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A Why light beams attract or repel each other even when they don't have charge

  1. Nov 10, 2017 #1
    Hi,

    Can someone please explain as to why light beams attract or repel each other even when they don't have charge. Seems like it behaves like two current carrying parallel wires. There is very little material about this which goes completely above the head.

    Thanks
     
  2. jcsd
  3. Nov 10, 2017 #2

    BvU

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    Is that good or bad ?
    Can you indicate where you got this idea about light beams that attract or repel each other ?
     
  4. Nov 10, 2017 #3

    Demystifier

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    Perhaps he is talking about bunching and anti-bunching in quantum optics. If so, it is caused by specific entanglement between photons in a light beam.
     
  5. Nov 10, 2017 #4

    Mentz114

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    There is a gravitational effect see
    (https://www.physicsforums.com/threads/parallel-light-beams-converge.473694/)
     
  6. Nov 10, 2017 #5

    vanhees71

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  7. Nov 10, 2017 #6

    pervect

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    Parallel light beams going in the same direction don't attract each other gravitationally. Parallel light beams going in the opposite direction do attract gravitationally, about 4x as strong as one gets by a naive calculation.
     
  8. Nov 11, 2017 #7

    Vanadium 50

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    Before we determine why something is true, we need to determine if it is true.
     
  9. Nov 14, 2017 #8
  10. Nov 14, 2017 #9
    Hello,
    I couldn't find any reference to bunching or anti-bunching. I hope this article helps: http://discovermagazine.com/2010/jan-feb/083

    Thank You
     
  11. Nov 14, 2017 #10

    vanhees71

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  12. Nov 14, 2017 #11

    Demystifier

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    Now I get it. This is not a force between light beams as such, but a force between waveguides of the light beams. The light beams induce the dipole moments in the guides, and those dipole moments cause the force. The effect is very similar to the Casimir effect. For more details see http://lanl.arxiv.org/abs/physics/0509073
     
  13. Nov 14, 2017 #12
    THANK YOU VERY MUCH FOR THESE REFERENCES ! Its easier to understand, though i still don't get how the transverse force is measured.
     
  14. Nov 14, 2017 #13
    Thanks,
    They have explained it very well, the original research paper in nature didn't really explain it nicely.
     
  15. Nov 14, 2017 #14
    Basically, if someone is shooting a Really powerful laser at you, you can use a tiny weak laser to deflect it ?!
     
  16. Nov 14, 2017 #15

    Demystifier

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    No.
     
  17. Nov 14, 2017 #16

    Demystifier

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    That's why you need to read theoretical papers, not experimental ones. :wink:
     
  18. Nov 14, 2017 #17
    :thumbup:
     
  19. Nov 16, 2017 #18

    Zafa Pi

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    Expository articles about old experiments can be fun and informative. It's a shame modern experimentalists can't do the same with their own work.
     
  20. Nov 16, 2017 #19

    Demystifier

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  21. Nov 16, 2017 #20

    vanhees71

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    Hm, the introductory textbooks for the experimental-physics course do not too bad a job. Of course, theoreticians, sometimes have problems to understand these books due to a lack of math in these books ;-)).
     
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