# Thread: deviation of light

1. Can light be deviated by a magnetic ( or electric ) field, or is it only gravitation that can do it?

2.

3. Originally Posted by logic
Can light be deviated by a magnetic ( or electric ) field
Nope.
Light is E.M. radiation.
Originally Posted by logic
or is it only gravitation that can do it?
Yes.

4. Thanks, neverfly, any explanation for that?
Light is E.M., but gravitational field is not. Or is it? not less , anyway, than magnetic field, I suppose.
I suppose there can be no practical evidence for an electric field, but surely there are stars with a huge magnetic field around, no sign of deviation of photons there?

5. It might be easier to re-direct you to reading up Here:
Electromagnetic radiation - Wikipedia, the free encyclopedia

Gravity is not an E.M. field, but what gravity is, exactly, is not yet determined. According to Einstein, gravity is the warping or curvature of spacetime.
According to the standard model (Q.M.), gravity is caused by particles called gravitons.
...Not sure what you mean by 'practical evidence for an electric field.' Since photons are not electrically charged, I have no idea what you are looking for, here...

Our sun has a very large magnetic field. No observed deviations, there.

6. Originally Posted by Neverfly
I have no idea what you are looking for, here...Our sun has a very large magnetic field. No observed deviations, there.
The magnetic field of the Sun is relatively small as compared to the huge field of magnetic stars. I suppose we cannot ditinguish its deviation.
Sure photons are not charged, but likewise gravity. Curvature of space does not account for gravitational redshift.

7. Originally Posted by logic
The magnetic field of the Sun is relatively small as compared to the huge field of magnetic stars.
Like a neutron star?
Originally Posted by logic
Sure photons are not charged, but likewise gravity. Curvature of space does not account for gravitational redshift.
What?
None of this made sense- unless you're saying that Relativity is wrong...

8. Originally Posted by logic
I suppose there can be no practical evidence for an electric field
What sort of evidence are you looking for?

We use electric fields to control the movements of electrons, for example. Or rub balloons and stick them to the ceiling. and form chemical bonds.

Originally Posted by logic
Curvature of space does not account for gravitational redshift.
GR explains gravity (and therefore gravitational red shift) through the curvature of space-time. This has been experimentally measured and shown to match the predictions of GR very accurately.
Pound–Rebka experiment

9. Originally Posted by logic
Can light be deviated by a magnetic ( or electric ) field, or is it only gravitation that can do it?
Yes and no. The "Faraday effect", something that you must have heard about in high school , rotates the polarization plane of light (doesn't change its direction though, like gravitation) in the presence of an em field.
Zeeman effect splits light in the presence of a magnetic field.
Stark effect splits light in the presence of an electrostatic field.

10. Thanks a lot, xyzt, that's something, you have proved that there is interaction between light and a magnetic field. Can you exclude that it can deflect direction when power is 10^11 tesla or so?

11. Originally Posted by logic
Thanks a lot, xyzt, that's something, you have proved that there is interaction between light and a magnetic field. Can you exclude that it can deflect direction when power is 10^11 tesla or so?
10^11 Tesla does not exist.See here.
Even if it existed, you would only get a very strong Zeeman effect. That's all.

12. Originally Posted by Neverfly
Gravity is not an E.M. field, but what gravity is, exactly, is not yet determined. According to Einstein, gravity is the warping or curvature of spacetime.
According to the standard model (Q.M.), gravity is caused by particles called gravitons.
Originally Posted by Neverfly

I disagree. Einstein interpreted the gravitational force as an inertial force and hence gravitational fields only exist in non-inertial frames, or regions of spacetime where the frame of reference may be considered inertial. On the other hand spacetime curvature is another way of speaking of tidal forces as well as altered spatial relations. You can certainly have a gravitational field in flat spacetime. In fact Einstein’s equivlance principle states
A uniformly accelerating frame of reference is equivalent to a uniform gravitational field.

Thus no observer is able to determine by experminents and observations made within his frame of reference whether or not he or she is in a uniformly accelerating frame of reference or a uniform gravitational field. And this includes an acclerated frame in flat spacetime.

Originally Posted by Neverfly
Originally Posted by logic
The magnetic field of the Sun is relatively small as compared to the huge field of magnetic stars.
Like a neutron star?
Originally Posted by logic
Curvature of space does not account for gravitational redshift.

What?
None of this made sense- unless you're saying that Relativity is wrong...

He’s wrong in the sense that if an observer is in a curved spacetime then no matter which ocally inertial frames of reference they are in their extent in spacetime is finite. Far enough out there will be a gravitational field present. In those regios a photon propagating through that region of spacetime (where it undergoes a change in gravitational potential energy and therefore a change in the kinetic energy of the photon and thus the frequency of the photon will change.

However, while spacetime curvature is a sufficient condition for gravitational redshift it is not a neccesary one. In fact one of Einstein’s first calculations of gravitational redshift was calculated in an accelerated frame of reference in flat spacetime! This is something people confuse a great deal of the time. However the literature is clear on this point. In fact there was an article in the American Journal of Physics on this point.
Does a gravitational red shift necessarily imply space-time curvature?, G.E. Marsh and C. Nissim-Sabat, Am. J. Phys. 43(3), March 1975

13. Originally Posted by xyzt
10^11 Tesla does not exist.
I quoted from here: Magnetar - Wikipedia, the free encyclopedia

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