[radford-neal]

If the black box is freely floating (which is what I was thinking of), then a particle within it can move to one side only if something else in it moves the other direction.

But on further thought, I wouldn't be surprised if some changes in the internals of the box could produce gravitational waves, so maybe my intuition for this is wrong. Although if I further clarify that the box isn't supposed to be emitting energy (which will obviously reduce its gravitational influence as it loses energy), then maybe the intuition is correct after all...

[100ideas]

“Electromagnetic waves” are the manifestation of relative motion between an electric charge and an observer’s reference frame. A detector inside a cryogenic ion trap would detect much lower energy EM radiation from the contained cloud of ions vs a sensor speeding towards the trap at 10% c. If this second detector slowed towards the inertial reference frame of the ions, the apparent EM radiation emanating from them would decay towards zero from the second detectors point of view as it became stationary relative to the charges.

Are gravity waves similarly observer-reference-frame-dependent? I.e. the gravitation of a given object is not intrinsic but rather dependent on the energy difference between the object and a given observer’s frame?

[radford-neal]

I think the charges need to be accelerating, not just moving, to emit radiation. Whether or not something is emitting radiation ought to be invariant to the motion of the observer.