  However this structure is to be exactly and completely described and  whatever its inner ground might be, all laws of nature show that it  constitutes the most decisive influence on the evolution of physical  events: the behavior of rigid bodies and clocks is almost exclusively determined through the metric structure, as is the pattern of the  motion of a force-free mass point and the propagation of a light  source. And only through these effects on the concrete natural  processes can we recognize this structure.