# The nature of the magnetic field.

1. Jun 17, 2010

### peron

QED states that the magnetic field is a kind of "photon lattice" and the force we feel when a magnet pulls of something is the exchange of these virtual photons. But I become confused right about here, if the magnetic field is virtual photons, which are themselves wave packets of magnetic and electric fields.

Is the magnetic field with in a photon made out of more photons? OF course this can't be, so I'm obviously missing a key part of the theory, please can someone explain?

2. Jun 18, 2010

### billbray

I'd like to see some answers to this one as well.....

3. Jun 19, 2010

### Antiphon

The photon is a quantum of the field. They are what the fields are made of.

There are no magnetic or electric field in the photons. If there are EM fields, there are photons.

4. Jun 20, 2010

### peron

So then what is a EM field?

5. Jun 20, 2010

### Phrak

I think you are asking what is a classical electromagnetic field. Quantum electrodynamics is a theoretical construction designed to replace the classical theory.

6. Jun 20, 2010

### peron

I apologize if I wasn't clear, my question was concerning the quantized view of the magnetic field in Quantum Electrodynamics. In QED, as I have come to understand, the magnetic field is nothing more than a "photon field" of sorts. But photons themselves are made out of magnetic fields.

I believe that I might be missing some big piece of the puzzle. So, what does Quantum field theory really say about magnetic fields?

Thanks.

7. Jun 20, 2010

### tiny-tim

Hi peron!
i] QED doesn't talk of the magnetic field … it talks of the electromagnetic field (of which the magnetic field is simply a component)

ii] can you tell us which book you got these statements from, and/or provide a link? …
iii] a photon "is" an electromagnetic field, with E.B = E2 - B2 = 0

iv] an electromagnetic field is sometimes said to be "mediated" by the photon, and to involve the "exchange" of both virtual photons and virtual electrons, but that is a mathematical description rather than a physical one.

8. Jun 20, 2010

### peron

http://en.wikipedia.org/wiki/Magnetic_field#Quantum_electrodynamics"

Ok, I have just become even more confused. What is the magnetic field then?

Last edited by a moderator: Apr 25, 2017
9. Jun 20, 2010

### tiny-tim

The magnetic field is three of the six components of the electromagnetic field.

The electromagnetic field is a 2-form (a vector is a 1-form), and has 6 components labelled xt yt zt xy yz and zx (a vector of course has 4 components, labelled t x y and z).

The xt yt and zt components are the electric field, and the xy yz and zx components are the magnetic field.

wikipedia's statement that "the electromagnetic field" (btw, not "the magnetic field") "is derived from the photon field" is both vague and weird … it certainly isn't a combination of photon fields.

What about "photon lattice" … where did that come from?

Last edited by a moderator: Apr 25, 2017
10. Jun 20, 2010

### jfy4

The electric and magnetic fields in the classical sense were entities in and of themselves, in the full sense, they were just that. Then as time progressed it could not help be noticed that the interactions taking place in the realm of electricity and magnetism were happening at the speed of light. Then the speed of light showed up in the E&M wave equation. Promptly thereafter light was decided to be made up of electric and magnetic waves oscillating.

Then Quantum arrives. The quantum field theory of the electric and magnetic fields in the radiation gauge ends up yielding a particle that resembles in every way, a photon. Thus, history, and physics must be rewritten, in a sense, and there never was an electromagnetic field in the sense that it was a unique entity, it was light all along!

Therefore do not get hung up on classical/quantum mix-ups such as a recursion where the electric/magnetic fields are made of photons, but photons are made of electric and magnetic fields, but electric/magnetic fields are etc... the convenient but ultimately unsatisfactory theory of classical electrodynamics must be circumscribed by a new theory, QED, of which we should extract the most current and almost canonical physics from.

11. Jun 21, 2010

### peron

So, the photon isn't made out of perpendicular magnetic and electric fields? And the electromagnetic field isn't made out of photons? So what is the magnetic field made out of?
I know i'm asking a What is? question which aren't really answered in science, like What is space?, but the magnetic field exists and it must be made out of something, I want to know what that something is.

12. Jun 21, 2010