Many worlds

Week 2: reality · quantum

Many worlds

Take the wave function literally; understand why this preserves locality and determinism.

In this lesson

  1. Read the core idea (3 min).
  2. Walk through one worked example.
  3. Take the 4-question quiz; pass with 4/4 or better.

Hook

After Bell, the foundations of physics had a problem: experiments forced you to give up either locality or realism. Hugh Everett, in his 1957 PhD thesis, proposed a third option that the working physicist had largely overlooked. Don't drop locality. Don't drop realism. Drop the assumption that there is exactly one outcome.

Everett's proposal, refined by David Deutsch and others into what we now call the many-worlds interpretation, takes the Schrödinger equation literally. The wave function, with all its branches, is the whole reality. There is no collapse. There is no special measurement step. There is just the linear, deterministic, local equation, and a universe whose history bifurcates whenever the equation says it does.