In the double-slit experiment, where a beam of light or a stream of photons passes through two closely spaced slits and creates an interference pattern on a screen, it might seem counterintuitive that photons, which are considered indivisible particles, exhibit interference effects similar to waves.
The key to understanding this phenomenon lies in the wave-particle duality of photons. While photons are indeed particles, they also exhibit wave-like behavior, as described by quantum mechanics. In the context of the double-slit experiment, each photon can be associated with a probability wave that describes the likelihood of finding the photon at different positions on the screen.
When a single photon is sent through the double slits, its probability wave passes through both slits and interferes with itself. This interference arises due to the superposition of different possible paths that the photon can take. The waves emerging from the two slits can either reinforce or cancel each other out at different points on the screen, creating an interference pattern.
Importantly, it is not the photons themselves that interact with each other, but rather their probability waves. The interference pattern emerges because the probability waves from different paths can interfere constructively or destructively, resulting in regions of high and low probability for the photon's detection.
However, when individual photons are detected on the screen, they are found as localized particles at specific positions. The interference pattern only emerges when a large number of photons are sent through the double slits and their individual detections are accumulated over time.
Therefore, while photons do not interact with themselves in the classical sense, their wave-like nature leads to interference effects in the double-slit experiment. This phenomenon demonstrates the wave-particle duality of photons and is a fundamental feature of quantum mechanics.