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Topic: Cosmological horizon

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	Event horizon - Wikipedia, the free encyclopedia
		An example of a cosmological model with an event horizon is a universe dominated by the cosmological constant (a de Sitter universe).
		For the case of a horizon perceived by an occupant of a de Sitter universe, the horizon always appears to be a fixed distance away for a non-accelerating observer.
		For the case of the horizon around a fl hole, observers stationary with respect to a distant object will all agree on where the horizon is. While this seems to allow an observer lowered towards the hole on a rope to contact the horizon, in practice this cannot be done.
	en.wikipedia.org /wiki/Event_horizon (1556 words)

	Particle horizon - Wikipedia, the free encyclopedia
		The particle horizon in physical cosmology is the maximum distance from which particles (of positive or zero mass) can have travelled to the observer in the age of the universe.
		The particle horizon is defined as the largest comoving distance from which light can have reached the observer — at the present moment.
		The event horizon is defined as the largest comoving distance from which light can ever reach the observer — at any time in the future.
	en.wikipedia.org /wiki/Particle_horizon (124 words)

	Cosmological Models
		The standard cosmological model is the "big bang", and while the evidence supporting that model is enormous, it is not without problems.
		The answer to the horizon problem from the inflationary point of view is that there was a period of incredibly rapid inflation very early in the big bang process which increased the size of the universe by 10
		If the universe inflated by 20 to 30 orders of magnitude, then the properties of an extremely tiny volume which could have been considered to be intimately connected were spread over the whole of the known universe today, contributing both extreme flatness and the extremely isotropic nature of the cosmic background radiation.
	hyperphysics.phy-astr.gsu.edu /hbase/astro/cosmo.html (943 words)

	The Cosmological Event Horizon
		One problem in the middle of the 20th century was that the Hubble expansion implied the age of the universe was less than that of the Earth.
		The cosmological horizon on the other hand works symmetrically - if B is out of the reach of A then A is out of reach of B. In many other aspects however it is similar to the event horizon of a fl hole.
		The cosmological event horizon hasn't shown up very much in works of popular science until now, but I feel it is likely to become much more widely known in the near future.
	www.chronon.org /articles/Cosmological_Event_Horizon.html (878 words)

	GET: horizon problem
		This allows to define a horizon of influence for each event - all events which may have had a common cause in the past.
		First, the horizon is too small to explain why the background radiation is homogeneous.
		Even if the horizon may be finite (if Einstein's cosmological constant is greater zero) the horizon size is nonetheless greater than the observable universe.
	ilja-schmelzer.de /GET/horizon.html (337 words)

	A Spacetime Map of the Universe: Implications for Cosmology
		Assuming the cosmological redshift has its origin only in the size difference between the Universes of observer and observed, we can directly calculate the redshift we "should" see for each of the billion year intervals of the Spacetime Map, simply substituting the map's radius in years for the wavelength of light.
		The rationale for this procedure is the assumption that the cosmological expansion is primarily driven by the entropy of free energy, the intrinsic motion of light.
		The "cosmological horizon problem" consists of the notion that widely separated regions of our Universe cannot have had enough time, given the finite velocity of light, to communicate with each other since their common origin in the Big Bang.
	www.people.cornell.edu /pages/jag8/spacetxt.html (10529 words)

	PHYS146 Notes Expansion and Ages
		The facts about the horizon of current interest are that first, objects can be currently affecting each others' behavior only if they are within each others' horizons, and second, properties of two regions can be correlated only if the two regions have been within each others' horizons at some time now or in the past.
		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)

	A Spacetime Map of the Universe
		Due to the cosmological red shift, all distant galaxies appear "red shifted" in proportion to their distance: the greater their distance, the smaller the size of the Universe in which we see them as compared to our own, and hence the greater their red shift.
		The cosmological red shift would exist if the observed galaxies were not moving at all; it is just a geometric effect involving light and the relative size of light's container.
		Assuming that the cosmological red shift has its origin in the size difference between the universes of observer and observed, we can directly calculate the red shift we "should" see for each of the billion year intervals of the Spacetime Map, simply substituting the map's radius in years for the wavelength of light.
	www.people.cornell.edu /pages/jag8/stext.html (9291 words)

	[Projet Horizon - Horizon Project :: Objectives ]
		Horizon Workshop 2006a 10, 11 and 12 april 2006 in Lyon.
		October 2005: Horizon was awarded a 500 k€ grant by ANR, the French Science Foundation.
		Horizon has submitted to INSU a proposal for funding a medium-size computer dedicated to the project.
	www.projet-horizon.fr /article68.html (435 words)

	GET: GR limit
		Cosmological observation leads to upper limits for the new constants.
		This solves the cosmological horizon problem, and is that's why a strong argument in favour of the assumption
		Note that the cosmological horizon problem is "solved" today by inflation theory, which is also used to explain the flatness of the universe.
	ilja-schmelzer.de /GET/GRlimit.html (497 words)

	Munch (Site not responding. Last check: 2007-10-23)
		In particular, we prove that the size of the apparent horizon of a primordial fl hole formed by causal processes in a flat Friedmann universe is considerably smaller than the cosmological apparent horizon size for an equation of state $p=k\rho$ ($1/3
		The apparent horizon of a primordial fl hole formed through hydrodynamical processes is also considerably smaller than the cosmological apparent horizon for $0
		For example, the ``degradation factor'' due to lensing is a factor of three reduction in the effective number of usable supernovae at z=1.5 (for sources with intrinsic flux dispersion of 10%).
	home.fnal.gov /~bertone/DM/JC121304.html (1491 words)

	Cosmological Horizons
		Unfortunately this leads to the analogy of a galaxy appearing from behind a cosmological horizon, and my claim is that this never happens.
		Note that graphs showing particle horizons are generally confusing, as they often show a background of the other parts of the universe evolving with time, implying that at a certain stage of their evolution they cross the particle horizon.
		The other thing to note is that for particle horizons to occur the rate of expansion of the universe (the derivative of the scale factor with time) must be infinite at time zero.
	www.chronon.org /articles/cosmichorzns.html (944 words)

	Dodging dark energy
		Since it no longer feel the force of gravity from the galaxies disappearing behind the event horizon, this is equal to an increase in a repulsive force that is added to gravity.
		It seems to me that this would be a cosmological constant that is very small at first, since little mass escapes behind the event horizon.
		But our cosmological event horizon is at a redshift of z=1'8 (comoving radial distance of 16 Gly) and actually there are galaxies crossing it.
	www.physicsforums.com /showthread.php?p=335245 (1930 words)

	The Present Invalid Nature of Humphreys' White Hole Cosmology
		Due to the dust-like properties of matter interior to the event horizon and due to a comparatively large cosmological constant, the collapse scenario for the dust-like (particle-like) material would be overcome and the material would escape through the event horizon and give a white hole effect.
		Thus, assuming that there is an event horizon at the earth's surface that is produced by the collapse of an event horizon at the outer boundary yields, for this metric, a cosmological constant that when applied to the entire universe does not yield the required event horizon at the outer boundary.
		Event horizons are produed for simple variations for the parameters for this metric but they appear contradictory if they are considered as constants over the entire cosmos.
	www.serve.com /herrmann/hump.htm (787 words)

	Citebase - Hairs on the cosmological horizon
		We investigate the possibility of having hairs on the cosmological horizon.
		The cosmological horizon shares similar properties of fl hole horizons in the aspect of having hairs on the horizons.
		For those theories admitting haired fl hole solutions, the nontrivial matter fields may reach and extend beyond the cosmological horizon.
	citebase.eprints.org /cgi-bin/citations?id=oai:arXiv.org:gr-qc/9708064 (177 words)

	IAU SYMPOSIUM 216 - abstracts (Site not responding. Last check: 2007-10-23)
		The generalized second law of thermodynamics states that entropy always increases when all event horizons are attributed with an entropy proportional to their area.
		We generalize for flat, open and closed Friedmann-Robertson-Walker universes by using numerical calculations to determine the cosmological horizon evolution.
		In most cases the loss of entropy from within the cosmological horizon is more than balanced by an increase in cosmological event horizon entropy, maintaining the validity of the generalized second law of thermodynamics.
	www.atnf.csiro.au /iau-ga/iau216/abstracts/iau01588.html (161 words)

	List Of Articles (Site not responding. Last check: 2007-10-23)
		Different cosmological constants are assumed for the space between and outside of the plates to have general results applicable to the case of domain wall formations in the early universe.
		In this paper we show that the entropy of cosmological horizon in 4-dimensional Topological Kerr-Newman-de Sitter spaces can be described by the Cardy-Verlinde formula, which is supposed to be an entropy formula of conformal field theory in any dimension.
		The special case of the dS bulk is considered then different cosmological constants are assumed for the space inside and outside of the shell to have general results applicable to the case of cylindrical domain wall formations in the early universe.
	phys-www.ipm.ac.ir /papers/setare.html (3522 words)

	Big Bang Paradox - Advanced Physics Forums (Site not responding. Last check: 2007-10-23)
		I however do not see how the horizon can prove that our space is either infinite, or finite (for we can\'t observe the beyond).
		Since you can\'t see past the cosmological horizon, it\'s sort of silly to spend a lot of time arguing about what is or isn\'t beyond it.
		That is, they\'d assume that the regions beyond the cosmological horizon are basically the same as the regions near Earth.
	www.advancedphysics.org /forum/showthread.php?t=1250 (577 words)

	Physics Inside-Out: A Physics of Peace, by Loren Booda
		The solutions to cosmological constant, isotropy, flatness, magnetic monopole and horizon problems - tentatively addressed by the inflationary model - arise from the model of bivalent spacetimes, aboriginally evolving apart from a common, correspondent state.
		The distortion of the mutual horizons' surface area indicates an overall increase in their entropy which is accounted for while evolving toward the final combined singular state.
		The universe's event horizon is defined at the radius where spacetime's recessional velocity from the observer equals the speed of light.
	www.quantumdream.net (7976 words)

	No Title
		The standard cosmological model is very successful in explaining many observational facts, but it has some problems.
		Before inflation, our current horizon was a tiny-tiny region of the universe, much smaller than a horizon at that epoch.
		However, fluctuations on galaxy scales and larger moved inside the horizon rather recently, after recombination, and the thermal equilibrium was not maintained at that time.
	lcd-www.colorado.edu /astr2010/Lectures/part4/part4_06.html (1432 words)

	From Inflation to Galaxies
		Like the horizon on the earth, it is the point beyond which we're unable to look.
		Unlike the earth's horizon, this distance is increasing with time because light from more distant regions has had more time to reach us.
		A useful property of the microwave background is that when we look out across widely separated angles, we're looking at wrinkles on such large scales that this process of infall hasn't yet begun.
	background.uchicago.edu /~whu/beginners/infl.html (209 words)

	The Cosmological Principles by Konrad Rudnicki
		While the ancient thinkers believed in the existence of non-observable parts of our Universe consisting of imponderable sublime and invisible matter, according to most contemporary astronomers there is a surface called the “cosmological horizon”.
		Cosmological principles are the assumptions which allow us to deduce the whole of nature on the basis of the observable to the unobservable.
		Cosmological results are especially conditioned by personal ways of thinking.
	www.southerncrossreview.org /22/rudnicki.htm (3207 words)

	Re: Gravitation and acceleration horizons
		A cosmological horizon is the boundary of a region of spacetime from which light could never reach us - i.e., lightlike geodesics emanating from this region would never intersect our worldline.
		This question appears to be premissed on an incorrect concept of "cosmological horizon", so I think it's best if you think more about what a cosmological horizon actually is before we continue with this line of discussion.
		Also, it is interesting to consider the question of whether our universe has cosmological horizons.
	www.lns.cornell.edu /spr/2002-05/msg0041370.html (560 words)

	Home Sitters
		It is also a cosmological model for the universe.
		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.
		Eventually there will be nothing left but the cosmological constant, and our universe will have become a de Sitter universe.
	www.artistbooking.com /trips/83/home-sitters.html (1079 words)

	[No title] (Site not responding. Last check: 2007-10-23)
		> an object just inside the event horizon of a fl hole would > apparently be swept beyond the event horizon by the expansion > of space.
		Since we do not yet have anything like a quantum theory of gravity, this is just an educated guess about what the "classical limit" of whatever such a theory would say about realistic gravitational collapse might look like.
		Above this you see a Cauchy horizon, a spherical shell collapsing "at the speed of light" onto the curvature singuarlity (contrary to what the diagram suggests, this horizon is disjoint from the event horizon).
	math.ucr.edu /home/baez/PUB/Schwarz_deSitter (673 words)

	A626: Clustering of Dark Matter
		The simplest available hypothesis is that the primordial fluctuation spectrum produces bound structures with length and mass scales growing in direct proportion to the cosmological horizon and the mass contained therein.
		Observations of temperature fluctuations in the microwave background are consistent with a scale-invariant spectrum with an amplitude on the horizon scale of
		The characteristic scale of the smallest surviving fluctuations is comparable to that of superclusters; then in a HDM universe these structures form first as in the `pancake' theory (Zel'dovich 1970).
	www.ifa.hawaii.edu /~barnes/ast626_95/cdm.html (1290 words)

	(Linearised) Spatially Inhomogeneous Perturbations of FLRW Models
		NB: Confuses the cosmological particle horizon with the Hubble radius $H^{-1} = S/\dot{S}$.
		Nesteruk A V: Cosmological Density Perturbations in the Universe with Non-Trivial Topology of Spacetime, Class.
		Zimdahl W: Gauge-Invariant Cosmological Perturbations and the Spectrum of Primeval Density Fluctuations, Phys.
	www.mth.uct.ac.za /~webpages/henk/ref_dir/chsip.html (710 words)

	[No title]
		We show that if the matter fields satisfy the dominant energy condition and cosmic censorship holds in the considered space time, the area of the cosmological event horizon for an observer approaching a future timelike infinity does not decrease; i.e., the second law is satisfied.
		Assuming that the phase space evolution of the universe starts from an initial squeezed cosmological state towards a final thermal one, a Fokker-Planck equation for the time-dependent, cosmological Q phase space probability distribution can be written down.
		For a Schwarzschild fl hole this invariant reduces to the area of the event horizon (or equivalently the Bolt charge) and it reduces to the square of the NUT charge (or equivalently the length of the closed timelike orbits) in the case of a Taub-NUT magnetic monopole.
	acg.media.mit.edu /people/rich/research/entropy/entropyBib.txt (5007 words)

	Boarder of universe
		If distant galaxies are leaving behind a cosmological event horizon, then what does that say about the entropy/information content of the observable universe?
		Perhaps it is more than a coincidence that the universe started to expand about the same time that life arose.
		Perhaps the complexity of life is compensation for information disappearing behind the cosmological event horizon.
	www.physicsforums.com /showthread.php?t=63386&page=2 (2693 words)

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