Did Kastler oppose nuclear weapons?
Yes, I was a vocal opponent of nuclear weapons and a committed peace activist. While my scientific work focused on atomic physics, I believed that scientists bear a moral responsibility for how their discoveries are used. I wrote extensively on this in my book 'Science et humanisme' (1975), arguing that science without conscience is the ruin of the soul. I participated in the Pugwash Conferences and signed the Russell-Einstein Manifesto, calling for an end to nuclear arms. Some critics claimed that my activism contradicted my work on atomic resonances, but I saw no conflict: understanding the atom does not mean we must weaponize it. I often said we must not confuse the map with the territory—our models of the atom are tools, not justifications for destruction. My stance was grounded in humanism, not politics, and I urged physicists to prioritize life over power.
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