- Many Worlds permits universes where physics breaks down entirely
- The Born rule cannot be derived from Many Worlds without extra assumptions
- Barandes compares MWI's hidden complexity to the Stone Soup fable
Jacob Barandes keeps a copy of Stone Soup on his desk at Harvard. The children's book sits right next to his Einstein doll, a quiet joke about what happens when a theory promises too much from too little.
For Barandes, a physicist and philosopher of science who teaches in Harvard's physics department, the fable captures something precise about the many worlds interpretation of quantum mechanics.
The Library That Contains Every Possible Universe
In a conversation with quantum computing theorist Scott Aaronson on the podcast Theories of Everything (video posted above), Barandes reached for an older metaphor first. Jorge Luis Borges' Library of Babel, a fictional library containing every book that could ever be written, in every possible arrangement of letters.
Imagine entering that library and claiming it explains the universe. Somewhere on its shelves sits a book that perfectly describes our world. But it also contains a book where gravity runs backwards, where elephants speak French, where the laws of physics change every Tuesday.
The library explains everything. Which means it explains nothing.
The Many Worlds Interpretation
Proposed by Hugh Everett in 1957, the Many Worlds Interpretation (MWI) says that every quantum measurement causes the universe to split into parallel branches, one for each possible outcome. No wave function ever collapses. Every possibility simply happens, in its own branch.
Barandes argues that the Many Worlds Interpretation faces exactly this problem.
The theory predicts branches where physics works as we observe it, but also "super maverick branches" where the rules break down entirely. Once you include those, he contends, you are back in the Library of Babel: a framework so permissive it places no constraints on which universes we should expect to inhabit.
The Stone Soup Problem
This is where the children's book enters. In the folktale, soldiers convince a town they can make soup from water and stones. They just need a little seasoning. Then some vegetables. Then meat and broth. By the end, an amazed townsperson exclaims: "All this from just water and stones!"
Barandes sees the same pattern in how the Many Worlds Interpretation gets defended. Its proponents advertise radical simplicity: just the Schrodinger equation and unitary evolution. But to derive anything resembling the physics we actually observe, they quietly add assumption after assumption.
The most stubborn addition involves the Born rule, the equation that tells physicists how to calculate probabilities from quantum states. In a theory where every outcome happens with certainty across parallel branches, probability becomes philosophically strange.
Why should any branch be more "likely" than another if all of them exist?
Key figure
1957
The year Hugh Everett proposed the Many Worlds Interpretation in his PhD thesis. Bryce DeWitt broadcast it to the wider physics community 13 years later, in 1970.
Aaronson, the Schlumberger Chair of Computer Science at the University of Texas at Austin and director of its Quantum Information Center, agrees on this point. "I don't believe any of the so-called derivations of the Born rule from many worlds," he said during the exchange. "Neither Everett's original derivation nor any of the later ones. They all sneak in some additional assumption."
What a Theory Owes Us
Yet Aaronson resists a complete dismissal. He finds Many Worlds indispensable as a teaching tool, particularly when explaining decoherence to quantum computing students. A qubit that has been copied to another qubit behaves exactly as if someone measured it.
The many-worlds picture, he admits, is sometimes the only explanation that clicks.
If a theory doesn't rule anything out, if it doesn't tell us that anything is impossible or at least vanishingly unlikely, then it's vacuous. Then it's not doing anything for us.
Scott Aaronson, University of Texas at Austin
His pragmatism has limits, though.
"I am ultimately not satisfied by a theory that doesn't account for my experience of the world," he said, echoing a point the ancient atomist Democritus made around 400 BC: how can you ignore the senses when the senses provide your evidence?
Barandes pushes the critique further. Even if you accept that the Born rule cannot be derived and simply add it as an extra axiom, there is a structural mismatch. The branches in Many Worlds only emerge approximately, through decoherence at macroscopic scales.
You cannot assign fundamental axioms to objects that are not part of your fundamental ingredients, he argues. That would be like writing axioms of chemistry that assign special properties to tables and chairs.
Two Physicists, No Easy Answers
The exchange reveals something worth noticing about the current state of quantum foundations. Neither physicist claims to have solved the interpretation problem. (For a contrasting defence of Many Worlds, see Sean Carroll's case for the theory.)
Aaronson describes himself as someone who borrows whichever interpretive car gets him where he needs to go.
More On Multiverses
Multiverse: A Journey Through Parallel Worlds
Do we live in a universe which is just one of many? This Science Reader Special provides a basic introduction to the multiverse.
→Barandes has proposed his own alternative, a framework called "indivisible stochastic" quantum mechanics that drops the wave function entirely in favour of real degrees of freedom with fundamentally random dynamics.
Their disagreement is not about whether Many Worlds contains useful ideas. It does. The disagreement is about what counts as a scientific explanation, and whether a theory that permits every possible universe can meaningfully explain any particular one.
That question, first sharpened by Everett in 1957, remains genuinely open. A 2025 paper in Pramana revisited the Born rule problem using ergodic theory, and at least three distinct programmes for deriving quantum probability from Many Worlds remain active.
The debate has not stalled. It has deepened.
Sources
- Primary Source: Harvard Physicist Dismantles the "Many Worlds" Theory (Theories of Everything with Curt Jaimungal, 2025)
- Additional Context:
- Jacob Barandes (Harvard University)
- Born Rule and Many-Worlds Interpretation of Quantum Mechanics: An Ergodic Approach (Pramana, 2025)
- Jacob Barandes and Me (Scott Aaronson, Shtetl-Optimized)
Fact Check: Claim-by-Claim Verification Verified
The article's core history and attributions check out: Everett's 1957 origin of Many Worlds, DeWitt's ~1970 popularization, Aaronson's UT Austin titles, the Born rule definition, Barandes' "indivisible stochastic" alternative, and the 2025 Pramana ergodic-theory paper are all supported. No factual errors found; no corrections needed.
Commentary
- This is a conversation-based explainer. Attributed quotes from the Theories of Everything podcast are sourced from the primary video but could not be cross-checked against a public transcript; they are consistent with both physicists' documented public positions.
- "Maverick branches" and the Library-of-Babel framing are critics' rhetoric, correctly presented as Barandes' argument rather than settled physics.
- The MWI probability/Born-rule problem is genuinely unresolved and actively debated — the article's "the debate has deepened" framing is accurate.
Sources used for verification
Academic/Peer-reviewed:
- Born Rule and Many-Worlds Interpretation of Quantum Mechanics: An Ergodic Approach - link.springer.com (Pramana, 2025)
- Review of the quantum measurement problem and MWI - arxiv.org
- Born Rule and the Many-Worlds Interpretation - philarchive.org
- Everettian Interpretations of Quantum Mechanics - iep.utm.edu
- Democritus - iep.utm.edu
Other reliable sources:
- Jacob Barandes and Me - scottaaronson.blog
- Many-worlds interpretation - wikipedia.org
- Indivisible stochastic process interpretation - ncatlab.org
- Jacob Barandes show notes - curtjaimungal.substack.com
Fact-checked by Perplexity Sonar Pro on 2026-05-25
