The formation of wave is determined by The double-focus principle. In the spherical time-space, there are two focuses according to the duality principle of curvature. One is real focus caused by contraction motion of time-space. A nother is virtual focus decided by expansion motion of time-space. Two focuses overlap and interplay each other, which causes a serial vabration of time-space. So, wave is born by it. This is just theSo-called double-focus principle. Reference:THING AND ITS LAW (ISBN 1-58939-525-5), chapter 2: timedistance and timecurvature (the active and passive motion of time-space) and chapter 5: natural force(the durality of time-space and energy)published by Virtualbookworm.com publishing Inc.