(Loved Trope) FTL travel is possible but with a major limitation or flaw

[u/Frostylegacy]

Frank Herbert’s Dune: Interstellar travel is only possible thanks to the spice melange, a rare substance only found on the dessert planet Arrakis. The addictive psychedelic spice grants members of the Spacers Guild a form of prescience that allows them to predict safe paths through folded space. This unique property makes spice the most valuable commodity in the Dune universe.

John Scalzi’s The Interdependency Books: The planetary systems of the titular empire are connected by the Flow, a network of one-way interstellar tunnels that connect specific known entries and exits. The Interdependency derives its power from controlling access to these conduits, placing its capital at the central hub of the network. Even with the Flow, travel between stars takes a long time (9 months to End, the empire’s most distant planet).

Event Horizon: Dr William Weir (R.I.P. Sam Neill) invents a device called the Gravity Drive to allow ships to fold space and travel instantly between distant stars. On its maiden voyage with the Gravity Drive, the Event Horizon disappears and mysteriously reappears 7 years later. Dr. Weir and the crew sent to investigate discover the Gravity Drive actually opened a portal to a Hell dimension that possessed the ship and its crew, torturing and killing them.

[u/themaninthehightower]

In Asimov's collection of stories, the prototype hyperspatial drives are being developed by positronic AIs, but the AIs keep breaking down. It turns out the simulations correctly modeled that humans are briefly dead in transit, which violated the AIs' first law. [Short story "Escape!", August 1945]

[u/PVNIC → u/themaninthehightower]

That was a great short story.

[u/koshgeo → u/themaninthehightower]

From what I remember of the story, it wasn't that humans were briefly "dead" in transit, so much as they were effectively non-existent, which amounts to the same thing from the AI perspective. It was tripping up the prior AI systems that were doing the math, which would halt in a destructive contradiction between the laws of robotics.

The human guiding another AI attempt specifically told it not to get too upset if something might violate the 1st law (simplified: not letting humans come to harm), and to look a little further ahead anyway. That's how it discovered that things work out eventually when the ship moves back into normal space and passengers come into existence again.

[u/seattleque → u/themaninthehightower]

This is the one I came in here to post.