Which is the physics of the wave of gravity of the spacetime? 
The author emphasizes the very serious problem of the physics of the wave of the spacetime itself  that would be the wave of gravity according to Einstein.
As much the particle movement as the propagation of the packages of energy of the electromagnetic wave happens within a frame that is the spacetime with dimensions x, y, z, t. Which is the frame of the gravity wave?. How it is possible to speak of wave? Speed? Moment? Impulse? Inertia?