Both men accept the same core ontological claim — a single, universal wave function obeying unitary (Schrödinger) evolution with no collapse and no hidden variables — but they draw almost opposite conclusions from it about what the wave function is and what matters about it.

Shared commitments

• Wave function monism: Reality is one universal quantum state, not many substances. Carroll defends "the extremist position that the fundamental ontology of the world consists of a vector in Hilbert space evolving according to the Schrödinger equation," with space, time, and fields emerging from it ( Springer, "Reality as a Vector in Hilbert Space"). Pearce likewise treats the universal wave function as all that exists, with no collapse: decoherence scrambles phase relations but never literally destroys superpositions ( IAI, "The universe cancels itself out to zero").
• Everettian quantum mechanics: Both reject the collapse postulate and Copenhagen obscurantism. Carroll champions Everett's many-worlds reading as the simplest reading of the formalism, not a baroque add-on ( University of Chicago Library); Nature's review of Something Deeply Hidden notes his view that "there is one wave function, and only one, for the entire Universe" ( Nature).
• No strong emergence / reductionism: Both insist the special sciences cash out into fundamental physics, and both reject vitalism and substance dualism ( Pearce, Machine Consciousness slides).
• Emergent classicality: Spacetime and the everyday classical world are higher-level, decoherence-generated descriptions rather than fundamental furniture (Carroll makes emergent spacetime from Hilbert space a research program) ( Carroll's research page).

The core divergence: what "breathes fire into" the equations

This is where the two systems fork completely.

• Carroll — plain structural realism. The wave function is quantum-mechanical structure all the way down: a vector in Hilbert space. Nothing in the fundamental ontology is experiential. Consciousness is an emergent, higher-level pattern in the "poetic naturalist" sense — real as a description, not as fundamental furniture.
• Pearce — non-materialist physicalism / physicalist idealism. Physics only ever describes the relational/structural properties of the world; its formalism is silent about the intrinsic nature of what instantiates those relations. Pearce's move is to identify that intrinsic nature with phenomenality — experience is what the quantum field is from the inside, echoing Lockwood's claim that what "breathes fire into" the quantum-theoretic equations isn't physical in the traditional sense ( PhilPapers, "Mind, brain and the quantum"). Hence one-state monism, but experiential in its intrinsic nature. He also argues phenomenal binding — the unity of a mind — is a non-classical quantum effect (Schrödinger's "unity of wave function mechanics"), which is why he denies that classically organized computers could ever be conscious ( Pearce, Machine Consciousness slides). Carroll, predictably, is sympathetic to mainstream neuroscience and skeptical of quantum-mind proposals.

Side-by-side

Two further contrasts

• Why there's something rather than nothing: Pearce leverages the wave function's complex amplitudes to argue the universe's information content cancels to zero, so existence requires no explanation ( IAI). Carroll has no such commitment; his project aims at how the wave function gives rise to spacetime and complexity, treating "why existence?" as a question physics may simply leave at the level of a self-contained quantum state.
• Motivation: For Carroll, wave function monism is a physicist's bet — the simplest ontology that fits the data and connects to quantum gravity ( Carroll's research page). For Pearce, it is the metaphysical linchpin of his ethical system: if experience is the intrinsic nature of the physical, then physics and value are continuous, and the suffering of all sentient life becomes a target for engineering ( Pearce, Machine Consciousness slides).

In one line: they agree the universe is a single never-collapsing wave function, but Carroll reads it as austere mathematical structure from which minds and worlds emerge, while Pearce reads it as intrinsically experiential — a monism of pure physics versus a monism of experience in structural disguise.