The double-slit experiment, which is often used to demonstrate wave-particle duality, typically involves two openings or slits through which waves or particles can pass. The reason for using two slits is to observe the interference pattern that arises when waves or particles pass through them.
When waves, such as light or water waves, pass through two slits, they diffract or spread out, and the resulting waves from each slit interact with each other. This interaction leads to the phenomenon of interference, where the peaks and troughs of the waves can either reinforce or cancel each other out at different points in space.
The interference pattern that emerges on a screen placed behind the slits consists of alternating bright and dark regions, indicating constructive and destructive interference, respectively. This pattern is a characteristic signature of waves and demonstrates their ability to interfere with each other.
Similarly, when particles like electrons or photons are sent through the double-slit setup one at a time, they can exhibit interference patterns on a screen over time. This suggests that even individual particles can exhibit wave-like behavior and interfere with themselves. This phenomenon is a key feature of wave-particle duality.
Using more than two slits would introduce additional complications to the interference pattern. While it is possible to create interference patterns with multiple slits, the fundamental principles of interference and diffraction can be sufficiently demonstrated and understood with just two slits. Therefore, the double-slit experiment is often used as a simplified and illustrative example to study the wave-like behavior of particles.