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Phase cancellation of light - Is it possible to make light disappear?

  1. Jan 2, 2012 #1
    Based on the principle of noise cancelling headphones, I was wondering if it would be possible to do the same thing with light? I.E. If you had a light source and then introduced a device that output a light wave with the same amplitude but with inverted phase, would the interference cancel out the light source and create darkness?

    I'm a writer working on a piece with some science fiction elements, so I'm mainly interested in the theoretical possibility rather than actually making something. You can assume that any required technology that we don't have could exist.

    I'm not a physicist so please don't just reply with - oh that's not possible due to [insert scientist here]'s Principle. I won't know what you mean. But please if you have any thoughts on how this could be done theoretically or actually, let me know. Thanks
     
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  3. Jan 2, 2012 #2

    Vanadium 50

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    You don't get to ask a question and also to provide the answer. It can't be done. I know you don't want to hear that answer, but nonetheless, it is the truth.
     
  4. Jan 2, 2012 #3
    I wasn't providing the answer, I was just asking people not to dismiss the idea without explanation. Like you did.

    I'm happy to hear people say no it isn't possible. There are many things we don't consider possible but then later on someone solves it. And any answer will be limited by current scientific knowledge, whereas science fiction is not.

    But with infinite resources and technology we can't yet imagine, is there any current knowledge that could be the basis for this idea?
     
  5. Jan 2, 2012 #4

    Vanadium 50

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    Actually, you specifically asked for no explanation.

    Your argument that since you don't know enough to see that it's impossible therefore it must be possible is illogical. And even though you have asked not to get an explanation, I am going to give you one anyway. If you cancel the light everywhere, you will have the same outcome as if you put an opaque object in front of the light source. That's what it means to cancel the light everywhere. Since obviously, that's not what you want - otherwise you wouldn't need a technological development - whatever it is that you do want is impossible.

    "Two plus two continue to make four, despite the whine of the amateur for three and the cry of the critic for five." (J.M. Whistler)
     
  6. Jan 2, 2012 #5
    Light and sound do not propagate the same way, so you cannot find a wavelength of visible light that will cancel out another wavelength, as they don't interfere with each other the way sound waves do.

    Sound requires a medium to travel through...air typically for our purposes. This means you can generate a wave that will vibrate out of phase and "cancel" the unwanted noise, etc.

    Light can be transmitted through a vacuum, and there are no out of phase lights that can be out of phase with it...as there are no vibrations in the air that are produced, etc.

    You may need to continue to use an ordinary light switch for now...this will cancel the light for most people. :D


    If for science fiction purposes, you can try having a media we don't know about as being the media light is transmitted through, the way air or water, etc, work for sound. You can then have your mechanism follow accordingly.
     
  7. Jan 2, 2012 #6
    Thankyou Tea Jay for your thoughtful and helpful response. It is interesting to hear about the differences between light waves and sound waves; the fact that light waves don't interfere with eachother sounds like the main reason why light cancellation wouldn't work.



    Vanadium 50 please cease posting in this thread and go "mentor" somewhere else.
     
  8. Jan 2, 2012 #7
    It can be done in principle but in practice the frequencies are simply too high for any coherent electronics to function, and the wavelengths are simply too short for antennas on the wavelength scale to be anything but fragile.

    The physics of it is quite straitforward though.
     
  9. Jan 2, 2012 #8
    The photons either pass through each other or form mass. If they form mass, they did not disappear. If they pass through each other, they only cancel their phases so as long as they overlap that way. Once they already passed each other, they are separating from each other and no longer cancel their phases.

    Photon phase cancellation exists, but it is never permanent. And to be more precise about it, not everything about the photons gets cancelled. Cancellation of phases doesn't mean cancellation of their existence. Light doesn't "disappear".

    Short answer: No.
     
  10. Jan 2, 2012 #9
    Using only passive means the answer is no. But using electronics the answer is yes.

    Your equipment would absorb photons and create new ones. It's not difficult.
     
  11. Jan 2, 2012 #10

    Vanadium 50

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    Of course they do. Waves are waves and interference is interference. Sound and light interfere in exactly the same way.
     
  12. Jan 2, 2012 #11
    LOL - I meant in his context of an explanation w/o an explanation.

    For example, given his context, probably to have a science fiction device that can "cloak" etc, it would emit such an interference to cancel out the light analogous to the way noise cancelling headphones do for sound, etc.

    What would "out of phase light" be that would therefore cancel out the visible light if they are exactly the same, in the context that he is going for?

    IE: Sure, they can interfere, and I winced a little due to oversimplification, but not the way he wants them to.

    Again, I was assuming he was going for invisibility to hide a person or ship, etc.
     
  13. Jan 2, 2012 #12
    To clarify, the effect I am interested in producing would be along the lines of a windowless room with a single light source, and then introducing an electronic device which emits photons in such a way as to "cancel" out the photons from the light source, effectively putting the room into darkness.

    Sorry if I'm oversimplifying or mangling the terminology...
     
  14. Jan 2, 2012 #13
    Don't forget, that when two waves with mediums are interfering, it's not like they interfere everywhere. They interfere destructively only at SPECIFIC nodal points, meaning that it wouldn't work to thrust an entire room into darkness.
     
  15. Jan 3, 2012 #14
    This is only the case with certain source distributions. In general it is not true.

    For example, a spherical surface distribution of electric and magnetic currents enclosing the light bulb could completely cancel its emissions.

    The magnetic currents cannot be realized directly but are approximated (mathematically and in the engineering sense) by small electric current loops whose axis is parallel to the surface enclosing the lamp.

    Look up "Schelkunoff's equivalence principle" for the equations behind this.
     
  16. Jan 3, 2012 #15

    Vanadium 50

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    Yes, but let's consider the sort of charge distribution that will cancel an arbitrary (and incoherent) light source - you'd want something like a metal box. Well, in that case, why not use a metal box? Or a wooden box.

    Any scheme you are going to come up with requires the gadget to be in between the eyes and the object. And, by definition, the response of this gadget will be the same as if it were opaque. And we're back to the box.
     
  17. Jan 3, 2012 #16

    nsaspook

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    Use Dark Sucker theory in your book.
    http://www.rogermwilcox.com/darksucker.html
     
  18. Jan 3, 2012 #17
    I have some sympathy for infinity 3000, in PRINCIPLE cancellation is possible....isn't that called interference? What he makes of that is up to him to research and good luck to him and his imagination in his area.
    "two plus two continues to make four, despite the whine of the amateur for three and the cry of the critic for five"
    If J.M Whistler had any background in basic vector mathematics he may have had a different view.
    Pythagaros knew that 2 + 2 could be √8
     
  19. Jan 3, 2012 #18
    You are not looking for a specific change. you are looking for complete change.

    It's easy really.

    Refract all light so that it's either higher or lower than the spectrum of human visibility.

    No calculations are needed.

    It does the job of canceling it out, without actually thinking about it. Now, if you wanted to cancel out specific lights, that would be more fun. Say, cancel all light that is not in the field of vision of an individual.
     
  20. Jun 14, 2013 #19
    You didn't actually think you would receive a positive reply detailing methods and application did you ? I realise my reply is long overdue and will simply tell you why I initially came to ask the same question. Many years ago a Rapier Squadron tracked on radar a US Stealth Aircraft coming into land at a UK Base, the guy in question puzzled by this asked one of the US Officers on station how this was possible, the reply he received was " Son, when that that thing doesn't want to be seen you won't see it" Now then, maybe thats why you won't see a true answer to your excellent and thought provoking question.
     
  21. Jun 14, 2013 #20

    ZapperZ

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    But the physics of the stealth fighter actually isn't that much of a secret. If you read the book "Skunk Works", you'll realize the history of the physics involved, and the fact that it was contained in a rather old russian paper on a particular E&M problem. What is classified is how it is achieved and the kind of material used to turn that into reality.

    That is not the same here. The OP has received several answers that essentially explain why what is trying to be accomplished isn't that clearly obtained based on the physics, not just trying to find a way to achieve it. There's a distinct difference here.

    Zz.
     
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