Missing Mass and the Acceleration of the Universe. Is Quintessence the only Explanation?

Detailed observations of the temperature fluctuations in the microwave background radiation indicate that we live in an open universe. From the size of these fluctuations it is concluded that the geometry of the universe is quite close to Euclidean. In terms Friedmann models, this implies a mass density within 10% of the critical density required for a flat universe. Observed mass can only account for 30% of this mass density. Recently, an outstanding observation revealed that cosmos is accelerating. This motivated some astronomers to explain the missing 70% as some exotic dark energy called quintessence. In this essay, we present an alternative explanation to these cosmological issues in terms of the Friedmann Thermodynamics. This model has the capability of making definite predictions about the geometry of the universe, the missing mass problem, and the acceleration of the universe in-line with the recent observations. For future observations, we also predict where this model will start differing from the quintessence models. (This essay received an honorable mention in the Annual Essay Competition of the Gravity Research Foundation for the year 2002-- Ed)Comment: Accepted for publication in IJMP-D December 200

An Open Singularity-Free Cosmological Model with Inflation

In the light of recent observations which point to an open universe $(\Omega_{0}<1)$, we construct an open singularity-free cosmological model by reconsidering a model originally constructed for a closed universe. Our model starts from a nonsingular state called prematter, governed by an inflationary equation of state $P=(\gamma_{p}-1)\rho$ where $\gamma_{p}$ $(\simeq 10^{-3})$ is a small positive parameter representing the initial vacuum dominance of the universe. Unlike the closed models universe cannot be initially static hence, starts with an initial expansion rate represented by the initial value of the Hubble constant H(0). Therefore, our model is a two-parameter universe model $(\gamma_{p},H(0))$. Comparing the predictions of this model for the present properties of the universe with the recent observational results, we argue that the model constructed in this work could be used as a realistic universe model.Comment: 6 pages Journalref: Int.J.Mod.Phys. A17 (2002) 445

Fractional Boundaries for Fluid Spheres

A single Israel layer can be created when two metrics adjoin with no continuous metric derivative across the boundary. The properties of the layer depend only on the two metrics it separates. By using a fractional derivative match, a family of Israel layers can be created between the same two metrics. The family is indexed by the order of the fractional derivative. The method is applied to Tolman IV and V interiors and a Schwarzschild vacuum exterior. The method creates new ranges of modeling parameters for fluid spheres. A thin shell analysis clarifies pressure/tension in the family of boundary layers.Comment: to appear in J. Math. Phy