The double-slit experiment is a fundamental experiment in quantum mechanics that demonstrates the wave-particle duality of matter and light. It shows that particles such as electrons or photons exhibit both wave-like and particle-like properties.
In the experiment, particles, such as electrons, are sent towards a barrier with two closely spaced slits. Behind the barrier, a screen records the pattern of particles that pass through the slits and arrive on the screen. Surprisingly, even when particles are sent through the slits one by one, an interference pattern emerges on the screen, similar to what is observed when waves pass through two slits.
If particles were purely behaving as waves, they would indeed spread out and create a wave-like pattern on the screen. However, what's observed in the double-slit experiment is an interference pattern formed by the particles. This indicates that particles interfere with themselves, which is a characteristic behavior of waves.
The key insight of quantum mechanics is that particles and other quantum entities have a dual nature. They can exhibit wave-like behavior or particle-like behavior depending on how they are observed or measured. The behavior observed in the double-slit experiment suggests that particles possess wave-like properties and can interfere with themselves, even when they are sent through the slits one at a time.
The wave-particle duality can be understood through the concept of wavefunction, which describes the probabilistic behavior of particles in quantum mechanics. The wavefunction can be thought of as a mathematical description of a particle's wave-like nature. When particles are observed or measured, the wavefunction "collapses" into a specific state, and the particle behaves like a localized entity with definite properties.
In summary, while the idea of particles moving purely as waves might seem intuitive, the experimental observations in the double-slit experiment and many other experiments in quantum mechanics demonstrate that particles exhibit wave-like and particle-like behaviors simultaneously. This wave-particle duality is a fundamental aspect of the quantum world and is crucial to our understanding of its unique behavior.