The Japanese began surrender negotiations one day after the Nagasaki bombing. Communities everywhere experienced the war's end with heartfelt relief. Los Alamos scientists were particularly proud of the unique role they had played in bringing the war to a close. The relief – and pride – were short-lived, for most of those who had worked on the bomb suffered loss of focus, while confronting an array of difficult choices, for example, whether to feel guilty for adding atomic bombs to the world's arsenal, and whether to continue working at Los Alamos. For a short time, the technical work of the laboratory slowed down, almost to a halt.

Responses to the war's end at Los Alamos varied a great deal. Laura Fermi recalls children parading through the streets, banging on pots and pans and joyfully making mini-explosions, while their parents grappled with the sobering implications of their achievement. Depression typically followed a short period of relief. Richard Feynman recalls that while he sat on a jeep and pounded on drums during one of the many end-of-the-war parties held at Los Alamos, he noticed that Robert Wilson was not jubilant. Feynman also became depressed soon afterward. Only a few of the scientists saw hope in the fact that the bomb was so destructive – believing that nuclear weapons might actually end all wars because the second use of so terrible a weapon was unlikely.