Maybe, but velocity is relative. So that would mean that the drive is pushing against something which has its own rest frame, relative to which velocity can be measured.<p>It&#x27;s not clear what that rest frame would be. Virtual particles in the quantum vacuum are often mentioned together with the emDrive, but those particles are thought to be frameless.<p>I&#x27;ll admit that it&#x27;s not entirely implausible to have a special rest frame like that. We already know that the cosmic microwave background has a rest frame, and this is something that you would start to feel in the form of frontal radiation pressure as you gain speed relative to the CMB.