Assuming that the matter filling the background geometry in the Early
Universe was a free gas and no phase transitions took place, we discuss the
thermodynamics of this closed system using classical approaches. We found that
essential cosmological quantities, such as the Hubble parameter H, the
scaling factor a and the curvature parameter k, can be derived from this
simple model. The results are compatible with the Friedmann-Robertson-Walker
model and Einstein field equations. Including finite bulk viscosity coefficient
leads to important changes in the cosmological quantities. Accordingly, our
picture about evolution of the Universe and its astrophysical consequences
seems to be a subject of radical revision. We found that k strongly depends
on thermodynamics of the cosmic background matter. The time scale, at which
negative curvature might take place, depends on the relation between the matter
content and the total energy. Using quantum and statistical approaches, we
introduced expressions for H and the bulk viscosity coefficient.Comment: 15 pages, 4 eps figures, invited talk given at the "Second
IAGA-Symposium", Cairo-Egypt, 4-8 Jan. (2010