The Double Slit Experiment was first devised by Physicist Thomas Young in 1801. Young developed this experiment in order to demonstrate the wave properties of light. Since 1801 I believe the Double Slit Experiment has become one of the most important experiments in Quantum Physics. It most definitely had a strong impact on my interest in the subject.
The Experiment has evolved a great deal since 1801. To give you a simple overview of the Double Slit Experiment I found this informative video by Dr. Quantum. This video explains the basics.
What is so amazing about this experiment is that it strongly infers that the conscious mind has a physical effect on our reality. I would not say this experiment proves it, but it does provide strong evidence. What this experiment does show is that the very act of “observing” this experiment, changes it. The particles behave one way until they are “observed” and then they behave another.
The initial theory was that very small particles only exist as probability waves until they are observed. The act of observing, collapses the wave into our physical reality. The idea that our minds play such an important role falls under what is known as the Copenhagen interpretation. This is still the most commonly taught interpretation and is what I tend to believe.
There are other interpretations of the apparent collapse of the wave function, such as Quantum Decoherence and the Many Worlds interpretation. Quantum Decoherence is becoming very popular, but I think that is physicists seeing what they want to believe, if Decoherence is the answer, it opens the door to quantum computers, which would change everything. I think the Many World Interpretation ties in rather nicely with the Copenhagen Interpretation but I am really an amateur at this.