Thanks. For the supposed violations - aren&#x27;t we still then only discussing the device working within <i>known</i> physics? There is no violation if the device were to slowly lose mass due to some unknown process (making it a form of Ion thruster), or if it accelerates some yet unknown weakly interacting massive particle in the opposite direction of the thrust, or if it somehow only conserves invariants for a &quot;larger&quot; system, potentially the entire universe?<p>Given an exotic enough explanation (negative energies&#x2F;faster than light particles&#x2F;spacetime warping&#x2F;..) it <i>feels</i> like you can cheat your way around almost any invariant? Occam is left weeping in a corner of course.