threesongs

Violation of causality is equivalent to travelling back in time. Lots of problems there, and no good model for such things.

It is an important paper. However, it is also important to realise that superluminal solutions introduced there are still prohibited by the laws of physics. Making such superluminal drives is at least as hard as making superluminal matter, which we believe requires infinite amount of energy. In physics, they say that such spacetimes violate the dominant energy condition. The issue is relatively clearly stated in E.Lentz's paper accepted in the journal, but not in his arxiv paper or the press-release.

IMO the paper clarifies the misconceptions about all warp drives. They all need propulsion, for example, to be consistent with physics.

A conclusion of the paper is that any warp drive, including all the ones proposed in the literature, fits in the categories explained in the paper.

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.