There are so many unsolvable differential equation problems, and the three-body problem is still "abstract", at least the planet can be regarded as a mass point. But some problems cannot be transformed into particles, such as real-time collision detection of two-dimensional space line segments, even if it is only two finite-length line segments with independent angular acceleration functions and linear acceleration functions, and these acceleration functions are simple real coefficients Polynomials, the collision detection equations established with this product are still very complicated.As long as it is an "ordinary" physical problem that is close to reality, especially when it involves collisions, human beings are really helpless. For example, there is a theory of collisions and entropy changes in chemistry, and there has not been much progress so far.