Developed by British aerospace engineer Roger Shawyer, EmDrive is a theoretical propulsion device that promises to transform humanity into a true space-faring species. If it works, long-distance space travel and even flying cars may be possible. (Flying cars!) There's only one problem: Many scientists are skeptical that EmDrive actually works, let alone that it can fulfill any of the potential its developers have pledged. 

Whether you're a proponent or an opponent to the concept behind EmDrive, you likely have a fierce opinion. Many who believe in it think it could bring about a new era for humanity akin to the "Star Trek" universe. Many who doubt it think the technology amounts to little more than snake oil, and its developer, Roger Shawyer, its snake oil salesman. Even worse, there are those who have argued that the concept behind EmDrive violates the rules of physics.

So who is right? The debate over the science behind EmDrive has recently reheated after NASA's Advanced Propulsion Physics Laboratory (also known as "Eagleworks") decided to test out the device, apparently with some success, reports io9. They found that 10 kilowatts of power allowed the device to produce 0.00061183 tonnes of force. More importantly, the test was performed in a vacuum chamber, which means EmDrive could work in space.

This is all very good news for the optimists, but the results should still be taken with a grain of salt. First, the thrust produced in these tests is small, less than Shawyer and the device's proponents have proposed. Second, the team at Eagleworks still isn't sure how the device works, and so long as that remains a mystery it will be impossible to say for sure if EmDrive can actually be developed into a viable technology. 

Theories

At its heart, EmDrive is little more than a metallic chamber with a greater area at one end of the device than the other. It purportedly works by repeatedly bouncing microwaves back and forth inside of it. The real stunner is that it has no moving parts and requires no fuel to operate, just an electrical power source to produce its reflecting internal microwaves. Some have pointed out that this ought to violate the conservation of momentum, a fundamental law of physics. But therein lies the mystery of exactly how EmDrive manages to produce any thrust at all.

Shawyer's original theory is that the thrust is generated thanks to radiation pressure inside the device, but his argument has been called into question by many who claim it shows a lack of understanding about the laws of physics. Shawyer has countered by arguing that the device exploits a loophole within general relativity, but this rebuttal has not won over many skeptics. 

Eagleworks' own Harold G. White has speculated that EmDrive's resonant cavities may operate by creating a virtual plasma toroid that could realize net thrust using magnetohydrodynamic forces acting upon quantum vacuum fluctuations. Some have even gone so far as to suggest that EmDrive is some sort of far-out version of a "Star Trek" warp drive, capable of producing thrust by contracting space in front of the drive and/or expanding it behind the drive. Needless to say, this is all just guesswork at this point, with varying degrees of plausibility.

Reason for hope

Though it's anyone's guess how EmDrive works, the fact that NASA's Eagleworks was able to show positive results, however small, is reason enough to give the device more serious consideration. At the very least, the status of the issue has been raised from scientific controversy to full-blown scientific curiosity. If EmDrive is proven to produce reliable thrust with follow-up study, and scientists can get a handle on what the heck is really going on inside its conical chamber, maybe science fiction really can be transformed into science fact. 

Don't book your ticket on the Enterprise just yet, but a next-gen future of "Star Trek"-like spaceflight can't be ruled out either. If EmDrive can be developed — and that's still a whopping big "if" — then not even the sky will be the limit.

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