[spottedquoll]

Extraordinary claims require extraordinary yada yada.

A working reactionless drive isn't just extraordinary. It's utterly mind-boggling. The least interesting thing is that it's a free-energy device.

It requires breaking spatial symmetry. If it works, it's not some edge-case theoretical law that's being broken. It's the geometry of space.

https://en.wikipedia.org/wiki/Noether%27s_theorem

[api]

Even if this works, reactionless drive would be my last hypothesis after exhausting all possible things it might be interacting with via some as-yet-unknown means: dark matter, nearby gravitational bodies, etc.

The infinite energy device claim is easy enough to test. Since a working infinite energy device would be perverse, I'd predict that an EmDrive rigged up so as to produce infinite energy would fail to do so. Exactly how it fails to do so might tell us what's going on. Do the energy requirements rise with momentum (as they should in a sane universe), or do you pass a point at which the effect ceases, or does something truly wacky occur like space-time distortion in such a way as to cancel the effect?

My reading of the McCullough hypothesis is that it's pushing against all matter in the universe at once, or some such thing, but that could be way off. I'm not a physicist.