According to the Copenhagen interpretation of quantum mechanics, the behavior of particles in the double-slit experiment is described by a wavefunction that evolves in a superposition of states. The interpretation suggests that before a measurement is made, the particle can exist in a superposition of passing through both slits simultaneously.
In the double-slit experiment, when particles such as electrons or photons are sent through two slits and allowed to interfere, they exhibit an interference pattern on a screen behind the slits. This pattern suggests that the particles exhibit wave-like behavior, with regions of constructive and destructive interference.
The Copenhagen interpretation emphasizes that the wavefunction describes the probabilities of different outcomes. It suggests that the particle does not have a well-defined position or trajectory before a measurement is made. Instead, the particle exists in a superposition of possible states, including passing through both slits simultaneously.
However, once a measurement is performed to determine which slit the particle goes through, the wavefunction collapses into a single outcome. This collapse destroys the interference pattern, and the particle is found to have passed through only one of the slits. This phenomenon is often referred to as the "collapse of the wavefunction."
The Copenhagen interpretation does not provide a detailed description of how the particle simultaneously passes through both slits. It rather emphasizes the statistical nature of quantum mechanics and encourages focusing on the observable results rather than trying to ascribe a classical trajectory to the particle.
In summary, according to the Copenhagen interpretation, the particle in the double-slit experiment can exist in a superposition of passing through both slits simultaneously until a measurement is made. The interpretation does not provide a definitive answer to how the particle accomplishes this, but rather highlights the probabilistic nature of quantum mechanics and suggests refraining from asking questions about the precise trajectory of the particle.