looking for a book, just know basic plot.

[JimmyMJB2]

I think the story is: Due to a cataclysmic event, the human race is forced to leave earth. They leave in a giant spaceship. While they are waiting to reach their destination, hundreds of years pass. They forget they are on a spaceship, believing it is their home planet.

Please help me out, plot searches on the net are killing me. I've been curious for a while now, and would like to put this to rest.

Anything would be helpful at this point.

 

[Wolhay]

It could be "Orphans of the Sky" by Robert A. Heinlein.

But from what I've heard this plotline isn't entirely uncommon.