The phenomenon you're referring to is known as the double-slit experiment, which is a fundamental experiment in quantum mechanics. In the double-slit experiment, when a beam of particles, such as electrons, is directed toward a barrier with two narrow slits, an interference pattern emerges on a screen placed behind the slits.
In classical physics, if a particle were to pass through one slit, it would be expected to create a single band on the screen corresponding to the position directly opposite the slit. However, in the double-slit experiment, even when particles are sent through the slits one at a time, an interference pattern is observed, indicating that the particles exhibit wave-like behavior.
When an electron passes through the double slits, it behaves as both a particle and a wave simultaneously. This is a core concept in quantum mechanics called wave-particle duality. The electron's wave-like nature allows it to pass through both slits simultaneously and interfere with itself, creating an interference pattern on the screen. The interference pattern arises due to constructive and destructive interference of the electron waves as they interact with each other.
This phenomenon challenges classical intuitions and highlights the probabilistic nature of quantum mechanics. It suggests that particles, at the quantum level, can exist in multiple states or locations simultaneously until observed or measured, at which point their wave-like behavior collapses into a specific state or position.
The double-slit experiment and similar experiments have been conducted with various particles, such as electrons, photons, and even large molecules like buckyballs, consistently showing wave-particle duality and interference patterns. This experiment is a cornerstone of quantum mechanics and has profound implications for our understanding of the nature of particles and the fundamental principles governing the microscopic world.