The Emthruster: Thrust without reaction?

[stevebowers]

Photon drives aren't reactionless drives, since photons carry momentum, if not mass. This is because of mass/energy equivalence.

The 'Cannae drive', or the E-M drive, or the Shawyer drive, which all seem to be roughly the same thing, all are supposed to have no net photon emissions in any one direction.
http://en.wikipedia.org/wiki/EmDrive

Science fiction writer Greg Egan distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" was making the magazine's coverage sufficiently unreliable "to constitute a real threat to the public understanding of science". In particular, Egan found himself "gobsmacked by the level of scientific illiteracy" in the magazine's coverage of the EmDrive, where New Scientist allowed the publication of "meaningless double-talk" designed to bypass a fatal objection to Shawyer's proposed space drive, namely that it violates the conservation of momentum. Egan urged those reading his letter to write to New Scientist and pressure the magazine to raise its standards, instead of "squandering the opportunity that the magazine's circulation and prestige provides" for genuine science education. The letter was endorsed by mathematical physicist John C. Baez and posted on his blog.[11] Egan has also recommended[11] that New Scientist publish Dr. Costella's refutation[10] of Shawyer's theory paper.[35]