system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] How does space travel work?

Why is seeing into the future necessary, and how far are they traveling typically?
gpt
Space travel isn't so much "travel" as it is space-time being folded upon itself and the guild heighliners slightly moving to take advantage of this bridge between destinations. This is called the Holtzman Effect, and it can be achieved through extremely complex space-drive engines. The technical range of this is unknown, but it's possible to jump from one end of the known universe to another, assuming you knew the exact coordinates you wished to travel to. It's much safer, easier, and economically feasible to simply travel within the confines of human civilization. 

However, just because the engines are capable of punching holes in reality doesn't mean they can do so safely on their own. You need a navigator to ensure the destination is safe and capable of handling the sudden change in the universe around it. In ancient times, powerful computers used to be able to make these calculations in the blink of an eye, and humans could travel space without having to severely mutate themselves. But now that AI is not only illegal but heretical, people have to do it for themselves. Guild navigators see into their future, to the destination they intend to go, and chart the course for their vessel. They don't fold space themselves, but the journey does not happen until they make sure the "route" is safe. 

There does exist a more standard form of slightly beating the universal constant of c, but that technology is very old. And it BARELY breaches the speed of light, and is only useful in severe emergencies and inter-system travel like between Earth and Mars.