# Amount of a magnetic force to alter the trajectory of a photon

1. Jan 16, 2012

### ectro

hello, I was just thinking since a photon trajectory is affected by a magnetic force.then I would like to know how much force does it take to do just so.

2. Jan 16, 2012

### Bobbywhy

ectro, Welcome to Physics Forums!

As far as I know a photon's trajectory will not be affected by a magnetic field.

Can you give us some reference for your source of this idea?

3. Jan 16, 2012

### ectro

well its a built up conclusion from various text books.
if does not then what would effect its trajectory ?

4. Jan 16, 2012

Staff Emeritus
A photon's path is not affected by a magnetic field. If you think your texts say otherwise, please give us a citation.

5. Jan 16, 2012

### Drakkith

Staff Emeritus
Gravity would, along with interactions with just about any material.

6. Jan 16, 2012

### meldraft

Or, put differently, out of all the fields we know, only the gravitational field can change the trajectory of a photon. And, of course, as suggested, also interactions with matter (diffraction, refraction, reflection)

7. Jan 16, 2012

### ectro

Thanks to whom replied and corrected my conclusion. Now since its affected by gravity then how would I if possible to create an artificial field of gravity

8. Jan 16, 2012

### Drakkith

Staff Emeritus
Artificial Gravity is not possible according to our current knowledge.

9. Jan 17, 2012

### ectro

10. Jan 17, 2012

### Drakkith

Staff Emeritus
Nope.

11. Jan 17, 2012

### trueacoustics

Artificial gravity can be simulated in a zero gravity environment through rotation. However, an actual gravitational field cannot.

12. Jan 17, 2012

### mrspeedybob

Continuous acceleration of your frame of reference. If you were in a rocket with the engine always on you would feel a gravity-like force pulling you toward the rear of the rocket.

13. Jan 17, 2012

### Drakkith

Staff Emeritus
I think the OP is asking about something that would change the path of light like a normal gravitational field would. This would not.

14. Jan 17, 2012

### mrspeedybob

If I were in the rocket I would observe the light to have a curved path, just like gravity would produce. The rocket reference frame is no less valid then a frame in which the light travels straight.
The principal that gravitation and acceleration are equivalent is the foundational idea of GR. At least that is my understanding.

15. Jan 17, 2012

### Drakkith

Staff Emeritus
But we are not talking about how it appears, but about actually changing the path of the photon. This requires a real gravitational field.

16. Jan 17, 2012

### mrspeedybob

I'm not talking about illusion. If I am on the rocket the beam of light is actually curved. Furthermore this curvature causes it to take a longer path from point A to point B which it will take at the same speed as it would a straight path, thus it will take longer. So there we have time dilation, just like a "real" gravitational field would cause.

The way I understand relativity it is not about describing illusions, It's about describing reality which can be different between 2 frames of reference. A path can be both curved and straight. They are not mutually exclusive concepts.

17. Jan 17, 2012

### Drakkith

Staff Emeritus
I'm not talking about the difference between two reference frames, I'm talking about changing the direction of light. This change would appear in BOTH frames.

18. Jan 18, 2012

### DrDu

In matter this can be observed: A magnetic field can change the index of refraction in certain directions which leads to a refraction of the light passing through that material . Search wikipedia for Faraday and Kerr effect.
I am convinced that sufficiently strong magnetic fields will theoretically also interact with light in vacuo.
However, these effects from quantum electrodynamics are extremely small and have not jet been detected experimentally.

19. Jan 19, 2012

### ectro

so we would need a very powerful force fo gravity to alter the path if the light can we use magnetic force as such.

20. Jan 19, 2012

### Drakkith

Staff Emeritus
I can't understand your post. Could you try to use a little better grammar?

EDIT: Ok, I think I understand after a minute of going over it. I belive a very very stong magnetic field can Polarize the vacuum, but this is not the same as gravity altering the path of the light. Short answer is no, you cannot use a magnetic force to alter the path of light.