I remember reading the article in Wikipedia years back, but I never bookmarked it, and now I'd like to read the story/novel.
It was about a group of people who live in another place/dimension, and who influence our history, trying to make it safer. As a result nuclear power isn't discovered until maybe 30th century, and it's the same with many other things.
So they make the world safer, but mankind isn't as innovative as it should've been.
I also remember about someone being stuck in the 1930s or 40s, and something about a signal in the form of a photo of a nuclear mushroom.

  • scifi.stackexchange.com/… – John Rennie Sep 18 '14 at 8:02
  • @Otis Sure, the answer is the same, but the question is a bit different in each case ( so there's no way I could've found the previous question at the time, and not ask a duplicate about the same book ). – Rick Sanchez Sep 18 '15 at 21:54
  • @Kushtrim, my comment was not intended as a criticism! Just cross-linking the questions for the reference of other readers and/or admins. – Otis Sep 19 '15 at 2:57

Looks like "The end of Eternity", from Asimov.

(btw it was not a photo, but a text in the form of the mushroom, spelling "atom")

  • This is it. Thanks :) – Rick Sanchez Sep 17 '14 at 14:50

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