The double-slit experiment is a classic experiment in quantum mechanics that demonstrates the wave-particle duality of matter and the phenomenon of interference. It involves shining a beam of particles, such as electrons or photons, through two parallel slits and observing the resulting pattern on a screen placed behind the slits.
When particles pass through the slits, they interact with the matter that makes up the slits. This interaction can be thought of as a scattering process, where the particles are deflected or altered in some way. It may seem intuitive to expect that these interactions would destroy the interference pattern because the particles would lose their wave-like behavior.
However, the key factor that allows the interference pattern to emerge is the probabilistic nature of quantum mechanics. The behavior of particles in quantum mechanics is described by wavefunctions, which are mathematical entities that contain information about the probability distribution of a particle's position or momentum.
When a particle passes through the slits, its wavefunction spreads out and undergoes interference. The wavefunction describes the probability distribution of finding the particle at different positions on the screen. The interference arises from the superposition of different possible paths that the particle can take to reach the screen.
The interaction between the particle and the matter of the slits does introduce some changes to the wavefunction of the particle. However, these changes affect all the possible paths that the particle can take uniformly. The scattering or deflection of the particle by the material in the slits introduces a phase shift to the different components of the wavefunction, but the interference pattern is determined by the relative phases between these components.
Importantly, the interaction with the matter in the slits does not provide any information about which path the particle actually took. The interference pattern arises from the superposition of all possible paths, and it is only when a measurement is made that the particle's position is determined.
In summary, the interaction between the passing particle and the matter in the slits does introduce changes to the particle's wavefunction, but it does not provide any information about which path the particle took. The interference pattern still emerges because the probabilistic nature of quantum mechanics allows for the superposition and interference of different possible paths.