In quantum mechanics, particles are often described by wave functions that exhibit wave-like behavior. The double-slit experiment is a classic example that illustrates the wave-particle duality of quantum objects.
Before the wave function is measured, it exists in a superposition of states, which means the particle can exist in multiple possible states simultaneously. In the case of the double-slit experiment, the wave function describes the probability distribution of the particle's position or momentum. It determines the likelihood of finding the particle at different positions on a screen placed behind the double slits.
When the particle's wave function interacts with the double slits, it undergoes interference, producing an interference pattern on the screen. This pattern arises from the superposition of the wave function passing through both slits and interfering with itself. The interference pattern indicates that the particle behaves like a wave.
However, when we measure the particle's position or momentum by placing a detector at one of the slits or on the screen, the wave function "collapses" into a single state. The act of measurement forces the particle to be localized to a specific position, and the interference pattern disappears. The collapse of the wave function is often referred to as the "observer effect" or "measurement problem."
In summary, the particle waves in the double-slit experiment exist as a superposition of states described by the wave function before they are measured. The act of measurement collapses the wave function and determines the particle's position or momentum. The wave-like behavior, characterized by interference patterns, is observed when the particle's wave function is allowed to evolve freely without measurement.