Henry Kuttner & C L Moore's "Time Enough" (as by Lewis Padgett) (short story, immortality, free): Sometimes the best argument is a demonstration
Story summary.A nuclear catastrophe destroyed most human culture & artifacts. Among the human survivors were a few people with a mutation - they were practically immortal. Immortal, but aging in a natural way - so senility, bodily troubles, etc are norm among them.
Now, 500 years down, a new human civilization has arisen. With "Old 'Uns" isolated by the government to avoid envy among the normals.
But Sam Dyson, working with radiation in a lab, has figured out a way to achieve immortality. How do the powers-that-be convince him to give it up? Well - they do have an effective argument, but it doesn't involve speaking...
Fact sheet.First published: Astounding, December 1946.
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Listed among the stories from John Campbell's Astounding/Analog.
Related: Stories of Henry Kuttner, C L Moore (as by Lewis Padgett); Stories involving immortality; Mutants in fiction.