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Magnetic and Electric Fields in Gravity

  1. Jan 16, 2010 #1
    Is there any effects on electric fields or magnetic fields in a Gravitational field?

    I know that electro-magnetic waves(photons) are effected from the bending of space and time, from gravity.

    however i was just wondering how magnetic fields or virtual photons respond to gravity.

    Any insight would be appreciated.
     
  2. jcsd
  3. Jan 16, 2010 #2
    The best example of the gravitational effect on photons is the Pound and Rebka Mossbauer Effect experiment in the physics building at Harvard ~1959, that verified the gravitational redshift of the 14-KeV photons in the cobalt-57 decay. See
    http://en.wikipedia.org/wiki/Pound–Rebka_experiment
    When the photons fell from the top to the bottom of the physics biulding, they were blue-shifted by a measurable amount. I am not aware of any gravitational effects on either magnetic or electric fields.
    Bob S
     
  4. Jan 16, 2010 #3
    I don't understand this part of BobS's answer.

    Anything carrying energy (or having mass, or presssure) is affected by gravity according to General Relativity, even heat. We can quibble about terminology since it's energy 'density' that enters general relativity, but whatever you call it, photons and magnetic/electric fields have it.

    You can search here on physics forums and get conflicting answers. You can do so to gain perspective. My example is gravitational lensing...the bending of light (photons, electromagnetic waves, whatever you want to call it) as light (visible or otherwise) passes planets. Seems like black holes "locking in" all electromagnetic waves are another example.

    This thread includes a reference to a paper discussing the gravitational field of photons

    https://www.physicsforums.com/showthread.php?t=366542&highlight=photons+in+gravity

    That paper is here: http://www.springerlink.com/content/b87v628331668g2r/fulltext.pdf

    I'm not specifically endorsing this paper, but I found it useful and interesting as one point of view.



    Virtual photons, as far as I know, carry no average energy relative to an observer in an inertial rest frame...once they do I think they become "real", as at an horizon for example which separates one of the virtual pair from an observer. But this IS frame dependent, see Unruh (william) radiation. An accelerating observer DOES measure temperature in "empty" space, so there IS energy present relative to an accelerating frame.
     
    Last edited: Jan 16, 2010
  5. Jan 16, 2010 #4
    "I am not aware of any gravitational effects on either magnetic or electric fields."
    I was referring to dc electric or dc magnetic fields, not electromagnetic radiation.
    Bob S
     
  6. Jan 16, 2010 #5
    ok thanks for responses, i was curious about whether light actually created its own gravitational field.

    As for magnetic and electric fields, i know it takes energy to create them, so i am guessing this would have to cause a mass increase in the object containing the field.

    so there is no actual energy in the field that can pinpointed in a specific place and time, so it can't be bent by gravity.
    but if gravity bends space and time, then i would assume that an electric or magnetic field would bend with it.

    this is what i was confused about, but i thought someone might have conducted and experiment or something to clear things up.
     
  7. Jan 16, 2010 #6
    Still don't get it...is not an electric field an electric field??
     
    Last edited: Jan 17, 2010
  8. Jan 16, 2010 #7
    electromagnetic radiation comes from an accelerating electric charge.
    it is the acceleration of the charge that emits photons.
    It is different from an electric field from a stationary charge.
     
  9. Jan 16, 2010 #8
    I think one time in a relativity thread someone said that a magnetic field can create gravitational field , so a B field would have to be affected by gravity . But don’t quote me on that . a magnetic field would haft to have an effect on space-time, And I imagine that a strong magnetic field would slow down time just like a strong gravitational field would .
     
  10. Jan 16, 2010 #9

    diazona

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    Electric and magnetic fields do make a contribution to the stress-energy tensor, so sure, they should theoretically produce some gravity... although I would think that effect would be tiny compared to the gravity of matter.

    Regarding the original question, gravity should have some influence on the possible EM field configurations. The covariant derivative in the relativistic form of Maxwell's equations depends on the curvature of spacetime. But again, I'd expect the effect to be pretty small, except in the vicinity of a black hole or something like that.
     
  11. Jan 17, 2010 #10
    sure its small but it's there .
     
  12. Jan 17, 2010 #11
    Both statements are false. (Am not trying to be harsh, just make the poster understands these statements contradict what has been posted.)
     
  13. Jan 17, 2010 #12
    You cannot have an electric field without a magnetic filed, and vice versa....what is observed depends on whether the observational frame is stationary or moving. What appears as a magnetiuc field to one observer may appear as an electric field to another observer.
     
  14. Jan 17, 2010 #13
    Right i should have said E and B field .
     
  15. Jan 17, 2010 #14
  16. Jan 17, 2010 #15

    Andy Resnick

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    In addition to several good posts, I just wanted to bring up the idea of the gravitomagnetic field

    http://en.wikipedia.org/wiki/Gravitomagnetism

    which should not be confused with a direct coupling between gravity and electromagnetism (see the 'fringe science' paragraph at the end of the above article).
     
  17. Jan 18, 2010 #16
    I am seeing the first statement in a different light today....and I now think it's ok...an example might be magnetite where magnet spins are all oriented by an external magnetic field, and are in a slightly higher energy state....???
     
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