Can a magnet bend a ray of light?

[sqljunkey]

Can an everyday magnet disturb a ray of light. I have seen many answers online saying no, and some saying yes, but only if the magnetic field is large enough.

 

[sysprog]

There's a lot that's implicated here. The simple answer is no. The magnetic field of an 'everyday magnet' is not energetic enough to produce gravitational effects sufficient to 'disturb' a ray of light. Light and magnetism are both aspects of the electromagnetic force. A handheld magnet can strongly bend an 'electron beam', but not even slightly bend a light beam, and a flashlight beam isn't deflected by the field of such a magnet, or by the beam of another flashlight.

 

[sophiecentaur]

only if the magnetic field is large enough

Not in free space, however powerful the magnet. The same applies to crossing beams of light; no interaction.
However, in some substances, the fields due to an intense beam of light can cause non-linear effects and the fields can affect each other. This is only in extreme cases, though. A non-optical case can be observed when high power HF Radio signals 'cross each other' in the Ionsosphere and can cause cross modulation which can produce waves of other frequencies that spread out.
I have no actual experience of optical examples but I believe laser beams can interact in some substances. This is all new-fangled stuff.

 

[davenn]

The magnetic field of an 'everyday magnet' is not energetic enough to produce gravitational effects sufficient to 'disturb' a ray of light

Huh??


Magnetic fields don't produce gravitational fields

Mass does

 

[Comeback City]

@davenn
Maybe the magnet has a very large mass 😉

In all seriousness, I don't see how the magnetic field would affect the gravitational field... @sysprog did you mean it does not create "magnetic" effects strong enough... ?

 

[sysprog]

The magnetic field of an 'everyday magnet' is not energetic enough to produce gravitational effects sufficient to 'disturb' a ray of light

Huh??

Magnetic fields don't produce gravitational fields

Mass does

At high enough energies the EM Force can produce 'gravitational effects', including bending light rays, by curving spacetime.

From: a stackexchange post by user M. J. Steil (Sep 5 '16 at 21:02):

Just looking at general relativity: the answer to the question: "Can a light be bent by a magnetic field?" is yes it can be bent due to the curvature of spacetime produced by a strong magnetic field. I can give a very short answer why, without going into too much detail, how the resulting bent geodesics might look ...

The rest of that post includes material (e.g. tensor field equations) that I think exceeds 'B' level thread standards.

 

[davenn]

At high enough energies the EM Force can produce 'gravitational effects', including bending light rays, by curving spacetime.

From: a stackexchange post by user M. J. Steil (Sep 5 '16 at 21:02):
The rest of that post includes material (e.g. tensor field equations) that I think exceeds 'B' level thread standards.

I suspect you misunderstand the answers in that link because the poster goes on to describe mass gravitational effects NOT magnetic field
effects

I still stick with, no it cannot, till some one, wise in such things, here ... @Dale, @DrClaude , @Nugatory tell me otherwise
with some reasons

 

[sysprog]

@davenn OK.

 

[sqljunkey]

However, in some substances, the fields due to an intense beam of light can cause non-linear effects and the fields can affect each other.

You mean the Zeeman effect by that? https://en.wikipedia.org/wiki/Zeeman_effect ,

 

[ZapperZ]

You mean the Zeeman effect by that? https://en.wikipedia.org/wiki/Zeeman_effect ,

You need to understand what you are citing. Here, the magnetic field is interacting with the ATOMS in the flame.

This has nothing to do with your original question or with what you were quoting.

The ordinary magnet cannot affect light. Period.

Zz.

 

[sqljunkey]

yikes

 

[Comeback City]

You mean the Zeeman effect by that? https://en.wikipedia.org/wiki/Zeeman_effect ,

I also found this video after looking up the question. @ZapperZ is right... this doesn’t relate to a magnet bending light. @sysprog ’s post about the magnetic field contributing to the gravitational field is more consistent with the question, but even then I’m not sure if that meets the criteria of the magnetic field itself bending the light. QM and GR might give different answers to this question.

Truthfully, I’m not smart enough to answer this question properly. Maybe someone else could clear this up?

 

[haushofer]

I suspect you misunderstand the answers in that link because the poster goes on to describe mass gravitational effects NOT magnetic field
effects

I still stick with, no it cannot, till some one, wise in such things, here ... @Dale, @DrClaude , @Nugatory tell me otherwise
with some reasons

An electromagnetic field curves spacetime by its energy-momentum tensor. This tensor sources gravity in Einsteins theory of general relativity.

This effect is, however, very weak.

 

[ZapperZ]

An electromagnetic field curves spacetime by its energy-momentum tensor. This tensor sources gravity in Einsteins theory of general relativity.

This effect is, however, very weak.

Instead of describing it as "... very weak.. ", try "...has never been observed before...". This is clearer to the general public, and probably will straighten out the OP who may have read similar statement and thinks that this has been verified.

Zz.

 

[sysprog]

An electromagnetic field curves spacetime by its energy-momentum tensor. This tensor sources gravity in Einsteins theory of general relativity.

This effect is, however, very weak.

I think I introduced some confusion when I made reference to 'gravitational effects'. @davenn correctly pointed out that gravitational effects are due to mass. You correctly made reference to EMF spacetime curvature being due to the energy-momentum tensor. At very high energies, this 'very weak' effect is no longer so weak as to be negligible, but at ordinary energies, it is well-established that electromagnetic fields produce no observable bending of light.

 

[sysprog]

Instead of describing it as "... very weak.. ", try "...has never been observed before...". This is clearer to the general public, and probably will straighten out the OP who may have read similar statement and thinks that this has been verified.

Zz.

I was under the impression that observations of neutron stars and pulsars had been accounted to evince the EMF contribution to spacetime curvature, i.e. the observed mass doesn't account for all of the observed curvature in their vicinity, but with inclusion of the EMF energy-momentum tensor it does.

 

[sqljunkey]

However, in some substances, the fields due to an intense beam of light can cause non-linear effects and the fields can affect each other.

You meant Faraday Effect instead of the Zeeman effect?


Like so:




https://en.wikipedia.org/wiki/Faraday_effect


I get it now. I guess one could argue that since an "everyday magnet" is surrounded by air molecules usually, which is a medium , there would be slight disturbance in the light ray due to the Faraday Effect.

;)

 

[ZapperZ]

You watch all these videos, but I still doubt you actually understand the physics being described.

Zz.

 

[sqljunkey]

I doubt that too ZapperZ. This wasn't clear to me at the start, we can say it's clearer now. Maybe idk. :3

 

[sysprog]

I get it now. I guess one could argue that since an "everyday magnet" is surrounded by air molecules usually, which is a medium , there would be slight disturbance in the light ray due to the Faraday Effect.

The magnetic field is not even slightly disturbing the light ray itself; it's strongly affecting the material through which the light is passing.

 

[sqljunkey]

The magnetic field is not even slightly disturbing the light ray itself; it's strongly affecting the material through which the light is passing.

Which in turn disturbs the light yes.

 

[Comeback City]

it's strongly affecting the material through which the light is passing.

In other words, it's affecting the geodesic by which the light follows, yes?

 

[sysprog]

Which in turn disturbs the light yes.

Yes, just as a ferrometallic metal mirror being warped by a magnet could change the path of reflected light, but that wouldn't be EMF bending light -- other than under certain very limited exceptional conditions, EMF cannot bend or otherwise affect light.

 

[sysprog]

it's strongly affecting the material through which the light is passing.

In other words, it's affecting the geodesic by which the light follows, yes?

No. Those are not other words for the same thing. The geodesic in GR is referential to spacetime curvature; not to such things as refractive index or polarization characteristics of semi-transparent materials.

 

[Comeback City]

No. Those are not other words for the same thing. The geodesic in GR is referential to spacetime curvature; not to such things as refractive index or polarization characteristics of semi-transparent materials.

Let me clarify... I was referring to the original question, not anything to do with the Zeeman effect or the Faraday effect. Your quote from the stack exchange post seems to say that the magnetic field affects the geodesic which light follows... is that correct?

 

[sysprog]

Let me clarify... I was referring to the original question, not anything to do with the Zeeman effect or the Faraday effect. Your quote from the stack exchange post seems to say that the magnetic field affects the geodesic which light follows... is that correct?

Yes. That's possibly-inferentially-observably true only in very exceptional high-energy conditions. An 'everyday magnet', as in the original question, cannot bend light.

 

[sophiecentaur]

You meant Faraday Effect instead of the Zeeman effect?

Not sure. The waves will both have E and H fields so I don't know how you would classify it. (But why bother if it doesn't contribute to the understanding?)

 

[sysprog]

The following referenced and quoted article probably isn't what PF means by 'B' level (it's probably mostly 'I' level), but it might be edificational to those who are skeptical regarding the possibility of high-energy EMF producing 'gravitational effects' -- in this lecture, Feynman, after his customary friendly introduction, transits to arguing that all mass can be viewed as EMF, then shows how that argument fails, then goes on to show some of what remains to be discovered -- (from: http://www.feynmanlectures.caltech.edu/II_28.html):

28–3 Electromagnetic mass

Where does the mass come from? In our laws of mechanics we have supposed that every object “carries” a thing we call the mass—which also means that it “carries” a momentum proportional to its velocity. Now we discover that it is understandable that a charged particle carries a momentum proportional to its velocity. It might, in fact, be that the mass is just the effect of electrodynamics. The origin of mass has until now been unexplained. We have at last in the theory of electrodynamics a grand opportunity to understand something that we never understood before. It comes out of the blue—or rather, from Maxwell and Poynting—that any charged particle will have a momentum proportional to its velocity just from electromagnetic influences.

Let’s be conservative and say, for a moment, that there are two kinds of mass—that the total momentum of an object could be the sum of a mechanical momentum and the electromagnetic momentum. The mechanical momentum is the “mechanical” mass, $m_{\text{mech}}$, times $v$. In experiments where we measure the mass of a particle by seeing how much momentum it has, or how it swings around in an orbit, we are measuring the total mass. We say generally that the momentum is the total mass $(m_{\text{mech}}+m_{\text{elec}})$ times the velocity. So the observed mass can consist of two pieces (or possibly more if we include other fields): a mechanical piece plus an electromagnetic piece. We know that there is definitely an electromagnetic piece, and we have a formula for it. And there is the thrilling possibility that the mechanical piece is not there at all—that the mass is all electromagnetic.