Yet time continues to go on in the rest frame relative to that velocity c, is perfectly well defined, and does not require division by zero in order to make perfect sense and ordering of events including the position of the wavefront while this occurs. That's because nothing is actually 'moving'. When you knock down a row of dominoes, does any single domino move ahead as fast as the wave? No. Each one simply ROTATES a bit as it falls. THAT IS WHAT CARRIES THE ENERGY OF GRAVITY. This even works in the non rotating, otherwise empty quantum 'Higgs' field. The direction of the force depends only on which direction the Higgs mechanism imparted linear inertia to mass from its own zero spin quantum field. Mass = Energy = rotational / linear inertia = disturbance of a quantum field. Time and quantum entanglement and the temporal permanence of the form of energy we refer to as matter derives of quantum spin (faster than c), not from c. Time dilation is not 'constant', even if the speed of light, or that of the rest frame, is. Time and events related to energy = inertia = 'disturbance of a lossless quantum field'', is all that exists in this universe. The totality of physics derives of this, and unifies perfectly without reference to anything involving what we commonly refer to as 'space' = 'light travel time'.