Sean Carroll | The Many Worlds Interpretation & Emergent Spacetime

The Cartesian Cafe

Sean Carroll is a theoretical physicist and philosopher who specializes in quantum mechanics, cosmology, and the philosophy of science. He is the Homewood Professor of Natural Philosophy at Johns Hopkins University and an external professor at the Sante Fe Institute. Sean has contributed prolifically to the public understanding of science through a variety of mediums: as an author of several physics books including Something Deeply Hidden and The Biggest Ideas in the Universe, as a public speaker and debater on a wide variety of scientific and philosophical subjects, and also as a host of his podcast Mindscape which covers topics spanning science, society, philosophy, culture, and the arts.

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In this episode, we take a deep dive into The Many Worlds (Everettian) Interpretation of quantum mechanics. While there are many philosophical discussions of the Many Worlds Interpretation available, ours marries philosophy with the technical, mathematical details. As a bonus, the whole gamut of topics from philosophy and physics arise, including the nature of reality, emergence, Bohmian mechanics, Bell's Theorem, and more. We conclude with some analysis of Sean's speculative work on the concept of emergent spacetime, a viewpoint which naturally arises from Many Worlds. This video is most suitable for those with a basic technical understanding of quantum mechanics.

Part I: Introduction

• 00:00:00 : Introduction
• 00:05:42 : Philosophy and science: more interdisciplinary work?
• 00:09:14 : How Sean got interested in Many Worlds (MW)
• 00:13:04 : Technical outline

Part II: Quantum Mechanics in a Nutshell

• 00:14:58 : Textbook QM review
• 00:24:25 : The measurement problem
• 00:25:28 : Einstein: "God does not play dice"
• 00:27:49 : The reality problem

Part III: Many Worlds

• 00:31:53 : How MW comes in
• 00:34:28 : EPR paradox (original formulation)
• 00:40:58 : Simpler to work with spin
• 00:42:03 : Spin entanglement
• 00:44:46 : Decoherence
• 00:49:16 : System, observer, environment clarification for decoherence
• 00:53:54 : Density matrix perspective (sketch)
• 00:56:21 : Deriving the Born rule
• 00:59:09 : Everett: right answer, wrong reason. The easy and hard part of Born's rule.
• 01:03:33 : Self-locating uncertainty: which world am I in?
• 01:04:59 : Two arguments for Born rule credences
• 01:11:28 : Observer-system split: pointer-state problem
• 01:13:11 : Schrodinger's cat and decoherence
• 01:18:21 : Consciousness and perception
• 01:21:12 : Emergence and MW
• 01:28:06 : Sorites Paradox and are there infinitely many worlds
• 01:32:50 : Bad objection to MW: "It's not falsifiable."

Part IV: Additional Topics

• 01:35:13 : Bohmian mechanics
• 01:40:29 : Bell's Theorem. What the Nobel Prize committee got wrong
• 01:41:56 : David Deutsch on Bohmian mechanics
• 01:46:39 : Quantum mereology
• 01:49:09 : Path integral and double slit: virtual and distinct worlds

Part V. Emergent Spacetime

• 01:55:05 : Setup
• 02:02:42 : Algebraic geometry / functional analysis perspective
• 02:04:54 : Relation to MW

Part VI. Conclusion

• 02:07:16 : Distribution of QM beliefs
• 02:08:38 : Locality

Further reading:

• Hugh Everett. The Theory of the Universal Wave Function, 1956.
• Sean Carroll. Something Deeply Hidden, 2019.

More Sean Carroll & Timothy Nguyen:

Fragments of the IDW: Joe Rogan, Sam Harris, Eric Weinstein: https://youtu.be/jM2FQrRYyas
Twitter: @iamtimnguyen

Webpage: http://www.timothynguyen.org