I have been wondering for a long time now on how to calculate the time taken for two masses in space to collide by force of gravity. Now what ive basically done was integrate the formula a = GM / R^2 between the two points corresponding to the distances appart from the masses (assuming the masses are equal.) And with the acceleration, T = sqrt ( 2S / a ) (S being the distance between masses). And ive gotten values of, say two 1 tonne masses at a distance of 1 Km would take approx 70 years to collide with eachother. Now ive got no idea whether ive gotten it right, or im way off. It seems like a fair answer (then again they only weigh one tonne). Can anyone confirm my working is correct and or what im doing wrong. Thanks -Denton.