here's where i am but you're just going to tell me i'm wrong without letting me understand it. you don't like my interest in finding what's possible # the collision point is the earliest intersection of the swept-sphere paths the two spheres travel on # selfdot(pos1+vel1*t) = rsquared # selfdot(pos2+vel2*t) = rsquared # selfdot(touchpt - (pos1 + vel1*t)) = rsquared # selfdot(touchpt - (pos2 + vel2*t)) = rsquared # simpler is to compare their distances to the sum of their radii (inhibition forced us to look up on the internet >( ) # selfdot(pos1 + vel1*t, pos2 + vel2*t) = 4rsquared # even simpler is to consider one the reference frame for the other # selfdot(pos12+vel12*t) = 4rsquared # sum(pos12)**2 + sum(pos12*vel12)*t + sum(vel12)**2*t # it's a quadratic equation where A = sum(vel12)**2, B = sum(pos12*vel12), and C = sum(pos12) # the quadratic equation is (-B +- sqrt(B^2-4AC))/(2A) # so it's immediately rational from A, meanwhile you'd need B^2-4AC to be a square number or a rational of square numbers