[threesongs]

The version accepted in the journal clearly states that superluminal warp drives are physically unachievable because they violate the dominant energy condition. It means that superluminal drives require superluminal matter. This is in agreement with the conclusions in the IPWD paper. However, the version E.Lentz uploaded on arxiv or the press-release did not state this clearly.

[Causality1]

If superluminal matter existed, would we know it?

[abobrick]

In principle, yes, for sure, we could detect it. For example, it would still generate gravity and be uniquely identifiable this way. But then, superluminal matter breaks causality, allows sending signals back in time and, to the best of our knowledge, is unphysical.

[drran]

Superluminal speed is called "instant" in physics.

[abobrick]

Indeed, a superluminal object will appear to have an infinite velocity for some physical observers.

[drran]

The superluminal speed is not an infinite speed, it's just faster than the speed of light, of course, but it called "instant". For example, a photon of light is emitted or absorbed "instantly", which is not true, obviously, because it means infinite speed of transition.