The bigger something is, however, the harder it is to coax it into existing in two places at once. (Big things tend to behave more “classically,” and less quantum-mechanically.) The reason lies not so much with the physical size of the object as with its visibility. The bigger something is, the more interactions it tends to have with its surroundings, thus the easier it is to detect. In order to go through both slits at once and produce an interference pattern, a particle must pass through the slits undetected.
