Far be it from me to claim physic powers, because those aren’t real, but the moment the news of weird results coming from experiments to test the EmDrive came to my attention, I knew that one day I’d have to write a post about it. Not sure whether to jump on the bandwagon to simply join the chorus of voices explaining that it was impossible, I waited until proper experiments will show that the minuscule thrust being recorded in earlier tests was within the margins of error, a little bit of interesting noise but nothing beyond that to prove my premonition wrong. But as odd as it sounds, the EmDrive is still being tested and showing faint signs of life, and getting a whole lot of press claiming we’re on the verge of building a warp drive. And so, it’s time to quit stalling, roll up my sleeves and explain why the EmDrive can show us some interesting physics in weird environments, but simply would not work as a viable spacecraft engine as it was planned.
Getting right to the point, the biggest concern with the EmDrive is that it’s yet another version of a reactionless drive proposed by those who thought they spied something that isn’t there when looking at general relativity and tortured complex equations until they seemed to say what they wanted them to say. But such devices are impossible because they violate fundamental laws of physics we know to be true after centuries of observation and study. Objects at rest stay at rest until energy is added to the system and causes other objects to act on them. That’s what we’re taught in our very first physics class as one of the fundamental laws governing motion. When a device like the EmDrive comes along, it asks us to throw out this law and believe that whatever is going on inside the object can act as an external force large enough to make it move without actually adding energy to the mix. How that happens is usually peppered with tortured ret-cons of general relativity and buzzwords about group motion, frequencies, and reference frames.
Basically, think of piloting spacecraft with EmDrives as trying to make sailboats in a vacuum go simply by blowing into the sails. Sure, they’ll react a little at first as you introduce the initial tidbit of new energy, but in a closed system, the air you blow out of your lungs will simply dissipate as the system reaches equilibrium and all motion will stop fairly quickly. Same with the EmDrive. It seems that bouncing microwaves do produce some odd effects as they collide in the resonant chamber, but in a closed system, in which it has never actually been tested by the way, this too will dissipate and reach equilibrium so even the infinitesimal thrust currently being detected will be gone. Tellingly, the experiments on the versions of the EmDrive that seemed to be the most promising deviate in principle from the original design by including a nozzle to expel photons in the chamber as the reaction takes place, while the original was just supposed to propel craft by resonating away with no propellant or thruster like an alien warp drive in a sci-fi movie.
In the end, we’re left with pop sci blogs and news telling us the the EmDrive works while citing a few possibly intriguing experiments with a very inefficient Q-thruster design that departs from a core principle of the EmDrive’s planned implementation. That’s how it works. It’s not breaking a fundamental law of physics, it’s trying to resonate well known, but still rather poorly understood quantum particles that pop in and out of existence from the fabric of space and time. It’s a cool concept and not out of the realm of plausibility, but it’s very unclear whether it could actually be used as a real spacecraft engine and it’s not a reactionless drive we are being told it is by pretty much all of the media. That’s what a small skunk woks lab at NASA actually tested just to see if the concept was plausible, not the “impossible drive that violates the laws of physics,” and while it might not really go anywhere and seems rather buggy and hard to definitively verify today, it’s still a pretty interesting way to if we can actually do anything with zero point energy.