When I was a kid I read the Exiles Trilogy, by Ben Bova. The third book was gripping and fantastic. I can’t remember the first two thirds.
A year or so ago I saw Pandorum and thought it was a fantastic movie. I probably had an unusal resposne, I really, really wanted to know what langauge the ship board native spoke.
I was hoping there was a book, but there wasn’t. I tracked down a Heinlein book “Orphans of the Sky” which seems to be one of the earlier (earliest?) The book is pretty good, but in the last chapters Heinlein got bored with the story and rushed to move the characters to a suitable endpoint.
On wikipedia I found generation ship stories is a subgenre of maybe a dozen or more books.
I’m working my way through Greg Bear’s Hull Null Zero. So far it kind of feels like a first person shooter adventure, with characters doing a ship search in a dangerous ship. Bear’s ship is drowning in gidgits and doodads, so I often have a hard time visualizing what the heck is going on.
Social collapse and primitivization. A reversion to hunter and gatherer times.
Return to superstition and/or Religious zeal. A sort of reversion to medeival times.
Stratefied societies. Same idea but rolling back the clock to feudal times.
Cannibalism. Food shortages are okay for the story, but shortages in radiation shielding, air, water, heat would make for a really short story.
Simplification of language. The ship inhabitants start to lose personal experience with a lot of the words in their earthly mother tongue. This leads to “there’s-no-word-for” which is nonsense and “I-don’t-know-what-this-word-is” which makes perfect sense. Also, since the trips take forever, the language evolve.
Generation ships are a type of hard science fiction, in the sense that the story doesn’t appeal to magic to solve problems that are currently without a solution in the real world, namely faster than light travel.
Lowtech. After civilization collapses, the survivors are primative. No computers or AI. Sci-fi writers before the 80s completely missed the coming computer revolution and generally omit AI.
High tech. On high tech ships, manufactoring goes on or gadgets just work. There might be some computers or AI.
Organic technology. Evolution, cloning and genetic engineering are common themes. If not, then the travelers tend to arrive at new planets that just happend to be exactly like Earth.
Waking trips, sleeping trips. In waking trips, civilization collapses. In sleeping trips, the machinery malfunctions.
Invisible destinations. Most Sci-fi writers missed the recent revolution in detecting planets outside of our own.