Childhood's End

By ARTHUR C. CLARKE

"My work here is nearly ended," said Karellen's voice from a million radios. "At last, after a hundred years, I can tell you what it was.

"There are many things we have had to hide from you, as we hid ourselves for half our stay on Earth. Some of you, I know, thought that concealment unnecessary. You are accustomed to our presence: you can no longer imagine how your ancestors would have reacted to us. But at least you can understand the purpose of our concealment, and know that we had a reason for what we did.

"The supreme secret we kept from you was our purpose in coming to earth--that purpose about which you have speculated so endlessly. We could not tell you until now, for the secret was not ours to reveal.

"A century ago we came to your world and saved you from self-destruction. I do not believe that anyone would deny that fact--but what that self-destruction was, you never guessed.

"Because we banned nuclear weapons and all other deadly toys you were accumulating in your armories, the danger of physical annihilation was removed. You thought that was the only danger. We wanted you to believe that, but it was never true. The greatest danger that confronted you was of a different character altogether--and it did not concern your race alone.

"Many worlds have come to the crossroads of nuclear power, have avoided disaster, have gone on to build peaceful and happy civilizations--and have then been destroyed by forces of which they knew nothing. In the twentieth century, you first began to tamper seriously with those forces. That was why it became necessary to act.

"All through that century, the human race was drawing slowly nearer to the abyss--never even suspecting its existence. Across that abyss, there is only one bridge. Few races, unaided, have ever found it. Some have turned back while there was still time, avoiding both the danger and the achievement. Their worlds have become Elysian islands of effortless content, playing no further part in the story of the universe. That would never have been your fate--or your fortune. Your race was too vital for that. It would have plunged into ruin and taken others with it, for you would never have found the bridge."