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Gauss's law describes the behaviour of fields with infinite range and helps us to understand how extra dimensions influence the gravitational interaction. In three (infinite) dimensions Gauss's law states that the force associated with such a field falls off as 1/r2 because the lines of force are spread over an area that is proportional to r2. In general, Gauss's law predicts that a force that falls off as 1/rn-1, where n is the number of space dimensions. The figure shows the gravitational lines of force (red) produced by a point mass in a space with one infinite dimension (the horizontal green line) and one finite or "curled up" dimension (the green circle). The gravitational force felt by a second point mass a distance r away is proportional to the number of force lines per unit area. When r is less than the size of the curled up dimension, the lines spread uniformly in two dimensions (blue circle), so, according to Gauss's law for n = 2, the gravitational force should vary as 1/r. But for much larger separations the lines become parallel and the force does not change with distance. In the scenario proposed by Arkani-Hamed and co-workers with three infinite dimensions and two "large" curled-up dimensions, the gravitational force would be proportional to 1/r4 for separations less than the smallest of the "large" extra imensions.