In the double-slit experiment conducted with single photons, it is true that each individual photon will ultimately be detected at a specific location on the screen or detector. However, the path that a single photon takes to reach that detection point is not directly observable. Instead, it is described by the wave function, which evolves over time according to the laws of quantum mechanics.
The wave function of the photon spreads out from the source and passes through both slits simultaneously, resulting in an interference pattern on the screen. This wave-like behavior is a characteristic of quantum particles. The interference pattern arises due to the constructive and destructive interference of the overlapping waves from the two slits.
When a photon is detected at a specific location on the screen, it is associated with a particular point of impact. The probability distribution described by the wave function determines the likelihood of the photon being detected at different positions. The intensity of the resulting pattern at a given location on the screen corresponds to the probability of detecting the photon there.
While it is theoretically possible for a photon to hit locations on the screen where there are no slits, the probability of such an event is generally very low. The interference pattern resulting from the two-slit setup will dominate the detection statistics, as it represents the most likely outcome according to the wave nature of the particles involved.
In summary, each individual photon in the double-slit experiment is detected at a specific location, but its exact path through the slits is not directly observable. The wave function describes the probability distribution for the photon's location, and the resulting interference pattern arises due to the wave-like behavior of quantum particles passing through the slits.