The Last Question by Isaac Asimov

Funny how that one is coming back again and again:

- 3 years ago: https://news.ycombinator.com/item?id=3691113

- 6 years ago: https://news.ycombinator.com/item?id=595419

- 1 year ago: https://news.ycombinator.com/item?id=6752785

- 5 years ago: https://news.ycombinator.com/item?id=1078831

- 7 months ago: https://news.ycombinator.com/item?id=8376716

And so on... [minor edit for text]

This story was first published in 1956. As far as I know, it's still under copyright (I don't know whether the copyright is owned by Asimov's estate, by the publisher, or by someone else).

One of my favorite short stories.