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Recreating Thomas Young's Double Slit Experiment

  1. Feb 9, 2009 #1
    I need to recreate this experiment. It doesn't have to be exactly the same, nor does it have to use very high tech and expensive equipment, it just has to be able to demonstrate interference patterns created by light. I cannot find any specifications on how to build this experiment, and I don't want to make any guesses on specifications while building it, so I need some help.

    First and foremost, what kind of light should I use? Then, what dimensions should the slits be, and how far should the slits be away from the light. From what I understand, Thomas Young used photographic plates to capture the interference patterns. Would regular 35mm film work? Lastly, I read that if you tried to use a device to determine which slit a photon went through, the interference pattern would not form. Would it be possible to demonstrate this aspect of the double slit experiment without expensive equipment.

    I don't want to spend a lot of money, so please keep that in mind when posting your answer. Thanks.
  2. jcsd
  3. Feb 10, 2009 #2
    Here are three, two minute methods for getting Youngs fringes:

    Get a red laser pointer and then find a dark place, then:

    1) Put a single piece of thin fuse wire over the laser aperture and shine at a light painted surface more than 1 metre away. Observe fringes. Does not work with a torch because non coherent light.

    2) Shine a laser at a dvd (or better a cd rom) and look at the reflected interference pattern - normally just 3 or 5 crests because the slits are very close together. Also you can scrape off the surface silver and lines are left on the plastic that work very well - either reflected or straight through.

    3) Get a microscope slide, use a candle to black it, then with a pin, rule two lines very
    close together on the blackened slide. Then shine the laser through the slits and view interference on a light painted surface more than a metre away.
  4. Feb 10, 2009 #3
    The question of which slit a particle went through IMO is a confusion because a 'wave function' went through both slits. At the screen you choose to look at a particle by observing the position state (using telescopes aimed at each slit - not easy in practice) or a wave by looking at the wave (momemtum) state with a screen (- easy in practice). If you look for a particle you will see a particle and if you look for a wave you will see wave - thats just how the wave function works - you cannot see both at once because observing one destroys the other (they are non commutable).

    Note 1: If you look at a wave function passing through one slit then it collapses - so to speak - the whole thing as you see a particle in one or the other slits. You can have hundreds of spilt paths, but as soon as you observe any one then the wave function is collapsed in every path (ie you see a particle in one only of the paths and the wave like properties are then gone).

    Note 2: A wave function is not a real object in the ordinary sense, its a mathematical description. But at the quantum level, in a sense, ordinary objects are no longer there - they are described by wave functions.

    Note 3: I am using the Copenhagen Interpretation here, but not everyone agrees with it. And the wave function itself is a conundrum still, it just mathematically predicts correctly what happens in practice..
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