The phenomenon of particles "interfering with themselves" in the double-slit experiment is a fundamental aspect of quantum mechanics known as wave-particle duality. It arises from the wave-like nature of particles at the quantum level.
In the double-slit experiment, a beam of particles, such as electrons or photons, is directed towards a barrier with two narrow slits. Behind the barrier, a screen is placed to detect the particles. When the particles pass through the slits and reach the screen, an interference pattern emerges.
This interference pattern consists of alternating bright and dark regions, indicating regions of constructive and destructive interference, respectively. The key point is that this pattern can only be explained if we consider the particles as waves.
According to quantum mechanics, particles such as electrons or photons are described by wave functions that determine their behavior and probabilities. The wave function represents the probability distribution of finding a particle at different positions on the screen.
When a particle passes through the double slits, its wave function spreads out and interferes with itself. The wave function evolves and interacts with the two paths available, each passing through one of the slits. As a result, there are regions where the two waves (corresponding to the two paths) reinforce each other, resulting in constructive interference and producing bright regions on the screen. Conversely, there are regions where the waves cancel each other out, leading to destructive interference and resulting in dark regions on the screen.
This interference pattern indicates that the particles exhibit wave-like behavior and can interfere with themselves. It demonstrates the inherent probabilistic nature of quantum mechanics, where the wave function provides information about the likelihood of a particle being detected at different positions on the screen.
It's important to note that once a measurement or observation is made to determine which slit the particle passes through, the interference pattern disappears. This is because the act of measurement collapses the wave function, causing the particle to behave more like a localized particle rather than a spread-out wave. This illustrates the delicate relationship between the wave-like and particle-like aspects of quantum entities.