4 ms·

I believe it's "The Gods Themselves", though Wikipedia doesn't have anything about it starting as a short story (at least skimming on my phone)

• rukuu001 10y ago
  I was thinking that's exactly what it sounded like, which is my hands-down favourite Asimov book.
  • jholman 10y ago
    That's because it's the best Asimov book. :P
    • gpderetta 10y ago
      Pfff, The End of Eternity is obviously the best Asimov book :) edit: and probably the best time travel novel as well
• rootbear 10y ago
  I believe you are correct. That was supposed to be a short story but it just kept growing. I like that one quite a bit.