How David Bohm and Hugh Everett changed quantum theory
Debate over David Bohm’s pilot‑wave theory and Hugh Everett’s many‑worlds view of quantum mechanics centers on whether these are genuinely testable theories or merely philosophical interpretations layered on top of the same math. Commenters contrast many‑worlds with the older Copenhagen stance and the pragmatic “shut up and calculate” attitude, arguing over falsifiability, Occam’s razor, and how to make sense of probability and measurement when every outcome may occur in parallel branches. Underneath the technical points is a deeper question: is the goal of physics simply to predict experiments, or to describe how reality actually works, even if that means embracing ideas like an ever-branching multiverse.
Status of Bohmian Mechanics and Many‑Worlds
- Several commenters dispute the claim that “science now accepts” Everett and Bohm; both are seen as interpretations, not confirmed new theories.
- Many report that most working physicists they know default to “shut up and calculate” rather than committing to an interpretation.
- Bohmian mechanics is viewed as hard to extend to quantum field theory; many doubt it as a long‑term contender.
Falsifiability and Testing Interpretations
- Strong disagreement over whether Many‑Worlds (MWI) is falsifiable.
- One side: MWI is just standard quantum mechanics (QM) with unitary Schrödinger evolution; it’s falsified if that fails, or if extra variables/collapse are detected.
- Other side: that only distinguishes QM+MWI from non‑QM theories; MWI is not falsifiable against other interpretations that keep the same math.
- Collapse‑type theories are noted to make distinct, in‑principle‑testable predictions, some already constrained by experiment.
Copenhagen vs Many‑Worlds vs Others
- Copenhagen is criticized as vague: “measurement,” “macroscopic,” and collapse are not precisely defined, and it can’t cleanly analyze the measuring device itself.
- Defenders argue it’s the de facto default for historical and pragmatic reasons, and reasonable to use while the measurement problem is unresolved.
- MWI advocates emphasize: wavefunction is real, Schrödinger holds always, and “worlds” are emergent decohered branches.
- Objections to MWI: trouble with probability/Born rule, and claims that it contradicts the observed “single outcome” unless you accept branching as unobservable.
Parsimony and “Theory Cost”
- One camp: MWI is more parsimonious—no special collapse rule, just one dynamical law.
- Critics: positing exponentially many concrete branches massively increases “theory cost” (number of real states/entities), so Copenhagen or collapse may be simpler overall.
Measurement, Decoherence, and Scale
- Ongoing debate on what counts as a “measurement” and whether there is an objective macroscopic threshold.
- Decoherence is seen by some as pushing toward MWI; others think it doesn’t rescue Copenhagen but also doesn’t uniquely select MWI.
Attitudes and Alternatives
- Many see interpretations as largely philosophical given identical predictions; focus should be on new theories with new testable consequences.
- Alternative frameworks mentioned include relational quantum mechanics; some hope future “completion” of QM will clarify these issues.