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Topic: De Sitter universe

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De Sitter space

Dioxybenzone

Erlangen program

Amedeo Avogadro

Tychonoff space

Topological space

Empty set

Metric space

Lorentz group

Homeomorphism

ManiFold

Matter

Life (magazine)

Gruffydd ap Cynan

Invariant (mathematics)

	De Sitter universe
		A de Sitter universe is one with a positive cosmological constant and zero matter density.
		There is no Big Bang in a de Sitter universe - expansion is self-similar from an infinite time in the past to an infinite time in the future.
		The model has practical implications as an approximation during the future of the Universe when the cosmological constant is likely to dominate (assuming no changes from the present version of the standard Big Bang model), and during the early universe during a hypothesised period of inflation.
	www.xasa.com /wiki/en/wikipedia/d/de/de_sitter_universe.html (136 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		De Sitter space can be defined as a submanifold of Minkowski space in one higher dimension.
		The metric on de Sitter space is the metric induced from the ambient Minkowski metric.
		De Sitter space is an Einstein manifold since the Ricci tensor is proportional to the metric:
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=de_Sitter_space (557 words)

	Creation - Holographic Universe - Crystalinks
		The original de Sitter spacetime is a model universe first obtained by Dutch astronomer Willem de Sitter in 1917 as a solution of Einstein's equations, including the repulsive force known as the cosmological constant.
		De Sitter's spacetime is empty, expands at an accelerating rate and is very highly symmetrical.
		Using anti-de Sitter spacetime, theorists have devised a concrete example of the holographic principle at work: a universe described by superstring theory functioning in an anti-de Sitter spacetime is completely equivalent to a quantum field theory operating on the boundary of that spacetime [see box above].
	www.crystalinks.com /holouniverse1.html (5110 words)

	Home Sitters
		Trip sitter is a term used by recreational drug users to describe a person who remains sober to ensure the safety of the drug user while he or she is under the influence of a drug.
		De Sitter is a lunar crater that is located near the northern limb of the Moon, to the north of the Baillaud-Euctemon crater pair.
		The interior floor of De Sitter is somewhat irregular and hummocky, with a slender central ridge near the mid-point.
	www.artistbooking.com /trips/83/home-sitters.html (1079 words)

	Sitter biography
		In 1913 de Sitter produced an argument based on observations of double star systems which proved that the velocity of light was independent of the velocity of the source.
		De Sitter's work led directly to Eddington's 1919 expedition to measure the gravitational deflection of light rays passing near the Sun, results which, at that time, could only be obtained during an eclipse.
		De Sitter, unlike Einstein, maintained that relativity actually implied that the universe was expanding, theoretical results which were later verified observationally and accepted by Einstein.
	www-gap.dcs.st-and.ac.uk /~history/Biographies/Sitter.html (497 words)

	Predicting the Expanding Universe: Einstein, De Sitter, Friedman, Lemaitre, & Early Cosmology
		Hubble's work convinced Einstein that the universe is expanding after all and that his cosmological constant was not needed to keep his general theory of relativity from predicting that the universe is expanding.
		In de Sitter's purely theoretical description of the universe, motions in the universe produced the effects of redshifts from large distances.
		De Sitter did this work before Hubble's redshift work, but it was after Vesto Slipher had noticed the tendency for the spiral galaxies to have redshifts.
	astrophysics.suite101.com /article.cfm/predicting_the_expanding_universe (680 words)

	Willem de Sitter - Definition, explanation
		Willem de Sitter (May 6 1872 – November 20 1934) was a mathematician, physicist and astronomer.
		De Sitter was also famous for his research on the planet Jupiter.
		De sitter crater on the Moon is named for him, as is the asteroid 1686 De Sitter.
	www.calsky.com /lexikon/en/txt/w/wi/willem_de_sitter.php (232 words)

	Willem de Sitter - Encyclopedia.com
		Willem de Sitter, 1872-1934, Dutch astronomer and mathematician.
		He suggested a dynamic universe in which there is motion but no matter, in contrast to Einstein's static universe containing matter but no motion.
		In the combined Einstein-de Sitter model, the universe is expanding at a decreasing rate that approaches zero.
	www.encyclopedia.com /doc/1E1-Sitter-W.html (1259 words)

	The Expanding Universe (Cosmology: Ideas)
		De Sitter hoped the model might somehow be adjusted to describe the real universe, provided the density of matter was close enough to zero.
		The most striking thing about his empty universe was an odd effect on light — the farther one went from the mathematical center (the origin of coordinates), the slower the frequency of light vibrations.
		De Sitter had supposed that the density of matter in the universe might be close enough to zero so that his model could work.
	www.aip.org /history/in-progress/cosmology/ideas/expanding.htm (2602 words)

	De Sitter universe - Wikipedia, the free encyclopedia
		A de Sitter universe is a solution to Einstein's field equations of General Relativity which is named after Willem de Sitter.
		If the current acceleration of our universe is due to a cosmological constant then as the universe continues to expand all of the matter and radiation will be diluted.
		Another application of de Sitter space is in the early universe during cosmic inflation.
	en.wikipedia.org /wiki/De_Sitter_universe (404 words)

	AllRefer.com - Willem de Sitter Information
		He contributed to the birth of modern cosmology and was influential in English-speaking countries in bringing the relevance of the general theory of relativity to the attention of astronomers.
		De Sitter was born in Sneek, Friesland, and studied at the University of Groningen and the Royal Observatory, Cape Town, South Africa.
		In 1911 de Sitter outlined how the motion of the constituent bodies of our Solar System might be expected to deviate from predictions based on Newtonian dynamics if Albert Einstein's special relativity theory were valid.
	www.allrefer.com /willem-de-sitter (294 words)

	faqs1_a1
		What mitigates this effect is the expansion of the universe during the dark energy dominated phase and the contraction of the universe after the dark energy dominated phase ends.
		During the contraction phase, the horizon shrinks to an exponentially small size, and the new observable universe is born from just a tiny subvolume of the observable universe of the previous cycle.
		In de Sitter space, there is a well-known bound that the total entropy in an observer's past light cone must be less than the area of the Hubble horizon.
	www.physics.princeton.edu /~steinh/cyclicFAQS/index.html (4862 words)

	World Almanac for Kids
		Nonstatic models of the universe were developed in 1917 by the Dutch astronomer Willem de Sitter (1872–1934), in 1922 by the Russian mathematician Alexander Friedmann (1888–1925), and in 1927 by the Belgian abbé, Georges Lemaître (1894–1966).
		The fate of the Friedmann universe is determined by the average density of matter in the universe.
		Gamow proposed that the universe was created in a gigantic explosion and that the various elements observed today were produced within the first few minutes after the big bang, when the extremely high temperature and density of the universe would fuse subatomic particles into the chemical elements.
	www.worldalmanacforkids.com /explore/space/cosmology.html (2391 words)

	Highbeam Encyclopedia - Search Results for sitter
		Exceptional baby-sitters mean safer children: thanks to the Safe Sitter program, more than 20,000 young people know the basics of superior child care.
		Sitter, Richard J. The Milwaukee Journal Sentinel; 3/7/2006; 341 words; Sitter, Richard J. Age 74.
		Richard John Sitter was born on January 3, 1932 to Alphonse and Margaret (Browning) Sitter.
	www.encyclopedia.com /searchpool.asp?target=sitter (1326 words)

	Friedmann Equation
		The Friedmann equation which models the expanding universe has a parameter k called the curvature parameter which is indicative of the rate of expansion and whether or not that expansion rate is increasing or decreasing.
		This is often referred to as the Einstein-de Sitter universe in recognition of their work in modeling it.
		This kind of universe is described as being a closed universe, or a gravitationally bound universe.
	hyperphysics.phy-astr.gsu.edu /hbase/astro/fried.html (615 words)

	De Sitter space - Wikipedia, the free encyclopedia
		De Sitter space is most easily defined as a submanifold of Minkowski space in one higher dimension.
		The metric on de Sitter space is the metric induced from the ambient Minkowski metric.
		De Sitter space is an Einstein manifold since the Ricci tensor is proportional to the metric:
	en.wikipedia.org /wiki/De_Sitter_space (504 words)

	cosmology
		The more specific study of the origin of the universe and of astronomical systems, such as the solar system, is often called cosmogony.
		It was not until the 16th century that Nicolaus Copernicus developed a model for the universe in which the sun was at the center instead of the earth.
		Nonstatic models of the universe were developed in 1917 by the Dutch astronomer Willem de Sitter, in 1922 by the Russian mathematician Alexander Friedmann, and in 1927 by the Belgian abbé, Georges Lemaître.
	www.geocities.com /SiliconValley/Circuit/7615/cosmology.html (2212 words)

	The Bruce Medalists: Willem de Sitter
		Willem de Sitter studied mathematics at the University of Groningen, where a chance meeting with David Gill led to an invitation to work at Her Majesty’s Observatory at the Cape of Good Hope.
		De Sitter-Suermondt, Eleonora [wife], Willem de Sitter, een Mensenleven (Tjeenk Willink and Zoon, Haarlem, 1948) [in Dutch].
		University of Frankfurt, with Einstein, Ehrenfest, Eddington, and Lorentz
	www.phys-astro.sonoma.edu /BruceMedalists/deSitter/index.html (371 words)

	HubbleSite - Astrofiles about "Hubble Completes Eight-Year Effort to Measure Expanding Universe" (Site not responding. Last check: 2007-10-26)
		Willem de Sitter counters in 1917 with an expanding universe model, also consistent with Einstein's theory.
		De Sitter's universe, however, is devoid of matter.
		A lower Hubble constant implies that the universe is expanding slowly and that it has taken a longer time to reach its current size.
	hubblesite.org /newscenter/newsdesk/archive/releases/1999/19/astrofile (1079 words)

	The Universe Around Us: Chapter 6
		Thus we cannot observationally distinguish between universe models that are strictly homogeneous in the large (implying conditions are the same at a distance 1 million times the Hubble size away from us, as they are here), and those that are not.
		Firstly, the expansion of the Universe results in the received light from distant galaxies being redshifted; this causes a diminution in the intensity of light received (proportional to the inverse fourth power of the redshift), greatly reducing the expected radiation from distant stars.
		What from the viewpoint of an ensemble of Universes is just one of a whole set of possible boundary conditions, may critically affect the nature of local physics within a specific Universe in a way that is experienced as absolute and immutable, so that (in that Universe) it is indistinguishable from a immutable physical law.
	www.mth.uct.ac.za /~ellis/cos6.html (6042 words)

	PhysOrgForum Science, Physics and Technology Discussion Forums -> The Space-Stretch
		A discontinuous extropy expansion of the universe (surfure tension breaking apart the initial singualrity) and a subsequent mini big expansion phase could cause the universe to expand uniformly with respect to the galaxies.
		Internally the size of the Universe stays virtually the same and because for almost all Spacetime is being "frame dragged" along.
		When D equals 0 everywhere in the universe there is a force discontinuiity (infinite force and no force at the same time).
	forum.physorg.com /index.php?showtopic=2607 (2223 words)

	The roots of cosmological perfection / Review of 'The Invented Universe: The Einstein-De Sitter Controversy (1916-17)' ...
		The principal sources for the author's study of the Einstein-De Sitter correspondence are the letters and postcards in the De Sitter archives in Leiden and the Einstein archive in Princeton.
		We are then faced by De Sitter's withdrawal from cosmological research during the 1920s and the strange neglect of Friedman and Lemaitre before De Sitter re-emerges in 1932 to concur with Einstein over the simplest solution of his field equations, the expanding Universe.
		It is interesting to recall Eddington's account of Einstein and De Sitter's reconciliation of their longstanding disagreements concerning the nature and interpretation of cosmological models which was mediated by their subscription to this Einstein-De Sitter universe, as it has become known.
	www.newscientist.com /article/mg12416864.100-the-roots-of-cosmological-perfection--review-of-theinvented-universe-the-einsteinde-si (1030 words)

	Digital Library > History of science and scholarship in the Netherlands > Author detail
		Willem de Sitter was born in Sneek on May 6, 1872.
		The latter was involved in measuring photographic plates from the Cape Observatory in South Africa, in collaboration with Sir David Gill to chart the southern skies.
		In 1908 de Sitter was appointed in Leiden as professor in theoretic astronomy and in 1918 he was appointed as director.
	www.historyofscience.nl /author.cfm?RecordId=4 (497 words)

	[No title]
		As it turns out, everyone's right, according to his or her own definition of "de Sitter space" and "spatially finite." When cosmologists talk about de Sitter space, we slice it up into constant-time hypersurfaces that are spatially flat and infinite.
		The de Sitter universe > > > can be described as a hyperboloid in 5-dimensional space, therefore, > > > its slices are 3-spheres which are definitely spatially finite.
		When de Sitter first wrote the metric for this space, little was understood about what cosmological metrics should look like.
	www.math.niu.edu /~rusin/known-math/00_incoming/universe (1835 words)

	The Expanding Universe (Cosmology: Ideas)
		It meant that the light from distant nebulae was red-shifted not from some peculiar de Sitter effect, but because the nebulae were actually moving away from us.
		Cosmologists recognized at once that an expanding universe means that in the far future the galaxies will be spread much farther apart.
		The recognition that the universe is expanding was no less revolutionary — the culmination of a truly exceptional period in the history of science.
	www.aip.org /history/cosmology/ideas/expanding.htm (2662 words)

	Information in the Holographic Universe
		The Christodoulou-Hawking theorem fails in the face of this phenomenon (the mass of the fl hole, and therefore its horizon area, decreases), but the GSL copes with it: the entropy of the emergent radiation more than compensates for the decrement in fl hole entropy, so the GSL is preserved.
		In 1986 Rafael D. Sorkin of Syracuse University exploited the horizon's role in barring information inside the fl hole from influencing affairs outside to show that the GSL (or something very similar to it) must be valid for any conceivable process that fl holes undergo.
		His deep argument makes it clear that the entropy entering the GSL is that calculated down to level X, whatever that level may be.
	sufizmveinsan.com /fizik/holographic.html (3814 words)

	QI Talk Forum \| View topic - De Sitter Horizon
		The de Sitter horizon would also place limits on our knowledge, as we would be unable to look beyond it, or receive information from it.
		This means that the longer the universe continues expanding, the less chance we have of observing the earlier parts of it, because they will pass beyond the horizon and will not be visible anymore.
		If, however, the universe expanded before and this is the second or third or three billionth expansion, the constant is no longer valid, as each expansion-de Sitter-coalesence and re-expansion would produce a universe based on different conditions.
	www.qi.com /talk/viewtopic.php?p=79349&highlight= (632 words)

	String Theory and Cosmology
		The method that gives a possibility to calculate generation of perturbations in the non-linear regime and their back reaction of the locally de Sitter (before the end of inflation) or locally FRW space-time (after its end) is known as stochastic inflation.
		As a whole, the resulting structure of space-time during and after inflation, described in terms of many-point probability distributions for the inflaton field as a function of the logarithm of the FRW scale factor (this variable is the most convenient when speaking about space-time perturbations) or many-point correlation functions, appears to be exceedingly complicated.
		This suggest the natural quantum interpretation of this quasi-classical de Sitter space-time foam picture as a process of continuous creation of correlated inflationary patches "from anything" which in turn either decay into multiple post-inflationary low curvature quasi-FRW universes, or (in some inflationary models) may return to the Planck curvature, to the "Planck space-time foam".
	www.nobelprize.org /nobelfoundation/symposia/physics/ns127/abstract-starobinsky.html (362 words)

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