In the early 19th century, Thomas Young and August Fresnel clearly demonstrated the interference and diffraction of light, and by 1850 wave models were generally accepted.
James Clerk Maxwell's 1865 prediction that light was an electromagnetic wave—which was confirmed experimentally in 1888 by Heinrich Hertz's detection of radio waves—seemed to be the final blow to particle models of light. The Maxwell wave theory, however, does not account for all properties of light.
James Clerk Maxwell's 1865 prediction that light was an electromagnetic wave—which was confirmed experimentally in 1888 by Heinrich Hertz's detection of radio waves—seemed to be the final blow to particle models of light. The Maxwell wave theory, however, does not account for all properties of light.
Recently, photons have been studied as elements of quantum computers, and for applications in optical imaging and optical communication such as quantum cryptography. ==Nomenclature== The word quanta (singular quantum, Latin for how much) was used before 1900 to mean particles or amounts of different quantities, including electricity.
In 1900, the German physicist Max Planck was studying black-body radiation, and he suggested that the experimental observations, specifically at shorter wavelengths, would be explained if the energy stored within a molecule was a "discrete quantity composed of an integral number of finite equal parts", which he called "energy elements".
This symbol for the photon probably derives from gamma rays, which were discovered in 1900 by Paul Villard, named by Ernest Rutherford in 1903, and shown to be a form of electromagnetic radiation in 1914 by Rutherford and Edward Andrade.
This symbol for the photon probably derives from gamma rays, which were discovered in 1900 by Paul Villard, named by Ernest Rutherford in 1903, and shown to be a form of electromagnetic radiation in 1914 by Rutherford and Edward Andrade.
In 1905, Albert Einstein published a paper in which he proposed that many light-related phenomena—including black-body radiation and the photoelectric effect—would be better explained by modelling electromagnetic waves as consisting of spatially localized, discrete wave-packets.
In 1905, Einstein was the first to propose that energy quantization was a property of electromagnetic radiation itself.
(See and , below.) Einstein's 1905 predictions were verified experimentally in several ways in the first two decades of the 20th century, as recounted in Robert Millikan's Nobel lecture.
In 1909 and 1916, Einstein showed that, if Planck's law regarding black-body radiation is accepted, the energy quanta must also carry momentum , making them full-fledged particles.
However, Debye's approach failed to give the correct formula for the energy fluctuations of black-body radiation, which were derived by Einstein in 1909. In 1925, Born, Heisenberg and Jordan reinterpreted Debye's concept in a key way.
Ironically, Max Born's probabilistic interpretation of the wave function was inspired by Einstein's later work searching for a more complete theory. ==Quantum field theory== ===Quantization of the electromagnetic field=== In 1910, Peter Debye derived Planck's law of black-body radiation from a relatively simple assumption.
This symbol for the photon probably derives from gamma rays, which were discovered in 1900 by Paul Villard, named by Ernest Rutherford in 1903, and shown to be a form of electromagnetic radiation in 1914 by Rutherford and Edward Andrade.
The same name was used earlier but was never widely adopted before Lewis: in 1916 by the American physicist and psychologist Leonard T.
In 1909 and 1916, Einstein showed that, if Planck's law regarding black-body radiation is accepted, the energy quanta must also carry momentum , making them full-fledged particles.
By the spin-statistics theorem, all bosons obey Bose–Einstein statistics (whereas all fermions obey Fermi–Dirac statistics). ==Stimulated and spontaneous emission== In 1916, Albert Einstein showed that Planck's radiation law could be derived from a semi-classical, statistical treatment of photons and atoms, which implies a link between the rates at which atoms emit and absorb photons.
Troland, in 1921 by the Irish physicist John Joly, in 1924 by the French physiologist René Wurmser (1890–1993), and in 1926 by the French physicist Frithiof Wolfers (1891–1971).
Troland, in 1921 by the Irish physicist John Joly, in 1924 by the French physiologist René Wurmser (1890–1993), and in 1926 by the French physicist Frithiof Wolfers (1891–1971).
However, this cannot be an uncertainty relation of the Kennard–Pauli–Weyl type, since unlike position and momentum, the phase \phi cannot be represented by a Hermitian operator. ==Bose–Einstein model of a photon gas== In 1924, Satyendra Nath Bose derived Planck's law of black-body radiation without using any electromagnetism, but rather by using a modification of coarse-grained counting of phase space.
However, Debye's approach failed to give the correct formula for the energy fluctuations of black-body radiation, which were derived by Einstein in 1909. In 1925, Born, Heisenberg and Jordan reinterpreted Debye's concept in a key way.
Lewis, who coined the term in a letter to Nature on December 18, 1926.
Troland, in 1921 by the Irish physicist John Joly, in 1924 by the French physiologist René Wurmser (1890–1993), and in 1926 by the French physicist Frithiof Wolfers (1891–1971).
Not long thereafter, in 1926, Paul Dirac derived the B_{ij} rate constants by using a semiclassical approach, and, in 1927, succeeded in deriving all the rate constants from first principles within the framework of quantum theory.
This photon momentum was observed experimentally by Arthur Compton, for which he received the Nobel Prize in 1927.
Not long thereafter, in 1926, Paul Dirac derived the B_{ij} rate constants by using a semiclassical approach, and, in 1927, succeeded in deriving all the rate constants from first principles within the framework of quantum theory.
Arthur Compton used photon in 1928, referring to Gilbert N.
Although the evidence from chemical and physical experiments for the existence of photons was overwhelming by the 1970s, this evidence could not be considered as absolutely definitive; since it relied on the interaction of light with matter, and a sufficiently complete theory of matter could in principle account for the evidence.
Nevertheless, all semiclassical theories were refuted definitively in the 1970s and 1980s by photon-correlation experiments.
The unification of the photon with W and Z gauge bosons in the electroweak interaction was accomplished by Sheldon Glashow, Abdus Salam and Steven Weinberg, for which they were awarded the 1979 Nobel Prize in physics.
Nevertheless, all semiclassical theories were refuted definitively in the 1970s and 1980s by photon-correlation experiments.
In the same papers, Einstein extended Bose's formalism to material particles (bosons) and predicted that they would condense into their lowest quantum state at low enough temperatures; this Bose–Einstein condensation was observed experimentally in 1995.
It was later used by Lene Hau to slow, and then completely stop, light in 1999 and 2001. The modern view on this is that photons are, by virtue of their integer spin, bosons (as opposed to fermions with half-integer spin).
It was later used by Lene Hau to slow, and then completely stop, light in 1999 and 2001. The modern view on this is that photons are, by virtue of their integer spin, bosons (as opposed to fermions with half-integer spin).
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