In the double-slit experiment, the outcome of a specific measurement is not known in advance unless the state of the system is prepared in a particular way. The double-slit experiment is often used to demonstrate the fundamental principles of quantum mechanics, including the concept of wave-particle duality and the probabilistic nature of measurements.
When a beam of particles or a stream of photons is directed at the double-slit apparatus, each individual particle or photon behaves as if it passes through both slits simultaneously and interferes with itself. This interference leads to an observable pattern on a screen or detector behind the slits, known as an interference pattern. The interference pattern consists of alternating dark and bright fringes.
The outcome of a measurement in the double-slit experiment is determined by the interaction between the particles or photons and the detection apparatus. Each particle or photon is detected at a specific location on the screen, contributing to the overall pattern. However, for a single particle or photon, the specific location where it will be detected cannot be predicted precisely. Instead, the measurement outcome is probabilistic in nature and described by a probability distribution.
So, in the double-slit experiment, even if we have knowledge of the possible outcomes in terms of the probability distribution, the actual outcome for a single particle or photon is not known in advance until a measurement is made. The act of measurement collapses the wave function and determines the specific outcome for that particular particle or photon.