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Encyclopedia > Quantum

In physics, a quantum (plural: quanta) is an indivisible entity of energy. For instance, a photon, being a unit of light, is a "light quantum." In combinations like "quantum mechanics", "quantum optics", etc., it distinguishes a more specialized field of study. The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the branch of science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ... An entity is something that has a distinct, separate existence, though it need not be a material existence. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... In physics, the photon (from Greek φοτος, meaning light) is a quantum of excitation of the quantised electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED) which is the oldest part of the Standard Model of particle physics. ... Fig. ... Quantum optics is a field of research in physics, dealing with the application of quantum mechanics to phenomena involving light and its interactions with matter. ...


The word comes from the Latin "quantus," for "how much." Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ...


Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. For example, the energy of an electron bound to an atom (at rest) is quantized. This accounts for the stability of atoms, and matter in general. In physics, quantization is a procedure for constructing a quantum field theory starting from a classical field theory. ... This article discusses the use of the word Number in Mathematics. ... e- redirects here. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ... This article or section does not cite any references or sources. ...


An entirely new conceptual framework was developed around this idea, during the first half of the 1900s. Usually referred to as quantum "mechanics", it is regarded by virtually every professional physicist as the most fundamental framework we have for understanding and describing nature, for the very practical reason that it works. It is "in the nature of things", not a more or less arbitrary human preference.

Contents

Development of quantum theory

Quantum theory, the branch of physics which is based on quantization, began in 1900 when Max Planck published his theory explaining the emission spectrum of black bodies. In that paper Planck used the Natural system of units he invented the previous year. The consequences of the differences between classical and quantum mechanics quickly became obvious. But it was not until 1926, by the work of Werner Heisenberg, Erwin Schrödinger, and others, that quantum mechanics became correctly formulated and understood mathematically. Despite tremendous experimental success, the philosophical interpretations of quantum theory are still widely debated. Fig. ... Year 1900 (MCM) was an exceptional common year starting on Monday (link will display the full calendar) of the Gregorian calendar, but a leap year starting on Saturday of the Julian calendar. ... Max Karl Ernst Ludwig Planck (April 23, 1858 – October 4, 1947 in Göttingen, Germany) was a German physicist. ... A materials emission spectrum is the amount of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited). ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... In physics, Planck units are physical units of measurement defined exclusively in terms of the five universal physical constants shown in the table below in such a manner that all of these physical constants take on the numerical value of one when expressed in terms of these units. ... The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. ... Year 1898 (MDCCCXCVIII) was a common year starting on Saturday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 12-day-slower Julian calendar). ... Classical mechanics is a branch of physics which studies the deterministic motion of objects. ... Year 1926 (MCMXXVI) was a common year starting on Friday (link will display the full calendar) of the Gregorian calendar. ... Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics, and acknowledged to be one of the most important physicists of the twentieth century. ... Bust of Schrödinger, in the courtyard arcade of the main building, University of Vienna, Austria. ... Fig. ...


Planck was reluctant to accept the new idea of quantization, as were many others. But, with no acceptable alternative, he continued to work with the idea, and found his efforts were well received. Eighteen years later, when he accepted the Nobel Prize in Physics for his contributions, he called it "a few weeks of the most strenuous work" of his life. During those few weeks, he even had to discard much of his own theoretical work from the preceding years. Quantization turned out to be the only way to describe the new and detailed experiments which were just then being performed. He did this practically overnight, openly reporting his change of mind to his scientific colleagues, in the October, November, and December meetings of the German Physical Society, in Berlin, where the black body work was being intensely discussed. In this way, careful experimentalists (including F. Paschen, O.R. Lummer, Ernst Pringsheim, Heinrich Rubens, and F. Kurlbaum), and a reluctant theorist, ushered in a momentous scientific revolution. WERD Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ... The Deutsche Physikalische Gesellschaft (DPG) is a worldwide operating physics organization. ... This article is about the capital of Germany. ... Ernst Pringsheim: Ernst Pringsheim, Sr. ... Heinrich Rubens (30 March 1865 - 17 July 1922) was a German physicist. ...


The quantum black-body radiation formula

When a body is heated, it emits radiant heat, a form of electromagnetic radiation in the infrared region of the EM spectrum. All of this was well understood at the time, and of considerable practical importance. When the body becomes red-hot, the red wavelength parts start to become visible. This had been studied over the previous years, as the instruments were being developed. However, most of the heat radiation remains infrared, until the body becomes as hot as the surface of the Sun (about 6000 °C, where most of the light is green in color). This was not achievable in the laboratory at that time. What is more, measuring specific infrared wavelengths was only then becoming feasible, due to newly developed experimental techniques. Until then, most of the electromagnetic spectrum was not measurable, and therefore blackbody emission had not been mapped out in detail. Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the objects temperature. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... Image of two girls in mid-infrared (thermal) light (false-color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... The wavelength is the distance between repeating units of a wave pattern. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High...


The quantum black-body radiation formula, being the very first piece of quantum mechanics, appeared Sunday evening October 7, 1900, in a so-called back-of-the-envelope calculation by Planck. It was based on a report by Rubens (visiting with his wife) of the very latest experimental findings in the infrared. Later that evening, Planck sent the formula on a postcard, which Rubens received the following morning. A couple of days later, he informed Planck that it worked perfectly. At first, it was just a fit to the data; only later did it turn out to enforce quantization. Heinrich Rubens (30 March 1865 - 17 July 1922) was a German physicist. ...


This second step was only possible due to a certain amount of luck (or skill, even though Planck himself called it "a fortuitous guess at an interpolation formula"). It was during the course of polishing the mathematics of his formula that Planck stumbled upon the beginnings of Quantum Theory. Briefly stated, he had two mathematical expressions:

  • (i) from the previous work on the red parts of the spectrum, he had x;
  • (ii) now, from the new infrared data, he got x².

Combining these as x(a+x), he still has x, approximately, when x is much smaller than a ( the red end of the spectrum); but now also x² (again approximately) when x is much larger than a (in the infrared). The formula for the energy E, in a single mode of radiation at frequency f, and temperature T, can be written

E = frac{h f}{e^{frac{h f}{k T}} - 1}

This is (essentially) what is being compared with the experimental measurements. There are two parameters to determine from the data, written in the present form by the symbols used today: h is the new Planck's constant, and k is Boltzmann's constant. Both have now become fundamental in physics, but that was by no means the case at the time. The "elementary quantum of energy" is hf. But such a unit does not normally exist, and is not required for quantization. A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... The Boltzmann constant (k or kB) is the physical constant relating temperature to energy. ...


The Birthday of Quantum Mechanics

From the experiments, Planck deduced the numerical values of h and k. Thus he could report, in the German Physical Society meeting on December 14, 1900, where quantization (of energy) was revealed for the first time, values of the Avogadro-Loschmidt number, the number of real molecules in a mole, and the unit of electrical charge, which were more accurate than those known until then. This event has been referred to as "the birthday of quantum mechanics". Avogadros number, also called Avogadros constant (NA), named after Amedeo Avogadro, is formally defined to be the number of carbon-12 atoms in 12 grams (0. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ...


References

  • J. Mehra and H. Rechenberg, The Historical Development of Quantum Theory, Vol.1, Part 1, Springer-Verlag New York Inc., New York 1982.
  • Lucretius, "On the Nature of the Universe", transl. from the Latin by R.E. Latham, Penguin Books Ltd., Harmondsworth 1951. There are, of course, many translations, and the translation's title varies. Some put emphasis on how things work, others on what things are found in nature.
  • M. Planck, A Survey of Physical Theory, transl. by R. Jones and D.H. Williams, Methuen & Co., Ltd., London 1925 (Dover editions 1960 and 1993) including the Nobel lecture.

See also

Fig. ... A quantum state is any possible state in which a quantum mechanical system can be. ... A quantum number describes the energies of electrons in atoms. ... Quantum cryptography is an approach based on quantum physics for secure communications. ... Quantum electronics is an area of physics dealing with the effect of quantum mechanics on the behaviour of electrons in solid-state matter. ... The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers. ... It has been suggested that Quantum coherence be merged into this article or section. ... Quantum coherence refers to the condition of a quantum system whose constituents are in-phase. ... It has been suggested that Quantum suicide be merged into this article or section. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... The magnetic flux quantum Φ0 is the quantum of magnetic flux passing through a superconductor. ... Quantum Cellular Automata (QCA) is any device designed to represent data and perform computation, regardless of the physics principles it exploits and materials used to build it, must have two fundamental properties: distinguishability and conditional change of state. ... Generally, quantization is the state of being constrained to a set of discrete values, rather than varying continuously. ... A subatomic particle is a particle smaller than an atom: it may be elementary or composite. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... Photon polarization is the quantum mechanical description of the classical polarized sinusoidal plane electromagnetic wave. ...

External links

  • http://www.scienceagogo.com/news/20050110221715data_trunc_sys.shtml A demonstration of quantum effect

  Results from FactBites:
 
Quantum mechanics - Wikipedia, the free encyclopedia (5673 words)
Quantum mechanics is a more fundamental theory than Newtonian mechanics and classical electromagnetism, in the sense that it provides accurate and precise descriptions for many phenomena that these "classical" theories simply cannot explain on the atomic and subatomic level.
For instance, the well-known model of the quantum harmonic oscillator uses an explicitly non-relativistic expression for the kinetic energy of the oscillator, and is thus a quantum version of the classical harmonic oscillator.
Quantum electrodynamics is a quantum theory of electrons, positrons, and the electromagnetic field, and served as a role model for subsequent quantum field theories.
Quantum - Wikipedia, the free encyclopedia (1354 words)
For instance, a "light quantum", being a unit of light (that is, a photon).
Usually referred to as quantum "mechanics", it is regarded by virtually every professional physicist as the most fundamental framework we have for understanding and describing nature, for the very practical reason that it works.
Quantum theory, the branch of physics based on quantization, began in 1900 when Max Planck published his theory explaining the emission spectrum of fl bodies.
  More results at FactBites »

 
 

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