The double-slit experiment is a fundamental experiment in quantum physics that demonstrates the wave-particle duality of particles, such as electrons or photons. In this experiment, particles are fired towards a barrier with two slits, and they create an interference pattern on a screen behind the barrier.
When particles are fired one at a time, they behave as individual particles and produce a pattern of hits on the screen that gradually builds up to reveal the interference pattern. This indicates that particles exhibit wave-like behavior and interfere with themselves, creating regions of constructive and destructive interference.
However, when we introduce a measurement device to determine which slit a particle passes through, something interesting happens. The act of measurement disturbs the system and causes the interference pattern to disappear. Instead, the particles behave like classical particles and create a pattern on the screen that resembles the pattern produced by two separate point sources.
This phenomenon is known as the "collapse of the wavefunction" or "quantum decoherence." In quantum mechanics, particles are described by wavefunctions, which represent the probability distribution of their possible states. The interference pattern arises from the superposition of different states of the particle. When we measure the particle's position or which slit it passes through, we gain information about its state, causing the wavefunction to "collapse" into a definite state corresponding to the measurement outcome.
The collapse of the wavefunction is a fundamental aspect of quantum mechanics and is still not fully understood. It is related to the interaction between the measuring device and the particle, which disturbs the delicate quantum system and destroys the interference. This interaction, known as the "observer effect," plays a crucial role in the double-slit experiment and many other quantum phenomena.
It's worth noting that there are different interpretations of quantum mechanics that provide different explanations for the collapse of the wavefunction. The Copenhagen interpretation, for example, views the collapse as an inherent property of quantum systems when they interact with classical measuring devices. Other interpretations, such as the many-worlds interpretation or the pilot-wave theory, propose alternative explanations for the apparent collapse. Nonetheless, the collapse of the wavefunction and the disruption of interference in the double-slit experiment are well-established experimental observations in quantum physics.