Quote by htg
Consider a Gaussian beam of EM waves, propagating in the X direction. Consider a parallelopiped, whose edges are parallel to the X, Y and Z axes, the axis of the parallelopiped parallel to X not coincinding with X (best of all, shifted away from it by a distance comparable to the "width" of the beam, defined as so many standard deviations of the Gaussian function). Let the edges parallel to Y and Z be short compared to the "width"of the beam. Let the edge parallel to X be shrt compared to the wavelength of the EM wave considered. Is The Gauss law valid?

Since divE=0 at all points in the beam, I would think Gauss' law must be valid. That is, flux in through one surface of the parallelopipid must equal flux out through the opposing surface. More generally, I believe that Gauss' law is universally true. All of my own personal attempts to find a violation have been fruitless.