Wave-particle duality is a fundamental concept in quantum mechanics that describes the behavior of particles at the microscopic level. According to this principle, particles such as electrons and photons can exhibit both wave-like and particle-like properties, depending on the experimental setup. This idea challenges our classical intuition and has profound implications for our understanding of the nature of matter and light.

To understand wave-particle duality, let's consider the famous double-slit experiment. Imagine shooting a beam of electrons or photons at a barrier containing two narrow slits. If these particles were purely particles, we would expect them to pass through either one of the slits and form two distinct patterns on a screen behind the barrier. However, the experimental results reveal something astonishing.

When performing the double-slit experiment, we observe an interference pattern on the screen, much like what we would expect from two overlapping waves. This indicates that the particles interfere with themselves, suggesting that they possess wave-like characteristics. The particles seem to pass through both slits simultaneously and create an interference pattern when they interact with each other.

On the other hand, when we try to detect which slit the particles pass through by placing a detection device at the slits, the interference pattern disappears, and we observe two distinct patterns corresponding to the particles passing through each slit individually. This implies that the act of measurement or observation collapses the wave-like behavior and forces the particles to behave as discrete entities. Hence, we see the particle-like nature of these particles.

Wave-particle duality can be further understood through other experiments, such as the photoelectric effect and electron diffraction. In the photoelectric effect, light energy is absorbed by electrons, causing them to be ejected from a metal surface. The observed behavior can be explained by considering light as a stream of particles with discrete energy packets called photons. However, in electron diffraction experiments, electrons exhibit wave-like behavior by interfering with each other and forming diffraction patterns when passing through a diffraction grating. These experimental observations confirm the dual nature of particles in the quantum realm.