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Topic: Cosmological constant

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	Cosmological constant - Wikipedia, the free encyclopedia
		The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as part of his theory of general relativity to achieve a stationary universe.
		In lieu of the cosmological constant, cosmologists often quote the ratio between the energy density due to the cosmological constant and the current critical density of the universe.
		Einstein included the cosmological constant as a term in his field equations for general relativity because he was dissatisfied that otherwise his equations did not allow, apparently, for a static universe.
	en.wikipedia.org /wiki/Cosmological_constant (1027 words)

	Cosmological constant Summary
		The cosmological constant is a mathematical term (symbolized by the Greek letter lambda, &lgr;) that German-born physicist Albert Einstein placed in his general relativity equations in 1917.
		Einstein made up the cosmological constant because he was attempting to reconcile a theory with the established view of what the universe actually looks like.
		Moreover, adding the cosmological constant to Einstein's equations does not lead to a universe at equilibrium because the equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion.
	www.bookrags.com /Cosmological_constant (1232 words)

	The Cosmological Constant (Site not responding. Last check: 2007-09-17)
		A sufficiently large cosmological constant will cause galaxies to appear to accelerate away from us, in contrast to the tendency of ordinary forms of energy to slow down the recession of distant objects.
		A positive cosmological constant increases the volume of space in between us and a source at any fixed redshift, and therefore the probability that such a source undergoes lensing by an intervening object.
		The value of the cosmological constant is an empirical issue which will ultimately be settled by observation; meanwhile, physicists would like to develop an understanding of why the energy density of the vacuum has this value, whether it is zero or not.
	pancake.uchicago.edu /~carroll/encyc (1913 words)

	cosmological constant
		Einstein's cosmological constant was later interpreted as the energy density of the vacuum.
		The observational upper bound on the value of the vacuum energy density is 40 to 120 orders of magnitude smaller than that predicted from quantum field theories of elementary particles – the so-called cosmological constant problem.
		The cosmological constant may be the cause of the acceleration of the universe recently inferred from observations of Type Ia supernovae, but again there is as yet no theoretical understanding of why it would have the small, non-zero value needed to explain these observations.
	www.daviddarling.info /encyclopedia/C/cosmological_constant.html (214 words)

	Friedmann Equation (Site not responding. Last check: 2007-09-17)
		Besides the density and gravitation constant G, the equation contains the Hubble parameter H, a scaling parameter R, and a factor k which is called the curvature parameter.
		The original motivation for the cosmological constant was to make possible a static universe which was isotropic and homogeneous.
		A non-zero value for the cosmological constant could be implied from measurements of the volume densities of distant galaxies, but such measurements give a negative result, showing an upper bound of
	hyperphysics.phy-astr.gsu.edu /hbase/astro/fried.html (556 words)

	The Expanding Universe - Quantum Theory
		However the cosmological constant had a right to be there, from a mathematical point of view, and it turns out that the math knew something that no one else did.
		When they plotted up the distance-redshift diagram for their supernovae, these astronomers found one of the most remarkable results of twentieth-century physics: not only is there a cosmological constant, but it has a bigger effect on the expansion of the Universe than all the ordinary matter in it.
		This is the evidence for the cosmological constant.
	www.seed.slb.com /en/scictr/watch/cosmos/quantum.htm (1736 words)

	WMAP Cosmology 101: Cosmological Constant
		The main attraction of the cosmological constant term is that it significantly improves the agreement between theory and observation.
		A cosmological constant term added to the inflationary model, an extension of the Big Bang theory, leads to a model that appears to be consistent with the observed large-scale distribution of galaxies and clusters, with COBE's measurements of cosmic microwave background fluctuations, and with the observed properties of X-ray clusters.
		By characterizing the detailed structure of the cosmic microwave background fluctuations, WMAP should be able to accurately determine the basic cosmological parameters, including the cosmological constant, to better than 5%.
	map.gsfc.nasa.gov /m_uni/uni_101accel.html (474 words)

	Session EB22 - The Cosmological Constants.
		As seen in the previous talks, new cosmological observations are closing in fast on a model for the Universe that is of surprise and perhaps delight to both theorists and observers.
		The debate about the cosmological mass density now strongly favors a low value, about 1/4 to 1/3 of that needed to close the Universe, made up of a mix of baryons, neutrinos and some as yet to be determined cold dark matter.
		Evidence for a cosmological constant is improving, and it appears as if the debate on the total value of Ømega is being resolved in favor of the favored theoretical value of unity, with Ømega_matter \sim 0.3 and Ømega_\Lambda \sim 0.7.
	flux.aps.org /meetings/YR99/CENT99/abs/S1517.html (569 words)

	Cosmological Constant - Bad Astronomy and Universe Today Forum
		The “cosmological constant” was added to the theory to keep gravity from acting in a way that would cause the universe to collapse.
		With the discovery that the universe was expanding, Einstein no longer needed the cosmological constant, and he later called it the biggest blunder of his life.
		"Lambda" (the cosmological constant) represents the hypothesized negative pressure of the vacuum that causes spacetime to expand.
	www.bautforum.com /showthread.php?t=8572 (3816 words)

	UFO Area - 'Cyclic universe' can explain cosmological constant (Site not responding. Last check: 2007-09-17)
		The cosmological constant represents the energy of empty space, and is thought to be the most likely explanation for the observed speeding up of the expansion of the universe.
		At every big bang, the amount of matter and radiation in the universe is reset, but the cosmological constant is not.
		But he points out that there are other cosmic coincidences that the cyclic model cannot explain, like why the size of the cosmological constant is so similar to the density of matter in the universe today.
	www.ufoarea.com /physics_cosmology_cyclicuni.html (499 words)

	The Epoch Times \| Cyclic Universe May Solve Einstein Mystery
		Einstein first introduced the cosmological constant in his theory of general relativity in the 1920s as a way to mathematically explain why the universe didn't contract under the force of gravity.
		Scientists have tried various mechanisms to solve this question, but for the cosmological constant to reach the present estimated value it would take far longer than the 14 billion years our universe is said to have been in existence for — so long that all matter in the universe would dissipate in the meantime.
		In their "cyclic universe" theory, the universe spends most of its time with a small cosmological constant, and the repeated creation of matter means that each expansion cycle would include a significant amount of matter, as we see today.
	www.theepochtimes.com /news/6-6-22/42612.html (546 words)

	PHYS146 Notes Expansion and Ages
		The Hubble constant implies the length of time the galaxies would have been travelling to get where they are now, and hence the lifetime of the Universe, only if the galaxies have been travelling at constant speed.
		The simplest, and therefore the preferred procedure, was to assume that the cosmological constant vanishes and that the matter density is that predicted by the theory of inflation (see above).
		These observations suggest that the cosmological constant is nonzero and are consistent with either a closed or an open Universe and with a Universe which recollapses as well as one which expands forever.
	www.udel.edu /mvb/PS146htm/146noeu.html (3437 words)

	cosmological constant Comparison Table (Site not responding. Last check: 2007-09-17)
		A parameter that determines the strength of the cosmological term in the equations of general relativity.
		This term was added by Einstein because he thought the universe was static, and the term provided a repulsive gravitational force that was needed to prevent the universe from collapsing under the force of ordinary gravity.
		The cosmological constant is often assumed to be zero, but it might make a significant contribution to the evolution equations of our universe.
	www.site.uottawa.ca:4321 /astronomy/cosmologicalconstant_table.html (138 words)

	deseretnews.com \| Scientist casts new doubts on Einstein's cosmological constant
		An astronomer from Louisiana State University said Wednesday that a new analysis of cosmic history cast doubts on Einstein's cosmological constant, the leading explanation for the mysterious force that appears to be pushing apart the universe.
		Einstein proposed the constant in 1917 as a way of explaining how the universe could be static despite the force of gravity.
		But in 1998, the cosmological constant gained new life when astronomers, using exploding stars known as Type 1a supernovas as cosmic mileage markers, discovered that the expansion of the universe appeared to be accelerating, as if a dark antigravitational force were indeed at work.
	deseretnews.com /dn/view/0,1249,635175921,00.html (338 words)

	Extreme Fine Tuning - Dark Energy or the Cosmological Constant
		The supernovae results suggested that there was a "springiness" to space, an energy density often referred to as "dark energy" or the "cosmological constant," that causes the universe to expand at a faster rate the more it expands.
		In examining problems with the cosmological constant, the authors are concerned that ultimate fate of the universe is complete entropy with all the matter and energy distributed over maximally expanded spacetime.
		Evidence for a positive cosmological constant from flows of galaxies and distant supernovae Nature 401: 252-254 401: 252-254.
	www.godandscience.org /apologetics/cosmoconstant.html (1954 words)

	The Cosmological Models
		This is not the age of the universe unless H is constant, but is rather an extrapolation of the current expansion rate and scaling factor of the universe backward in time.
		This constant was added to the cosmological equations by Einstein in order to force the universe to be static, as he believed it had to be.
		At early times, the model is the same as the Einstein-de Sitter model (model#1), however, a positive cosmological constant acts as a repulsive force in the universe, which makes the universe expand faster than it would without the so-called lambda-force.
	mywebpages.comcast.net /bondono2/cosmodel/cosmodel.html (7021 words)

	How does the cosmological constant fit into general relativity?
		The inclusion of the cosmological constant term in this equation is of course dictated by whether it is zero or not.
		Because the cosmological constant term is proportional to the metric, the pressure associated with the vacuum is then given by the relation:
		Therefore the cosmological constant remains truly constant, and its gravitational repulsion (or attraction) never changes during the universe's evolution.
	super.colorado.edu /~michaele/Lambda/gr.html (608 words)

	Cosmological Constant (Site not responding. Last check: 2007-09-17)
		Einstein postulated the existence of the Cosmological Constant in 1917 (or so) and then quickly renounced it (on aesthetic grounds) in the 1920's when Hubble announced that the Universe was expanding.
		Today, we believe that a nonzero Cosmological Constant could explain the discrepancy between the ages of the oldest stars in the Milky Way and the age of the Universe as implied by the Hubble constant.
		In order to bring the observed Cosmological constant and its theoretical estimate into line requires that the fluctuations in the vacuum be arranged so that there there is some fierce cancellation going on.
	zebu.uoregon.edu /~imamura/123/lecture-9/lambda.html (401 words)

	Glossary of Astronomical and Cosmological Terms
		cosmological constant: a term in Einstein's general relativity equations that leads to an acceleration of the expansion of the Universe.
		inflationary scenario: a modification of the Big Bang model in which a large cosmological constant exists temporarily early in the history of the Big Bang, leading to a rapid accelerating expansion of the Universe, which is then followed by the normal Big Bang model with a decelerating expansion.
		Lambda: the upper case Greek Lambda is usually used to denote Einstein's cosmological constant.
	www.astro.ucla.edu /~wright/glossary.html (1935 words)

	Nonvanishing cosmological constant or manysheeted spacetime?
		The increase could be due to the nonvanishing cosmological constant corresponding to a vacuum energy density about 40 per cent of the critical density: the origin of this vacuum energy density remains a mystery.
		Hence the Hubble constant for nearby supernovas is larger and the rate of the expansion of the Universe is found to apparently increase in the course of time.
		The decrease of the Hubble constant as a function of the (p-adic) length scale characterizing a given spacetime sheet would follow from the fractality of the TGD:eish Universe implying that the mass density as a function of the p-adic length scale decreases in the long length scales.
	www.helsinki.fi /~matpitka/vacerg.html (557 words)

	THE COSMOLOGICAL CONSTANT
		The search for such a solution was Einstein's original motivation for introducing the cosmological constant, as the data at the time did not indicate an expanding universe, but his solution was both unstable to small perturbations and unnecessary once HUBBLE'S LAW was discovered.
		Perhaps the most direct way of measuring the cosmological constant is to determine the relationship between redshifts and distances of faraway galaxies, known as the HUBBLE DIAGRAM.
		The cosmological constant derived by Einstein,"self-admitted greatest blunder", has been making a comeback as of late.
	www.gnostics.com /cosmo.html (2230 words)

	Open Questions: The Cosmological Constant
		Theoretical estimates of the magnitude of the constant, based on the conjectured physics of Higgs fields, are very far in excess of possible values based on observation.
		But such a constant would imply an increase in the rate of the expansion of the universe, hence an older age than allowed by a constant rate of expansion.
		Provides a non-technical description of the cosmological constant and how it is involved in describing the structure and evolution of the universe.
	www.openquestions.com /oq-re002.htm (359 words)

	Cosmological Constant
		Obviously, this is the opposite of what a gravity-driven universe should exhibit which means that the force of expansion continues to be increasing, in effect, nullifying the effect of gravity.
		What is remarkable is that Einstein came up with the idea of the Cosmologic Constant at a time when the universe was believed static and he couldnt explain why the universe just didnt collapse, so he invoked an antigravitational ad hoc force to allow for a static universe.
		He apparently plagiarized most of the special theory of relativity and he couldnt quite get a handle on the Cosmologic Constant, his greatest discovery that he recanted on when he was right.
	einstein52.tripod.com /alberteinsteinprophetorplagiarist/id7.html (673 words)

	The cosmological constant (Site not responding. Last check: 2007-09-17)
		This modification corresponds to the assumption that the whole universe is permeated with a constant pressure (which in his case balanced the expansion yielding a steady universe).
		Though subsequently the data showed that the universe is in fact expanding and Einstein rejected the modification, on a philosophical basis the question still remains whether the measured cosmological constant is indeed zero (remember that on philosophical grounds Aristotle rejected heliocentrism: one must eventually back assumptions with observations).
		For many years the best value for the cosmological was assumed to be zero since no measurement gave positive indication to the contrary.
	phyun5.ucr.edu /~wudka/Physics7/Notes_www/node123.html (213 words)

	Evidence for the Fine Tuning of the Universe
		This cosmological constant is a force that increases with the increasing size of the universe.
		First hypothesized by Albert Einstein, the cosmological constant was rejected by him, because of lack of real world data.
		However, recent supernova 1A data demonstrated the existence of a cosmological constant that probably made up for the lack of light and dark matter in the universe.
	www.godandscience.org /apologetics/designun.html (1698 words)

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