You Still Shouldn't Believe in the emDrive

Extraordinary claims require extraordinary proof. Which is why you should still be suspicious of the "emDrive," a theoretical propulsion system that supposedly could propel objects to near-relativistic speeds, despite this week's headlines touting the technology.

The emDrive, invented by Roger Shawyer, purportedly works by repeatedly bouncing microwaves back and forth in a chamber. Though it would appear to violate the laws of physics, the idea is to create a propellant-less thruster that can move a spacecraft at extraordinary speeds if enough pressure is applied. He claims that it could gain 3 tonnes of thrust with 1 kilowatt of power input by essentially moving the particles around the chamber of the thruster in a vacuum.

The latest news: The site NASA Spaceflight has published an article claiming that this time, the emDrive is really real, and it's gotten picked up a lot by other outlets. In their experiment, 10 kilowatts of power produced 0.00061183 tonnes of force. (Here's some more detail about it from io9.) That's far less than Shawyer's predictions, but at least a weak confirmation that something was going on inside the chamber.

However, there are a few things you should know. Previous tests of emDrive haven't held up to scrutiny. And the NASA agency investigating the EmDrive, informally known as Eagleworks, is specifically devoted to investigation of fringe or far-future ideas such as the Alcubierre Drive, a futuristic warp drive that is both (marginally) technically possible and completely unfeasible due to bonkers energy demands. So just because you hear that NASA is intrigued by an idea, don't assume that it's going to work tomorrow.

Propulsion without propellant

EmDrive dates back at least 15 years. The thrust of the theory, as Shawyer explained in a book published in 2006, goes like this: "A new principle of electric propulsion for spacecraft is introduced, using microwave technology to achieve direct conversion of d.c. power to thrust without the need for propellant." He sought out investors in the United States and Britain but didn't find a ton of well-heeled believers, and by 2008, he was already going abroad for investors. So he moved to China, where one scientist, Prof. Juan Yang, claimed that it worked.

Elsewhere, Shawyer encountered plenty of skeptical push-back. Sci-fi writer Greg Egan was ... not a fan. Responding to the claim that emDrive could produce thrust with a small amount of influence from microwaves, Corey Powell at Discover pointed out in August 2014 that the idea is riddled with holes. That write-up followed a slew of headlines declaring that NASA had verified the emDrive. The reality was closer to NASA engineer shrugging and saying "oh, that's neat."

One of the Shawyer's latest claims is that the EmDrive can create warp bubbles. He says the emDrive created a warp-like bubble in a NASA lab, bending space and time around it and enabling photons to go faster than the speed of light. Yes, it's true that there are concepts out there for a warp drive that are theoretically possible—and which require an absolutely enormous amount of power to work. Take the afore-mentioned Alcubierre Drive, taken ever so slightly seriously by at least a couple NASA scientists. But even if that idea has a solid grounding in physics, it still is unlikely to come into life. At least not soon.

Meanwhile, there's very little scientific literature on Shawyer's proposed spacecraft. There is a recent NASA paper suggesting that a similar device can produce thrust, but a small fraction of the power proposed by Shawyer. And this research, too, was conducted by the NASA Eagleworks lab, whose purpose in life is to investigate the outer limits of physics and find out what might work, someday, to make humans into a true spacefaring society. When New Scientist published Shawyer's findings in 2006, it was lambasted for giving the idea the time of day.

Debate ignited

This week's article over at NASA Spaceflight was the result of a cacophony of debate on the site's forums about the reality of emDrive. The piece includes this:

"The NASASpaceflight.com group has given consideration to whether the experimental measurements of thrust force were the result of an artifact. Despite considerable effort within the NASASpaceflight.com forum to dismiss the reported thrust as an artifact, the EM Drive results have yet to be falsified. After consistent reports of thrust measurements from EM Drive experiments in the US, UK, and China – at thrust levels several thousand times in excess of a photon rocket, and now under hard vacuum conditions – the question of where the thrust is coming from deserves serious inquiry."

That's true—it does deserve serious inquiry. But that's a long way from saying the technology is confirmed. Maybe, one day, the emDrive eventually works and we all eat our hats. In space. But the initial results will have to hold up against the forces of peer reviews and repeated tests (which it hasn't so far). Until then, it remains a far-out idea waiting for its day in the sun, or its timely death.