[r9etb]

"It is well known that Roger Shawyer's 'electromagnetic relativity drive' violates the law of conservation of momentum, making it simply the latest in a long line of 'perpetuum mobiles' that have been proposed and disproved for centuries," wrote John Costella, an Australian physicist. "His analysis is rubbish and his 'drive' impossible."

You know ... I want Shawyer's theory to be right, just to see Mr. Costella have to eat his words.

[steve86]

Particles bouncing off a surface, even at a shallow angle, impart a force perpendicular to the surface, not at the angle of the incoming particle (my summary). I had to think about that, as it is counter-intuitive unless you think it through, but sure enough, that objection is valid. The change in the particle’s direction uses up the rest of the momentum (approximate statement).