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Double-Slit Experiment Variations List

  1. Sep 2, 2014 #1
    Hi all, first post and an amateur enthusiast here. I'm a 33 year old programmer who takes an interest in the mysteries of quantum mechanics and trying to nurture my own little theories.

    I've came across variations of the double slit experiment and was wondering if there's such a resource that lists all of the variations that have been attempted? Purely for me to get a more rounded idea of what's been attempted and what was sought.

    - One that has the detectors perpendicular to the slits
    - One where the emitter shoots particles at a slower velocity
    - One where the detector is not flat and/or solid

    Thanks and regards
  2. jcsd
  3. Sep 2, 2014 #2
  4. Sep 2, 2014 #3
    Thank you for the follow-up and perhaps I can ask a question that is still relevant to the thread.

    Do you know if there been such an experiment where the detectors are designed to measure 'everything' but the slits? I guess I'm asking along the lines of the 'weak observation' approach, such as having detectors perpendicular to the slits, to begin with, and gradually moving them away.

    Apologies if I get the terminology wrong, my understanding is that initially the wave function would collapse when it's detected on the other side of the slit, but I'm unsure whether increasing distance and at what distance the detectors would no longer register and affect the movement of the wave/particle.
  5. Sep 3, 2014 #4


    Staff: Mentor

    Here is a correct Quantum analysis of the double slit experiment:

    Once you understand it its fairly easy to figure out the results of variants.

  6. Sep 3, 2014 #5
    I'm not sure what you mean by "detector perpendicular to the slits", or by a "flat or solid detector".
    I think the point here is that one always reads of the double-slit experiment in a rather "abstract" way, which while allows you to appreciate the strangenesses of quantum mechanics without being stuck in all of the technical details involved in a real experiment, at the sime time can can make you forget that you are talking of an actual, physical experiment here, i.e. of something real. Even more, of a kind of experiment that you could actually replicate without any complicated laboratory equipment (just think that the original Young's experiment was in the 1803, and he wasn't even really a physicist but a medical student). You can actually replicate a version of this experiment using solar light, a common mirror, and a needle.

    Said that, back to your question:

    1) it does not really matter how the detector is placed. The experiment can be replicated varying all the details you want, as long as the "key elements" are there. The point is really that if the electron (or the photon, or whatever particle) can reach the target in two ways, you will see (given the suitable conditions of course) the interference pattern which is explained saying that the particle actually "traverses both" the paths. If only one path can be used (for example because you placed a detector in one or both the slits, forcing the particle to "decide" one or the other) no interference is seen.
    As long as you implement this concepts, you can change all the experimental details you want (and I'm pretty sure all the conceivable variants have been tried by now).
    Another thing I want to point out here is that even talking of "one or two" paths the particle can take across the slit/slits is not really exact. Even when only one slit is used there are an infinite number of ways the particle can cross it, and you still have your interference pattern in the form of a diffraction pattern.

    On this regard note that the original Young's experiment only used a single slit. See also all of the single slit diffraction effects of light (e.g. Arago spot, Airy disk) the concept of which is in principle still valid for any particle.
    About the "many paths" concept a very very nice divulgative (at least in principle) book by Feynman on the subject is QED

    2) The velocity does not really matter here, aside from the experimental difficulties of detecting electrons "too slow" or "too fast". However the intensity of the beam is a quite relevant parameter. The intensity is connected with the number of particles crossing the slit/slits in a given amount of time, and makes the difference between seeing single detection events on the screen or seeing interference patterns. (see also this question on a similar subject).

    3) Well... do you know of a flat, not solid camera? Same thing for detectors :).

    A few other interesting (at least for me) basic experiments, in some way or the other correlated to the double-slit one: Diffraction Grating, Hanbury Brown and Twiss.
    Last edited: Sep 3, 2014
  7. Sep 3, 2014 #6
    Thank you to both of you for the replies, good reading and I shall look at the links in closer detail.

    >note that the original Young's experiment only used a single slit

    This probably is more relevant to my current thoughts... ultimately I'm not interested in "which hole did it go through", perhaps more interested in potential manipulation of the probability distribution and also wondering whether the wave collapse is a boolean event caused by simple yes/no parameters "is this other particle going to share information with me".

    I shall read to formulate some better questions...
  8. Sep 3, 2014 #7


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    Assuming I understand your question: You can continuously vary the amount of information you receive about "which slit" between 0 and 100%. Said another way: you can vary between the wave and particle views continuously (i.e. anywhere between one and the other); or your knowledge of non-commuting observables in a similar fashion. There is no particular border.
  9. Sep 3, 2014 #8
    Thank you for posting. I'm glad that a neophyte like myself can post something and not be rubbished for lack of knowledge :)

    Am I right in making the statement that any interaction at all will result in the wavefunction collapse? Or perhaps it is the more abstract idea of any interactor that can derive information from contacting the wave/particle causes the resultant collapse?

    I'm curious about the vicinity of the interactor particle... does it simply have to be "close enough" in order to exchange information?

    TBH in my basic interpretation and understanding, I'm thinking at Planck scales there is something deterministic going on, but is immutable to measurement, much like trying to compute something in between the 'ticks' of a processor.
  10. Sep 3, 2014 #9


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    1. No, that is not correct at all. You can do all kinds of things and not collapse the wave function. For example, placing polarizers completely in front of the slits that are parallel does NOT collapse things. But if they are perpendicular, they do collapse. Good luck figuring that one out using a physical particle model. :smile:

    2. Are you familiar with Bell's Theorem?
  11. Sep 3, 2014 #10
    I read your home page last night when I signed up to here and read a few of the more popular thread and eye catching titles. I am familiar with Bell's Theorem in its role but clearly I lack a cohesive understanding of the big picture... or successfully applying what I've read into fact:) Still, there is time.

    So as it goes, he proves that there are no hidden variables, contrary to what EPR (or Einstein) believed...if my understanding is correct.

    I was thinking that there are finite states to a particle/wave and that perhaps that could define the way in which it will interact wth other matter. i.e. 8 states could be represented in a 3 dimensional cube 2x2x2 of planck distances.

    I was thinking along the lines of entanglement and how the "spooky action at a distance" could simply be that any measurement was already pre-determined by its location in that 'planck space', and that the property of entanglement involved a correlation of positions between two particles.

    If I ever come across a retirement amount of money the first thing I'll be doing is getting a degree in this field... it truly blows my mind in amazement.
  12. Sep 3, 2014 #11


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    :smile: The more you learn about this stuff, the cooler it gets.
  13. Sep 3, 2014 #12


    Staff: Mentor

    In the modern view only a specific type of interaction causes 'collapse' - its a kind of entanglement called decoherence:
    http://www.ipod.org.uk/reality/reality_decoherence.asp [Broken]

    Collapse was in inverted commas because it really isn't part of QM - without going into the details.

    In modern times collapse is replaced with the problem of definite outcomes:

    The so called measurement problem has a number of parts - they are all explainable these days, except the most difficult one - the problem of definite outcomes. Other assumptions, that varies with interpretation, are required for that.

    Last edited by a moderator: May 6, 2017
  14. Sep 3, 2014 #13
    Thank you. Lots of reading for me.
  15. Sep 4, 2014 #14
    Bohmian mechanics and pilot wave theory seem to line up with my ideas, so that'll be one of my initial lines of enquiry. thanks all.
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