  Take a torus with a Riemannian metric. Lift the metric on its universal
cover. You get a distance which in turn yields balls. On these balls you can
look at the Laplacian. Focus on the spectrum for the Dirichlet or Neumann
problem. We describe the asymptotic behaviour of the eigenvalues as the radius
of the balls goes to infinity, and characterise the flat tori using the tools
of homogenisation our conclusion being that "Macroscopically, one can hear the
shape of a flat torus".
