The 1/r2 distance dependence of gravitational attraction was formulated by Isaac Newton and is familiar to anyone who has taken an elementary physics class. However, new physics phenomena may modify the inverse square law — for example, string theory requires extra ‘rolled up’ gravitational space dimensions that would cause the inverse square law to break down at short distances. Measuring the distance dependence of gravity for objects with small separations would thus potentially reveal new physics, but is hard to do, because gravitational forces are weak and easily drowned out by noise. Writing in Physical Review Letters, Eric Adelberger and colleagues report the separation dependence of gravity between 52 μm and 3 mm, finding results consistent with Newton’s law of gravitation and tightening the upper limit on the radius of hypothesized extra dimensions to 30 μm.