At the same time, Einstein defined a new entity: a particle of light, the "light quantum," now called the photon.
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Although his theory differed from the quantum theory of light introduced by Albert Einstein in 1905, his name was adopted for what Einstein had called a light quantum (Lichtquant in German).
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Mark worked on X-ray diffraction. Linus Pauling learned X-ray diffraction from Mark, and that knowledge led to Pauling's seminal work on the structure of proteins. Albert Einstein asked Mark and his colleagues worked to use the intense and powerful X-ray tubes available at their laboratory to verify the Compton Effect; this work provided the strongest confirmation yet of Einstein's light quantum theory for which he won the Nobel Prize in Physics.
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Modern optics encompasses the areas of optical science and engineering that became popular in the 20th century. These areas of optical science typically relate to the electromagnetic or quantum properties of light but do include other topics. A major subfield of modern optics, quantum optics, deals with specifically quantum mechanical properties of light. Quantum optics is not just theoretical; some modern devices, such as lasers, have principles of operation that depend on quantum mechanics.
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From that time to the 1920s, physicists were seeking to explain atomic spectra and blackbody radiation. One attempt to explain hydrogen spectral lines was the Bohr atom model. Experiments including electromagnetic radiation and matter - such as the photoelectric effect, Compton effect, and spectra of sunlight the due to the unknown element of Helium, the limitation of the Bohr model to Hydrogen, and numerous other reasons, lead to an entirely new mathematical model of matter and light: quantum mechanics.
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According to the formalism of quantum theory, the effect of measurement happens instantly, no matter how far apart the particles are. It is not possible to use this effect to transmit classical information at faster-than- light speedsRoger Penrose, The Road to Reality: A Complete Guide to the Laws of the Universe, London, 2004, p. 603. (see Faster-than-light § Quantum mechanics). Entanglement is broken when the entangled particles decohere through interaction with the environment—for example, when a measurement is madeAsher Peres, Quantum Theory: Concepts and Methods, Kluwer, 1993; p. 115.
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The transmission of energy from opposite sides of the bubble to a single point would occur faster than light, violating the principle of locality. In the end, it was experiment, not any theoretical argument, that finally enabled the concept of the light quantum to prevail. In 1923, Arthur Compton was studying the scattering of high energy X-rays from a graphite target. Unexpectedly, he found that the scattered X-rays were shifted in wavelength, corresponding to inelastic scattering of the X-rays by the electrons in the target.
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Einstein was the first physicist to say that Planck's discovery of the quantum (h) would require a rewriting of the laws of physics. To support his point, in 1905 he proposed that light sometimes acts as a particle which he called a light quantum (see photon and wave–particle duality). Bohr was one of the most vocal opponents of the photon idea and did not openly embrace it until 1925.Pais The photon appealed to Einstein because he saw it as a physical reality (although a confusing one) behind the numbers.
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He assumed a hypothetical electrically charged oscillator in a cavity that contained black-body radiation could only change its energy in a minimal increment, E , that was proportional to the frequency of its associated electromagnetic wave. He was able to calculate the proportionality constant, h , from the experimental measurements, and that constant is named in his honor. In 1905, the value E was associated by Albert Einstein with a "quantum" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle.
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The result of the experiment might have shocked Albert Einstein (he died in 1955 long before the experiment was performed) who had a local, realistic outlook on physics. His outlook led him to the conclusion that if the act of measurement influences both systems, then there would exist an influence capable of propagating from one system to the other, at a speed not limited by the speed of light. Quantum mechanical formalism anticipates that the influence of measuring the components of an entangled system has an immediate effect on both components, no matter the distance. Later in 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen (E.
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1926 Gilbert N. Lewis letter which brought the word "photon" into common usage 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". 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.. An English translation is available from Wikisource. He called such a wave-packet the light quantum (German: das Lichtquant).
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