A Contentious Technology

Documents were leaked earlier this month about NASA's study of a proposed EmDrive. It generated the usual host of reactions, ranging from "it totally works" hype to outright dismissal. It's rare for a piece of technology to inspire such polarizing reactions; however, these reactions are rather understandable.

The EmDrive, otherwise known as a radio frequency resonant cavity thruster, makes use of microwaves that are bounced around inside an asymmetrical-shaped cavity. To break this down a bit more, the claim is, you bounce microwaves back and forth inside a truncated cone, and the result will be a thrust toward the narrow end of the cone.

That seems simple enough, yes? After all, you are just converting kinetic energy into another form of energy. Well, here is the kicker: The total momentum increases as the device begins to move. That is like placing yourself inside a box, pushing on the side, and generating thrust.

In short, it provides thrust without the need for a propellant, which at face value, violates Newton's Third Law of Motion. This means that, based on the current laws of physics, it's not supposed to work. Yet, that leaked paper from NASA was just peer-reviewed and published; its results suggest that it does work, barring other possible explanations.

Commenting on the work, astrophysicist Brian Koberlein states, "I’ve been pretty critical of this experiment from the get go, and I remain highly skeptical. However, even as a skeptic I have to admit the work is valid research. This is how science is done if you want to get it right. Do experiments, submit them to peer review, get feedback, and reevaluate."

In a paper published in the Journal of Propulsion and Power, Scientists from NASA Johnson Space Center constructed their own EmDrive and tested it in near-vacuum. Their results show that the system was able to produce a thrust-to-power ratio of 1.2 ± 0.1 millinewtons per kilowatt (mN/kW).

Experimental setup of the EmDrive. Credit: White, et al.

A Chance To Explore The Tech Further

It should be noted, though, that a peer-reviewed paper means that the methodology is sound, but the results (the conclusions) could still be invalid. Indeed, the authors of the paper do list some error sources for their results, error sources which could potentially invalidate their findings—like a thermal expansion of the device that could lead to a false positive.

Still, having a peer-reviewed paper on EmDrives is a significant development, as it is now open for more scientists to test the device and explain how it can (or could) produce thrust. As Koberlein states, "It doesn’t guarantee that the results are valid, as we’ve seen with other peer-reviewed research such as BICEP2. But this milestone shouldn’t be downplayed either. 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."

So it seems that it may be a little early to assert that we have figured out how EmDrive really works. As Koberlein concludes, "The biggest challenge they still have is that these results are so extraordinarily small that lots of things can explain them. They aren’t there yet, though."

Will the EmDrive be just a glorified microwave oven or the next step in interstellar travel? For now, we just have to wait and see. But, we should take the next few developments on this technology with both an open mind and a healthy bit of skepticism.

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