Rapiditate de lumine

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Rapiditate de Lumine
Le distantia ab le Sol al Terra es monstrate como 150 million kilometros.
Lumine del Sol require circa 8 minutas, 19 secundas de arrivar le Terra
Valores exacte
metros per secunda 299.792.458
unitates Planck 1
Valores approximative
kilometros per secunda 300.000
kilometros per hora 1079 million
millias per secunda 186.000
millias per hora 671 million
astronomic unitates per die 173
Approximative duration de percurrition de signals luminal
Distantia Tempore
un pede 1,0 ns
un metro 3,3 ns
un kilometro 3,3 µs
un millia 5,4 µs
ab orbita geostationari al Terra 119 ms
le longitude del equator del Terra 134 ms
ab le Luna al Terra 1,3 s
ab le Sol al Terra (1 AU) 8,3 min
one parsec 3,26 annos
ab Alpha Centauri al Terra 4,4 annos
ab le galaxia le plus proxime al Terra 25,000 annos
trans le Via Lactee 100.000 annos
ab le Galaxia de Andromeda al Terra 2,5 million annos

Le rapiditate de lumine, normalmente denotate per c, es un constante physic que es importante in multe areas del physica. Lumine e omne altere radiation electromagnetic semper propaga a iste rapiditate in spatio vacue (un vacuo), indifferente del motion del origine o le referimento inertial del observator. Le valor de c equala exactemente 299.792.458 metros per secunda[1] (circa 186.282 millias per secunda o 1 pede per nanosecunda). In le theoria de relativitate, c connecte spatio e tempore, e illo appare in le equation famose del equivalentia de massa e energia E = mc2.[2] Le rapiditate de lumine es le rapiditate de omne particulas sin massa e campos associate in vacuo, e isto es predicite per le theoria currente de esser le rapiditate de gravitate e de undas gravitational e un limite superior pro le rapiditate del motion de energia, materia, e information.

Le rapiditate de lumine in un material transparente, tal como aqua o vitro, es minus de c. Le ratio inter c e le rapiditate v a qual lumine move in un material es appelate le indice de refraction n del material (n = c/v). Pro exemplo, pro lumine vidibile, le indice de refraction de vitro es circa 1,5; dunque, lumine in vitro propaga a c/1,5 ≈ 200.000 km/s. Le indice de refraction del aer pro lumine vidibile es circa 1,0003, quo le rapiditate de lumine in aer es quasi c.

In multe casos practic, lumine pote esser considerate de mover instantaneemente, sed pro distantias longe e mesurations multe sensibile, le finite rapiditate de lumine pote haber effectos observabile. In communications con distante sondas spatial, es pote requirer minutas a horas pro un message de ir ab le Terra al satellite e retornar. Le lumine de stellas nos vide partite los stellas multe annos passato; lumine ab le plus proxime stella, Alpha Centauri, require 4,4 annos de arrivar al Terra. Le rapiditate finite de lumine limites le rapiditate maximal theoric de computators, depost information propaga in le computator in circuitos de dimension finite. Finalmente, le rapiditate de lumine pote esser usate con mesurations de tempore de volo de mesurar distantias grande a precision alte.

Ole Rømer esseva le primo de demonstrar (in 1676) que lumine move a un rapidate finite (in loco de instantaneemente) per le studio de le motion apparente de Io, un luna de Jupiter. In 1905, Albert Einstein postulate que le rapiditate de lumine in vacuo esseva independente del origine o referimento inertial, explorate le consequentias de lo postulato in le theoria de relativitate special, e monstrate que le parametro c habeva pertinentia extra del contexto de lumine e electromagnetismo. Post seculos de accrescentemente precise mesurations, in 1975 le rapiditate de lumine esseva sapite de esser 299.792.458 m/s con un incertitude relative de mesuration de of 4 partes per billion. In 1983, le metro esseva redefinite in le Systema International de Unitates (SI) como le distantia movite per lumine in vacuo in in 1/299792458 de un secunda. Como resultato, le valor numeric de c in metros per secunda es nunc fixate exactemente per le definition del metro.[3]

Valor numeric, notation, e unitates[modificar | modificar fonte]

Le rapiditate de lumine in vacuo es un dimensional constante physic, si su valor numeric depende sur le systema de unitates usate. In Systema International de Unitates (SI), le metro es definite per le distantia lumine move in vacuo in 1/299792458 de un secunda. Le effecto de iste definition es de fixar le rapiditate de lumine in vacuo a exactemente 299.792.458 m/s. Le rapiditate de lumine pote anque esser exprimite in unitates imperial e S.U.A., basate sur un unicia de exactemente 2,54 cm, como 186.282 millis, 698 yardes, 2 pedes, e 5 21/127 uncias per secunda. [4] [5] [6]

Le rapiditate de lumine in vacuo es normalmente denote per c, pro "constante" o le latin celeritas. Originalmente, le symbolo V esseva usate, introducite per James Clerk Maxwell in 1865. In 1856, Wilhelm Eduard Weber e Rudolf Kohlrausch habite usate c pro un constante depost monstrava de equalar √2 vice le rapiditate de lumine in vacuo. In 1894, Paul Drude redefinite c con su signification moderne. Einstein usate V in su original discursos (in german) sur relativitate special in 1905, sed in 1907, ille cambiate a c, que de alora habite devenite le symbolo standard. [7] [8] Aliquandos c es usate pro le rapiditate de undas in alicun medio material, e c0 pro le rapiditate in vacuo. [9] Iste subindicate notation, que es appoiate per official literatura del SI, ha le mesme forma como altere connexe constantes: a saper, µ0 pro le permeabilitate del vacuo o constante magnetic, ε0 pro le permittivitate del vacuo o constante electric, e Z0 pro le impedantia de spatio libere. Iste articulo use c exclusivemente pro le rapiditate de lumine in vacuo. In areas de physica in que le rapiditate de lumine es importante, pro exemplo in relativitate, il es commun de usar systemas de unitates natural de mesuration in que c = 1.0. Quando tal systema de mesuration es usate, le rapiditate de lumine evanesce del equationes de physica, perque multiplication o division per 1 non affice le resulto.

Rolo fundamental in physica[modificar | modificar fonte]

Le rapiditate de lumine in vacuo es independente ambe del motion del origine del lumine e del referentia inertial del observator. Iste invariantia del rapiditate de lumine esseva postulate per Einstein in 1905, motivate per le theoria de electromagnetismo de Maxwell e le manco de evidentia pro le luminifere ether. [10] Le invariantia ha depost essite consistentemente confirmate per multe experimentos. [11] [12] Le theoria de relativitate special explora le consequentias del realitate del invariantia de c e le hypothese que le leges de physica es le mesme in omne referentias inertial. [13] [14] Un consequentia is que c es le rapiditate a le qual omne particulas e undas sin massa, includente lumine, debe mover.

Le Lorentz factor γ es un function de velocitate v (o rapiditate). Il comencia a 1 e approcha infinitate como v approcha c. Relativitate special ha multe contra-intuitive implicationes, que ha essite verificate in multe experimentos. [15] Istos include le equivalentia de massa e energia (E = mc2), contraction de longitude (objectos movente abbrevia), e dilation de tempore (horologios movente decelera). Le factor γ per le qual longitudes contrahe e tempores dilata, sapite como le Lorentz factor, es date per (1 - v2/c2), ubi v es le rapiditate del objecto. A quotidian rapiditates (v << c), γ ≈ 1 e relativitate special es approximate per relativitate de Galileo. Comocunque, como v accresce, γ > 1 e effectos relativistic appare, e γ → ∞ como vc.

Le resultatos de relativitate special pote esser summarisate si on considera spatio e tempore como un structura unificate sapite como spatio-tempore (con c refere le unitates de spatio e tempore), e require que theorias physic satisface un symmetria special appelate Lorentz invariantia, cuje formulation mathematic contine le parametro c. [16] Lorentz invariantia ha devenite un quasi universal supposition de moderne theorias physic, tal como electrodynamica quantic, chromodynamica quantic, le Modello Standard del physica de particulas, e relativitate general. Como tal, le parametro c es omnipresente in physica moderne, que appare in multe contextos que sembla esser non connexe a lumine. Pro exemplo, relativitate general predice que c es anque le rapiditate de gravitate e de undas gravitational. [17] [18] In referentias non-intertial, (spatio curvate per gravitate o accelerate referentias), le rapiditate local de lumine es constante e equal de c, sed le rapiditate de lumine preter un trajectoria de longitude finite pote differer ab c, dependente sur como le distantias e durations es definite. [19]

Il es supponite generalmente in physica que constantes fundamental tal como c ha le mesme valor in omne partes de spatio-tempore, que significa illos es independente de location e invariante in tempore. Comocunque, alicun physicos ha propone le possibilitate que le rapiditate de lumine ha alterate durante tempore. [20] No evidentia conclusive pro tal alterations ha essite fundate, sed illes remane le subjecto de recerca. [21] [22] Il es anque supponite generalmente in physica que c ha le mesme valor indifferente del direction de propagation, significante que illo es isotropic. Le Michelson-Morely experimento prescribe un limite sur le anisotropia de circa 10-4. Comocunque, plus recente observationes del emissions ab nivellos energetic nucleari per un function del orientation del nucleos emittente in un campo magnetic ha reducite iste limite a 10-21. [23] Provas de isotropia continua esser de experimental interesse. Pro exemplo, un accostamento nove al provas de Lorentz invariantia pro undas electromagnetic compara le resonante frequentias de resonatores optical como un function de orientation in spatio. Tal provas ha constatate un limite sur anisotropia de circa 10-10. [24]

Vide etiam[modificar | modificar fonte]

Referentias[modificar | modificar fonte]

  1. Penrose, R (2004). The Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books. pp. 410–1. ISBN 978-0-679-77631-4.
  2. Uzan, J-P; Leclercq, B (2008). The Natural Laws of the Universe: Understanding Fundamental Constants (http:/ / books. google. com/ ?id=dSAWX8TNpScC& pg=PA43). Springer. pp. 43–4. ISBN 0-387-73454-6.
  3. International Bureau of Weights and Measures (2006), The International System of Units (SI) (http:/ / www. bipm. org/ utils/ common/ pdf/ si_brochure_8_en. pdf) (8th ed.), p. 112, ISBN 92-822-2213-6
  4. Sydenham, PH (2003). "Measurement of length" (http://books.google.com/books?id=sarHIbCVOUAC& pg=PA56).In Boyes, W. Instrumentation Reference Book (3rd ed.). Butterworth–Heinemann. p. 56. ISBN 0-7506-7123-8
  5. "CODATA value: Speed of Light in Vacuum" (http://physics.nist.gov/cgi-bin/cuu/Value?c).The NIST reference on Constants, Units, and Uncertainty. NIST. . Retrieved 2009-08-21.
  6. Jespersen, J; Fitz-Randolph, J; Robb, J (1999). From Sundials to Atomic Clocks: Understanding Time and Frequency (http://books.google.com/?id=Z7chuo4ebUAC& pg=PA280) (Reprint of National Bureau of Standards 1977, 2nd ed.). Courier Dover. p. 280. ISBN 0-486-40913-9
  7. Gibbs, P (2004). "Why is c the symbol for the speed of light?" (http://www.webcitation.org/5lLMPPN4L). Usenet Physics FAQ. University of California, Riverside. Archived from the original (http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/c.html) on 2009-11-17. Retrieved 2009-11-16.
  8. Mendelson, KS (2006). "The story of c" (subscription required). American Journal of Physics 74 (11): 995–997. doi:10.1119/1.2238887.
  9. Lawrie, ID (2002). "Appendix C: Natural units" (http://books.google.com/books?id=9HZStxmfi3UC& pg=PA540). A Unified Grand Tour of Theoretical Physics (2nd ed.). CRC Press. p. 540. ISBN 0-7503-0604-1.
  10. Einstein, A (1905). "Zur Elektrodynamik bewegter Körper" (http://www.pro-physik.de/Phy/pdfs/ger_890_921.pdf) (in german). Annalen der Physik 17: 890–921.
  11. Hsu, L (2006). "Appendix A: Systems of units and the development of relativity theories" (http://books.google.com/books?id=amLqckyrvUwC& pg=PA428). A Broader View of Relativity: General Implications of Lorentz and Poincaré Invariance (2nd ed.). World Scientific. pp. 427–8. ISBN 981-256-651-1.
  12. Zhang, YZ (1997). Special Relativity and Its Experimental Foundations (http://www.worldscibooks.com/physics/3180.html). Advanced Series on Theoretical Physical Science. 4. World Scientific. pp. 172–3. ISBN 981-02-2749-3.
  13. d'Inverno, R (1992). Introducing Einstein's Relativity. Oxford University Press. pp. 19–20. ISBN 0-19-859686-3.
  14. Sriranjan, B (2004). "Postulates of the special theory of relativity and their consequences" (http://books.google.com/books?id=FsRfMvyudlAC& pg=PA20#v=onepage& q=& f=false). The Special Theory to Relativity. PHI Learning. pp. 20 ff. ISBN 81-203-1963-X.
  15. Roberts, T; Schleif, S; Dlugosz, JM (ed.) (2007). "What is the experimental basis of Special Relativity?" (http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html). Usenet Physics FAQ. University of California, Riverside.
  16. Hartle, JB (2003). Gravity: An Introduction to Einstein's General Relativity. Addison-Wesley. pp. 52–9. ISBN 981-02-2749-3.
  17. Hartle, JB (2003). Gravity: An Introduction to Einstein's General Relativity. Addison-Wesley. p. 332. ISBN 981-02-2749-3.
  18. Schäfer, G; Brügmann, MH (2008). "Propagation of light in the gravitational filed of binary systems to quadratic order in Newton's gravitational constant: Part 3: ‘On the speed-of-gravity controversy’" (http://books.google.com/?id=QYnfdXOI8-QC& pg=PA111). In Dittus, H; Lämmerzahl, C; Turyshev, SG. Lasers, clocks and drag-free control: Exploration of relativistic gravity in space. Springer. ISBN 3-540-34376-8.
  19. Gibbs, P (1997). "Is The Speed of Light Constant?" (http://www.webcitation.org/5lLQD61qh). In Carlip, S. Usenet Physics FAQ. University of California, Riverside.
  20. "‘c’ is the speed of light, isn’t it?". American Journal of Physics 73: 240–7.
  21. Uzan, J-P (2003). "The fundamental constants and their variation: observational status and theoretical motivations". Reviews of Modern Physics 74: 403.
  22. Farrell, DJ; Dunning-Davies, J (2007). "The constancy, or otherwise, of the speed of light" (http:/ / books. google. com/ books?id=CZzOKIcQqxMC& pg=PA71). In Ross, LV. New Research on Astrophysics, Neutron Stars and Galaxy Clusters. Nova Publishers. pp. 71ff. ISBN 1-60021-110-0.
  23. Lang, KR (1999). Astrophysical formulae (http://books.google.com/?id=OvTjLcQ4MCQC& pg=PA152) (3rd ed.). Birkhäuser. p. 152. ISBN 3-540-29692-1.
  24. Herrmann, S; Senger, A; Kovalchuk, E; Müller, H; Peters, A (2005). "Test of the isotropy of the speed of light using a continuously rotating optical resonator". Phys Rev Lett 95: 150401

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