io9 has the article New Test Suggests NASA’s “Impossible” EM Drive Will Work In Space.

The EM drive is controversial in that it appears to violate conventional physics and the law of conservation of momentum; the engine, invented by British scientist Roger Sawyer, converts electric power to thrust without the need for any propellant by bouncing microwaves within a closed container. So, with no expulsion of propellant, there’s nothing to balance the change in the spacecraft’s momentum during acceleration. Hence the skepticism.

I have just realized the value of dark energy and dark matter in physics. The answer to every seemingly impossible invention that seems to defy the laws of physics is “but what about dark energy and dark matter?” Since all we know about dark energy and dark matter are their effects on the expansion of the universe, we might as well attribute all unexplained behavior to them. Well, I don’t really mean attribute it to these factors. The issue is that you can’t say anything is impossible when you know you have something that affects physical objects, but you don’t know what that something is. As our <sarcasm>beloved</sarcasm> former Secretary of Defense, Donald Rumsfeld, would say this is something we know we don’t know. As he would go on to say, what about all the things we don’t know we don’t know?