The phenomenon you are referring to is known as wave-particle duality, which is a fundamental concept in quantum mechanics. It states that particles, such as electrons or photons, can exhibit both wave-like and particle-like properties depending on the experimental setup.
One of the key experiments that provided evidence for the wave-like nature of particles is the double-slit experiment. In this experiment, a beam of particles, such as electrons or photons, is directed towards a barrier with two small slits. Behind the barrier, a screen is placed to detect the particles' arrival.
When the particles are observed individually, they behave as discrete particles, creating two distinct bands on the screen corresponding to the two slits. However, when the particles are not observed and there is no attempt to measure which slit they pass through, an interference pattern emerges on the screen. This pattern is characteristic of waves and indicates that the particles have exhibited wave-like behavior.
The interference pattern arises because the particles, in the absence of observation, can pass through both slits simultaneously and interfere with themselves. This phenomenon is not intuitive from a classical perspective but is a fundamental feature of quantum mechanics.
Other experiments, such as the Davisson-Germer experiment with electrons and the Young's double-slit experiment with light, have also provided evidence for the wave-like nature of particles. These experiments demonstrate that particles can exhibit diffraction and interference patterns, which are characteristic of waves.
The wave-particle duality of particles is a fundamental concept in quantum mechanics and has been supported by numerous experimental observations. It implies that particles can exhibit both particle-like and wave-like properties, depending on the experimental conditions and the act of observation.