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Inhomogeneity and the Curvature of the Spacelike Cosmos\par

Christina Sormani
Lehman College, City University of New York

Thursday, October 21, 2004
102 Bradley Hall, 4 pm
Tea 3:30 pm, Math Lounge

Abstract: In the Friedman Model of cosmology the spacelike universe is assumed to have constant sectional curvature so that locally it is curved like a sphere, Euclidean Space, or hyperbolic space. This assumption is justified if one assumes that it is a locally isotropic complete Riemannian manifold. That is, if one assumes that at every point p\in M, there is an R>0 and a function F_p such that the length of the far side of a geodesic triangle with angle \theta at p and adjacent sides of lengths s,t is given by F_p(\theta, s,t), then by Schur's Lemma, M has constant sectional curvature. Note that this F_p formula is like having a law of cosines. \par Here we show that if the space is only locally ``almost" isotropic in the sense which allows for both the weak and strong gravitational lensing that has been observed, then the space is close to a space of constant sectional curvature in the Gromov Hausdorff sense but not in a smooth sense. We also prove that the formulas for F_p are uniformly close to the corresponding formulas in a space with constant sectional curvature, thus allowing one to estimate the distance between stars using formulas based on the Friedman model.

This talk is advertised as accessible to graduate students.