What is the principle of wave-particle duality?

The principle of wave-particle duality proposes that all particles exhibit both wave and particle properties.

The wave-particle duality is a fundamental concept in quantum mechanics, a branch of physics that describes the behaviour of particles at the smallest scales. This principle suggests that all particles, including light and matter, have characteristics of both waves and particles. This is a departure from classical physics, where entities are either waves (like light or sound) or particles (like electrons or protons), but not both.

The concept of wave-particle duality was first introduced in the early 20th century, when scientists were trying to understand the nature of light. Experiments showed that light could behave as a particle, in a phenomenon known as the photoelectric effect, where light striking a material can eject electrons from it. However, light also exhibits wave-like properties, such as interference and diffraction, which are phenomena typically associated with waves.

Similarly, matter, which was traditionally considered to be composed of particles, was found to exhibit wave-like behaviour. This was demonstrated by the famous double-slit experiment, where electrons (particles) were fired at a barrier with two slits. Instead of producing two distinct spots on the screen behind the barrier, as would be expected if electrons were simply particles, an interference pattern was observed, indicating wave-like behaviour.

The wave-particle duality principle is encapsulated in the de Broglie hypothesis, proposed by Louis de Broglie in 1924. He suggested that all matter has a wave-like nature and that the wavelength of this wave is inversely proportional to its momentum. This was a revolutionary idea, as it suggested that even everyday objects, like a football, have a wavelength, although it is incredibly small and not observable in practice.

In essence, the principle of wave-particle duality is a cornerstone of quantum mechanics. It challenges our classical understanding of the world, suggesting that reality is far more complex and counter-intuitive than we might think. It's a concept that continues to intrigue and puzzle physicists, and it's fundamental to our understanding of the universe at the smallest scales.