Quantum superposition is a term well-known to those who have tried to acquaint themselves with the basic concepts of quantum mechanics. It tells us that an object can simultaneously exist in multiple quantum states until we begin to observe it.
This effect is clearly demonstrated in the double-slit experiment. When we have a light source, a barrier with two parallel slits, and a projection screen, illuminating the screen through the barrier will produce an interference pattern (either an intensification or weakening of brightness when waves of light with the same frequency overlap), appearing on the screen as vertical bright bands intersecting with dark ones.
Interference is characteristic of waves, meaning light is a wave. However, if we were to emit light in portions and, for example, place a detector to determine through which slit the light passes, the interference pattern would disappear. We would see two bright bands, as if small particles had passed through the slits and projected the images of the slits onto the screen. Therefore, scientists believe that light is simultaneously both a wave and a particle and behaves differently depending on the conditions.
