Magnetic field is made of virtual photons?

[cesar314]

I hate talking about what is or is not 'fundamental'. Its philosophy more so than science.

Fine, fine. I agree, I fell prey, after such a long post, to laziness in my language. I did not mean 'fundamental' as in a fundamental entity of ontological existence, but rather that on the femtoscale the fields are quantized. I wanted to illucidate that, relevant to the post that started this thread asking about whether magnetic fields were made of photons (which was really the question I wanted to address in a fashion suitable to the class of question itself), the aforementioned virtual particles do not 'make' magnetic fields, but rather they do play a 'fundamental' role as quantizations of the quantum electromagnetic field. Please note that I did try to make a quick note to the philosophical uncertainty of the ontology:

But here is where the philosophy of science becomes unclear, because then we have all these photons and what exactly are they but quantizations of some action?

The local fields 'E' and the fields 'M' are not relativistic invariants, you can say boost your frame and arrange it so that they swap places.

You are of course right about the lack of invariance, especially considering the magnetic field itself even classically arises due to changes in reference frame.

In fact, in general the entire field formalism is redundant, what is or is not fundamental is of course only true up to 'field redefinition'.

Ah, philosophy.

Moreover they appear in quantum mechanics as sort of a derived concept, as combinations of the electromagnetic field strength potentials.

Its far worse w.r.t the point of view of particles being fundamental. In fact, you cannot make quantum mechanics consistent with special relativity without insisting that operators are built out of fields. So already you have particles relegated to being 'excitations of some field' or built out of 'lumps of energy and momentum'.

(addressed above) Though perhaps my language did delegate an unfair bias toward the particle interpretation of QFT, I wanted to clarify the concept that photons are not little elements of magnetic force.

In general I find convincing arguments against just about any ontology I can place on what is or is not fundamental and no good a priori bet (probably an indictment of my intellect, but I suspect I am in good company)

I totally agree with you. Perhaps this philosophical issue of ontology will never go away; with the current paradigms, I can see no plausible way to argue about what is 'fundamental' except within the confines of specific theories or mechanisms for computation. That is what I loosely meant about 'fundamental' in the sentence you commented upon, though obviously there are problems with photons as fundamental even within the well-established paradigm of QED. I do not suspect superstring theories will much remedy the situation, if indeed anything more philosophically 'fundamental' can be 'discovered' . It's all about falsifiability, really.

Thanks for the excellent link, by the way! It contains a most lucid discussion, thank you.

 

[seanreynoldsc]

I think the reason we can't see magnetic fields is because the magnet is stationary.
Its not waving.

A photon is a name for a waving magnetic field.
A photon is a name for a waving electric field.
A moving magnetic field creates an electric field.

I postulate that If we could spin a magnet at 10^14 rpm we could generate light.

What do you think about that?

 

[Hologram0110]

That's very nice, Interested Learner. A question -
the electric field from a point charge extends
to infinity in the absence of other charges. How is the electric field in a photon confined to a smaller region ?

Because a photon does not have charge. Also, even in the presence of other charges the electric fields still extend to infinity.

 

[DanteBR]

When a permanent magnet attracts an iron coin, there are only "virtual photons" involved in this process?

If the coin is on a table, and the permanent magnet is positioned a few centimeters above the coin, what about Earth's gravity attracting the coin? Why the virtual photons are "stronger" than the gravitons and make the coin "fly", defying Earth's gravity?

 

[jtbell]

We don't have a generally accepted theory that "explains" both electromagnetism and gravity, so we can't say why one is stronger than the other.

 

[tupos]

I really can't understand sense of this discussion. Why does everybody separate electric and magnetic field?

It is the same field!

People here speak about electric field more only because of the relation E=cB that's all.

There is no difference between "electric" and "magnetic" photons they both appears as a components of four-potential.

Photons appears as a quant of field (as it is the same field there is no sense to separate it) .

But on experiment u can't measure potential. People measure only strong characteristic of the field it means E and B.

Regards.

 

[cragar]

Doesn't anything with spin have a magnetic moment , like the neutron B moment ,
so doesn't the photon have its own dipole moment.

 

[Hans de Vries]

Doesn't anything with spin have a magnetic moment , like the neutron B moment ,
so doesn't the photon have its own dipole moment.

Only "things" which spin and have charge can have a magnetic moment. The
individual quarks of the neutron do have magnetic moments.

Charge is quantized and therefor cancels out exactly in the case of a Neutron.

The magnetic moments aren't quantized and can also be parallel or anti-parallel
to each other. Therefor neutral bound states of charged particles do generally
have non-zero magnetic moments.


Regards, Hans

 

[cragar]

what about the Anti neutrino and neutrino , does this imply that the neutrino has sub particles which have charge.

 

[Hans de Vries]

what about the Anti neutrino and neutrino

They have spin (1/2) but no charge nor magnetic moment. They are
elementary particles without any known substructure.

Regards, Hans

 

[cragar]

then what is anti-about them , like the neutron and the anti-neutron their quarks are opposite in charge. so is it possible the neutrino's have sub elements.

 

[Ghuggi]

Photons are massless particles. They carry forces as it is one of the bosons.

 

[jtbell]

then what is anti-about them

When a neutrino interacts with something by exchanging a virtual W boson, you get a negative lepton out (either an electron, a muon, or a tau, depending on which type of neutrino). When an antineutrino interacts similarly, you get a positive lepton out.

Examples:

\nu_\mu + n \rightarrow \mu^{-} + p

{\bar \nu}_\mu + p \rightarrow \mu^{+} + n

 

[cragar]

i see thanks jt bell