Light has been of interest to me for some time, one of those strange things that most people don’t even consider, yet drives our very existence.  Through the years I’ve read many books and articles on what science thinks of the strange substance, how we think it moves, how fast it moves and so forth, yet, for all the things we know about it, there are that many more we don’t.  One of its most fascinating properties to me, is the fact that it moves as a wave and a particle, or at least that is what we believe.  The duplication of the experiment that proved this, is the purpose of this article.

The experiment is called the “Two Slit Experiment”, and its mentioned in many of the books I’ve read related to Quantum Physics, Physics, Light…, yet despite many hours of searching, I’ve found very little on the actual experiment itself.  As a result, I’ve set out to try to duplicate the experiment and see for myself what it proves or disproves. 

The Proof: 

It was believed for many years that light was small packets of energy that moved in straight lines through space, bouncing off things that it hit.  But there were other strange properties that were seen, and eventually Thomas Young performed a rather simple experiment where he broke a beam of light into two pieces and documented what he saw.  To do this, he used a card, positioned edge wise, and shined a tight beam of sunlight across the edge.  He was thinking that he’d get two seperate areas of light with a darkspot in the middle, but what he really got was much more strange.  He saw a series of light and dark bands across the wall which resembled in every detail, what you’d expect to get if you crashed two waves together.  The light spots being spots where the two waves enhanced each other, and the dark bands where they destroyed each other.

As the single light wave hit the edge of the card, it creates two seperate waves that continue to move towards the back wall.  However, once created, they continue to spread out like a water wave would do, and begin to bump into each other on the other side of the card.  These interactions cause the wave to begin cancelling and enhancing itself until it eventually runs into the back wall and is shown for what it is, A Wave!

The Setup:

 

I wanted to be sure that I built a device that allowed me to change different parameters of the test without having to build a bunch of different pieces.  The design I ended up with consists of 4 pieces, mounted on a board which is then mounted to a tripod for easy placement.  The 4 pieces are designed to allow me to change the center divider thickness so that I could test different variations.  Once the divider is in place, the other two pieces are opened in order to create the slit openings.  So with this basic setup, I can change the slit width as well as the slit openings themselves.

 

I then purchased a lazer pointer to use as my light source because its necessary to use a light source that is steady.  Otherwise, it would cancel itself out due to the variations of light waves being sent and would never provide a good test subject.  Perhaps its what my problem is and I”m looking into it, but for now I have to assume the $60 I spent on the pointer was worth it.  I purchased a little nicer pointer to be sure it was steady.

Results:

I started the test out by leveling and aligning all the pieces.  I wanted to start out producing the lines and then work through the math to see if I could determine the wavelength of light I was using (which of course I already know).  But no matter how many times I redid the math or changed the position of the elements, I couldn’t get anything close to what I expected. During the process of moving things around, I removed the divider to try a new one, but when I removed it, I noticed that I still had an interference pattern on the wall.  This shouldn’t be possible!  I should only see the pattern if I’m breaking up the light, but I’m seeing a clear, absolute pattern, just by breaking up the beam.  Not by splitting it, just by interferring with it.

I’ve done the test over and over and get the same results.  I’ve tried narrower pieces of material to see if the pattern changed due to the thickness, but nothing changed.  The closer I put the two walls, the wider the pattern on the wall, but its there and its very steady.  So now you are probably wondering like me, what gives?  Well, at this point I can’t offer a solution to that question, but am still experimenting to see if I can figure it out.  I’ve also been in contact with the local high school to see if I can figure out how they do these experiments, but so far its been a complete dead end.

I’ll post new material when I get more information on what is going on.  At this point, I can only assume I’m doing something wrong, but will keep looking until I determine what is happening.

Here is the result with the dual slit in place:

 

And finally, the result with only a single slit in place:

  

–glenn hancock