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Thread: the double slit experiment in the '50's

  1. #1 the double slit experiment in the '50's 
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    I'm doing a bit of research about the double slit experiment for a writing project. I'm a scientist, so I have little tolerance for handwavy science in entertainment. My question is, if someone in the '50's where interested in performing this experiment, how might they go about it? Thanks in advance


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    Forum Junior c186282's Avatar
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    To do a double slit experiment one wants a spacial and temporal coherence source. But as you know in the 50's one can not just pull out a laser pointer.

    To get spacial coherence you can shine light through a pin hole. To get temporal coherence you must pick a narrow wavelength band.

    One could use a gas discharge. Image the light through a prism (or diffraction grating) to pick out one line from the discharge. Then image through a pin hole. The light coming out will have a fair spacial and temporal coherence which could them be used in a double slit experiment with film and a long integration time in a real dark room. The contrast ratio will not be as good as we see with a laser and the number of orders out to the sides will be less. Not just because they are really dim but because the path length diffidence will be large compared to the coherence length.


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    Isn't the point of the experiment to show the effect of the observer? Interference pattern when left alone, two bands when the electron detector is working? I thought you had to have some way of sending single particles through the slits...
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    We're talking about the photon version of the double slit experiment, right?

    It's not an observer effect. The most obvious result of the experiment is that light is a wave. The more subtle result is that light is also a particle (this is better demonstrated with the photo-electric effect, though).

    See wiki.

    You don't have to be able to send single particles through the slits, but if you are able to, you'll still get a diffraction pattern, which is neat/insane. The basic version just involves light with the same wavelength (most easily produced by lasers, but they didn't have those in the 50s)...
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    A remarkable result follows from a variation of the double-slit experiment in which detectors are placed in either or both of the two slits in an attempt to determine which slit the photon passes through on its way to the screen. Placing a detector even in just one of the slits will result in the disappearance of the interference pattern. The detection of a photon involves a physical interaction between the photon and the detector of the sort that physically changes the detector. (If nothing changed in the detector, it would not detect anything.) If two photons of the same frequency were emitted at the same time they would be coherent. If they went through two unobstructed slits then they would remain coherent and arriving at the screen at the same time but laterally displaced from each other they would exhibit interference. However, if one or both of them were to encounter a detector, time could be required for each to interact with its detector and they would most likely fall out of step with each other--that is, they would decohere. They would then arrive at the screen at slightly different times and could not interfere because the first to arrive would have already interacted with the screen before the second got there. If only one photon is involved, it must be detected at one or the other detector, and its continued path goes forward only from the slit where it was detected.[7]
    Wasn't this predicted from quantum theory, but only tested relatively recently?
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    Wasn't this predicted from quantum theory, but only tested relatively recently?
    It was both; quantum mechanics required this, and it was tested, oh, about twenty years ago.
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    Forum Junior c186282's Avatar
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    Here is a link to a set of posts that may help with the understating of a double slit experiment. I my reply there is a link to a double slit explication video. It is kind of corny but good.
    Other post

    Thomas Young did his double slit experiment in 1801.
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    So, I'm interested in bit of the experiment that shows how observation collapses the electron wave function. To do this, one must observe electrons. Was that possible in the '50s? If not, is there some other way to go about this?

    I'm not trying to be dense - the DS experiment seems to work two ways. One just shows the interference pattern, which is fairly easy. Showing that you don't get the pattern when the particles are observed seems more complex.
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    Sodium vapour lamps emit a nearly monochromatic light. I remember using it for some physics experiment, but I'm not sure which. It might not work.

    http://en.wikipedia.org/wiki/Sodium_vapor_lamp
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