Background cosmology

The basic assertion of the Hot Big Bang theory is that, as one goes back to early times, one encounters almost unlimited high temperatures and densities. The basic evidence for this is threefold  

The combination of high temperatures and densities at early times leads to the existence of a phase close to thermal equilibrium, when the signihcant particle reaction rates dominated over the expansion rate. This enables precise calculations to be made. 

Here r, 9, 4 are dimensionless co-moving coordinates attached to fundamental observers and R(t) a scale factor with a dimension of length depending only on cosmic time t. k is the curvature constant, which with suitable choice of units takes one of the three values +1 (closed world model with positive curvature), 0 (flat, open model) or —1 (open model with negative curvature). Some consequences of Eq. (4.7) are the relation between redshift and scale factor Eq. (4.2) and the variation of temperature 

The expansion of the Universe is governed by the field equations of General Relativity for isotropic expansion or contraction  

P = Peril = 3H2/8tzG, the critical density, which has the present-day value 

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The main goal of the Planck instrument is to improve the accuracy of the measurement of the cosmic microwave background (CMB), in order to extract cosmological parameters that remain poorly constrained after the results of WMAP (Wilkinson microwave anisotropy probe) and of the best ground-based experiments. The basic idea of HFI-Planck is to use all the information contained in the CMB radiation, i.e. to perform a radiometric measurement limited by the quantum fluctuations of the CMB radiation itself. In these conditions, the accuracy is only limited by the number of detectors and by the duration of the observation. 

The number rj, together with the known background temperature Tyf), measures the cosmological baryon density today ... 

Excellent introductions to cosmology, galaxy surveys, theories of structure formation and background radiation can be found in... 

M. S. Longair, Galaxy Formation, Springer, Berlin, 1998, and John A. Peacock, Cosmological Physics, Cambridge University Press 1999. Many aspects of background radiation at all wavelengths are discussed in... 

Harwit, M. Hauser, M. G. (eds.) 2001. IAU Symp. no. 204, The Extragalactic Infra-red Background and its Cosmological Implications, Dordrecht Kluwer. 

The fact that our eyes are so exclusively tuned to the Sun has thus blinded us to almost all forms of radiation. This includes radiation from media at very different temperatures, such as the relic cosmological background that filters down to us from the beginning of time, and the great majority of non-thermal emissions, such as the signals from pulsars and supernova remnants. 

FUSE (Far Ultraviolet Space Explorer) combs the sky in search of the spectra of hot bright background objects (quasars and stars) modified by absorption lines due to interposed clouds (both extragalactic and interstellar). Its main prey is deuterium, an atom of major cosmological significance. It shonld also establish a detailed breakdown of interstellar gases. FUSE is a NASA project with French participation. ... 

By comparing calculated values with the actual content of these various elements in the oldest astronomical objects, we deduce that the density of nuclear matter cannot exceed 5% of the critical density. Now it so happens that the best cosmological theory to date, the theory of cosmological inflation, predicts that the Universe has exactly the critical density. This conclusion is supported by recent observations of remote supernovas and the relic background radiation. 

It is therefore a Euclidean universe which lies at the meeting point between data from remote supernova studies and observations of the cosmic background radiation. Such a universe contains just enough matter and energy to keep the geometry Euclidean. In fact the Euclidean cosmology fits our Universe like a glove. 

The recession of the galaxies attests to the general idea that the Universe is expanding. The cosmological background provides indisputable evidence of a hot, dense beginning. Finally, the existence of the lighter atoms in the measured proportions is witness to very early nuclear synthesis. 

For most astronomers, the solution to these cosmological problems resides in a combination of various methods. The luminosity-redshift test must be combined with independent techniques, such as anisotropies in the cosmic background radiation and statistical study of gravitational lenses. 

Penzias, Wilson Discovery of cosmological background radiation... 

The region prohibited by the experiment, cosmology and 7-ray background radiation from the supernovae are also shown in Fig. 1 by the dotted region, the vertically hatched region, and obliquely hatched region, respectively. 

Both pieces of evidence concern spiral galaxies the first concerns the nature of the cosmological redshift measured for such objects, while the second concerns the nature of spiral galaxy dynamics. To have a clear appreciation of the issues, some background knowledge is useful. 

Persons from a Judaeo-Christian background conceive of an enormous gulf between divinity (which is "up there") and the self ("down here"). Christian mystics claims to unity with divine radiance has always posed problems for theologians who are committed to the cosmological subject-object distinction. Most Westerners, therefore, find it difficult to attain unity with the source-light. 

For the connection between the CN-predic-tion and the cosmic background radiation, see Kragh, Cosmology and Controversy, 134-135, 345-347. 

The above expression of the mass function depends on the cosmological background and on the characteristics of the fluctuations, specified by their... 

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