In the double slit experiment, the interference pattern is not the result of a collapsed wave function. Rather, it is a manifestation of the wave-like nature of particles such as electrons or photons.
In the experiment, a beam of particles, such as electrons, is directed at a barrier with two narrow slits. Beyond the barrier, a screen is placed to detect the particles. When the particles pass through the slits, they diffract and create an interference pattern on the screen, consisting of alternating bright and dark fringes.
This interference pattern arises from the superposition of different possible paths that the particles can take. Each particle can pass through either slit, and the wave-like nature of the particles allows them to interfere with themselves. This interference leads to constructive interference (bright fringes) where the peaks of the waves coincide and destructive interference (dark fringes) where the peaks and troughs cancel each other out.
The wave function describes the probabilistic behavior of a particle and includes information about the probability distribution of different outcomes. The interference pattern observed in the double slit experiment is a result of the wave nature of the particles and can be explained using the wave function. However, the wave function itself does not collapse during the experiment. The collapse of the wave function occurs when a measurement is made, and the particle's position or other observable properties are determined.
In summary, the interference pattern in the double slit experiment arises from the wave-like behavior of particles and is not directly related to the collapse of the wave function.