It's legitimate perpetual motion, but not a machine. In a vacuum the test mass will never stop moving, but you can't extract any work from the system if you wa

It's legitimate perpetual motion, but not a machine. In a vacuum the test mass will never stop moving, but you can't extract any work from the system if you want it to keep going forever. Technically you can't even look at it, because that requires bouncing photons off its surface. The resulting radiation pressure will slow it down eventually.