I just want to make sure I understand why a beam of light or shadow from a beam of light cannot move faster than light in the direction perpendicular to the direction of the photons. You all know the idea that if you point a laser to the moon and wiggle your hand, that a spot on the moon will appear to travel faster than light - the same with shadows. It is my understanding that, because the beam of light leaves the laser pointer at velocity c, as you change the angle of the pointer, the beam sort of lags behind as shown in the diagram below. Please Register or Log in to view the hidden image! So at a later time, although you are pointing the laser at a certain angle, the spot appearing on the moon will be at a different angle along the path L. Also, no matter how fast you change the laser angle, the spot on the moon cannot travel faster along the path L than c, and instead, the lag time between the laser and the spot grows larger. is this a sound argument?