“…axions are potentially detectable through their weak coupling to electromagnetism…” -Aaron Chou
We know, from hundreds of years of experience with the laws of physics, that momentum is strictly conserved, and therefore a reactionless drive is impossible. What’s not impossible is an engine that has a reaction that’s simply invisible, or otherwise undetectable to us. This has been seen in experiments involving neutrinos, but NASA’s impossible space engine, the EMdrive, offers another possibility: a dark matter reaction.
You see, one of the leading candidates for dark matter is the axion, an ultra-light, massive, abundant particle that would couple to microwave photons under the right conditions. While ADMX, the axion dark matter experiment, looks for this coupling in a microwave cavity, it’s come up empty so far. Could the tinkerer who invented the EMdrive have accidentally stumbled upon dark matter instead?
It’s a highly speculative possibility, and it’s far more likely that the EMdrive simply doesn’t work. But this is why we do the experiments in the first place, with more to follow!