Certain systems of three falling balls satisfy the Chernov–Sinai ansatz
The system of falling balls is an autonomous Hamiltonian system with a smooth invariant measure and non-zero Lyapunov exponents almost everywhere. For almost three decades now, the question of its ergodicity remains open. We contribute to the solution of the ergodicity conjecture for three falling balls with a specific mass ratio in the following two points: First, we prove the Chernov–Sinai ansatz. Second, we prove that there is an abundance of sufficiently expanding points. It is of special interest that for the aforementioned specific mass ratio, the configuration space can be unfolded to a billiard table, where the proper alignment condition holds.