# Magnetic field is made of photons?

1. Oct 23, 2006

### taylaron

i've been researching photons and i discovered on
http://http://van.physics.uiuc.edu/qa/listing.php?id=414" [Broken]
and
http://en.wikipedia.org/wiki/Photon" [Broken]

both resources state that all mangetic fields are made of photons. soooooo, this brings up a lot of questions... first, why (when im in the presence of a mangetic field) dont i see light? (because light is mad of photons)
im sure if i get a simple understanding of this concept, it will probably rule out most of my questions, so i'll wait for a reply to continue.

SO WHAT ARE PHOTONS MADE OF? -obviously they're charged (hence mangetic fields)

Last edited by a moderator: May 2, 2017
2. Oct 27, 2006

### Severian

Since it doesn't look like the lost replies that were made to this question will be coming back, I will answer it again.

Magnetic fields are indeed made of photons. The reason that you don't see them is simply that your eyes are not sensitive enough. Electric fields are also made of photons, but you don't see tham either. You also don't see infra-red or ultra-violet radiation, because your eyes are only sensitive to very specific photon energies.

3. Oct 27, 2006

### Burnsys

And photons are fundamental units of energy so they are not made of anything else.

4. Oct 27, 2006

### Meir Achuz

"both resources state that all mangetic fields are made of photons"

I couldn't get to the first website. The Wikipedia was confusing as usual, but I didn't see that it said "all magnetic fields are made of photons".
A static magnetic field is not made of photons. EM waves are quantized in packets called photons.

5. Oct 27, 2006

### taylaron

thank you,
i have a better understanding of photons now.
so photons arent really particles (no mass) since they're energy. energy that apparently takes form of light, and simply energy.
so photons are basically energy. there are more than one type of photon (light, mangetics. .... etc.....)

but if these photons that make up (most) mangetic fields, are in a frequency/energy frequency -such as frequencys of light-
what frequency are these in? there if they're not gamma, UV, x-ray, IF, visible light.
what are they? do we know??

6. Oct 28, 2006

### quinn

the force exchange from a magnetic feild to something else is via photons,

7. Oct 29, 2006

### Severian

No tayleron, photons are particles (see the photoelectrc effect), energy is not light (although photons (light) have energy), and photons are more than just energy (they have other quantum numbers). Finally the photons in light and the photons in magnetism are the same thing - just with different energies.

8. Nov 6, 2006

### FunkyDwarf

so photons are the force carriers for the electric and magnetic fields in the standard model? i thought it was something else?

9. Nov 6, 2006

### Severian

Yes.......

10. Nov 7, 2006

### taylaron

thanks severian
i get the basic idea

11. Nov 12, 2006

### petm1

Does this mean that we can think of a magnetic and/or a electric feild as a standing wave of photons, much like a river?

12. Nov 15, 2006

### petm1

Could you think of a magnetic field as being length contracted, because the photons are in a closed loop, and time contracted because they appears as a standing wave having no relative movement, instead of an expanding wave with relative movement. Keeping in mind they always travel at c relative.

13. Nov 17, 2006

### taylaron

that makes sence

14. Nov 22, 2006

### Demystifier

Photons, as they are usualy defined, are associated with electromagnetic fields in the absence of sources (charged currents). So a better defined question could be: Do Maxwell equations without the sources admit purely electric and purely magnetic fields? If the answer is no, then there is no photon state that corresponds to a purely electric or purely magnetic field.

Last edited: Nov 22, 2006
15. Dec 15, 2006

### Jacquesl

If Photons are light waves and you’re able you reflect them with a mirror, and some are saying magnetic waves are virtual photons so can you reflect magnetic waves.

And how could you reflect a magnetic wave “flux”, is it possible, a mirror will probably not work.

16. Dec 15, 2006

### DaveC426913

Now *I'm* confused. Electric fields and magnetic fields are made of photons? (What an embarrassing gap in my knowledge...) What frequency are they?

17. Dec 15, 2006

### marlon

OK, this is gonna be a long one...

First question, you say you have been researching photons. What exactly does that mean ? Also, when doing research you should NOT be using public libraries like Wikipedia.

Secondly, i am sure you know that photons are defined as pieces of energy. Hence, the basis in which the "live" is the energy base. Photons are NOT point particles but energy-particles. It is very important to realize that. Knowing this, and knowing how E/M field are defined, you should already see that photons do NOT make up E/M fields.

Thirdly, the theory that describes photons and their relations to E/M fields is QED. In QED we learn that photons are the force carriers of the EM interaction. This means that photons are the particles that mediate the electrical and magnetic interactions. In QED, you can also study (very important to know btw) how photons arise due to the vibration of quantum fields. Think of a mattress on which you jump in one place. The surface of the mattress vibrates and due to this vibration, there is energy coming free from the mattress (ie the vibrational energy).

If you replace YOU by AN ELECTRON and the mattress by the quantumfield and you take into account that energy is the same as mass (E=mc^2) you can see how the vibration of a quantumfield can mimic a certain particle with mass m and momentum p.

This is how photons arise in QED. Ofcourse photons do not have restmass m but still the principle of vibrating fields versus particles remains the same. How QED deals with the zero restmass of photons is a more complicated story. More specifically, the quantumfield in the photon case is the 4-vector potential A.

One can actually rewrite the Maxwell equations with this A potential in such a way that they respect all necessary symmetries that need to be respcted (i know, this may sound a bit vaque but i don't know what level you are on so let me know). From this A potential one can also calculate the E and B fields.

Finally, photons are NOT the constituent particles of EM fields, photons describe the interactions between electric charges (which exhibit an electric field) or/and magnetic dipoles, quadrupoles (which have an associated magnetic field) etc etc ...

In QED photons arise thanks to the vibrating A field (think of it as the A mattress ). In other words, photons arise thanks to the quantisation of the waves in the A field. This A field is closely related to the E and B fields, so being a bit less accurate, you could also say that photons correspond to the quantisized energy of vibrating E and B fields.

greets
marlon

Last edited by a moderator: May 2, 2017
18. Dec 15, 2006

### Severian

Any frequency you like. Any field of photons is an electric field or magnetic field. Which of the two it is is dependant on your frame of reference, since a Lorentz boost will transform one into the other.

I have no idea what Marlon is smoking... :tongue2:

Think of it this way. A charged particle moves in an electric or magnetic field. Where does it get the momentum from? It gets it from absorbing a (perhaps virtual) photon.

19. Dec 16, 2006

### marlon

:rofl:

Marlon is smoking QED

Oohh, so electrons are absorbing photons now ? I would suggest you study which processes allow for this to happen in high energy physics. You might be surprised.

When describing charged particles in fields (Maxwell, Lorentz force) we don't use photons. All is classical field theory here.

Indeed, in QED, charged particles interact through the exchange of virtual photons. But again, such photons do NOT MAKE UP and E/B field. In their original definition E and B are classical fields NOT quantumfields.

Also, as i told in my previous post. In field theory, particles arise through vibrations of quantumfields.
Photons are the quanta of the electromagnetic field (expressed by the A potential). You may also
think of it as the energy contained in the electric and magnetic fields which make up the
light wave. This duality is a basic part of quantum theory.

Clearly, one cannot just say...ohhh we have particles that make up a field...This is NOT WHAT QED teaches us.

marlon

Last edited: Dec 16, 2006
20. Dec 16, 2006

### Jacquesl

Guy’s I previously asked this question but it’s in the first page and nobody probably going to turn one page back.

Will I be able to reflect magnetic waves from a permanent magnet just like you should reflect light with a mirror?
Because some say magnetic waves are virtual photons or something and light are just photons.

And to my understanding the word photo means something that you can see with your eyes and virtual also has to do with the word photo?? So I don’t know if magnetic wave are virtual photons and a normal light bulb is also a photon generator because photons are light. Does someone have a clear answer for this confused understanding from me or maybe some other people to

21. Dec 16, 2006

### Severian

OK, very well, and QED is a quantum theory (that's what the 'Q' stands for).

So if you are smoking QED, why are you now refering to classical fields? There are really no such thing as classical fields - classical physics is just a limit of quantum physics.

I am not sure what you mean by 'original definition', but the definition of E and B in QED (that is what we are talking about, isn't it?) are the components of the field strength tensor $$F^{\mu \nu}$$. And the field strength tensor can be written directly in terms of the vector potential $$A^{\mu}$$, which (as you pointed out yourself earlier) is the photon field. Therefore photons do make up the E/B fields.

That would only reinforce my point. The only interaction present in QED is the three-point vertex involving one photon and 2 electrons. So the only way that you can transfer momentum to an electron is by absorbing or emitting a photon. Period.

22. Dec 16, 2006

### DaveC426913

I'm looking at it the other way around.

That means if I have a magnetic field around a magnet, it's made of photons, thus emitting EM radiation.

23. Dec 16, 2006

### Hans de Vries

Well, Static EM fields are of course associated with zero frequency photons
in QED with zero momentum transfer. A nice example is the magnetic anomaly
of the electron in a static magnetic field:

The calculation is made as if the electron interacts with a photon representing
the magnetic field. The magnetic anomaly represents the radiative correction
for this vertex. The first order (Schwinger) result is:

$$1\ +\ \frac{\alpha}{2\pi}\ \frac{\Theta}{\sinh{\Theta}}$$

Where $\Theta$ relates to the angle of deflection of the electron absorbing the
photon. Now only in the limit case of the interaction with a zero frequency
photon we get the correct expression for the first order term we measure
for the magnetic anomaly of an electron in a static magnetic field:

$$1\ +\ \frac{\alpha}{2\pi}, \qquad \mbox{for: }\ \ \Theta=0$$

(See Itzykson & Zuber, 7-1-3, Vertex Function, eqn: (7-58), page 341)

Regards, Hans

P.S. The exact expression for theta is: $p \cdot p\' \ =\ m^2\ \cosh{\Theta}$

Last edited: Dec 16, 2006
24. Dec 16, 2006

### marlon

The E abd B fields were first defined in "classical physics" and properly described by Maxwell. That is what i meant.

I disagree. In QED photons arise due to fluctuations of those fields, so the fields "are allready there". Thus, photons are not the particles that make up such fields nor generate such fields. Ofcourse, i am NOT saying they aren't closely related because THEY ARE (through the quantization of the A vector which is indeed directly related to E and B). But i object against the "constituent particles" terminology because this picture does not correspond to what QED teaches us.

I think there is a fundamental difference between :

1) how photons arise in QED
2) how E and B fields are defined (or introduced) in QED

Indeed, naively, E and B fields "are just there" in the field strength tensor, as you have pointed out. E and B are concepts that we already knew from classical physics. Beware, this does NOT imply they behave in the same way in QED. What is ofcourse special is the quantisation of these fields (described by A) which gives rise to the photons.

Ofcourse but this is not what i was talking about. I wanted to object against the fact that you said this :
What i didn't get is :

1) why perhaps a virtual photon ?
2) how does this prove that photons "make up electric fields"

In QFT (thus also in QED), force is introduced by the "vibrational mattress picture". Even A Zee uses this very nice analogy in his first chapters of "QFT in a Nutshell". My point, the A field (and thus the E and B fields) are quantisized. This quantisation of their vibrations generates the photons. look at the chronology here, THAT IS MY POINT.

Greets
marlon

25. Dec 17, 2006

### Flux

More of an outside question but does the Earth's quantum field have anything to do with gravity as a vacuum effect?
A large mass object could create a warp in space this way but I was wondering what the relationship was with EM fields in studies?