The EM drive, weird as it sounds, just keeps passing peer review. It’s starting to look like we’ve found something genuinely new here — an inertial drive! Until recently, that was considered science-fantasy by most — a way of changing velocity without “pushing” against something else.
In short, it throws Newton’s third law of motion out the window.
It’s a very small effect — about 1.2 millinewtons per kilowatt, give or take ten percent or so. That’s a very subtle effect — one millinewton is about one twentieth of the force needed to lift a dime — but one that can be constantly applied over hours, days, weeks, months, or years, with no propellent needed.
If it works — if this effect is real — we’ll be able to build much more efficient (meaning faster, cheaper, and larger) long- and medium-distance spacecraft.
And if past technologies are any indication, the test model is probably terribly inefficient. Faraday’s first electric motor, after all, was just a wire spinning around in a mercury bath. From such humble beginnings, however, came all of our modern electric motor technology.
TL;DR (physics geeks): Don’t look now, but conservation of momentum might not be a thing, after all.
TL;DR (everyone else): If this works, we just got a LOT better at building spaceships. Not faster-than-light better (at least this year), but way, way better. Like go-to-Mars-for-the-week-someday better.