Can you drive a car by getting on the front seat and pushing the windshield? The answer, as anyone familiar with high-school level physics would tell you, is no. Newton’s third law of motion — for every action has an equal and opposite reaction — explicitly prohibits this.
However, after months of rumors, speculation and criticism, a peer-reviewed study published last week in the Journal of Propulsion and Power claims to have shown a propulsion system that, to all appearances violates this cardinal law, actually seems to work.
Electromagnetic drive, or EmDrive, is a proposed fuel-free propulsion system that putatively works by bouncing microwaves around a closed chamber. The problem with this kind of propulsion system is that it’s impossible. A system cannot produce thrust without pushing something in the opposite direction.
Despite this, speculation that NASA was on the verge of developing an EmDrive, has been floating around for over a year now — even though physicists repeatedly dismissed it as “impossible.”
The new study, though, shows otherwise. It details experiments carried out by NASA’s Eagleworks Laboratories and describes a radio frequency resonant cavity thruster — EmDrive by another name — that is capable of producing thrust of up to 1.2 millinewtons per kilowatt in vacuum. The researchers achieved this by turning electricity into microwaves and bouncing them around in a closed copper cone.
Although an order of magnitude higher thrust can be produced using rocket fuel, the significance of the paper lies in the fact that it shows the existence of something that current laws of physics tell us shouldn’t exist.
“The issue involved here is whether the experiment is seeing something real or not,” Jim Woodward, a physicist at California State University, Fullerton, told Motherboard. “I know [study co-author] Paul [March] does clean work and to be honest, I suspect there may really be something there. But the result they're seeing can't actually be explained in terms of the theory they're proposing. So the question is: what is causing it?”
Although the exact cause is yet to be determined, the study does offer an explanation — one that invokes a controversial interpretation of quantum mechanics known as the pilot-wave theory, which, unlike the currently-accepted Copenhagen interpretation, states that subatomic particles do have fixed locations even when they are not being observed.
According to the researchers, if the pilot-wave interpretation is true, it would allow the EmDrive to generate thrust by acting on virtual particle pairs created by fluctuations in quantum vacuum.
“It is proposed that the tapered RF test article pushes off of quantum vacuum fluctuations, and the thruster generates a volumetric body force and moves in one direction while a wake is established in the quantum vacuum that moves in the other direction,” the researchers wrote in the study.
However, this is still a hypothesis that needs to be stringently tested before its passes muster. Moreover, it should be noted that just because a study has passed peer-review, it doesn’t mean its results are valid, only that the researchers’ methodology was considered sound.
“But this milestone shouldn’t be downplayed either,” astrophysicist Brian Koberlein wrote for Forbes. “With this new paper we now have a clear overview of the experimental setup and its results. This is a big step toward determining whether the effect is real or an odd set of secondary effects.”