The double-slit experiment is a classic experiment in physics that demonstrates the wave-particle duality of light and matter. It was originally conducted with light, but it has also been performed with electrons, atoms, and other particles.
In the basic setup of the experiment, a beam of light or a stream of particles is directed towards a barrier with two narrow slits. Behind the barrier, there is a screen that captures the pattern of light or particle impacts. When the experiment is conducted with light, a coherent light source, such as a laser, is typically used.
If light were purely a particle, one would expect to observe two separate bands of light on the screen, corresponding to the two slits. However, the surprising result is that an interference pattern emerges on the screen, characterized by a series of alternating light and dark bands. This pattern is similar to what would be expected if light were a wave.
The interference pattern arises because the light passing through the two slits interacts with itself, creating constructive and destructive interference. When the crests of two waves coincide, they reinforce each other and create a brighter region, whereas when a crest and a trough coincide, they cancel each other out and create a darker region. This interference phenomenon is a characteristic behavior of waves.
The double-slit experiment provided evidence for the wave nature of light. However, when the experiment is performed using very low-intensity light sources or one photon at a time, the interference pattern still emerges, indicating that light behaves as though it consists of individual particles called photons. This demonstrated the wave-particle duality of light, where light exhibits properties of both waves and particles.
In summary, the results of the double-slit experiment showed that light can behave as both a wave and a particle. The interference pattern observed on the screen demonstrated the wave-like nature of light, while the ability to observe individual photons and still see the pattern indicated the particle-like nature of light. This experiment played a fundamental role in shaping our understanding of quantum mechanics and the nature of light and matter.