energy equivalence E=mc2, we saw there is a close relationship between electromagnetic force and electromagnetic energy."

I absolutely agree. This is in sync with the electromagnetic perspective also, in which the relation between force and energy is also direct, because energy is given by the product of the Coulomb force by the distance between elementary charged particles.

If interested in this electromagnetic perspective, this is something that I analyzed closely in Section 6 of this recent paper, with Figure 1 attempting to visually put all aspects in perspective:

http://file.scirp.org/pdf/JMP_2018042716061246.pdf

Best Regards

André

Hello all,

The difference is none, both are misconceptions.

Virtual photons do not exist (by definition) and are not needed -- only real particles are needed to explain real particles.

Cheers, Ed Gerck

If we do not need a virtual photon and they do not exist, so how does electromagnetic force apply?

Dear André

Your description is very interesting and important.

Let's go back to your equation and figure 1. (see attachment).

I consider the relation E=Fd as follows:

E has mass because at least a moving photon has the mass equal to m=E/c^2.

It means the left side of the relation E=Fd, E has mass, so the side should be referred to a mass. In general, force is converted to energy and energy is convertible to mass (for example pair production electron-positron) and vice versa.

Force (every exchange particle that is called boson) carries momentum and mass.

In the special case, virtual photons have mass. So, we need to separate virtual photon that is carrying electromagnetic force from the real photon that carries electromagnetic energy. For detail see:

Hossein Javadi, et, at., Generalization of the Dirac’s Equation and Sea, 2016

https://www.researchgate.net/publication/303988070_Generalization_of_the_Dirac's_Equation_and_Sea

However, thank you very much for the link to your interesting article.

Roughly (very!) speaking, the difference between virtual and real photons is that between electromagnetic forces and electromagnetic energy. More precisely, virtual photons are a way of looking at electromagnetic interaction (exchange of virtual photons). It is mostly useful when only few photons are exchanged. In other cases this concept may be a nuisance, notably, infrared catastrophe. It is also very confusing in the classical limit. As opposed to a virtual photon, a real photon can exists on its own. Formally speaking, it can be an asymptotic state of the EM field, which a virtual one can not.

Furthermore, the difference between real and virtual photons exists only in stationary systems. Make a system parametric, and the difference disappears. Anyone interested, I can give references.

Dear L. I. Plimak

Thank you for comment and mentions. Please give me references.

Hi Hossein,

Tried to locate your e-mail bu in vain. A toy example of a parametric system that starts and ends in vacuum and nevertheless radiates is in P. and Stenholm, EPL, 96 (2011) 34002. The most relevant to this discussion is Kaplan's comment re the Unruh effect.

Best

Lev

Dear L. I. Plimak

Thank you very much.

Hello all,

Thanks Plimak and Kåre for your additions. I did not want to clutter my reply, and you have helped.

Hussein,

1 you would be REALLY careful to JUST use Wikipedia for your own education, not to be trusted as the final or even recent correct word, nor as a reference to others or here. It is has been changed wrongly, provably [1], by its own accredied revisors, and by any willy-nilly jokester, who can change it right now, and the wrong text is propagated with a surprising long lietime (err, lifetime), and claque effects, including sock-puppets!

[1] https://www.researchgate.net/publication/286676558_The_Wikipedia_Experiment_falsification_and_knowledge_decay_dynamics_in_physics_and_mathematics_online

2. The references on the current understading in physics that virtual photons, or anything virtual, should be deprecated, were given by me earlier in RG, and you can read in [2, 3] and [4]:

[2] https://www.perimeterinstitute.ca/news/new-face-feynman-diagrams

[3] http://arxiv.org/pdf/1212.5605v1.pdf

[4] https://www.researchgate.net/post/Do_we_need_to_abandon_the_Standard_Model_in_Physics

Cheers, Ed Gerck

Dear Ed Gerck

Thank you for your advising.

1 - Feynman diagrams are a summary of mathematical calculations.

Mathematics, without physical description, cannot fully reflect physical reality.

2 - To answer the unanswered questions in physics, we need to find the reason for the scattering.

3 - We do not need to abandon the Standard Model, we need to complete the standard model.

Hello Hossein,

You can certainly go along this road you point out and, if you are so sure about it, there is no need to ask questions if you think you do not need them. But, I will suggest that Feynman diagrams are NOT a summary of mathematical calculations.

Cheers, Ed Gerck

Dear Ed Gerck

Hello,

I appreciate your advising.

Feynman diagrams are pictures of processes that happen in space and time. Without any description of their mechanisms.

With Best Regards

Hossein

Hello Hossein,

Nice to see your improvement on stating Feynman diagrams, your previous statement was not correct at all. That is why "virtual particles" do not exist -- your question answered -- namely, virtual particles do not happen in space-time.

It is all an old language, to say that "even FTL " is considered, for example, but their probability is zero.

Only real particles have higher than zero probability, and need to be considered in the study of real particles, using a current stance (2018). Keep going, your new definition of your understanding of Feynman Diagrams still seems not to consider a couple of things, and it will be fun for you to find out. Others may not need it.

Cheers, Ed Gerck

Dear Ed Gerck

You have stopped on real space-time that is Not compatible with new experiments.

A photon has shape and 4 meters long, this is not the idea, the experiment shows it.

Victor Leong, et, at., Time-resolved scattering of a single photon by a single atom, Nature Communications, 2016

https://www.nature.com/articles/ncomms13716

I suggest update your knowledge

Hossein Javadi, et, at. , Interactions Between Real and Virtual Spacetimes

https://www.researchgate.net/publication/270339919_Interactions_Between_Real_and_Virtual_Spacetimes

Hossein Javadi, et, at. , Sub quantum space and interactions properties from photon structure to fermions and bosons

https://www.researchgate.net/publication/237009789_Sub_quantum_space_and_interactions_properties_from_photon_structure_to_fermions_and_bosons

Best Regards

Hossein