We investigate the macroscopic behaviour of the density fluctuations of a one dimensional dynamics of hard rods with random length. After recentering on the effective velocity (hyperbolic space-time scaling) the density fluctuations of particles of a given velocity v will evolve on the diffusive scaling driven by a browian motion with a diffusivity depending on v. This rigid evolution of fluctuations is expected in all completely integrable systems, in contrast with the behavior expected in chaotic dynamics. Joint work with Pablo Ferrari (U. Buenos Aires).
