Tau Zero

Poul Anderson.
1970 adaptation of his 1967 short story, To Outlive Eternity.
Brought up by a redditor at r/printsf in surprise at its absence on a list of hard scifi, and according to Wikipedia it's 'regarded as the quintessential example of "hard sci-fi"'.
Category:Works
Category:Literature
Category:Books
Category:Science fiction books
Category:Hard science fiction books
Category:1970s books
Category:American books