Impossible EmDrive

Humanity has come a long way in understanding the universe. We’ve got a physical framework that mostly matches our observations, and new technologies have allowed us to analyze the Big Bang and take photos of black holes. But the hypothetical EmDrive rocket engine threatened to upend what we knew about physics… if it worked. After the latest round of testing, we can say with a high degree of certainty that it doesn’t.

If you have memories from the 90s, you probably remember the interest in cold fusion, a supposed chemical process that could produce energy from fusion at room temperature instead of millions of degrees (pick your favorite scale, the numbers are all huge). The EmDrive is basically cold fusion for the 21st century. First proposed in 2001, the EmDrive uses an asymmetrical resonator cavity inside which electromagnetic energy can bounce around. There’s no exhaust, but proponents claim the EmDrive generates thrust.

The idea behind the EmDrive is that the tapered shape of the cavity would reflect radiation in such a way that there was a larger net force exerted on the resonator at one end. Thus, an object could use this “engine” for hyper-efficient propulsion. That would be a direct violation of the conservation of momentum. Interest in the EmDrive was scattered until 2016 when NASA’s Eagelworks lab built a prototype and tested it. According to the team, they detected a small but measurable net force, and that got people interested.

There was plenty of skepticism about the Eagelworks results, and other teams haven’t been able to duplicate the results. A team from the Dresden University of Technology has completed a comprehensive new test, attempting to replicate the results from Eagelworks. And they found nothing — zero thrust was generated by the Dresden EmDrive as electromagnetic radiation bounced around inside the resonator.

The Dresden EmDrive is an exact copy of the NASA Eagelworks setup.

The team also sought to explain the Eagelworks results, which they did by varying the experimental design. The Dresden researchers used better measurement techniques to show that the EmDrive doesn’t produce thrust, but by tweaking the measurement scale and changing resonator suspension points, they got the same small apparent thrust as NASA. That confirms the Eagelworks thrust was actually just a thermal effect. The researchers also speculate Eagelworks cherry-picked the data by reporting random fluctuations in a way that didn’t represent the full data set.

This really does feel like the end of the road for the EmDrive. Unless someone can identify some huge element of physics we have missed, there’s no way this engine can function as described. EmDrive proponents will have to pack it in unless they want to end up like cold fusion cranks from the 90s. That’s just science in action, but it’s also a bit of a bummer because the EmDrive would have changed the world if it wasn’t a fantasy.

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