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This is unsurprising. I doubt there was anyone with a modicum of understanding of the physics (even the teams doing the testing) who expected it to work. That doesn't, however, mean that testing it was a waste of time. There was an anomalous result that has now been resolved. I think it's a vital scientific virtue to follow up anomalous results until they're satisfactorily resolved, no matter how ridiculous or physics-defying they seem.

The EmDrive was always a long shot, but it wasn't the only reactionless drive under investigation. Unlike the EmDrive, which never had a plausible physical mechanism for how it could work, the Woodward Effect [0] does have such a mechanism and has yet to be experimentally disproven. It exists in this weird place where it seems to be a straightforward theoretical prediction from general relativity; where, almost by exploiting a loophole in physics, the maths says you can get thrust without propellant, and much more of it than possible with a photon rocket for the same power. This, apparently, doesn't violate conservation of momentum, either, because the momentum would be carried by gravity waves, essentially "pushing" against distant masses throughout the universe. Whether this is actually predicted by general relativity or is a misapplication of the theory, is very subtle and not something I'm capable of evaluating.

This is being evaluated by NASA [1] -- not that that says very much, NASA will evaluate some pretty crazy things, see exhibit A: EmDrive -- but they've yet to achieve a negative result. Not that that says very much either -- EmDrive didn't have a negative result until it did. Still, while the chances of the Woodward effect working are small, I would still rate it as much, much higher than the EmDrive ever seemed to be. It's something to keep an eye on, anyway. There's also this interview with James Woodward [2] that might be of interest.

[0]: https://en.wikipedia.org/wiki/Woodward_effect

[1]: https://www.nasa.gov/directorates/spacetech/niac/2018_Phase_...

[2]: https://medium.com/predict/james-woodward-on-machs-principle...




I came here to mention the Woodward Effect. I had never heard of it until last week when someone here on HN mentioned the blog of Tom Mahood (a former master's student of Woodward) in an entirely different context (namely: UFOs). It ended up sending me on a deep dive into the subject and, ultimately, led me to an article by Mahood[0] about the Woodward effect. The upshot is:

> But Tom, is this stuff ……real?

> I….don’t…. know. And I say that after being involved in chasing it down for 10+ years. At this point, I see arguements on both sides.

> Fundamentally, the mathematics are extremely compelling. I have yet to come across anyone credible in General Relativity who can say why the derivation is incorrect. About as damning as I’ve heard is something along the lines of, “Wait,…This can’t be right….But I don’t know why it’s not right”. The math is straightforward.

> The effect (or something like it) has been demonstrated in a wide variety of different types of devices and experimental setups. Something has been observed if it’s merely capacitors being shuttled back and forth, but also with later generation devices composed of all PZT discs.

> […]

> As time progressed and the experimental apparatus more refined, the “effect” seemed to get smaller, and that’s a REAL bad sign. It was already well below what the theory predicted. That sets off alarm bells. After all this time, if something isn’t in hand to float around a table top, its should still at least be producing unequivocal results.

[0]: https://www.otherhand.org/home-page/physics/graduate-studies...


Addendum: I just noticed that the EmDrive article has something to say about the Woodward effect:

> In a third paper, the Dresden physicists then describe their research on the “Mach-Effect Thruster”:

> “Here we have proven that the Mach-Effect-Thruster (an idea by J. Woodward) is unfortunately a vibration artifact and also not a real thrust.”




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