De Broglie Explains the Wave-Particle Duality of Light Summary

  • Last updated on November 10, 2022

Louis de Broglie provided a mechanical explanation for the wave-particle duality of light.

Summary of Event

In the early years of the twentieth century, scientists were having difficulty describing the nature of light. For a long time, light had been regarded as acting like a particle. In the late nineteenth century, the wavelike nature of light had been demonstrated. Early in the twentieth century, however, this belief was shifted again by experiments that confirmed the particle nature of light. The wave-particle duality of light was an experimental phenomenon in search of a theory. Wave-particle duality of light[Wave particle duality of light] Light, wave-particle duality[Light, wave particle duality] [kw]De Broglie Explains the Wave-Particle Duality of Light (1923) [kw]Wave-Particle Duality of Light, De Broglie Explains the (1923)[Wave Particle Duality of Light, De Broglie Explains the (1923)] [kw]Particle Duality of Light, De Broglie Explains the Wave- (1923) [kw]Duality of Light, De Broglie Explains the Wave-Particle (1923) [kw]Light, De Broglie Explains the Wave-Particle Duality of (1923) Wave-particle duality of light[Wave particle duality of light] Light, wave-particle duality[Light, wave particle duality] [g]France;1923: De Broglie Explains the Wave-Particle Duality of Light[05690] [c]Science and technology;1923: De Broglie Explains the Wave-Particle Duality of Light[05690] [c]Physics;1923: De Broglie Explains the Wave-Particle Duality of Light[05690] Broglie, Louis de Bohr, Niels Schrödinger, Erwin

At the beginning of the twentieth century, German physicist Max Planck Planck, Max had used the concept of the wave nature of light to explain blackbody radiation Blackbody radiation (radiation from a theoretical celestial body capable of completely absorbing all radiation falling on it). As a wave, light has a wavelength (the distance between crests) and a corresponding frequency (the number of crests passing a point in a given amount of time). Planck had shown that light of a particular frequency had a definite amount of energy; that is, energy is quantized. This seemed to favor the belief that light was wavelike in nature.

Nevertheless, five years later, in 1905, American physicist Albert Einstein Einstein, Albert reasoned that light behaved like particles. Einstein used Planck’s theory of quantized light to explain why light striking the surface of certain metals resulted in the ejection of electrons from that metal (the photoelectric effect), Photoelectric effect but only when this involved certain frequencies of light. He pictured the light striking the metal surface as particles of light, or photons, with sufficient energy to knock off electrons.

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The wave-particle nature of light was constantly debated and seemed dependent upon the experiment being performed. For example, the dispersion of white light into its component colors by a prism is a result of the wave nature of light. By contrast, the ability of a stream of photons to eject electrons from a metal surface points to the particle nature of light. Einstein had shown by his relativity theory that light could behave like both waves and particles and that the physical properties of each nature were related. He showed that the momentum of the photon Photons (a particle property) was related to the wavelength of the light (a wave property). Einstein’s results demonstrated that light has wave and particle duality.

Louis de Broglie had been studying Planck’s theories of quantized light and Einstein’s wave-particle concept of light. He wrote several papers calling attention to the dual behavior of light. De Broglie wished to provide a mechanical explanation for the wave-particle duality. Thus he needed to find a mechanical reason for a particle—the photon—to have an energy that was determined by a wave, or rather by the frequency of that wave. While he was thinking about light, de Broglie had the idea that matter (a particle) might have a wave nature also.

At about this time, Niels Bohr had revealed a theory for the electronic structure of atoms. Atoms;structure Bohr’s Bohr model of the atom theory was that the electrons Electrons in an atom were restricted to particular energy levels and positions called “orbitals.” Only by exact additions of unit amounts of energy could the energy and orbital of an electron be changed.

De Broglie was struck by the analogy of Bohr’s orbital energies to standing waves. As a result, de Broglie discovered an example of wave-particle duality in matter. De Broglie used his explanations of the wave-particle duality of matter in writing his doctoral dissertation in physics, which he presented before the Faculty of Sciences at the University of Paris in 1923. His theory demonstrated that matter, like light, has a wavelike nature.

De Broglie noticed that the momentum of the electron orbitals proposed by Bohr were whole number units of a fundamental quantity, Planck’s constant. Planck’s constant[Plancks constant] He knew that standing waves had unit changes in their momenta also. A standing wave can be thought of as a string, fixed at both ends, that is plucked. The string will oscillate back and forth, yet some points will remain at rest. The number of rest points will increase as the frequency of the vibration increases. De Broglie reasoned that Bohr’s orbitals could therefore be seen as a circular string, a snake swallowing its own tail.

Moreover, de Broglie discovered that the matter waves he had proposed fit Bohr’s electron orbits exactly. He also found that the momenta and wavelengths of his matter waves were related, like those of light. He had succeeded in explaining Bohr’s orbits: Each orbit was a steady wave pattern, and these orbits had determined and fixed sizes so that these distinct “quantized” wave patterns could exist.

When de Broglie somewhat reluctantly submitted his dissertation, the faculty at the University of Paris was unsure of the use of strings to explain Bohr’s orbits and asked Einstein to judge the acceptability of the dissertation. Einstein confirmed that it was sound. The thesis was accepted, and later de Broglie was awarded the Nobel Prize. Nobel Prize recipients;Louis de Broglie[Broglie]

Significance

De Broglie’s waves had offered a picture of what was occurring inside an atom. A way to visualize the shifting patterns of the wave was needed when the atom changed energy and produced light. Erwin Schrödinger, an Austrian physicist, found a mathematical equation that explained the changing wave patterns inside an atom. Schrödinger’s equation Schrödinger’s wave equation[Schrodingers wave equation] provides a continuous mathematical description of the wave-particle duality of matter. He viewed the atom as analogous to de Broglie’s vibrating string. The movement of the electron from one orbit to another was a simple change in the frequency of the standing waves of the string. In a musical string, this occurs as the harmony of two wave patterns, the result being the differences in the frequency of the two waves.

The understanding of the wave-particle duality of matter, as modeled by Schrödinger’s equation, was instrumental in the founding of quantum Quantum theory physics. Quantum physics has been responsible for many of the technological advances in the twentieth century. These advances are traceable to de Broglie’s pronouncement of the wave-particle duality of matter. Wave-particle duality of light[Wave particle duality of light] Light, wave-particle duality[Light, wave particle duality]

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Cropper, William H. Great Physicists: The Life and Times of Leading Physicists from Galileo to Hawking. New York: Oxford University Press, 2001. Presents portraits of the lives and accomplishments of important physicists and shows how they influenced one another with their work. Chapter 19 is devoted to Schrödinger and de Broglie. Includes glossary and index.
  • citation-type="booksimple"

    xlink:type="simple">Ford, Kenneth W. The Quantum World: Quantum Physics for Everyone. Cambridge, Mass.: Harvard University Press, 2004. Explains the concepts of quantum physics in nontechnical language for lay readers. Illustrated.
  • citation-type="booksimple"

    xlink:type="simple">Guillemin, Victor. The Story of Quantum Mechanics. 1968. Reprint. Mineola, N.Y.: Dover, 2003. Conveys for the general reader factual information and insight into the ways professional scientists think and work. Presents the historical background of quantum mechanics as well as the theories and models of atomic and subatomic particles. Concludes with consideration of the philosophical implications of quantum physics.
  • citation-type="booksimple"

    xlink:type="simple">Hoffmann, Banesh. The Strange Story of the Quantum. 2d ed. New York: Dover, 1959. Nontechnical guide to the development of quantum mechanics for the general reader provides a treasure of insight into the persons, places, and pitfalls encountered in the early history of quantum physics. Highly recommended for those interested in the development of quantum physics.
  • citation-type="booksimple"

    xlink:type="simple">Jammer, Max. The Philosophy of Quantum Mechanics. New York: John Wiley & Sons, 1974. Addresses the analysis of the concepts, philosophy, and interrelation of the mechanics and ideas of the new physics and provides a guide to the literature of the subject.
  • citation-type="booksimple"

    xlink:type="simple">McQuarrie, Donald A. Quantum Chemistry. Mill Valley, Calif.: University Science Books, 1983. Textbook traces the beginnings of quantum mechanics and utilizes the results in discussion of molecules. Provides background and conclusions based on the earliest works in quantum physics. Includes brief biographies of the principal characters in the development of the field. Excellent treatment of the historical beginnings of quantum mechanics on a technical level.
  • citation-type="booksimple"

    xlink:type="simple">Wolf, Fred Alan. Taking the Quantum Leap: The New Physics for Nonscientists. Rev. ed. New York: Harper & Row, 1989. Outstanding book traces the earliest debates and experiments concerning the philosophy and practice of quantum physics. Presents science from a humanized perspective that is accurate, historical, and conceptual, leading the reader to a solid, nontechnical grasp and beyond. Highly recommended for anyone interested in quantum physics.

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