Module 3 / Lesson 7.1

Risks of Developing Nuclear Weapons

1 min read

The Manhattan Project, basic nuclear physics, and the first time humanity calculated the probability of its own extinction.

Learning:
- Review the basic concepts of nuclear physics in the lecture notes.
- Watch Intro to Nuclear Physics (watch from beginning to 4:30; no need to watch all of it!).
- Watch Nuclear Fission and Nuclear Fusion.
Reflection: Consider why the distinction between fission (splitting atoms) and fusion (combining atoms) matters for the scale of existential risk (kilotons vs. megatons).

Learning: Read Ord, pages 89–96 (stop before "Close Calls").
Reflection:
- Why does Ord date the beginning of "The Precipice" specifically to the Trinity Test (July 16, 1945)?
- Reflect on the "structural uncertainty" of new technologies. If scientists were wrong about the Castle Bravo test, could they be wrong about the safety of modern AI or biotech?
Shore Notes:
- The "Berkeley Meeting" (Trinity Context): Before the Trinity test, physicists (Oppenheimer, Teller) calculated the risk that the bomb might ignite the atmosphere's nitrogen.
- The Prediction (Trinity): They calculated the risk was "near zero" (approx. 3 in a million), but not zero. They proceeded anyway without consulting elected officials.
- Prediction Error (Castle Bravo, 1954):
  - The Test: The U.S. detonated a bomb containing Lithium-6 and Lithium-7 at Bikini Atoll.
  - The Error: Scientists wrongly assumed Lithium-7 would be inert, so the reaction had much more power than expected.
  - The Result: The predicted yield was 6 Megatons. The actual yield was 15 Megatons (2.5x larger than expected and ~1,000x Hiroshima).
- Accuracy Record: In the early days, prediction accuracy for major tests (correct about Trinity but incorrect about Castle Bravo) was only 50%.

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