"you can say that sin(x) = x" Yes, this is the small angle approximation http://en.wikipedia.org/wiki/Small-angle_approximation http://en.wikipedia.org/wiki/Sm

"you can say that sin(x) = x" Yes, this is the small angle approximation http://en.wikipedia.org/wiki/Small-angle_approximation http://en.wikipedia.org/wiki/Small-angle_approximation and also the example I gave above: 3 points on a sin curve may be considered a straight line or a curved line; 1 meter on earth's orbit is a straight line. The same idea comes up in the string theory too as a pun between point and line. I am surprised that there is no mathematical theorem to express this fundamental property of nature. Or maybe I am not expressing myself clearly.