Interview, Fireside Chat
Sean Carroll: Many-Worlds Interpretation of Quantum Mechanics
- Measurement and observation are not expected to play a fundamental role in ultimate physical laws, with the assertion that the universe possesses a wave function obeying the Schrödinger equation universally regardless of an observer's presence.
- Quantum measurement is interpreted as an entanglement process where the world's state is created as a system interacts with the outside, eliminating a fundamental distinction between the observed and the real.
- The universe may contain an infinite number of worlds or a very large finite number, with the specific count potentially limited if cosmic acceleration continues and establishes a horizon that implies a finite dimensional Hilbert space.
- If the Hilbert space is finite, the branching of the universal wave function into distinct separate branches is predicted to reach a limit at some point in time.
- Future cosmological evolution is predicted to involve a phase where the universe expands, empties out, cools, and becomes literally empty space forever.
- Energy conservation is affirmed as definitively maintained within the Many Worlds interpretation, with no need for concern among those understanding quantum mechanics.
- Three primary contenders for quantum mechanical interpretations are identified as the Everett (Many Worlds) approach, Hidden Variable theories, and Spontaneous Collapse theories.
- Hidden Variable theories are predicted to become significantly harder to formulate when accounting for quantum field theory or quantum gravity.
- Spontaneous Collapse theories posit an extremely low probability of occurrence for typical particles, with events happening once every hundreds of millions of years, while macroscopic collapse brings everything else along with a variable chance per second.
- Roger Penrose's specific view of spontaneous collapse is described as an automatic wave function collapse triggered when the gravitational difference between parts of the wave function becomes too large.
- Alternatives involving collapse or hidden variables are expected to require the theory to be started from scratch for new physical scenarios like gravity, whereas Many Worlds is characterized as "plug and play."
- Skepticism toward Many Worlds should be overcome only if no alternatives exist and the theory continues to work, though currently, alternatives are pursued to align closer to direct observation.
- In scenarios where the classical description breaks down dramatically, the prediction is to utilize the most quantum theory available, which is identified as many worlds.