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Universe



Main articles: Big Bang, Timeline of the Big Bang, Nucleosynthesis, and Lambda-CDM model

The prevailing Big Bang model accounts for many of the experimental observations described above, such as the correlation of distance and redshift of galaxies, the universal ratio of hydrogen:helium atoms, and the ubiquitous, isotropic microwave radiation background. As noted above, the redshift arises from the metric expansion of space; as the space itself expands, the wavelength of a photon traveling through space likewise increases, decreasing its energy. The longer a photon has been traveling, the more expansion it has undergone; hence, older photons from more distant galaxies are the most red-shifted. Determining the correlation between distance and redshift is an important problem in experimental physical cosmology.

Chief nuclear reactions responsible for the relative abundances of light atomic nuclei observed throughout the universe.
Chief nuclear reactions responsible for the relative abundances of light atomic nuclei observed throughout the universe.

Other experimental observations can be explained by combining the overall expansion of space with nuclear and atomic physics. As the universe expands, the energy density of the electromagnetic radiation decreases more quickly than does that of matter, since the energy of a photon decreases with its wavelength. Thus, although the energy density of the universe is now dominated by matter, it was once dominated by radiation; poetically speaking, all was light. As the universe expanded, its energy density decreased and it became cooler; as it did so, the elementary particles of matter could associate stably into ever larger combinations. Thus, in the early part of the matter-dominated era, stable protons and neutrons formed, which then associated into atomic nuclei. At this stage, the matter in the universe was mainly a hot, dense plasma of negative electrons, neutral neutrinos and positive nuclei. Nuclear reactions among the nuclei led to the present abundances of the lighter nuclei, particularly hydrogen, deuterium, and helium. Eventually, the electrons and nuclei combined to form stable atoms, which are transparent to most wavelengths of radiation; at this point, the radiation decoupled from the matter, forming the ubiquitous, isotropic background of microwave radiation observed today.

Other observations are not answered definitively by known physics. According to the prevailing theory, a slight imbalance of matter over antimatter was present in the universe's creation, or developed very shortly thereafter, possibly due to the CP violation that has been observed by particle physicists. Although the matter and antimatter mostly annihilated one another, producing photons, a small residue of matter survived, giving the present matter-dominated universe. Several lines of evidence also suggest that a rapid cosmic inflation of the universe occurred very early in its history (roughly 10-35 seconds after its creation). Recent observations also suggest that the cosmological constant Λ is not zero and that the net mass-energy content of the universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the universe; by contrast, dark energy serves to accelerate the universe's expansion.

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Multiverse

Main articles: Multiverse, Many-worlds hypothesis, Bubble universe theory, and Parallel universe (fiction)
Artistic depiction of a multiverse of seven "bubble" universes, which are separate spacetime continua, each having different physical laws, physical constants, and perhaps even different numbers of dimensions or topologies.
Artistic depiction of a multiverse of seven "bubble" universes, which are separate spacetime continua, each having different physical laws, physical constants, and perhaps even different numbers of dimensions or topologies.

Some speculative theories have proposed that this universe is but one of a set of disconnected universes, collectively denoted as the multiverse.[10][45] By definition, there is no possible way for anything in one universe to affect another; if two "universes" could affect one another, they would be part of a single universe. Thus, although some fictional characters travel between parallel fictional "universes", this is, strictly speaking, an incorrect usage of the term "universe". The disconnected universes are conceived as being physical, in the sense that each should have its own space and time, its own matter and energy, and its own physical laws. Thus such physical disconnected universes should be distinguished from the metaphysical conception of alternate planes of consciousness, which are not thought to be physical places. The concept of a multiverse of disconnected universes is very old; for example, Bishop Étienne Tempier of Paris ruled in 1277 that God could create as many universes as he saw fit, a question that was being hotly debated by the French theologians.[46]

There are two scientific senses in which multiple universes can occur. First, disconnected spacetime continua may exist; presumably, all forms of matter and energy are confined to one universe and cannot "tunnel" between them. An example of such a theory is the chaotic inflation model of the early universe.[47] Second, according to the many-worlds hypothesis, a parallel universe is born with every quantum measurement; the universe "forks" into parallel copies, each one corresponding to a different outcome of the quantum measurement. Authors have explored this concept in some fiction, most notably Jorge Borges' short story The Garden of Forking Paths. However, both senses of the term "multiverse" are speculative and may be considered unscientific; the fact that universes cannot interact makes it impossible to test experimentally in this universe whether another universe exists.

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See also

Astronomy Portal
Space Portal

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Notes and references

  1. ^ The Compact Edition of the Oxford English Dictionary, volume II, Oxford: Oxford University Press, 1971, p. 3518.
  2. ^ a b Lewis and Short, A Latin Dictionary, Oxford University Press, ISBN 0-19-864201-6, pp. 1933, 1977–1978.
  3. ^ Liddell and Scott, A Greek-English Lexicon, Oxford University Press, ISBN 0-19-864214-8, p.1392.
  4. ^ Liddell and Scott, pp.1345–1346.
  5. ^ Yonge, Charles Duke (1870). An English-Greek lexicon. New York: American Bok Company, p. 567. 
  6. ^ Liddell and Scott, pp.985, 1964.
  7. ^ Lewis and Short, pp. 1881–1882, 1175, 1189–1190.
  8. ^ OED, pp. 909, 569, 3821–3822, 1900.
  9. ^ Feynman RP, Hibbs AR (1965). Quantum Physics and Path Integrals. New York: McGraw-Hill. ISBN 0-07-020650-3. 
    Zinn Justin J (2004). Path Integrals in Quantum Mechanics. Oxford University Press. ISBN 0-19-856674-3. 
  10. ^ a b Ellis, George F.R.; U. Kirchner, W.R. Stoeger (2004). "Multiverses and physical cosmology" (subscription required). Monthly Notices of the Royal Astronomical Society 347: 921–936. 
  11. ^ Lineweaver, Charles; Tamara M. Davis (2005). Misconceptions about the Big Bang. Scientific American. Retrieved on 2007-03-05.
  12. ^ Rindler (1977), p. 196.
  13. ^ Christian, Eric. How large is the Milky Way?. Retrieved on 2007-11-28.
  14. ^ I. Ribas, C. Jordi, F. Vilardell, E.L. Fitzpatrick, R.W. Hilditch, F. Edward (2005). "First Determination of the Distance and Fundamental Properties of an Eclipsing Binary in the Andromeda Galaxy". Astrophysical Journal 635: L37–L40. doi:10.1086/499161. 
    McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; Lewis, G. F.; Tanvir, N. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society 356 (4): 979–997. doi:10.1111/j.1365-2966.2004.08514.x. 
  15. ^ N. Mandolesi, P. Calzolari, S. Cortiglioni, F. Delpino, G. Sironi (1986). "Large-scale homogeneity of the Universe measured by the microwave background". Letters to Nature 319: 751–753. doi:10.1038/319751a0. 
  16. ^ Hinshaw, Gary (November 29, 2006). New Three Year Results on the Oldest Light in the Universe. NASA WMAP. Retrieved on 2006-08-10.
  17. ^ Hinshaw, Gary (December 15, 2005). Tests of the Big Bang: The CMB. NASA WMAP. Retrieved on 2007-01-09.
  18. ^ Rindler (1977), p. 202.
  19. ^ Hinshaw, Gary (February 10, 2006). What is the Universe Made Of?. NASA WMAP. Retrieved on 2007-01-04.
  20. ^ Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results. nasa.gov. Retrieved on 2008-03-06.
  21. ^ Britt RR (2003-01-03). Age of Universe Revised, Again. space.com. Retrieved on 2007-01-08.
  22. ^ Wright EL (2005). Age of the Universe. UCLA. Retrieved on 2007-01-08.
    Krauss LM, Chaboyer B (3 January 2003). "Age Estimates of Globular Clusters in the Milky Way: Constraints on Cosmology". Science 299 (5603): 65–69. American Association for the Advancement of Science. doi:10.1126/science.1075631. 
  23. ^ Wright, Edward L. (September 12, 2004). Big Bang Nucleosynthesis. UCLA. Retrieved on 2007-01-05.
    M. Harwit, M. Spaans (2003). "Chemical Composition of the Early Universe". The Astrophysical Journal 589 (1): 53–57. doi:10.1086/374415. 
    C. Kobulnicky, E. D. Skillman (1997). "Chemical Composition of the Early Universe". Bulletin of the American Astronomical Society 29: 1329. 
  24. ^ Antimatter. Particle Physics and Astronomy Research Council (October 28, 2003). Retrieved on 2006-08-10.
  25. ^ Landau and Lifshitz (1975), p. 361.
  26. ^ WMAP Mission: Results- Age of the Universe
  27. ^ Luminet, Jean-Pierre; Boudewijn F. Roukema (1999). "Topology of the Universe: Theory and Observations". Proceedings of Cosmology School held at Cargese, Corsica, August 1998. Retrieved on 2007-01-05. 
    Luminet, Jean-Pierre; J. Weeks, A. Riazuelo, R. Lehoucq, J.-P. Uzan (2003). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background" (subscription required). Nature 425: 593. 
  28. ^ Strobel, Nick (May 23, 2001). The Composition of Stars. Astronomy Notes. Retrieved on 2007-01-04.
    Have physical constants changed with time?. Astrophysics (Astronomy Frequently Asked Questions). Retrieved on 2007-01-04.
  29. ^ Misner, Thorne and Wheeler (1973), p. 754.
  30. ^ a b c d Misner, Thorne, and Wheeler (1973), p. 755.
  31. ^ Misner, Thorne, and Wheeler (1973), p. 756.
  32. ^ de Cheseaux JPL (1744). Traité de la Comète. Lausanne, pp. 223ff. . Reprinted as Appendix II in Dickson FP (1969). The Bowl of Night: The Physical Universe and Scientific Thought. Cambridge, MA: M.I.T. Press. ISBN 978-0262540032. 
  33. ^ Olbers HWM (1826). "Unknown title". Bode's Jahrbuch 111. . Reprinted as Appendix I in Dickson FP (1969). The Bowl of Night: The Physical Universe and Scientific Thought. Cambridge, MA: M.I.T. Press. ISBN 978-0262540032. 
  34. ^ Jeans, J. H. (1902) Philosophical Transactions Royal Society of London, Series A, 199, 1.
  35. ^ Rindler, p. 196; Misner, Thorne, and Wheeler (1973), p. 757.
  36. ^ Misner, Thorne and Wheeler, p. 756.
  37. ^ a b Einstein, A (1917). "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie". Preussische Akademie der Wissenschaften, Sitzungsberichte 1917 (part 1): 142–152. 
  38. ^ Rindler (1977), pp. 226–229.
  39. ^ Landau and Lifshitz (1975), pp. 358–359.
  40. ^ Einstein, A (1931). "Zum kosmologischen Problem der allgemeinen Relativitätstheorie". Sitzungsberichte der Preussischen Akademie der Wissenschaften, Physikalisch-mathematische Klasse 1931: 235–237. 
    Einstein A, de Sitter W (1932). "On the relation between the expansion and the mean density of the universe". Proceedings of the National Academy of Sciences 18: 213–214. doi:10.1073/pnas.18.3.213. 
  41. ^ Hubble Telescope news release
  42. ^ BBC News story: Evidence that dark energy is the cosmological constant
  43. ^ Zel'dovich YB (1967). "Cosmological constant and elementary particles". Zh. Eksp. & Teor. Fiz. Pis'ma 6: 883–884.  English translation in Sov. Phys. — JTEP Lett., 6, pp. 316–317 (1967).
  44. ^ Friedmann A (1922). "Über die Krümmung des Raumes". Zeitschrift für Physik 10: 377–386. doi:10.1007/BF01332580. 
  45. ^ Munitz MK (1959). "One Universe or Many?". Journal of the History of Ideas 12: 231–255. doi:10.2307/2707516. 
  46. ^ Misner, Thorne and Wheeler (1973), p. 753.
  47. ^ Linde A (1986). "Eternal chaotic inflation". Mod. Phys. Lett. A1: 81. 
    Linde A (1986). "Eternally existing self-reproducing chaotic inflationary universe". Phys. Lett. B175: 395–400. 

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Further reading

  • Weinberg S (1993). The First Three Minutes: A Modern View of the Origin of the Universe, 2nd updated edition, New York: Basic Books. ISBN 978-0465024377. 
  • Rindler W (1977). Essential Relativity: Special, General, and Cosmological. New York: Springer Verlag, pp. 193–244. ISBN 0-387-10090-3. 
  • Weinberg S (1972). Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity. New York: John Wiley and Sons, pp. 407–633. ISBN 0-471-92567-5. 

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