Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime

Author: Sean Carroll | Published: 2019

Summary

Something Deeply Hidden is a bold popular account of quantum mechanics that argues directly for the Everett (many-worlds) interpretation and against the dominant pedagogical tradition of Copenhagen agnosticism. Carroll, a theoretical physicist at Caltech, argues that the measurement problem in quantum mechanics—the question of why quantum systems appear to “collapse” into definite states when observed—is a genuine unsolved problem that the physics community has largely ignored by teaching students to “shut up and calculate.” The Everett interpretation, Carroll argues, is the most natural and complete solution: when quantum measurement occurs, the wave function does not collapse; instead, the universe branches into multiple branches in each of which one definite outcome occurs.

The book is structured as a pedagogical introduction to quantum mechanics followed by a sustained defense of many-worlds. Carroll explains the basics of quantum superposition, entanglement, and the measurement problem with unusual clarity—he is one of the best physics communicators currently writing—and then explains why he finds Copenhagen (which denies that a complete account of quantum reality can be given), pilot wave theory (de Broglie-Bohm), and dynamical collapse theories all less satisfactory than Everett. The many-worlds interpretation is not widely accepted by physicists (surveys put it at 15-20% of physicists), but Carroll argues that the resistance is largely sociological rather than logical—a combination of the interpretation’s counterintuitive implications and the pragmatic physics culture that disfavors metaphysical speculation.

The final third of the book ventures into speculative territory: the emergence of spacetime from quantum entanglement, the relationship between quantum mechanics and entropy, and the possible implications for questions about free will, consciousness, and identity. Carroll maintains a careful distinction between established physics and speculation, but the speculation is presented as motivated and scientifically respectable rather than merely philosophical. Something Deeply Hidden is the most readable sustained defense of many-worlds for general readers and a serious contribution to the public understanding of foundational physics.

Critical Takeaways

  • The measurement problem: Carroll’s diagnosis—that the measurement problem is a real unsolved problem that the physics community has been trained to ignore—is taken seriously by many philosophers of physics even by those who don’t accept the Everett solution.
  • Many-worlds: The Everett interpretation is a minority position among working physicists; Carroll’s defense of it is the most accessible and most philosophically serious in popular physics writing, but it does not represent consensus.
  • Copenhagen’s silence: Carroll’s critique of the Copenhagen interpretation—that it provides operational rules without a complete account of what quantum mechanics describes—is philosophically accurate, though defenders of Copenhagen argue that the operational account is all physics can or should provide.
  • Emergence of spacetime: The connection Carroll draws between quantum entanglement and the emergence of spacetime geometry is at the frontier of research and is not established; Carroll is careful to say so, but general readers may not distinguish established from speculative claims.
  • Physics communication: Carroll’s books (The Big Picture, Something Deeply Hidden, The Biggest Ideas in the Universe) represent a distinctive style of physics communication—philosophically serious, clear on uncertainty, willing to defend controversial positions—that is genuinely valuable.

My Takeaways

  1. Carroll’s explanation of why the measurement problem is a real problem—and not just solved by “observation causes collapse”—was the most clarifying account of quantum foundations I have found. The question is: what are the rules, and when do they apply?
  2. The many-worlds interpretation is counterintuitive (the universe branches every time a quantum event is measured), but Carroll’s argument that its competitors all have worse problems is logically compelling even if the conclusion is hard to fully believe.
  3. The distinction between “shut up and calculate” (effective for applications) and “explain what the calculation describes” (foundational physics) resonated with a broader distinction between pragmatic and explanatory adequacy that applies in many domains.
  4. The sections on the emergence of spacetime from entanglement suggested that the concepts we use to describe large-scale reality may emerge from quantum information relationships at small scales—one of the most vertiginous ideas in contemporary physics.

Footnotes