Generic stationary measures and actions

Lewis Bowen, Yair Hartman, Omer Tamuz

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Let G be a countably infinite group, and let µ be a generating probability measure on G. We study the space of µ-stationary Borel probability measures on a topological G space, and in particular on ZG, where Z is any perfect Polish space. We also study the space of µ-stationary, measurable G-actions on a standard, nonatomic probability space. Equip the space of stationary measures with the weak* topology. When µ has finite entropy, we show that a generic measure is an essentially free extension of the Poisson boundary of (G, µ). When Z is compact, this implies that the simplex of µ-stationary measures on ZG is a Poulsen simplex. We show that this is also the case for the simplex of stationary measures on {0, 1}G. We furthermore show that if the action of G on its Poisson boundary is essentially free, then a generic measure is isomorphic to the Poisson boundary. Next, we consider the space of stationary actions, equipped with a standard topology known as the weak topology. Here we show that when G has property (T), the ergodic actions are meager. We also construct a group G without property (T) such that the ergodic actions are not dense, for some µ. Finally, for a weaker topology on the set of actions, which we call the very weak topology, we show that a dynamical property (e.g., ergodicity) is topologically generic if and only if it is generic in the space of measures. There we also show a Glasner-King type 0-1 law stating that every dynamical property is either meager or residual.

Original languageEnglish (US)
Pages (from-to)4889-4929
Number of pages41
JournalTransactions of the American Mathematical Society
Issue number7
StatePublished - 2017


  • Poisson boundary
  • Stationary action

ASJC Scopus subject areas

  • General Mathematics
  • Applied Mathematics


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