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My thought on double slit experiment

  1. Jan 13, 2012 #1
    first of all: I take the opportunity to introduce myself and to say hello to every member of this forum.

    now. I'm not a pro-physicist: I'm a programmer/3d graphic artist/musician/and everything else curious; so go easy on me :)

    I was seeing a BBC's documentary about "what is reality" and when they was talking about the double slit experiment after a while I tought: what about if light would be indeed a wave and the object that receive the light gets resonant to that wave?
    shouldn't this explain why light produce a stripe between the "only-2-expected" ones?

    I would also wish to know how the photon/electron impact position gets detected and if it is the same method that cause the "extra" middle stripe phenome to stop

    I know: let do physic to physicist... but that's also my own world and I'm just curious :)
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  3. Jan 13, 2012 #2
    Well actually sometimes object do 'resonate' because of light striking it. That is for instance why the sky is blue! light hits all sorts of molecules and atoms in the atmosphere they absorb the white sunlight and then resonate and produce blue light when resonating! There are countless other examples actually.

    However the stripes are not caused because of this, by which I mean the fact that there are not just two but a whole lot of stripes. The idea is that waves come together and cancel eaach other out at some points while they amplify each other at other points. This concept is also sometimes used (I think don't pin me down on this) at noisy stuff (like ariplane engines) they produce another sound that is slightly of phase with the first one and together they (partly) cancel out. So making noise to reduce noise. This is of course related to the reason why you should carefully place you steroeboxes.

    Anyway the thing about the double slit epxperiment is exactly that everyone thought electrons where particles (they behave like little spheres), but creating more than two stripes like that is characteristic for a wave. The really mindboggling thing about it is that they actually produce two stripes if you're watching them but a whole bunch if you're not watching (as they pass through the slits).

    So this suggests htey are both particles and waves. In classical physics this is not okay but in quantum physics it's not so bad.
  4. Jan 14, 2012 #3
    and what about if they were like bullet shoot on a thiny foil? they would actually be particles but produces a wave effect. so when you look at them they are particles but the seen effect is wave... could this be an explanetion?

    and about the noisy stuff: I confirm that. I read that armonic/opposite wave are also used for headset for jackhammer
  5. Jan 14, 2012 #4


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  6. Jan 15, 2012 #5
    I looked at that material but it doesn't invalidate my thought: if i'm right using a source light with a frequency in a slit, armonic to another light in another slit on a surface, the interference stripes would show a sum of those frequency.
    for example: shooting in the first slit a 700nm (red) "wave/particle" and shooting in the first slit a 470nm (blue) "wave/particle" should produce a 420nm (purple) resonant stripe. (if I'm right)
    I also looked at the feynman's and heisenberg's microscope that are used to detect wich way the photon pass... they seems to be a lot obstructive! and I don't understand why they sometimes use to shoot electron instead of photons.
  7. Jan 15, 2012 #6

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    Let's go back to the basics - if I shine 700nm and 470nm light together at the same spot, it won't reflect back 420 nm light. "Red plus blue makes purple" is a statement about human perception and not one about light.
  8. Jan 15, 2012 #7
    in fact I said "for example" because I don't actually know what is the result of shining two different wavelength on the same spot. anyway I wouldn't do that. I actually think that shining two different armonic wavelength in each slit (so hitting different spot) would produce a sum of those wavelength as middle intereference. if so: couldn't this proof that the middle stripe is produced by the resonance of the surface?
  9. Jan 15, 2012 #8


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    The diffraction at the slits does not change the wavelength of the transmitted light.
  10. Jan 16, 2012 #9
    but what's the resulting frequency of the interference wavelength using different wavelength at the source? but first off: using 2 different lightsource (one for each slit) still produce interference? or maybe polarize the shined light only in one of the two slit to obtain an armonic wave and to see the resulting wavelength of the interference?
  11. Jan 16, 2012 #10


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    You cannot use 2 different light sources for each slit. Each light source MUST be able to go through both slits. This requires the slits be spaces very close together. Furthermore, the double slit experiment has done with SINGLE photons, with the result being that there is still an interference pattern.

    I'm not 100% sure, but I believe using two different wavelengths simply results in two interference patterns. One that matches the 700nm and one that matches the 420nm light. The different sources do not interfere with each other. Someone correct me if I'm wrong.

    What experiment are you referring to?
  12. Jan 16, 2012 #11
    I know. if so it wouldn't be a "double slit experiment" but a "single slit experiment".
    It was an example to try to explain what I wish to achieve and how I get to that.

    but waves have to "communicate" if "mixed". one of the main feature of a wave is to "interfere" with another wave (even of different length) of the same nature: radio, sound and so on to produce another wavelength... and being light (at the moment) also a wave it should do so.

  13. Jan 16, 2012 #12


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    I think you are still missing the point, and that is contained in my earlier post and link. Your suggest is not compatible with the single-particle interference. In other words, if I shoot one photo at a time, one electron at a time, etc.. what "wave" is "resonating" here?

    The double-slit patterns that we know and love are due to the particle "interfering with itself"! That is what it means as single-particle interference! This occurs whether you do a double slit, whether you have brag reflection off a crystal, or when you have superconducting current interference as in a SQUID! In other words, this is governed by a more general principle which I don't think you've realized or understood.

  14. Jan 16, 2012 #13


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    Two comments: Waves from different sources will only interfere if they are synchronized and therefore phase-stable. This is possible, but achieving that is a major pain. Even if you realize such a scenario, the interference of waves of different wavelengths does not create waves of a new wavelength. The intensity pattern gets redistributed in space and you may get an additional beating pattern in time, but all of that is just a linear superposition of wave amplitudes for waves of two different wavelengths. Interference does not change wavelengths, neither in the optical domain, nor for radio waves.

    They want to do it at the single-particle level. Getting single electrons is not that complicated. Getting single photons is a major pain.

    Indeed, I second ZapperZ's suggestion and suppose you should read up on and understand single-particle interference first. Any basic experiment on it rules out your scenario of producing different wavelengths in interference.
  15. Jan 16, 2012 #14


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    You may be confusing the two uses of the word 'interfere'. Unwanted received signals are referred to as interference but this has nothing at all to do with the mechanism of Wave Interference.
    Wave interference only works when there are waves of precisely the same wavelength, arriving at a point, having taken a number of different paths. Cancellation and augmentation in particular regions can only occur consistently when the phase relationship between the arriving waves is unchanging - that requires identical frequencies.
    In optical experiments, this has to be done using a single light source and splitting it in some way. Radio Wave interference can be achieved using two independent sources because it is fairly easy to produce identical frequencies (to within a tiny percentage of their frequency, say on part in 10^10).
    Wave interference can take the form of standing waves and resonances in wires etc.. In those cases, it is perhaps more obvious that identical wavelengths are involved.

    There is one other proviso and that is the medium of propagation should be linear, so the fields / displacements add arithmetically and don't for instance, 'limit', which would produce new spectral products (beats, etc.) to confuse the simple situation. We don't normally consider this, though - at least first time round.
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