On projections of metric spaces

Let X be a metric space and let μ be a probability measure on it. Consider a Lipschitz map T : X → Rn, with Lipschitz constant ≤ 1. Then one can ask whether the image TX can have large projections on many directions. For a large class of spaces X, we show that there are directions φ ∈ Sn−1 on which the projection of the image TX is small on the average (in L2(μ)), with bounds depending on the dimension n and the eigenvalues of the Laplacian on X. Our results can be viewed as a multidimensional extension of the concentration of measure principle.