nuclear-weapons

J. Robert Oppenheimer's life, quirks, and legacy: the Cambridge poisoning attempt, Bhagavad Gita at Trinity, and the security clearance that ended his career.

Nine countries possess nuclear weapons in 2025. Russia leads with approximately 5,580 warheads; the United States has 5,044. Together they hold over 87% of all warheads on earth. China is the fastest-growing nuclear power, having added roughly 100 warheads per year since 2023. And the arms control architecture that managed US-Russian competition for five decades has effectively collapsed.

The bombs dropped on Hiroshima and Nagasaki fissioned less than a kilogram of material each. Modern warheads are larger, but not a thousand times larger. Here is the physics, the arms-control record, and the evidence for and against the explanations of why none has been used in war since.

Nuclear war is the most discussed existential risk and the least understood. The bombs are the easy part. What comes after — nuclear winter, famine, collapse — is far more dangerous. Here's what science actually predicts.