This from the news.com.au site:
While criticism of his concept was abundant, nobody has managed to prove it wrong.
Behind it all is some pretty speculative quantum physics.
At the tiniest of all known scales, the universe does not seem to obey its own rules.
One of the concepts this drive claims to exploit is an effect called quantum vacuum fluctuation: Where particles spontaneously create themselves in the vacuum of space, before quickly blinking out of existence again.
Somehow, these rare — here one minute, gone the next — particles are being captured and turned into plasma inside the microwave drive. This plasma, when directed, imparts thrust.
If true, it’s a source of fuel delivered direct to the engine — without weighty or dangerous fuel tanks.
And it’s constantly re-creating itself.The theoretical physics behind zero-point energy has been around for years and the drive of the ship in Horizon also makes use of spontaneously created particles.
One of the big problems in stellar space travel is how much fuel a craft would need to carry to travel any appreciable distance in a relatively short space of time, the weight of that fuel and the difficulty of replacing it when it's gone. If this works, it could remove a major barrier to space travel.