A non-equilibrium distribution of electrons is set up when two quantum Hall edge states originating from sources at different potentials meet at a quantum point contact. Recently, several types of experiment have probed the consequences of this non-equilibrium distribution, first in interferometers, and recently by a direct measurement of the distribution and its evolution with distance downstream from the quantum point contact [1]. In this talk I will describe theoretical work [2] aimed at understanding aspects of these experiments. References [1] H. le Sueur, C. Altimiras, U. Gennser, A. Cavanna, D. Mailly, F. Pierre, Phys. Rev. Lett. 105, 056803 (2010). [2] D. L. Kovrizhin and J. T. Chalker, arXiv:1009.4555, and in preparation.