Gp is talking about forward-only time travel though, you don't need anything exotic for that at all, just lots of energy and an efficient way to turn it into thrust.

The Alcubierre drive “beats” the speed of light, for the effects described 0.7-0.9c are more than good enough (if slightly unpractical).

We can’t do that either for now, but is way easier on the feasibility scale.

> The Alcubierre drive “beats” the speed of light

The Alcubierre drive is only a thought experiment that requires "exotic matter" (aka fairy dust) to work.

Papers have been published that have found ways to create warp drives without the need for exotic matter: https://arxiv.org/pdf/2006.07125.pdf

I know, I was making reference to this

> They are only theoretically possible if you allow for negative mass and energy--not an engineering problem so much as a "need to find exotic matter"

Basically people ran the EFE "backwards" to see what matter distribution makes the wanted curvature. You get either negative mass-energy or the bubble doesn't travel ftl iirc.

No, for forward time travel you don’t need any sort of exotic matter. You just need a really fast rocket.