Spin polynomial invariants, as denned by Pidstrigatch and Tyurin, are used to define differentiable invariants for Dolgachev surfaces. In order to define and compute these invariants, some machinery is developed to study the wall structure for Spin polynomials, to deal with the fact that the moduli spaces have the wrong dimension and to handle nonreduced structures. The invariants are then computed.

METHODS AND APPLICATIONS OF ANALYSIS. 2000 International Press Vol. 7, No. 3, pp. 591-604, September 2000 012

1. Initial Data Set formulation The initial data set is given by (gij, pij) on a three dimensional manifold where gij is asymptotically euclidean (so that asymptotic quantities can be defined) and pij falls off quadratically. We also study the case when g^ is asymptotically hyperbolic and the three manifold is asymptotically null. Several important questions remain unsolved for the initial data set and its Cauchy development.

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This is the <i>Leonardo da Vinci Lecture</i> given in Milan in March 2006. It is a survey on the concept of space-time over the last 3000years: it starts with Euclidean geometry, discusses the contributions of Gauss and Riemannian geometry, presents the dynamic concept of space-time in Einsteins general relativity, describes the importance of symmetries, and ends with Calabi-Yau manifolds and their importance in todays string theories in the attempt for a unified theory of physics.