The behavior of a single photon in a double-slit experiment can be challenging to conceptualize within classical intuitions. However, quantum mechanics provides a framework to understand and explain such phenomena.
In the double-slit experiment, when a single photon is sent towards the barrier with two slits, it behaves as both a particle and a wave. The photon's wave nature is described by its probability wave or wavefunction, which represents the likelihood of finding the photon at different positions.
Initially, the photon's wavefunction spreads out and passes through both slits, creating two separate wavefronts that propagate beyond the slits. These wavefronts then interfere with each other as they overlap and interact. This interference produces an interference pattern on the screen placed behind the slits, resulting in bright and dark fringes.
The key point to understand is that the photon is not "splitting" into two separate photons; instead, it is described by a single wavefunction that simultaneously passes through both slits. The wavefunction contains information about the probability distribution of the photon being detected at different positions.
When the photon's wavefunction interacts with itself through interference, the probabilities of detection at different positions interfere as well. This interference pattern on the screen is a manifestation of the probabilistic nature of quantum mechanics.
When a measurement is made to determine the photon's position, such as placing a detector at one of the slits or on the screen, the wavefunction collapses, and the photon is found at a specific position corresponding to the measurement outcome. This collapse of the wavefunction is a fundamental aspect of quantum mechanics and is often referred to as the measurement problem or the collapse of the wavefunction.
It's important to note that the behavior of a single photon in the double-slit experiment is not easily explainable within classical intuitions. Quantum mechanics provides a probabilistic framework that describes the behavior of particles on a microscopic scale. The wave-particle duality and the probabilistic nature of quantum systems are fundamental principles that are supported by experimental observations and theoretical calculations.