Universe accelerated expansion

The mass of the universe is in general evenly distributed it acts as Einstein s cosmological constant and accelerates expansion. Poor Agrees well with most of the recent measurements, but the evidence is still thin, and theoretical problems are still unsolved. 

Observations of distant supemovae indicate expansion of the Universe accelerating. 

WIMPZILLAs Our last example of cold dark matter candidates illustrates a fascinating idea for generating matter in the expanding universe the gravitational creation of matter in an accelerated expansion. This mechanism is analogous to the production of Hawking radiation around a black hole, and of Unruh radiation in an accelerated reference frame. 

Re Entry [48], Ref. [48]) Reference [48] shows that previous measurements of the acceleration of the Universe s expansion may require reconsideration, owing to discrepancies between visible-light and UV observations of type la supernovae. 

Livio, M. The Accelerating Universe Infinite Expansion, The Cosmological Constant, and the Beauty of the Cosmos John Wiley Sons, Inc. New York, NY, 2000. 

Possesses the property of antigravitation, causing accelerated expansion of the Universe. 

Also the simplest version of the field-theoretical realization of inflation predicts a total energy density very close to the critical density p, which separates the parameter region of a recollapsing Universe from the region where a non-accelerating expansion continues forever. Such a Universe is spatially flat. In the apparently relevant case of accelerated expansion, the borderline is shifted and universes somewhat above the critical densities might expand with no return. It is customary to measure the density of a specific constituent of the Universe in proportion to the critical density 13, = Pilpc-... 

In the past decade several projects contributed to the luminosity distance measurements and by now (i.e., as of 2009) the list includes over 200 events. Specifically with the help of the Hubble telescope 13 new Sn la were found with spectroscopically confirmed redshifts exceeding z = 1 and at present the full sample contains already 23 z > 1 objects (Riess et al. 2007). Such objects most strongly influence the value of the deceleration parameter. A combined analysis of all Sn la data yields a deceleration parameter value of —0.7 0.1 (Kowalski et al. 2008). Its negative value signals an accelerating expansion rate at distance scales comparable to the size of the Universe. 

From observations of distant galaxies by the Hubble Space Telescope and other big telescopes evidence for an accelerated expansion was found. This can be explained by a repulsive force and is taken into account by A non zero value of means that the universe is not controlled by gravity alone. In fact A was the cosmological constant that was introduced by Einstein in order to keep the solutions of his field equations stable—at the time of propagating his general relativity theory (1916) it was not known that the universe expands. 

Today, it is generally thought that the Universe is open, by which it is meant that the expansion is eternal, and indeed, even accelerating. This strikes at the very heart of the old paradigm of eternal return. This announcement of a one-way diaspora originates from a certain type of exploding star, visible from... 

The expansion of the Universe is accelerating The news is too recent to accept without reserve. It must be checked again and again, in the most critical spirit, and yet with open mind, for it is of the utmost importance. 

Perlmutter, Riess, Smith Acceleration of the expansion of the Universe... 

In a Universe dominated instead by curvature or an accelerating component such as a cosmological constant, the expansion of the universe is more rapid than in a matter dominated universe. In both of these cases, there is no longer a growing mode neither solution to Equation 10.10 grows with time. 

There are several independent applications with supernovae to measure the current expansion rate, Hubble s constant, and the expansion history of the universe. The latter has led to the surprising discovery that the expansion is actually accelerating and a new component for the universe is needed. Supernovae are also poised to be a major player in the characterisation of the nature of the dark energy. 

Hubble constant The rate at which the velocity of recession of the galaxies increases with distance as determined by the redshift. The value is not agreed upon but current measurements indicate that it lies between 49 and 95 km s per megaparsec. The reciprocal of the Hubble constant, the Huhhle time, is a measure of the age of the universe, assuming that the expansion rate has remained constant. In fact, it is necessary to take account of the fact that the expansion of the universe is accelerating to get an accurate determination of its age. 

---