The double-slit experiment is a famous and fundamental experiment in quantum physics that demonstrates the wave-particle duality of particles such as electrons or photons (particles of light). It shows that particles can exhibit both wave-like and particle-like behaviors depending on how the experiment is conducted.
The setup of the double-slit experiment involves a barrier with two narrow slits cut into it, and a screen placed behind the barrier to detect the particles. The barrier is designed to allow particles to pass through the slits and reach the screen.
When particles, such as electrons or photons, are sent through the double slits one at a time, an intriguing pattern emerges on the screen. Instead of seeing just two bright spots corresponding to the locations of the two slits, an interference pattern appears, consisting of a series of light and dark bands.
This interference pattern arises because the particles behave like waves as they pass through the slits. Each particle's wave-like nature allows it to simultaneously pass through both slits and interfere with itself, resulting in regions of constructive interference (bright bands) and destructive interference (dark bands) on the screen.
However, when the experiment is modified to determine which path each particle takes through the slits (by placing detectors or observing the particles), the interference pattern disappears. The act of observation or measurement collapses the wave-like behavior, and the particles behave as particles, showing a simple two-slit pattern on the screen.
The double-slit experiment illustrates the fundamental principle of wave-particle duality in quantum mechanics. It demonstrates that particles can exhibit wave-like properties (interference) and particle-like properties (localized detection) depending on the experimental setup and whether or not they are observed. It challenges our classical intuitions about the behavior of particles and highlights the unique nature of quantum physics.