Mathematics Colloquia and Seminars

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Recently Nemirovski and myself showed that causal relation
of two events in a globally hyperbolic spacetime is equivalent
to the non triviality of the Legendrian link of the spheres
in the space of all light rays formed by the lights rays
through the two event points.

The result was obtained under the condition that the universal
cover of a Cauchy surface of the spacetime is not compact.

In this talk we review these results and discuss
the generalization of them to the case of Cauchy surfaces
with compact universal coverings using contact Bott-Samelson Theorem of Fraunfelder, Labrousse
and Schlenk.

If time permits we will discuss possible relations
between causality and linking in causally simple spacetimes
which are more general than globally hyperbolic ones.