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Double Slit In The Round?

  1. Sep 7, 2015 #1
    Has the double slit experiment ever been performed 'in the round' ?

    I mean within a circle, a fence, all around the source?

    Electromagnetic radiation is promulgated in three dimensions, is it not?

    To be fired like a bullet in one direction requires deliberate artificial constraint.

    I'd have thought experiments would not only be performed 'in the round' but 'in the sphere'.
  2. jcsd
  3. Sep 7, 2015 #2


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    How would you like to orient the slits for such an experiment ?
  4. Sep 7, 2015 #3
    Various. How about starting with four sets, N,E,S.W. ?
  5. Sep 8, 2015 #4


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    Wouldn't that make it an octuple slit experiment ?
  6. Sep 8, 2015 #5
    I guess it would.

    I wonder where the photon would be? Electromagnetic propagation is spherical isn't it? A pulse goes out in a sphere. What happens then? Where do we find a discrete photon then?

    And when we are dealing with discrete photons they are firing them at double slits. What do they mean by that? I never see any explanations in detail about that. Obviously not a problem, not a matter of any concern to those in the field, the scientists and physicists, mathematicians, etc. I realise that. It's only my curiosity.

    They aim them. Well where do they aim them? At this slit or that slit? Or between the two slits? They send a 'spray' of them? How could that be when they send them one at a time? Possible. I can see that. Is that what they do?

    What happens when you stop aiming and stop making discrete photon? What's a photon anyway I wonder when I come to think of it.

    I accepted the idea easily enough years ago because I was thinking of 'rays of light' like light from a torch. Beams. Rays.

    But now I know that 'light' is a misnomer. Light being merely a small part of the electromagnetic spectrum and electromagnetic emissions not being normally - that I know of - directional singular 'corpuscular' emissions but instead omnidirection waves.
  7. Sep 8, 2015 #6


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    I was teasing a little bit, sorry. Your wondering about this is praiseworthy.

    It is correct that electromagnetic 'disturbances' propagate in all directions. Good old Huygens principle. A pulse goes out in a sphere as you put it. But that's not how a 'discrete photon' comes into the world. That happens when an electromagnetic interaction takes place, e.g. an electron changes orbit in an atom. And then the photon (I don't know what a photon is and I mistrust everyone who claims to know. But we can describe and discuss the behavior of photons as if they were close friends :smile:) - a photon can be described as a wave packet with a polarization, a direction, momentum, an energy and frequency and what have you. All with a high but finite precision (all except the speed which we define to be c if in vacuum).

    Studying the behavior of photons taught humanity an awful lot. And studying is best done under the simplest possible, controlled circumstances. Hence the simple single or double slit with diffraction in one dimension. Teaches us about Fourier transforms and a whole lot more. Can be done in two dimensions as well: then you are in the realm of image analysis. Very powerful stuff, but the basics are the same as in one dimension, only applied in two. And from there, Fourier analysis can be done in three or more dimensions just as well, but that requires still more abstract thinking.

    So, for experimenting, teaching, understanding, etc. we start with hurling them photons at slits as if they were tiny baseballs. Can be done with lamps and lenses, or with mirrors ( a laser has two mirrors where the photons (each photon that 'fits'...) bounce back and forth until they escape with a pretty well defined wavelength and direction -- almost ideal for experimenting.

    So accepting the idea of rays, beams, whatever, is a wise thing to do. Questioning why we do that so easily when there is a lot going on underneath is even wiser !

  8. Sep 8, 2015 #7
    Well thank you for that. I can see that you are being very kind and I appreciate it.

    Googling around a bit I quickly learned that I should have googled a lot earlier.

    It seems one requires quite some knowledge before one can know the appropriate quarter for a query.

    I should not have asked such a question in such a forum, I think. But it is done now.

    Can I ask one more, in regard to that quote? So 'ordinary' light doesn't comprise 'discrete photons' ?

    And if each point on a wavefront is the source for a spherical wave and if light waves are comprised of packets - photons - then what happens at the moment of creation of each of these spherical waves? The instantaneous creation of a myriad of packets each of which sets off on its own particular journey along its own vector? Making up a radiating pattern of packets like the seed heads on a dandelion?

    How are they created? Randomly, according to probabilities or in some forecastable pattern?

    How totally wrong is all that?
  9. Sep 8, 2015 #8


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    Ordinary light is definitely a bunch of discrete photons.

    Light waves aren't comprised of packets, but the other way around: A photon can be described as a packet of electromagnetic waves.

    When we talk of light waves we emphasize the wave-like character. Propagation, interference, etcetera. Propagation is in answer to your "what happens at the moment of creation of each of these spherical waves?" when you have the Huijgens principle in mind: all waves spreading out sideways interfere destructively and only the waves in the direction of the propagation vector interfere constructively.

    When we talk of photons, we have the 'particle' picture in mind (e.g. in the photoelectric effect: a single photon can knock a single electron out of a metal - if it has sufficient energy).

    Your "what happens at the moment of creation of each of these spherical waves?" can also be understood in a different way, e.g. with a light bulb in mind. There you do indeed have (the reverse of the photoelectric effect) a very hot filament spewing out photons in all directions !

    But, waves or particles, in both cases we are talking about one and the same thing.

    And this is admittedly a very tough issue to get your head around. The double slit experiment is already allowing a lot of very hard to explain questions: single photons also cause an interference pattern ! So "how wide (in x and y) is a photon propagating in the z-direction" ? Again, there are answers to that, but not so easy ones.
  10. Sep 8, 2015 #9
    I think the best introduction to the layman on these matters is Richard Feynman's little book: "QED: The Strange Theory of Light and Matter".
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