Almost sure results on the closeness of orbits
Almost sure results on the closeness of orbits
We review the problem of identifying distance rates for which almost sure asymptotic closeness properties between orbits of measure-preserving dynamical systems can be ensured. More precisely, we consider the set $E_n$ of pairs of points $x,y$ whose orbits up to time $n$ have minimal distance to each other less than the threshold $r_n$. If $(r_n)_n$ shrinks sufficiently slowly, almost every pair $x, y$ will meet this condition for all large enough $n$, i.e., $(\mu\times \mu)(\limsup_n E_n)=1$. On the other hand, if $(r_n)_n$ shrinks too quickly, then the measure of this set is zero. In joint work with Mike Todd, Maxim Kirsebom, and Tomas Persson, we obtain bounds on the sequence $(r_n)_n$ to guarantee that $\limsup_{n}E_n$ and $\liminf_{n} E_n$ are sets of measure 0 or 1.