I wonder if it is possible to express a simple principle into a mathematical form. The simple principle says if at time t0 an isolated system is composed of some elements with some properties then at t1 it is composed of other elements with different properties, then in principle it is possible to explain the elements the system has at t0 and t1 using lower level elements that are present at t0 as well as at t1 in a different configurations. For example at t0 we identify elements of type E0 with certain properties then at t1 we have elements of type E1. There must be lower level elements of type e0,e1,..,en that when combined they form E0 and E1. If not, the elements e1 can never occur. This principle may not be correct, but to me it seems true. This is like saying if catterpillars can turn to butterflies the they must share the same DNA. This is related to phtons as elementary particles creating virtual electron- positron pairs which are also elementary.