Deutsch's influential argument holds that the exponential speedup of quantum algorithms such as Shor's is best explained by computation distributed across ontologically real parallel branches of the wavefunction. This paper interrogates that claim by asking what minimal ontological commitments are actually required to underwrite observed quantum computational advantages. Drawing on the framework of final-state constraints and informational pruning developed in prior work, we argue that Deutsch's computational argument depends on an unpruned Everettian ontology in which all branches persist as computational substrates. We show that pruned-histories interpretations—in which boundary conditions or decoherence-based selection mechanisms restrict the space of ontologically realized branches—can preserve the empirical predictions of quantum computation while denying the parallel-universes inference. The argument requires three positive commitments: a records-based criterion for ontological commitment, a thermodynamically graded boundary between unitary computation and outcome-stabilization, and a positive account of computational speedup grounded in global Hilbert-space structure and entanglement rather than in a population of parallel worlds. We situate this result within the ontological models framework and recent observer-dependence theorems—including Frauchiger-Renner, Bong et al., and Walleghem et al.—and engage directly with Hewitt-Horsman's functionalist defense of computational branch realism. We conclude that the Deutsch argument, while rhetorically powerful, is interpretation-laden rather than interpretation-neutral.
Deutsch's influential argument holds that the exponential speedup of quantum algorithms such as Shor's is best explained by computation distributed across ontologically real parallel branches of the wavefunction. This paper interrogates that claim by asking what minimal ontological commitments are actually required to underwrite observed quantum computational advantages. Drawing on the framework of final-state constraints and informational pruning developed in prior work, we argue that Deutsch's computational argument depends on an unpruned Everettian ontology in which all branches persist as computational substrates. We show that pruned-histories interpretations—in which boundary conditions or decoherence-based selection mechanisms restrict the space of ontologically realized branches—can preserve the empirical predictions of quantum computation while denying the parallel-universes inference. The argument requires three positive commitments: a records-based criterion for ontological commitment, a thermodynamically graded boundary between unitary computation and outcome-stabilization, and a positive account of computational speedup grounded in global Hilbert-space structure and entanglement rather than in a population of parallel worlds. We situate this result within the ontological models framework and recent observer-dependence theorems—including Frauchiger-Renner, Bong et al., and Walleghem et al.—and engage directly with Hewitt-Horsman's functionalist defense of computational branch realism. We conclude that the Deutsch argument, while rhetorically powerful, is interpretation-laden rather than interpretation-neutral.
Deutsch's influential argument holds that the exponential speedup of quantum algorithms such as Shor's is best explained by computation distributed across ontologically real parallel branches of the wavefunction. This paper interrogates that claim by asking what minimal ontological commitments are actually required to underwrite observed quantum computational advantages. Drawing on the framework of final-state constraints and informational pruning developed in prior work, we argue that Deutsch's computational argument depends on an unpruned Everettian ontology in which all branches persist as computational substrates. We show that pruned-histories interpretations—in which boundary conditions or decoherence-based selection mechanisms restrict the space of ontologically realized branches—can preserve the empirical predictions of quantum computation while denying the parallel-universes inference. The argument requires three positive commitments: a records-based criterion for ontological commitment, a thermodynamically graded boundary between unitary computation and outcome-stabilization, and a positive account of computational speedup grounded in global Hilbert-space structure and entanglement rather than in a population of parallel worlds. We situate this result within the ontological models framework and recent observer-dependence theorems—including Frauchiger-Renner, Bong et al., and Walleghem et al.—and engage directly with Hewitt-Horsman's functionalist defense of computational branch realism. We conclude that the Deutsch argument, while rhetorically powerful, is interpretation-laden rather than interpretation-neutral.
Quantum mechanics permits time-symmetric formulations in which intermediate events are conditioned by both an initial state and a final boundary condition. In this paper, I develop a model of quantum history in which a final boundary condition constrains the admissible-history ensemble rather than serving as a passive terminal state. I represent the universe’s possible macroscopic development as a history graph and define an admissible subgraph by imposing a final-state condition. I then examine whether, under a history-ensemble encoding, this restriction can reduce the effective description length of realized histories relative to unconstrained branching descriptions. I argue that the informational significance of the model depends on the structure of the terminal condition. Trivial terminal states impose weak selectivity and provide little compression. Structured terminal states impose stronger constraints and better support the emergence of organized intermediate worlds. Computational terminal states impose the strongest selectivity because they favor histories that generate information-processing structures, self-replicating systems, and explicit forms of computation. On this basis, I propose that sufficiently selective computational endpoints are most naturally interpreted in agentic terms, provided agency is understood structurally rather than psychologically. The model is retrocausal in a boundary-conditioned sense but not interventionist. It excludes inconsistent histories rather than revising an already fixed past and does not require operational backward signaling. I also distinguish between maximal pruning and robustness-preserving selectivity within computational endpoint classes. I conclude that a boundary-conditioned agentic interpretation of sufficiently selective computational endpoints is not established here as empirical fact, but it is rendered a mathematically serious interpretive hypothesis by the combination of dual-boundary quantum formalism, informational pruning, and endpoint complexity analysis.
The Physical Impossibility of Quantum Computational Speedup: Two Independent Arguments from Quantum-Geometry Dynamics Quantum computing promises computational advantages that are, in the most celebrated cases, exponential. Shor's algorithm factors integers exponentially faster than the best known classical algorithm; Grover's algorithm searches an unstructured database with a quadratic speedup. These results are mathematically rigorous within their assumed framework. This paper asks not whether the mathematics is correct but whether the physical assumptions underlying it are. I argue that Quantum-Geometry Dynamics (QGD) — an axiomatic framework for physics derived from the discreteness of space and the kinetic nature of matter — establishes two independent foundational preclusions of quantum computational speedup. These are not engineering obstacles or decoherence problems that better technology can overcome. They are consequences of the physical structure of discrete space, and no improvement in qubit isolation, error correction, or fabrication technique can supply a physical resource that does not exist. The first preclusion concerns physical states. In QGD, matter is composed of preons⁺ that propagate through quantum-geometrical space by preonic leaps, each of which is a definite transition from one spatial unit to the next in the direction of the momentum vector. A preon(+) always occupies a definite position. There is no ontological superposition. What quantum mechanics represents as a superposed state is, in QGD, an epistemic description of our ignorance of the system's actual preonic microstate. Since ontological superposition is the physical resource on which quantum parallelism depends, its absence means that no physical system can instantiate the state required for exponential speedup. The second preclusion concerns physical processes. Causal succession in discrete space is categorically and structurally irreversible: every preonic leap has a definite direction, and no physical process can reverse the causal order of preonic states. This is not thermodynamic irreversibility arising from large numbers but a property of every individual preonic transition. Since the quantum circuit model is built on reversible unitary gates, and reversible computation has no physical instantiation in a discrete-space framework, the operational basis of quantum computing is equally precluded. I show how both arguments bite at specific steps in Shor's algorithm and Grover's algorithm. In Shor's algorithm, the first preclusion destroys the state preparation step and the second destroys the quantum Fourier transform. In Grover's algorithm, the first preclusion destroys the uniform superposition and the second destroys the diffusion operator and oracle. Either preclusion alone is sufficient; together they attack quantum speedup at both ends — what goes in and how it is processed. The black hole information paradox, correctly understood within QGD, provides independent confirmation: the paradox dissolves precisely because physical states are always definite and physical evolution is categorically irreversible — the same two features that preclude quantum speedup. The Uniqueness Theorem for QGD further strengthens the claim: if the two-axiom discrete-space structure is the unique viable foundational description of physical reality, these preclusions are not features of one possible framework among many but consequences of the physical structure of the universe. This paper supersedes the earlier paper Quantum Computing Under Quantum-Geometry Dynamics (Zenodo, DOI: 10.5281/zenodo.19522137) and should be read in its place. This paper is part of the Minimal Physically Derivable Theory (MPDT) programme.
Quantum computing's most consequential claim — that quantum computers provide exponential computational speedup over classical computation — rests on a specific physical assumption: that superposition is ontologically real, that a qubit genuinely and simultaneously occupies multiple states, and that quantum algorithms exploit this simultaneity as a physical resource. A quantum computer with n qubits is claimed to process 2ⁿ computational paths in parallel by virtue of this simultaneous occupation. This paper argues that all three foundational assumptions are precluded by Quantum-Geometry Dynamics (QGD), the physical theory derived from the Minimal Physically Derivable Theories (MPDT) framework established by the Uniqueness Theorem. In QGD, physical reality is strictly and absolutely deterministic. Every fundamental constituent — every preon(+) — has a definite position and definite intrinsic momentum at every moment. There are no indeterminate states, no superpositions, and no wave function collapse at the fundamental level. What quantum mechanics describes as superposition is not a physical state of simultaneous occupation but an epistemic description of ignorance of the deterministic microstate of a preonic configuration. The wave function is a probabilistic description of deterministic preonic dynamics — a calculational tool that correctly predicts statistical outcomes — not a description of a physical state in which a system genuinely occupies multiple configurations simultaneously. This distinction has a direct and specific consequence for quantum computing. Quantum computing devices are genuine physical systems that exploit real quantum mechanical phenomena — phenomena that QGD derives from the deterministic dynamics of preons(+) and preons(−) in the finite discrete preon(−) lattice. The MPDT framework does not forbid the construction or operation of quantum computing devices. What QGD precludes is the ontological foundation on which the exponential speedup argument rests. A quantum computing device is a deterministic preonic configuration occupying one microstate at each moment. The 2ⁿ simultaneous amplitude states of the quantum formalism are elements of a probabilistic description of that microstate — not physical states simultaneously instantiated in the device. Quantum parallelism is a feature of the formalism, not of the underlying physics. The paper develops this argument systematically across eight sections. Section 2 establishes QGD's account of quantum phenomena as emergent from deterministic preonic dynamics, including the derivation of wave-like interference patterns and Bell correlations without superposition. Section 3 examines precisely what superposition is and is not in QGD, culminating in the formal statement that a qubit in the state α|0⟩ + β|1⟩ is not a system simultaneously occupying both states but a deterministic preonic configuration whose microstate determines measurement outcomes but is not individually accessible at the observational level. Section 4 identifies the exact point at which the exponential speedup argument fails: the physical resource it invokes — simultaneous occupation of 2ⁿ states — does not exist in the physical universe that QGD describes. Sections 5 examines three specific quantum algorithms: Shor's factoring algorithm, whose polynomial-time complexity is demonstrated within the quantum formalism but whose underlying preonic complexity remains an open question; Grover's search algorithm, whose quadratic speedup rests on the same ontological assumption; and quantum simulation, which survives the critique more robustly because it does not require exponential parallelism as a resource. Section 6 addresses decoherence, reinterpreting it not as an engineering challenge to be solved by better isolation but as a fundamental feature of reality — the inevitable influence of the instantaneous gravitational field of the entire preon(−) lattice on every qubit configuration, which cannot be shielded against in principle. Sections 7 and 8 develop the implications for the quantum computing programme and conclude. The argument connects directly to the P vs NP analysis in the companion Physicality of Logic paper. Shor's algorithm is the canonical example of a quantum algorithm claimed to solve a classically hard problem — integer factoring — in polynomial time, with significant implications for the security of RSA encryption. If QGD is correct and the exponential speedup argument fails, the classical hardness of factoring is preserved and the cryptographic implications attributed to quantum computing do not follow. The paper does not claim that quantum computing devices are useless — it claims that the specific resource driving the most dramatic projections for quantum computing does not physically exist, and that whatever computational advantages quantum devices possess must be explained within the deterministic preonic framework rather than by appeal to quantum parallelism. The paper is intended for physicists working on quantum computing and quantum foundations, philosophers of physics, and computer scientists working on computational complexity. It is submitted to Foundations of Physics. It is a companion to the author's papers on the Uniqueness Theorem and the Physicality of Logic, and to the book Quantum-Geometry Dynamics: An Axiomatic Approach to Physics.
Working philosophical/foundational draft.This paper extends the logic of the companion BCT paper The A=A Problem for Everettian Branching from subject-individuation to observer-world individuation. Its central claim is that branch or microphysical multiplicity should not automatically be counted as observer-world multiplicity unless it induces observer-relevant record differentiation. The paper does not deny decoherence, emergent branch structure, or the universal quantum state. It argues instead for an observer-equivalence constraint: physically distinct realizations that agree on all accessible, persistent, update-constraining records for a finite observer A do not define distinct observer-worlds for A.Related companion paper: The A=A Problem for Everettian Branching, available in the recently published BCT philosophical working-papers record (DOI: 10.5281/zenodo.19649860).Background: independent researcher.Web site: https://bit-collapse-theory.netlify.app/Main DOI: 10.5281/zenodo.18496128 AbstractEverettian quantum mechanics is often presented as ontologically economical because it preserves unitary dynamics and avoids physical collapse. This paper argues that such economy remains incomplete unless Everettian realism supplies a principled criterion for counting worlds, branches, histories, or observer-relevant realities. The central worry is not mathematical branching, but ontological overcounting: the move from branch-level or microphysical multiplicity to full world-multiplicity may assign ontological weight to distinctions that make no difference to any observer-constituting record. The paper introduces an observer-equivalence constraint: two physical or branch-relative realizations are equivalent for a finite observer A if they agree with respect to all physically accessible, persistent, update-constraining records available to A within its finite integration window. In the conscious case, the relevant record-structure is understood as temporally integrated over a finite window rather than as an instantaneous observer-slice. The resulting picture does not refute Everettian quantum mechanics, nor does it deny decoherence or branch structure. It instead challenges the interpretation of branch multiplicity as unpriced ontological multiplicity and proposes a record-based constraint on ontological economy: worlds should not be counted more finely than the record-structures that make them difference-making for observers. Keywordsquantum foundations; Everett interpretation; observer-equivalence; ontological economy; branching worlds; records; subject-individuation; informational identity
The Many-Worlds Interpretation (MWI) of quantum mechanics preserves unitary evolution by rejecting wavefunction collapse and treating all outcome branches as equally real. While mathematically consistent, this move elevates admissible descriptions of a system to ontological status without an accompanying principle of physical selection. In this paper, we argue that quantum branching need not imply ontological multiplicity once structural admissibility, temporal constraint, and recoverability are made explicit. Unitary evolution defines the space of allowable continuations, but only a subset of these persist forward in time due to structural resolution. Within this framework, the appearance of branching reflects under-resolved admissible paths rather than the realization of multiple worlds. Many-Worlds is thus reinterpreted as a transitional bookkeeping scaffold rather than a necessary ontological commitment.