The double-slit experiment is a fundamental experiment in quantum mechanics that demonstrates the wave-particle duality of matter and challenges our classical intuitions. It does not disprove the Copenhagen interpretation of quantum mechanics, but rather highlights some of its peculiarities and profound implications.
The Copenhagen interpretation, developed by Niels Bohr and Werner Heisenberg, provides a framework for understanding quantum phenomena. It states that particles exist in a superposition of all possible states until measured, at which point the wave function collapses into a single state. This interpretation emphasizes the probabilistic nature of quantum mechanics and the role of the observer.
In the double-slit experiment, a beam of particles, such as electrons or photons, is directed towards a barrier with two closely spaced slits. Beyond the barrier, a screen is placed to observe the pattern formed by the particles that pass through the slits. Surprisingly, even when particles are sent through the slits one at a time, an interference pattern emerges on the screen, similar to what would be expected for waves. This interference pattern suggests that the particles behave like waves that interfere with each other.
The apparent contradiction arises when we consider that observing which slit a particle goes through disrupts the interference pattern. If a measurement is made to determine the path of the particle, such as by placing detectors at the slits, the interference pattern disappears, and particles behave as distinct particles without wave-like behavior. This is known as the "which-path" information.
The challenge this experiment poses to the Copenhagen interpretation lies in the role of measurement and observation. According to the interpretation, the act of measurement collapses the wave function, forcing the particle to take on a definite position or path. However, in the double-slit experiment, the measurement of the which-path information disrupts the interference pattern.
This implies that the mere possibility of obtaining information about the particle's path affects its behavior, even if the measurement is not actually performed. The Copenhagen interpretation does not provide a clear explanation for why the act of observation, or the potential for observation, has such a significant impact.
Alternative interpretations, such as the Many-Worlds interpretation or the Transactional interpretation, offer different perspectives to explain the double-slit experiment. These interpretations propose that the interference and collapse of the wave function arise from different aspects of reality or interactions between the particle and its environment. However, it is worth noting that interpretations of quantum mechanics remain a topic of active debate among physicists, and there is no widely accepted consensus beyond the mathematical formalism of the theory.