Shawyer's "Electromagnetic Drive" Hi, I'm sure you've heard of this proposed concept by Robert Shawyer for an "electromagnetic drive" which is claimed to generate an unbalanced force inside of a resonant QED-cavity, thus causing acceleration that appears to violate Conservation of Momentum. http://technology.newscientist.com/article/mg19125681.400 http://blog.wired.com/defense/2008/09/chinese-buildin.html http://emdrive.com/faq.html Now, we all know about the inviolability of Conservation of Momentum, but the claim being made is that there is supposed to be some kind of "loophole" for the small-scale quantum world. The claim is that if the resonant cavity is asymmetric and tapered, that somehow there can be a net force acting against one side of it that is not balanced from the other side. I can't picture this -- if you have a balloon that is asymmetrically shaped, it doesn't mean that the gas molecules will hit and impart more force on side than than on others. But I realize that a balloon is a macroscopic cavity, and not a small quantum-sized one. Anybody can see in a macroscopic cavity diagram that even with a tapered end, there will be a component of force that would be in an axial direction, that would cancel out any imbalance or "thrust". Point #3 in the FAQ site linked above attempts to boldly contradict this: I'm not understanding what they're trying to assert, here. Could anyone kindly debunk this above statement for me, so that I can understand the error in its reasoning? Are they saying that all dimensions/axes are not equal, to a wave inside a resonant cavity? In regular macroscopic situations, when a particle or ray or wave hits a surface, it will reflect off with an angle of reflection that is equal to the angle of incidence, with the overall momentum conserved. Does this rule somehow change when you go down to the tiny quantum scale? The assertion quoted above seems to imply that wavelength confinement within a QED cavity can trump regular rules of reflection. (ie. if the diameter along the tapered end is too tight to accommodate the incident wave, then the surface of that tapered section will not reflect back the incident wave in a regular normal way) But what does actually happen in such a small-scale situation? What does happen to an oscillating wave that is striking a surface whose proximity to other confining surfaces is tighter than the wavelength itself? The author seems to imply that some kind of "downconversion" of the incident wave occurs. Is "downconversion" (a known phenomenon) then analogous to an "inelastic collision"? In the quantum world, is it possible to selectively have inelastic collisions with just one side of a cavity? Thanks for any serious replies.