Earlier this week we wrote about a leaked paper that apparently confirmed that NASA had built a working electromagnetic drive (or EmDrive), a theoretical (and "impossible") rocket propulsion system that seemingly violates Newton's Third Law of Motion. It's such a controversial subject that the the moderators of the /r/Physics subreddit deleted their thread with our post out of a conviction that the EmDrive is unscientific.
But yesterday, following months of rumors and criticisms, the full and official peer-reviewed paper regarding the drive appeared online through the American Institute of Aeronautics and Astronautics (AIAA)'s Journal of Propulsion and Power. It's a big milestone, but keep in mind that peer-review doesn't mean the argument necessarily holds water, only that the measures taken to arrive at the conclusion were considered sound.
The content is much the same as what we saw last Monday, but the latest version is notable for confirming that, yes, NASA EmDrive consistently performs at 1.2 millinewtons per kilowatt of thrust in a vacuum, even after a "number of error sources were considered and discussed." This, even though nothing about its design adheres to the notion that "everything must have an equal and opposite reaction" for thrust.
Faster thrust is available with rocket fuel, but the entire appeal of an EmDrive is that it doesn't need rocket fuel at all. Instead, as we described it earlier this week, it works by "turning electricity into microwaves and bouncing them around a closed metal funnel." It's thus extremely light, and the paper affirms that the EmDrive performs "two orders of magnitude higher than other forms of "zero-propellant" propulsion, such as light sails, laser propulsion, and photon rockets." And with the heavy loads from rocket fuel out of the picture, the EmDrive could be the engine that gets us to Mars and perhaps beyond.
Of course, the EmDrive still seems to violate the established laws of physics, even though it apparently worked fine in multiple tests. By way of explanation, the paper somewhat briefly proposes that the answer might have something to do with pilot-wave theory, a deterministic approach to quantum mechanics that states that particles have fixed locations, but that the physics must act in strange ways for this to be the case. Veritasium's Derek Muller recently posted a good video on the subject to YouTube:
More tests need to be run, of course, and there's plenty of reason to be skeptical. But the paper does much to nudge the concept closer to scientific fact. And in an era when science itself seems to be under bombardment, it's a massive thing to be excited about.
For a more in-depth discussion of the physics involved, be sure to read Daniel Oberhaus' article from Monday.