In this series of three lectures I will consider SRB measures (after Sinai, Ruelle and Bowen) which arguably form one of the most important classes of invariant measures with “chaotic” behavior in dynamics. This ensures a crucial role they play in applications of dynamical systems to science (this is why they are often called “physical measures”).

In the first lecture I introduce these measures and describe their ergodic properties. I also outline a construction of SRB measures for Anosov systems.

In the second lecture I consider the case of partially hyperbolic dynamical systems and outline a construction of SRB measures in this case. I also discuss an important role SRB measures play in the Pugh-Shub Stable Ergodicity problem (and I will also discuss this problem in a general setting).

The third lecture deals with the most general situation of the so-called “chaotic” attractors (or attractors with non-zero Lyapunov exponents), which appear in many models in physics, biology, etc. I will present a general rigorous definition of chaotic attractors and outline a construction to build SRB measures for this attractors.

While the first lecture will serve as an introduction to the subject and will be accessible for students, the other two lectures are more advanced.

I present joint work with B. Weiss that describes a concrete operation on words that allows one to generate symbolic representations of Anosov-Katok diffeomorphisms. We show that each A-K diffeomorphism can be represented this way and that each symbolic system generated by this operation can be realized as an A-K diffeomorphism.

I present joint work with B. Weiss that describes a concrete operation on words that allows one to generate symbolic representations of Anosov-Katok diffeomorphisms. We show that each A-K diffeomorphism can be represented this way and that each symbolic system generated by this operation can be realized as an A-K diffeomorphism.

A real number x is called diophantine if its distance to rationals p/q is large relative to q -- more precisely, if for every d > 0 there is a positive C such that for every reduced rational p/q, we have |x - p/q| > Cq^{-2-d}, or equivalently |qx-p| > Cq^{-1-d}. Almost all reals have this property. Furthermore, almost every pair (x_1, x_2) has the property that for every d > 0 there is a C such that |q_1x_1+q_2x_2 -p| > C||q||^{-2(1+d)} for all p, q_1, q_2. In this talk, we discuss a noncommutative analog of this property for elements of SO(3). Namely, a pair (A,B) is called diophantine if there exists a constant D such that for every positive integer n and every reduced word W of length n in A, B, A^{-1}, B^{-1}, we have ||W - E|| > D^{-n}, where E is the identity matrix. It is conjectured that almost every such pair (in the sense of Haar measure) is diophantine. We will present a paper of Kaloshin and Rodnianski, in which the weaker bound D^{-n^2} is obtained.

I present joint work with B. Weiss that describes a concrete operation on words that allows one to generate symbolic representations of Anosov-Katok diffeomorphisms. We show that each A-K diffeomorphism can be represented this way and that each symbolic system generated by this operation can be realized as an A-K diffeomorphism.