# Can a light be bent by a magnetic field?

I'm struck with two competing ideas on the question in the title.

• How far can a magnetic field bend light?

A: Unfortunately, the path light takes is not affected by the presence of a magnetic field. Light itself is composed of an oscillating electric and magnetic field, and one very important property of electric and magnetic fields is what we call linearity. That is, if you have two sources of electric and/or magnetic fields, you can predict what the combined field is just by adding the two source fields together. The two fields don’t change each other at all.

• Does electric charge affect the space time fabric? If so, why?

I'm more inclined to consider the latter question and answer as the correct interpretation. Anyway, if anyone could help me out with this conceptualization that would be great, thanks.

• What exactly are you asking? It's not clear the way the question is written. Jun 9 '13 at 3:45
• I think by "ladder" you meant "latter" - anyway I edited it for you Jun 9 '13 at 6:29
• @twistor59 thanks, I was shorted by the "ladder operators " :) Jun 9 '13 at 6:59
• classically, probably never (by superposition principle); but quantum physically(i.o.w. the real world), I have no idea. Dec 25 '15 at 9:54
• You should look up the Faraday Effect. Dec 16 '17 at 3:04

The first link you give the questioner wants to use magnetic fields to turn light in a circle, and is answered correctly .

You are asking about bending. In both of your links the answer exists that the magnetic field with its energy will contribute to the gravitational field about the source of the magnetic field and and might contribute to the observed gravitational lensing, and in that sense the magnetic field will contribute to the bending of light in gravitational lensing.

Think of geodesics. Light follows geodesics, straight if the gravitational sources are very small. The geodesic bends where the gravitational sources are strong ( gravitational lensing) . A strong magnetic field will contribute with its energy to the mass creating the geodesic, and that is all. The effect is very weak because the gravitational "interaction" is very weak with respect to the electromagnetic.

If you were thinking of the single photons comprising light then you have to go to the particle interactions and exchanges, where the rules follow quantum electrodynamics. In this frame the magnetic field will interact with a photon through higher order diagrams,( which means low probability).Photons can be scattered from virtual photons of the magnetic field , and change direction, which can be considered a bent ;if the beam photons have enough energy ( gamma rays) pair creation can appear.

Because these interactions are on individual photons, with low probability, the beam direction which depends on a huge ensemble of photons that comprise it will not change. It will just lose a few photons randomly in direction .

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.

Einstein's field equations state:

$$G_{\mu\nu}=8\pi T_{\mu\nu},$$ Energy-Momentum curves spacetime. We know from things like the Shapiro delay and gravitational lensing that light travels through the curved spacetime of massive objects and the geodesics are "bent".

Now the energy-momentum tensor can have many contributions, sure the most prominent in GR may be the energy-momentum of a perfect fluid: $$T_{\mu\nu}^{(M)}=(p+\rho)u_\mu u_\nu+g_{\mu\nu}p$$ but another contribution comes from the electro-magnetic field: $$T_{\mu\nu}^{(EM)}=\frac 1 {4\pi}\left(F_\mu^{~\lambda}F_{\nu\lambda}-\frac 14 F_{\sigma\lambda}F^{\sigma\lambda}g_{\mu\nu}\right).$$ So the curved space around a massive, magnetized objects (Neutron stars; Pulsars and Magnetars) is described by field equations with an energy momentum tensor which has contributions from matter and electro magnetic fields: $$T_{\mu\nu}= T_{\mu\nu}^{(M)}+T_{\mu\nu}^{(EM)}.$$

For objects with weak fields the EM contribution is relatively small but for objects with strong magnetic and electric fields the EM contribution to the energy-momentum tensor can not be neglected. So let's say for example in a magnetosphere of a strongly magnetized Neutron star (Magnetar) magnetic fields of a magnitude of some $\sim10^{13}$ Gauss have a significant effect on the metric/curvature of space. Photons travelling in such regions will follow geodesics which are affected by the strong EM fields in such extreme regions.

It can't be bent however it can be rotated using the faraday effect. To say you can't affect light with magnets is false. What you can do is bend the medium light travels through and it will follow the path of density. You can bend almost any material with a strong enough magnet.

Light changes direction when there is a switch in the medium through which it travels. For example, from air to water. Probably it is the density of the medium which matters. This is why you see waving images when looking over a hot car on a sunny day. If so, if one would create a sequence of progressively denser mediums, he could divert it considerably from its original trajectory.

Creating such sequence is a challenge. A sandwich of air streams of different temperatures? A sandwich of gases of different weights?

The problem lies in the fact that no one knows what the medium through which light travels in the vacuum of space actually is. We observe light "bending" or changing course in the presence of a massive object like the sun or an entire galaxy. However, we still have absolutely no idea of what the medium is that's being bent. "The fabric of Spacetime is bent" is always the answer. But we have no clue at all what that fabric is or why light follows it. We now know that gravitational waves propagating in space exist. But what do they propagate in? We have no clue whatsoever. It's the ether!

• Welcome on Physics SE. For answers containing "physics" that is clearly not mainstream, I think you should give a bit more of references and arguments to convince people, otherwise not many people are going to pay too much attention. Sep 5 '16 at 20:02
• From a point of General Relativity (GR) we know exactly what is "bent": the four dimensional space time is curved due to energy-momentum. We know that light follows geodesics on that curved space time. Graviational waves are small pertuations of four dimensonal space time. With GR we are able to describe both phenomena consistently and the predictions and calculations based on that theory can explain our observations of both phenomena. "What space time is" is maybe ment as more of philosophical question. But I would not make a statement "It`s the ether!" in 2016 on a physics community.
– N0va
Sep 5 '16 at 21:47

light consists of a magnetic wave and a electric wave.Due to the perpendicular infleunce of electric wave(particle) the magnetic field is very strongly influenced it(the magnetic wave) cannot be disturbed.According to my obsorvation if we are able to avoid the influence the two waves(magnetic and electric)the it is realy possible.One way is out of the two waves one should be less potential than the other one then we surely can bend the light wave.

by Eye-man.

First, the electromagnetic frequency spectrum, (EFS) is just a definition. It represents the change in intensity of the electric field and the magnetic field and they are defined as being at right angles to each other. The frequency is defined as the inverse of the average time from one null to the next or one peak to the next peak in field intensity.

Don’t confuse the properties of light with the properties of light’s interaction with the medium in which it is traveling.

If light had a magnetic property, it would be affected by a magnetic field in a pseudo vacuum. It isn’t.

If light had an electric property, it would be affected by an electric field in a pseudo vacuum. It isn’t.

Light, in fact, is a particle of energy that scientists have called a photon.

The “frequency” property of light is set by the distance between the photons that are emitted in a linear path to the detector, the eye. When the photon strikes the detector (eye), it is believed that its energy releases an electrical charge that the brain can sense and ultimately give an image if enough photons are received.

Light is in fact no more a part of the EFS than sound is.

Sound can be an acceptable analogue for light, where sound is the externala mechanical moving of existing medium particles and light is the generation of particles. Sound has two frequency components when viewed in a singular linear path. First is the spacing of the medium particles (which has a large swing in frequency/period when reaching the detector (ear)). It would be interesting to see if this frequency had any affect on the ear. Second is the spacing of the “pressure’ peaks or nulls. This is what the ear senses and the brain converts.

Keep in mind that the classic right angle sine wave representation of the EFS is just a representation and doesn’t actually exist. It is just to help us understand the properties we can observe. Unconfined light and sound emanations are spherical in nature.

It’s a shame that our science community refuses to admit they were wrong in claiming light was a part of the EFS.

• Frequency is not the distance between emitted photons. A single photon has a frequency defined by $E=h\nu$, which is independent of the distance between it and any other photon. A photon is a propagating perturbation in the background EM field where the strength of the fields oscillate at the given photon's frequency. As a perturbation, it is not affected by the value of the background field. It is, by all definitions, a wave through the background EM field, and as such, it is what makes up the EM frequency spectrum
– Jim
Dec 21 '14 at 20:56