TB: Third Thoughts (Weinberg)
Core Thesis
Science advances by asking the right questions, not merely accumulating better answers. Weinberg revisits foundational issues — the nature of physical law, the status of effective field theory, free will, and the demise of positivism — with the perspective of a physicist who has watched the field evolve across half a century.
Key Takeaways
Asking the right questions
- The history of physics is largely a history of identifying which questions are well-posed and which are category errors.
- Mach's refusal to believe in atoms — on the grounds they were unobservable — delayed physics. The lesson: positivism is a bad philosophy of science; unobservable entities are legitimate if they explain observable phenomena.
- Progress often requires rejecting a question rather than answering it (e.g., "what is absolute velocity?" has no answer; the question is ill-posed).
Effective field theory
- Every physical theory is an effective field theory: it describes phenomena at a given energy scale without requiring knowledge of what happens at higher scales.
- This is why physics is possible at all — you don't need quantum gravity to predict the trajectory of a baseball.
- Reductionism is correct as a matter of principle but wrong as a research strategy for most questions.
Free will
- Compatibilism: free will is compatible with determinism if "free will" means acting from one's own desires rather than external compulsion.
- The felt experience of deliberation is real even if the underlying process is deterministic.
Mental Models
- Inversion — Weinberg's method: when stuck, ask whether the question itself is wrong
- The Map is Not the Territory — EFT as explicit acknowledgment that our maps are scale-limited approximations, not the territory