In the double-slit experiment with light, the phenomenon of interference occurs when light passes through two narrow slits in a screen. While it may seem intuitive that the particles (photons) would collide with each other, there are several reasons why this doesn't happen:
Low particle density: In a typical experimental setup, the intensity of light is adjusted such that the number of photons passing through the slits is low enough to ensure a relatively sparse distribution. The probability of two photons colliding with each other within the narrow region between the slits is therefore quite low.
Independent particle behavior: Photons are elementary particles that exhibit wave-particle duality. When passing through the double slits, they behave both as particles and waves. As individual particles, they follow probabilistic trajectories, and their positions are not precisely determined. Thus, even if two photons were to approach the same region simultaneously, their probabilistic behavior would lead to independent outcomes.
Non-interacting particles: Photons, as bosons, do not have a direct interaction with each other like other particles with strong interactions (e.g., electrons with electromagnetic forces or nucleons with nuclear forces). The electromagnetic interaction between photons is mediated by virtual particles, such as virtual electrons and positrons, but these interactions are typically negligible in the context of the double-slit experiment.
Superposition and interference: One of the key features of the double-slit experiment is the phenomenon of interference. When passing through the slits, photons undergo superposition, where their wave functions combine and interfere with each other. The resulting interference pattern on the screen is a consequence of these wave-like properties. The interference pattern arises from the constructive and destructive interference of the waves, and it does not require actual physical interactions between individual photons.
It's important to note that in certain scenarios, such as extremely high-intensity lasers or ultra-high-energy particle beams, photon-photon interactions and collisions can occur. These phenomena are studied in specialized experimental setups, but they are not relevant to the standard double-slit experiment with light.