page_title: Introduction to quantum mechanics
section_title: Wave–particle duality
hierarchical_section_title: Introduction to quantum mechanics / Wave–particle duality
caption_attribution_description: Louis de Broglie
context_page_description: Quantum mechanics is the science of the very small. It explains the behavior of matter and its interactions with energy on the scale of atomic and subatomic particles. By contrast, classical physics explains matter and energy only on a scale familiar to human experience, including the behavior of astronomical bodies such as the Moon. Classical physics is still used in much of modern science and technology. However, towards the end of the 19th century, scientists discovered phenomena in both the large and the small worlds that classical physics could not explain. The desire to resolve inconsistencies between observed phenomena and classical theory led to two major revolutions in physics that created a shift in the original scientific paradigm: the theory of relativity and the development of quantum mechanics. It describes these concepts in roughly the order in which they were first discovered.
  Light behaves in some aspects like particles and in other aspects like waves. Matter—the "stuff" of the universe consisting of particles such as electrons and atoms—exhibits wavelike behavior too.
context_section_description: Just as light has both wave-like and particle-like properties, matter also has wave-like properties.
  Matter behaving as a wave was first demonstrated experimentally for electrons: a beam of electrons can exhibit diffraction, just like a beam of light or a water wave. Similar wave-like phenomena were later shown for atoms and even molecules.
  The wavelength, λ, associated with any object is related to its momentum, p, through the Planck constant, h:
  The relationship, called the de Broglie hypothesis, holds for all types of matter: all matter exhibits properties of both particles and waves.
  The concept of wave–particle duality says that neither the classical concept of "particle" nor of "wave" can fully describe the behavior of quantum-scale objects, either photons or matter.  Wave–particle duality is an example of the principle of complementarity in quantum physics. An elegant example of wave–particle duality, the double slit experiment, is discussed in the section below.
caption: Louis de Broglie in 1929. De Broglie won the Nobel Prize in Physics for his prediction that matter acts as a wave, made in his 1924 PhD thesis.
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