Can Magnets Bend Light for Invisibility Cloaks?

[Charlie G]

I was wondering if it was possible to bend a beam of light with a magnet. If this is possible could someone tell me what the requirements for the magnet be to do such a thing.

 

[pallidin]

The following is from: http://www.wonderquest.com/extinctions-safetyglass-magnetslasers.htm

Q: Can a magnetic field interrupt the path of a laser? Can a magnet bend light? —"Bending light", Vancouver, British Columbia, Canada

[NASA] Laser light reflected by mirrors but unbent by magnets

A: A magnet can bend the path of any moving charged particle. In fact, that’s how your TV screen displays a video picture. A magnet deflects a beam of electrons to create a video pattern on the screen. Light, however, has no charge and therefore its path is unaffected by a magnet.

But, you mention a magnetic field, which includes changing fields. If it’s a changing field, things get more complicated. Any changing magnetic field generates a changing electric field and that produces an electromagnetic wave.


Electromagnetic (EM) waves cannot interact directly with light photons since photons have no charge. EM waves do not bend light, at least enough that we can measure. If radio waves, for example, bent light appreciably then a transmitting radio station would look blurry. But stations don’t go blurry.

Actually, electromagnetic waves can bend light through an indirect, quantum effect—but to such a tiny degree that we cannot measure it. This quantum effect (called Delbrück scattering) "is a process where, for a short time, the photon disintegrates into an electron and positron pair," says Norbert Dragon, physicist at the Institute for Theoretical Physics in Hanover, Germany. The charged pair interacts with an EM wave and then recombines into the photon with a changed direction. Thus, the EM wave bends the light.

"More probably the charged pair will annihilate into two or more photons—this process has been observed under extreme conditions—but, then, the light ray is not bent but rather split into several rays," says Dragon.

 

[Charlie G]

Darn. There goes my invisibility cloak lol. The only other option to bend light around myself would be gravity, but I am sure a suit like that would have some major consequencies(everything flying at it lol). Oh well, thanks for the reply :)

 

[Tac-Tics]

Electromagnetic (EM) waves cannot interact directly with light photons since photons have no charge. EM waves do not bend light, at least enough that we can measure. If radio waves, for example, bent light appreciably then a transmitting radio station would look blurry. But stations don’t go blurry.

I'm probably mixing theories, but can't photons interact with EM waves, seeing as EM waves *are* photons, and photons, being bosons, tend to clump into similar states?

I was wondering if it was possible to bend a beam of light with a magnet. If this is possible could someone tell me what the requirements for the magnet be to do such a thing.

If you have a standard bar magnet and an old CRT television or computer screen, try it for yourself. As you bring the magnet near the screen, you'll see the picture go crazy. This is due to the force of the magnet on the stream of electrons through the television. In fact, bending light with magnets is the fundamental principle behind CRT televisions!

 

[Cspeed]

Light, however, has no charge and therefore its path is unaffected by a magnet.

Does that mean that because light has no mass it is not affected by gravity?

 

[JANm]

Electromagnetic (EM) waves cannot interact directly with light photons since photons have no charge. EM waves do not bend light, at least enough that we can measure. If radio waves, for example, bent light appreciably then a transmitting radio station would look blurry. But stations don’t go blurry.

Always thought that stations did get blurry called Mexican thing... hound?. Automatic Frequency Control is a device which follows the changes in receptance of a carrier wave!

Greetings

 

[HallsofIvy]

The following is from: http://www.wonderquest.com/extinctions-safetyglass-magnetslasers.htm
Electromagnetic (EM) waves cannot interact directly with light photons since photons have no charge.

Does that mean that because light has no mass it is not affected by gravity?

No, that quote has nothing to do with either mass or gravity. And, in fact, while it is true that light has no mass, it is affected by gravity. The fact that light bends around stars was one of the first important tests of relativity.

 

[JANm]

Eddington 1919 I presume? Bending of starlight by the the sun 1,75 arcseconds nearest to the Sun. By comparing starcharts of 1 the stars during the eclipse and 2 at a moment that sun and moon are enough away (mostly I say half a year later) it seems that the stars have moved away from the sun. Explicitly not toward the Sun! In our conceptual scheme we think light going straight...

 

[Nick89]

If you have a standard bar magnet and an old CRT television or computer screen, try it for yourself. As you bring the magnet near the screen, you'll see the picture go crazy. This is due to the force of the magnet on the stream of electrons through the television. In fact, bending light with magnets is the fundamental principle behind CRT televisions!

This is a bit of a weird statement (sorry)... First you say correctly that CRT tv's bend a stream of electrons with magnets. Then you conclude that they are bending light with magnets?

CRT tv's are not bending the path of light with magnets, they are bending the path of electrons.

I assume you meant electrons in your last sentence? (But if you do, the post would not really be relevant in the topic of bending light with magnets...?)

 

[Tac-Tics]

This is a bit of a weird statement (sorry)... First you say correctly that CRT tv's bend a stream of electrons with magnets. Then you conclude that they are bending light with magnets?

CRT tv's are not bending the path of light with magnets, they are bending the path of electrons.

This is very true. I must have misread X-(

 

[JANm]

Photons have no restmass yet bend because of their relativistic mass = hf/c^2. Have sought for some construction like: no rest charge but yet relativistic charge, but I was assured that no charge at all is associated with photons...

Yet perhaps GRAVITOMAGNETISM yields anything for your problem?

 

[JANm]

Electromagnetic (EM) waves cannot interact directly with light photons since photons have no charge. EM waves do not bend light, at least enough that we can measure. If radio waves, for example, bent light appreciably then a transmitting radio station would look blurry. But stations don’t go blurry.

The last time I quoted this something went wrong. I mentioned "the mexican hound" The effect that stations actually used to get blurry
when received with old radio's. This effect has been corrected by the automatic frequency control: a way to let the receiving radio follow the base frequency of the carrier wave.
I still don't have an answer to this remark Pallidin, stations used to get blurry before this invention!
greeting Janm

 

[pallidin]

The last time I quoted this something went wrong. I mentioned "the mexican hound" The effect that stations actually used to get blurry
when received with old radio's. This effect has been corrected by the automatic frequency control: a way to let the receiving radio follow the base frequency of the carrier wave.
I still don't have an answer to this remark Pallidin, stations used to get blurry before this invention!
greeting Janm

I understand what your saying, but read the statement again.
It's saying that the physical radio tower does not get visually blurry while emitting large amounts of EM radiation. Thus it does not distort light.
It's NOT talking about a "blurry" received radio signal.

 

[Lok]

One effect a magnet has on a photon is rotate it's plane of polarization (must be very strong). Maybe u could use that for your invisibility cloak.

 

[ZapperZ]

I'm probably mixing theories, but can't photons interact with EM waves, seeing as EM waves *are* photons, and photons, being bosons, tend to clump into similar states?

We have not yet seen any photon-photon interaction, which is one of the higher-order interactions predicted within QED. For such a thing to have an appreciable probability to occur, we need very high energy photons (gamma-gamma interaction). Without that, the probability of such interaction is minuscule to non-existent.

Coming back to this thread, we need to make sure we FRAME the scope/range of this question properly. It is asking for the typical classical E&M scenario within the typical working range that we can achieve under ordinary condition. So let's not start messing about with exotic circumstances, tempting as they may be. Magnetic fields do not bend light under a typical and large range of parameters. Period.

Zz.

 

[JANm]

... we need to make sure we FRAME the scope/range of this question properly...
... Magnetic fields do not bend light under a typical and large range of parameters. Period.
Zz.

Hallo ZapperZ,
So if people as important as Eddington and/or Einstein state that light bends by gravitation that is to be taken seriously and this question that it could possibly be the magnetic field of the Sun which could be the cause for this bending has to be closed?
I might say magnetic field is a better candidate for bending light then gravitation!
greetings Janm

 

[ZapperZ]

Hallo ZapperZ,
So if people as important as Eddington and/or Einstein state that light bends by gravitation that is to be taken seriously and this question that it could possibly be the magnetic field of the Sun which could be the cause for this bending has to be closed?
I might say magnetic field is a better candidate for bending light then gravitation!
greetings Janm

What does "light being bent by gravitational field" has anything to do with "light being bent by magnetic field"?

It really is a simple question. It doesn't involved higher-order QED interactions, nor does it involve exotic particles such as axions. If it does, it will be in either BTSM forum, or even HEP forum.

The classical Maxwell Equation provides no mechanism for light to be bent in a magnetic field. If you know of a peer-reviewed publication that has something to the contrary, please cite it, and then, we'll open that discussion.

Zz.

 

[Count Iblis]

I was wondering if it was possible to bend a beam of light with a magnet. If this is possible could someone tell me what the requirements for the magnet be to do such a thing.

See the English translation of the original paper by Euler and Heisenberg:

http://arxiv.org/abs/physics/0605038

In the low energy limit, there are small nonlinear corrections to Maxwell equations. If you have a magnetic field in a region and an electromagnetic wave moves through thast reason, then theeffect of the magnetic field is the same as if the vacuum were a so-called birefringent medium. I.e. the medium has an index of refraction that depends on the polarization of the electromagnetic wave relative to the magnetic field orientation.


Details are given here:

http://arxiv.org/abs/hep-ph/9806417


Now, the fact that you have an effective index of refraction, means that the light will indeed be deflected by a magnetic field. This doesn't mean that you can measure it. If you take a laser and shine it through the field of an ordinary magnet with a field strength of 1 tesla, then you should take into account that the photons emitted by the laser do not have an infinitely sharply defined momentum.


So, if they are deflected in some direction, a miniscule amount of mometum is added to a state of which the momentum was spread out quite widely. The final state and the initial state are then almost identical as far as the momentum is concerned. According to quantum mechanics, you then cannot detect that any momentum has been added at all, at least not in a case by case basis. You would have to average over a huge number of photons to see a tiny effect. And so far we haven't even considered the effect of noise...


In case of so-called mnagnetars which are neutron stars that have field strengts of billions of teslas, the effect can be more easily detected. But so far it hasn't.

 

[Count Iblis]

ZapperZ, but what we call "classical electromagnetism" is in reality quite complicated quantum mechanics involving coherent states of photons.

Why can't we call the Euler-Heisenberg lagrangian classical too? I mean, if the nonlinear corrections had been larger (e.g. if the fne structure constant had been larger or electron mass smaller), then Faraday could have measured a vacuum birefringence effect and Maxwell's would have been able to put everything together and write down the Euler-Heisenberg equations. The coefficients of the nonlinear terms would then be phenomenological parameters.

Euler and Heisenberg would then later explain the origin of these terms. But everyone would refer to the Euler Heisenberg equation as the "classical Maxwell eqations".

 

[Naty1]

Over wide ranges of conditions photons (electromagnetic waves) do not interact...but gravitational waves do interact...to say it another way, photons don't interact, gravitons do...hence the formulation of gravity in general relativity is considerably more difficult than in Maxwell's electromagnetic fields...Einsteins tensor is more complex than its counterpart in EM.

 

[ZapperZ]

ZapperZ, but what we call "classical electromagnetism" is in reality quite complicated quantum mechanics involving coherent states of photons.

Why can't we call the Euler-Heisenberg lagrangian classical too? I mean, if the nonlinear corrections had been larger (e.g. if the fne structure constant had been larger or electron mass smaller), then Faraday could have measured a vacuum birefringence effect and Maxwell's would have been able to put everything together and write down the Euler-Heisenberg equations. The coefficients of the nonlinear terms would then be phenomenological parameters.

Euler and Heisenberg would then later explain the origin of these terms. But everyone would refer to the Euler Heisenberg equation as the "classical Maxwell eqations".

.. and how would this change what I've said about light and magnetic fields? And how is this useful in answering the OP's level of the question?

Zz.

 

[JANm]

The classical Maxwell Equation provides no mechanism for light to be bent in a magnetic field. Zz.

Hello ZapperZ
The issue of bending of light was first brought to us by Laplace isn't it?
What I meant to say is light electromagnetic wave. So the chance that it is bent by magnetism or electric field, but that is not the issue in this thread, is there. Why not look into it? Having no restmass it is more farfetched to think it is bended by gravitation than magnetic field. That is what I tried to pose.
The classical Maxwell Equation provides no mechanism for light to be bent in gravitational field either!
greetings Janm

 

[Charlie G]

So, photons don't interact with other photons? If so then how does interference happen?

 

[jtbell]

Interference is not caused by different photons interfering with each other. Individual photons interfere with themselves. You can build up an interference pattern gradually, one dot at a time, by sending one photon at a time through the apparatus.

 

[Charlie G]

Hmm. Thats strange lol.

 

[ZapperZ]

Hello ZapperZ
The issue of bending of light was first brought to us by Laplace isn't it?
What I meant to say is light electromagnetic wave. So the chance that it is bent by magnetism or electric field, but that is not the issue in this thread, is there. Why not look into it? Having no restmass it is more farfetched to think it is bended by gravitation than magnetic field. That is what I tried to pose.
The classical Maxwell Equation provides no mechanism for light to be bent in gravitational field either!
greetings Janm

Luckily, valid physics has nothing to do with satisfying your comfort level.

This is pure speculation that is not supported by anything. Please cease this line of discussion.

Zz.

 

[JANm]

I've been reading some Maxwell lately and found that magnetic field has power to rotate the plane of polarisation...
greetings Janm

 

[ZapperZ]

I've been reading some Maxwell lately and found that magnetic field has power to rotate the plane of polarisation...
greetings Janm

You've "been reading some Maxwell"? Does Maxwell know about this?

And what does "rotate plane of polarisation" have anything to do with bending its path?

Zz.

 

[jtbell]

magnetic field has power to rotate the plane of polarisation...

Is that in a vacuum or in a medium?

 

[JANm]

Is that in a vacuum or in a medium?

Hello jtbell,
thank you for asking, because some of the answers I get look only as preventing anything that comes after the relativity theories bringing it back to it. So all that came after is pure technological improvements. Science stands still, yet has better ways to prove the relativity theories has brought us all what we need: rest.
I have the two parts of Maxwell: a treatise on electricity and magnetism lying next to me. The part on polarising by magnetic fields is one of the last chapters XX1 called: Magnetic action on light.

Was I reading the right chapter Zapperz?

Maxwell talks about through a Medium. He is some brain not only totally familiar with the genius Hamilton but also with the super handy man Faraday (with littler mathematic capabilities) so works with laboraty things instead of the more modern thought experiments of the relativity theory. Since high vacuum is defined by mercury damp above the 76 cm and even that can be called a medium compared to the vast emptiness there is in somany directions in space a part from the some directions in which are the clusters of clusters milky ways...
greetings Janm

 

[Born2bwire]

Darn. There goes my invisibility cloak lol. The only other option to bend light around myself would be gravity, but I am sure a suit like that would have some major consequencies(everything flying at it lol). Oh well, thanks for the reply :)

Oh, we already know how to do that... theoretically.. and not very practically... and in all essence we can currently only do this at a single frequency... but the problem is solved!

I can't remember the name of the articles, I think there was at least a general one published in Nature, but http://news.bbc.co.uk/2/hi/science/nature/6064620.stm . They do have a theoretical design for a complete 3D cloak, but really you would have to be enclosed in a hamster ball of sorts.

 

[Vanadium 50]

One effect a magnet has on a photon is rotate it's plane of polarization (must be very strong). Maybe u could use that for your invisibility cloak.

I've been reading some Maxwell lately and found that magnetic field has power to rotate the plane of polarisation...
greetings Janm

I think you're confusing a medium in a magnetic field rotating the plane of polarization and the magnetic field itself rotating the plane of polarization.

 

[Vanadium 50]

We have not yet seen any photon-photon interaction, which is one of the higher-order interactions predicted within QED.

Actually, we have. Melissinos and collaborators did this at SLAC (E-144) in the late 90's. They took GeV-scale photons from the beam stop and a laser, and observed upscattered photons. This is not a simple experiment: not only is it difficult getting enough photons in one place, once you do that, it's difficult to put detectors there without them getting fried.

But this is a digression. A magnetic field does not bend light. Full stop. The closest one could get, even in theory, would be for an ultra-intense magnetic field to scatter light (just as light can be scattered by the intense electric field surrounding an electron). I would challenge the folks here who are trying to defend this position to write down a calculation that shows how much this supposed deflection is.

Gravity is a red herring: light is gravitationally deflected by a magnet by the exact same amount that it would be deflected by an unmagnetized chunk of iron with the same mass.

 

[elect_eng]

One effect a magnet has on a photon is rotate it's plane of polarization (must be very strong). Maybe u could use that for your invisibility cloak.

That is a very good comment. There are practical devices called "optical isolators" and "optical circulators" that affect light differently based on whether the light is going forward or backward. These are common in the optical fiber industry. These devices are very strange since usually light rays follow the same path whether going forward or backward. (reflection, refraction, polarization rotation etc)

The principle used is called the Faraday Effect and is induced by magnets in a strongly birefringent crystal. The strong magnets induce a change in the polarization of light and then the light interacts with optical polarizers. The interesting and amazing thing is that even though this is a polarization effect, people have been clever enough to make devices that are polarization independent.

Still, I don't think this effect can make one invisible. Or, at least the encasement of magnets and crystals would give away your position.

 

[jtbell]

Maxwell talks about through a Medium.

The internal magnetic dipoles of the medium are an essential component of the effect. The applied magnetic field and the electromagnetic wave both interact with those dipoles, and it is these interactions that produce the change in the plane of polarization of the wave. The applied field and the wave do not interact directly with each other.

The principle used is called the Faraday Effect and is induced by magnets in a strongly birefringent crystal.

Right, not just any old medium will do, it has to have special properties.