The phenomenon you're referring to is known as the double-slit experiment, which demonstrates the wave-particle duality of light. It can be quite perplexing to understand how individual particles of light, called photons, can create an interference pattern when passing through two slits.
In the double-slit experiment, a beam of light is directed at a barrier with two narrow slits. On the other side of the barrier, a screen is placed to capture the pattern formed by the light passing through the slits. Surprisingly, instead of observing just two bright lines on the screen corresponding to the two slits, an interference pattern of alternating bright and dark fringes emerges.
The key to understanding this phenomenon lies in the wave-like nature of light. Although light can behave as particles (photons), it also exhibits wave-like properties. When light passes through the slits, each photon's wavefunction spreads out and interferes with itself. This interference creates regions of constructive interference (bright fringes) and destructive interference (dark fringes) on the screen.
To illustrate this, imagine each photon's wavefunction as a wave spreading out from the slits. When two waves meet crest-to-crest, they add up and create a stronger wave (constructive interference). Conversely, when a crest meets a trough, they cancel each other out, resulting in a weaker or no wave (destructive interference).
Even though individual photons are detected as discrete particles on the screen, their cumulative behavior creates an interference pattern that can only be explained by the wave-like nature of light. This wave-particle duality is a fundamental aspect of quantum mechanics and applies not only to light but also to other subatomic particles like electrons.
In summary, the orderly pattern observed in the double-slit experiment occurs due to the interference of the wave-like nature of light. While individual photons pass through either one or the other slit, their wavefunctions interfere with each other, resulting in the characteristic pattern on the screen.