The Double-Slit Experiment is one of the most groundbreaking, yet simple tests that changed the way we look at the light in general. It gave rise to the fascinating world of quantum mechanics and also toppled the Newtonian idea of light.
Before this experiment was created, White light was considered to be a particle. Newton used a prism to refract the white light into its constituent colors. He was one of the first to prove that white light was made up of several colors. To prove his theory, Newton used two white prisms and refracted the light backwards.
But this theory did not explain a lot of properties exhibited by light.
This is where the Double-Slit Experiment brought a new paradigm to the study of light. In its basic setup, a ray of light is allowed to pass through a double slit arranged parallelly on cardboard or another opaque object. The light will then pass through to fall on the screen. After passing through the slits, the light ray creates bright and dark bands of light on the screen due to a phenomenon called interference. The observation led to a belief that light rays were made up of waves and not particles as originally theorised by Newton.
Another interesting phenomenon of the experiment was that if you placed detectors at each slit, the interference pattern would not be seen at all, leading to a belief that consciousness can also play a part in how light behaves. When observed, it behaves as particles but when not observed it acts like waves.
This dual nature of light has given rise to the quantum theory which believes light has both the wave and particle properties. The double slit experiment gave rise to a lot of new ideas on how light works and contributed tremendously to the development of modern physics.