If you hit a grain of sand at 10% of light speed, very plausible in century travel, you can get a massive damage to the ship. You shold think to a way to repair the ship without external resources, you need recycling, so a foundry, factories or nanobots

This question is typical for someone with a pre-post-scarcity mindset. Claiming that they'd "have no reason to do so" makes no sense. In the post-scarcity world, the reason may be as simple as "why not?"

@Dragongeek Surely "pre-post-scarcity" is simply "scarcity"?

@StefanoBalzarotti that grain of sand is an extarnal factor, why not allow gathering resources from external sources if they come right to you?

@Dragongeek just what I was thinking and trying to formulate an answer around on. Assuming the challenges are solved, plausibility would only be determined whether it is reasonable to do so, and since reason is in the eye of the beholder, someone with enough resources and inspiration to do so is bound to do it.

@V. Sim The grain is not coming at you, you are hitting him at 10% of light speed, at that velocity it can make an hole big as a car. the damage is not comparable with the obtained resources. Also the Interstellar medium is almost empty, you need years of travel before hitting a single grain of sand.

@StefanoBalzarotti motion is relative, you going to the grain is the same as the grain coming to you. My point is that repairing the ship without the use of external resources is an unreasonable restriction for a high tech vessel with fusion that could literally satisfy most of not all of its resource requirements with just hydrogen.

@V. Sim to be able to get enough resources, the vessel must be able to accelerate/decelerate many times from 10% of light speed to 0 relative to the object speed/direction. I assume a generation ship will be very very big, so you need a very big amount of energy. If you have so much energy why don't do a single acceleration to 90% of light speed, so you can arrive at Proxima Centauri in 3 years?

@StefanoBalzarotti This is something better discussed in chat, but its similar to how you don't move your whole house to the grocery store to stock up resources. You would utilize smaller, quite possibly automated vessels to go and bring the resources back, if you process them at the larger vessel, then all you need is the energy to capture the resources needed to offset inefficiencies or growth of the needs of the ship. It's fine if you don't agree.

Proxima Centauri is 4.2ly away. so at .1c it would take 42 years, not a century. not a long time for a "generation" ship. things like genetic drift won't come into play at all here.

Following up on @Dragongeek's comment about them "having no reason". People still risk their lives climbing dangerous mountains that they could just fly over or past in luxury for less money. Just so long as our desire for risk and proving ourselves doesn't get evolved out, you will find people to get on that ship.

@ths Accelerating to 10% c at one Earth g would take almost 60 years.

@Muuski you might recalculate that. i get ~0.2 years at 1g.

On a side note, one of the solutions to mitigate radiation (as well as fast moving debris) is to surround the ship with water. It also happens to be something you'd need a lot of anyway.

@ths I got a result close to yours once I realized I forgot to convert minutes to seconds (hence the 60 in my comment)

Earth is generation ship, traveling through space, ETA to Andromeda is 4 billion years from now, distance 2.5 million light-years

Just to start.. 1) The whole idea of "post-scarcity" is pure fantasy. 2) It's not possible to live a decent life in space. The people on the generation ship may be altruistic enough to want to give their grandchildren a chance at a decent life. (Though it works better if they can "cold sleep" part of the voyage.)

I think this answer of mine sums up my thoughts.

After post scarcity, comes the final scarcity. "The Mote in God's Eye" explores this.

"Oh no! Earth will be ripped to shreds by tidal forces because Jupiter just swung in to inner system" No amount of fusion will solve that . And yes Jupiter did really just swung by. Everyone makes mistakes

In a post scarcity world the reason to move to the frontier is the same as it has always been, to get away from other people, to go out and try something new or at least something hinging on your own merit.

There are astronomical events that could sterilize a star system, but almost none that can sterilize two different ones at the same time. That alone is a reason to spread out to multiple star systems.

"Because it's there".

I think that, given sufficient study and time to consider all of the potential negative scenarios, it's possible to prove that anything is inherently implausible. This leads to the inescapable conclusion that all progress is driven by clueless dweebs who haven't done their homework. Hah-hah! The fools!!!

Note that if you have the technology to build a generation ship, you will long ago have solved the problem of "we have no idea whether there are any habitable destinations," because building giant space telescopes would be trivial for such a civilisation, and they'd easily be able to determine the chemical composition of distant planets' atmospheres. The colonists would likely have a very good idea of the conditions on the worlds they're heading to.

@JimmyJames mmmmmm tasty radioactive water :D

Also note that it is possible to have an oxygen atmosphere without life. You just need a planet with lots of water (much more than Earth), and gravity/solar wind such that hydrogen ions can escape easily but the heavier oxygen ions can't. We don't have such a world in our Solar system, but they're probably not uncommon in the universe. Of course, everything will be oxidised on such a world - there won't be any fossil fuel deposits or carbon-rich soil, so it presents its own survival challenges.

I read the generation ship article linked in the post, and feel most strongly that the article is an argument from incredulity - the author cannot understand how the problems can be solved and thus declares them to be impossible to solve. And also a side effect of the view I have seen more frequently recently that some how it is inappropriate to think of going to another planet. That we must accept that we never will and should not. Neither of these points of view can I empathise with.

@jamesqf The supposition that it is not possible to live a "decent life" in a space habitat is completely unfounded.

@LightnessRaceswithMonica The water helps protect from cosmic rays in much the same way our atmosphere does by turning it into secondary cosmic rays. A primary cosmic ray will slice up DNA like a Ginsu through a can.