Why doesn't a magnet interfere with light?

In summary, the magnetic field of a magnet does not have any effects on light passing through it because photons are not charged particles and do not react to the electromagnetic force. Additionally, the electric field of the magnet cancels out the magnetic field, similar to an atom with equal numbers of protons and electrons. The theory of electromagnetism, based on the superposition principle, explains that light and other electromagnetic waves do not interact with each other, but instead only sum up. However, in the presence of certain materials, such as in the Faraday effect, light can be affected by magnetic fields. Further research suggests that the universe itself may exhibit a form of electromagnetic birefringence, similar to the birefringence of
  • #1
brainstorm
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0
Since light consists in part of magnetic fields, I was wondering why the magnetic field of a magnet never has any effects on the light passing through it. Is it because the magnet's field is static while the light is moving?
 
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  • #2
I could be wrong but I suspect a magnetic field would affect a beam of light if it were concentrated in a space similar in scale to the wavelength of the light.
 
  • #3
I believe it is because photons are not charged particles and therefore do not react to the electromagnetic force. (Yet they are the force carrier for that force oddly enough)
I believe the magnetic field is canceled out by the electric field as it moves. This is slightly similar to an atom with equal numbers of protons and electrons. They balance each other out and therefore will not be attracted to or repulsed from a magnetic field as a whole.
 
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  • #4
brainstorm said:
Since light consists in part of magnetic fields, I was wondering why the magnetic field of a magnet never has any effects on the light passing through it. Is it because the magnet's field is static while the light is moving?


Magnets do interfere with light.

wiki said:
http://en.wikipedia.org/wiki/Faraday_effect"
In physics, the Faraday effect or Faraday rotation is a magneto-optical phenomenon, or an interaction between light and magnetic field in a medium.
 
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  • #5
The classical theory of an electromagnetic wave goes something like this...

A potential difference occurs between two points be it the two ends of a transmitting antenna or two energy states in an atom. As that potential voltage collapses it creates an expanding magnetic field. When the electrical potential is depleted the magnetic field is at it's maximum. With no more electrical potential to sustain it, it starts to collapse, in the process it induces a potential voltage, this voltage exists whether or not there are charged particles for it to affect. when the magnetic field has fully collapsed the potential voltage is at it's maximum and the cycle repeats. One consequence of this theory is that each magnetic field component will be oriented opposite from the previous magnetic field component. If an outside magnetic field is large compared to the wavelength of the light then it will distort each magnetic field component of the light just a little and it will affect every other cycle oppositely. If the magnetic field is concentrated enough to affect just one wave and to affect it significantly then I think that the effect would be noticeable.
 
  • #6
OmCheeto said:
Magnets do interfere with light.

Do they? I'd never heard that before. Where can i read more on this?
 
  • #7
OmCheeto said:
Magnets do interfere with light.

Only in the presence of certain materials. Not in empty space!

Photons do not interact with each other. Electromagnetism (light, radio, and all those waves) is regulated by the superposition principle, which would not hold if waves interacted with each other. They can only sum with each other.
 
  • #8
Dr Lots-o'watts said:
Only in the presence of certain materials. Not in empty space!

Photons do not interact with each other. Electromagnetism (light, radio, and all those waves) is regulated by the superposition principle, which would not hold if waves interacted with each other. They can only sum with each other.

What do you mean by "They can only sum with each other"?
 
  • #9
brainstorm said:
Since light consists in part of magnetic fields, I was wondering why the magnetic field of a magnet never has any effects on the light passing through it. Is it because the magnet's field is static while the light is moving?

The theory of electromagnetism is about the electric and the magnetic field. It is about both, combining it. The Maxwell equations are describing both, a magnetic field is nothing but the field of moved charge. These equations are linear. Linearity means always that the superposition principle is applyiable. The equations are perfectly valid in the domain of special relativity, it was one of the reasons Einstein discovered the SRT. If you accept that light is nothing but an "electromagnetic effect" you will see that the superposition holds: There is no interaction. An interaction would mean an nonlinear effect which is given in masses having interaction but not in the issue you wrote about.


Jens
 
  • #10
Drakkith said:
What do you mean by "They can only sum with each other"?

superposition is a fundamental feature of linearity:

F(x) + F(y) = F(x+y)

if y and x are coupled to each other (i.e the waves interact) this needn't be true.
 
  • #11
Dr Lots-o'watts said:
Only in the presence of certain materials. Not in empty space!

Photons do not interact with each other. Electromagnetism (light, radio, and all those waves) is regulated by the superposition principle, which would not hold if waves interacted with each other. They can only sum with each other.

Hmm.. I think I might have missed that part. Though it is possible that my wash machine of a brain took the Faraday Effect and the article I saw a few years ago and produced an erroneous conclusion.
Polarized Space
In 1997, Borge Nodland and John Ralston found in their analysis of astronomical polarization data that the universe had an optical axis: it was circularly birefringent! The universe appeared to behave in a similar way as a crystal with optical activity: it rotated the polarization direction of linearly polarized light! This cosmic "quartz crystal" had an optical axis parallel to the direction Aquila-Earth-Sextans. Is the universe birefringent? Is the universe rotating?

Ah ha! The following indicates that I was confused:

http://www.aip.org/png/html/birefrin.htm"
Since the new rotation we find has such a systematic directional dependence, it is implausible that it is generated by cosmic ions and fields via some mechanism similar to the Faraday effect. One may therefore surmise that it is the vacuum itself that flaunts a form of electromagnetic birefringence, or anisotropy - similar to the birefringence exhibited by many crystals.

Never mind.
 
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  • #12
Drakkith said:
What do you mean by "They can only sum with each other"?

Two electromagnetic waves (or photons, which are physically the same thing) don't interact with each other.

All that happens if they get near is that they add up (summation). This is what fundamentally causes interference. But this isn't really an interaction. Both remain independent of each other. Once two photons have crossed, they forget they've met, as if the other never existed.

That's why a magnet won't affect a light beam. A light beam ('s field) technically adds to nearby magnet's field, but they don't affect each other. A particle in that region of space will feel the effects of both fields however.
 
  • #13
like sound waves they (light waves) just pass through each other.
the net 'field' at any time is just the (linear) sum of the individual fields.
in other words, the fields just 'superpose' on top of each other
 
  • #14
The thing to keep in mind, is that the vector potential has a greater physical significance than the magnetic field. Consider Feynman, vol 2, section 15-5, "the vector potential and quantum mechanics". The idea here is that if a beam of light passes through a region of space where the vector potential is non-zero (even if the magnetic field is zero), that the light beam will interact with the vector potential, and this will have a measurable effect, in the sense that the vector potential will influence the quantum phase of the light beam.

The statement "the magnetic field of a magnet never has any effects on the light passing through it" is false. One very clear way to see this is to realize that photons do interact in QED through virtual particle production, this accounts for example, for the anomalous magnetic moment of the electron.

The physical significance of the vector potential over the magnetic field can be seen from a more fundamental perspective. In order to quantize the electromagnetic field, it is customary to work in the Lorentz gauge and to consider photons as the harmonic frequencies of the vector potential.
 
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  • #15
calhoun137 said:
The statement "the magnetic field of a magnet never has any effects on the light passing through it" is false. One very clear way to see this is to realize that photons do interact in QED through virtual particle production, this accounts for example, for the anomalous magnetic moment of the electron.
Maybe I should have specified that I meant an empirically visible effect, such as image distortion, prism effect, etc. Are there any observable effects of the virtual particle production you're talking about?
 
  • #17
one way to see this would be to compute the cross section for photon photon scattering to some order in the fine structure constant. In other words, the effect is that two photons will have some QED scattering interaction. I'm not sure about macroscopic effects...
 
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Related to Why doesn't a magnet interfere with light?

1. Why doesn't a magnet attract or repel light?

A magnet interacts with other magnetic objects or materials with magnetic properties. Light, on the other hand, is an electromagnetic wave and does not possess any magnetic properties. Therefore, there is no interaction between a magnet and light.

2. Can a magnet affect the speed of light?

No, the speed of light is a fundamental constant in physics and is not affected by external forces or influences such as a magnet. This is because light is not a physical object that can be influenced by other forces.

3. How does a magnet affect the polarization of light?

A magnet does not directly affect the polarization of light. Polarization refers to the direction of the electric field in an electromagnetic wave. Since a magnet does not produce an electric field, it does not have any effect on the polarization of light.

4. Can a magnet bend or deflect light?

No, a magnet cannot bend or deflect light. The path of light is determined by the properties of the medium it is traveling through and is not affected by external forces such as a magnet. However, a strong magnetic field can affect the path of charged particles, which in turn can emit light, leading to the appearance of light being bent or deflected.

5. Why does a magnet not produce a magnetic field around light?

As mentioned earlier, light is an electromagnetic wave, and it already has an electric and magnetic field associated with it. A magnet, being a source of magnetic field, cannot produce an additional magnetic field around light. This is because the magnetic field of light cancels out the magnetic field of the magnet, resulting in no net magnetic field around light.

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