I'm working on a story that requires travel at about convenient* speeds (see below). I want to keep this story as hard sci-fi as possible and I've heard about stuff like Alcubierre drives which sound like a good fit, but I'd also like to know what the pros and cons of such a method would be (for instance, I would like to not use a method such that, say, reaching a planet is comparable to a nuke going off. That would not be ideal). Additionally, I'd like to get, if possible, an indication of how advanced, a civilization with that kind of technology would be. What would their Kardashev rating be? What other tech would they have and how would it affect their culture? etc.

*By "convenient," I mean that, for instance, a team of diplomat's could, at the very least, travel about 5000 light years (not in any kind of suspended animation), work out the beginnings of relations with an alien species, and return to Earth, as the alien society facilitating the travel in this story has deemed methods such as generation ships unethical and, for the sake of diplomatic relations, would like as many of their human guests to return to Earth alive as possible.

  • $\begingroup$ One problem with the Alcubierre solution is mentioned in the "physics" section of the Alcubierre drive wiki article--unless exotic matter can locally move faster than light, you'd need technology laid all along the path of the ship beforehand in order to warp spacetime in the right way. Another issue is that FTL leads very naturally to backwards time travel in relativity (also discussed in the wiki). These issues may be avoidable if you use wormholes, see my answer here. $\endgroup$ – Hypnosifl Jun 25 '19 at 5:21
  • 1
    $\begingroup$ Possible duplicate of Science-based FTL drive $\endgroup$ – JBH Jun 25 '19 at 6:01
  • 1
    $\begingroup$ Hello and Welcome to Worldbuilding Avmara. Unfortunately your seem to have gotten overexcited and asked us a series of different questions. We usually use a One question format to keep questions on topic and relevant. FTL is a very tricky topic, because its only really been dealt with theoretically and there are some issues with going back in time once you break the speed of light. You can always use the standard Wormhole, FTL Drive, Warp speed or mycelial network to suit your needs. $\endgroup$ – Shadowzee Jun 25 '19 at 6:16
  • 1
    $\begingroup$ I recommend that you focus specifically on the "safe" aspect of the FTL method you're looking for – most of the science-based parts are answered in the question JBH linked. It needs to be edited so that you're focusing on a single, specific question. Rather than "what are the pros and cons of various FTL drives", this site prefers "what is the best FTL method given this bullet-pointed list of things that I want it to do". $\endgroup$ – Adrian Hall Jun 25 '19 at 6:49
  • 1
    $\begingroup$ As for the Alcubierre drive specifically, you might be interested in my question from a few years ago Does the Alcubierre drive have a theoretical upper speed limit? on our sister site Physics. Also check out the sidebar there; they have some reasonable coverage of details of the Alcubierre drive. $\endgroup$ – a CVn Jun 25 '19 at 8:58