Inessa Epstein : The Borel complexity of orbit equivalence of ergodic actions of non-amenable groups

Posted by , part of the Logic Seminar.

At

Aug. 26, 2008, 4 p.m.

In

SEO 612

Abstract

We consider a countable group G acting in a Borel way by measure preserving automorphisms on a standard probability space X. The orbits of this action give rise to an equivalence relation on X. We say two measure preserving actions of groups G and H on spaces X and Y, respectively, are orbit equivalent if there is a measure preserving bijection between conull subsets of X and Y identifying the orbits. We discuss the complexity of the classification problem of free, measure preserving, ergodic actions of a countable group under orbit equivalence and show that it is not classifiable by countable structures.

The seminar begins with tea.