The double-slit experiment is a classic experiment in quantum mechanics that demonstrates the wave-particle duality of particles like photons. While it can be challenging to reconcile our classical intuitions with the behavior observed in the experiment, here is an explanation based on the principles of quantum mechanics.
In the double-slit experiment, when a single photon is sent toward a barrier with two slits, it can exhibit interference patterns on a screen behind the barrier, as if it behaves like a wave. This can be explained using the concept of superposition and the wave-like nature of the photon.
According to quantum mechanics, before the photon is measured or detected, its state is described by a probability wave, often represented by a mathematical function called the wavefunction. The wavefunction contains information about the probabilities of finding the photon at different locations.
When the photon passes through the double slits, its wavefunction spreads out and interacts with both slits simultaneously. This superposition of possibilities allows the photon to effectively go through both slits at the same time, resulting in an interference pattern on the screen. The interference arises from the constructive and destructive interference of the photon's wavefunction as it interacts with itself.
When the photon is detected or measured, its wavefunction "collapses" to a specific location on the screen, corresponding to a single detection event. The collapse of the wavefunction is a probabilistic process, and the likelihood of the photon being detected at a particular location is given by the squared magnitude of the wavefunction at that location.
So, while the probability wave describes the chance of finding the photon at a particular location, the phenomenon of interference in the double-slit experiment arises due to the wave-like nature of the photon and the superposition of possibilities allowed by quantum mechanics. The photon doesn't split into two separate particles, but rather its wave-like nature allows it to exhibit behavior as if it has gone through both slits simultaneously, leading to the observed interference pattern.