C'mon, guys, it's radiation pressure; all conventional physics and it really can work. A photon of energy hv carries momentum hv/c where c is the speed of light. A beam of EM radiation of power W exerts a reaction force of W/c on the object that emits it. Each photon is a bit of energy, which is equivalent to a bit of mass as Einstein taught us. So yes, something is being ejected - photons. And yes the craft gets lighter as they leave. The craft really is using up reaction mass, and energy to accelerate it. It really does work for the same reason that a conventional rocket works. The only weird thing is that the exhaust velocity is the speed of light, so the specific impulse of the "fuel" is about 30 million seconds, not a few hundred as with chemical fuels. So the craft gets lighter very slowly. This is the natural engine for a nuclear powered long-mission spacecraft. It is hard to make much thrust this way, but you don't use up your fuel very fast. This electromagnetic thrust is well known to guys designing solar power satellites; the expected thrust from 10GW of power beam is 33 Newtons. Sunlight being absorbed by the solar panels exerts an even larger force. Another effect of light pressure is the force on a solar sail. (A so-called radiometer spinner is a quite different effect that you can look up.) Remember the spacecraft (Voyager?) that was experiencing anomalous acceleration in the outer solar system when the expected accelerations were extremely small? A thermal power generator was radiating its waste head in mostly one direction. Add in the tiny thrust from that and it all came out even. So this effect has even been tested in space, although unintentionally.