Abstract Wolfram's Principle of Computational Irreducibility asserts that for most non-trivial discrete systems there exists no analytical shortcut: to determine the state at time T, one must simulate all T steps. For finite-dimensional unitary graph systems, the evolution admits an exact spectral representation for a specific class of systems: finite quantum graphs with unitary evolution. Knowledge of the spectral slice - the quantum state |Ψ(t₀)⟩ and the spectrum of the evolution operator Û - fully and exactly determines the state at any moment T without stepping through intermediate times. The theorem is a principled, not a practical result: algorithmic complexity O( ) remains exponential. Practical significance is achieved in the coarse-graining limit at scale ℓ >> a, where the problem reduces to polynomial complexity. Three conditions - finiteness, unitarity, linearity - constitute the exact domain of applicability.
Abstract Wolfram's Principle of Computational Irreducibility asserts that for most non-trivial discrete systems there exists no analytical shortcut: to determine the state at time T, one must simulate all T steps. For finite-dimensional unitary graph systems, the evolution admits an exact spectral representation for a specific class of systems: finite quantum graphs with unitary evolution. Knowledge of the spectral slice - the quantum state |Ψ(t₀)⟩ and the spectrum of the evolution operator Û - fully and exactly determines the state at any moment T without stepping through intermediate times. The theorem is a principled, not a practical result: algorithmic complexity O( ) remains exponential. Practical significance is achieved in the coarse-graining limit at scale ℓ >> a, where the problem reduces to polynomial complexity. Three conditions - finiteness, unitarity, linearity - constitute the exact domain of applicability.
Computational Reducibility Theorem.Against S. Wolfram's Principle of Computational Irreducibility:The sufficiency of a single slice to predict the entire evolution.Time is not a fundamental step-by-step process—it emerges from the spectrum of the evolutionary operator. Therefore, the "future" is not ontologically inaccessible: it is already fully encoded in the spectral structure of the present. Computational reducibility is not a trick involving substitution into a formula. It reflects the fact that in Quantumograph, time and spectrum are the same thing, described in different languages.A Blow to Cryptography?Implications and Practical Outlook. The main consequence is not a universal cryptanalytic breakthrough, but a precise separation between principled and operational predictability. Exact microstate prediction remains exponentially costly, whereas coarse-grained observables admit polynomial forecasting. This makes the framework relevant for model reduction, spectral inference, and device-level analysis, while the cryptographic threat landscape remains governed by dedicated quantum algorithms and by the ongoing transition to post-quantum cryptography.
A Principled Limitation of Wolfram's Computational Irreducibility for Finite Unitary Quantum Systems. The sufficiency of a single slice to predict the entire evolution. After diagonalization, prediction cost is independent of the time horizon. Time is not a fundamental step-by-step process—it emerges from the spectrum of the evolutionary operator. Therefore, the "future" is not ontologically inaccessible: it is already fully encoded in the spectral structure of the present. Computational reducibility is not a trick involving substitution into a formula. It reflects the fact that in Quantumograph, time and spectrum are the same thing, described in different languages.
This note connects two claims in the Quantumograph program. The Computational Reducibility Theorem shows that a finite unitary quantum graph is, in principle, exactly forecastable from one spectral slice: the state at one time together with the spectrum of the evolution operator. The Fundamental Limit of Quantum Computation (FLQC) adds a physical constraint: any realizable quantum device has a finite phase resolution, so exact spectral data and exact phase gates cannot be implemented with arbitrary precision. Realism, in this setting, is the position between these two statements. The universe is computable in principle, but nature imposes a nonzero floor on the precision with which that computability can be instantiated. The note derives the phase floor, compares it with the phase resolution required by QFT- and Shor-type circuits, and gives a concrete experimental signature on superconducting quantum processors.
The Generalized No-Chaos TheoremBounded Complexity Growth at Any Fixed Coarse-GrainingWithin the Quantum Gravity Consistency Framework (QGCF) - any finite-dimensional, closed, unitarily evolving system satisfying (QGCF1)-(QGCF4) - three logically distinct results are established. First, ontic chaos is impossible in three senses: spectral quasiperiodicity, Poincaré recurrence, and exact vanishing of the asymptotic quantum Lyapunov exponent λL (§5). Second, dynamical (Lyapunov/0-1-test) chaos at any FIXED coarse-graining scale ℓ is also impossible, unconditionally - a direct corollary of the same almost-periodicity that gives λL=0 (§7); the one established quantum-chaos diagnostic that survives this obstruction is level (spectral) statistics, checked preliminarily against a non-integrable/integrable benchmark pair (§7.3). Third, and logically independent of the first two: no observer realized as a proper subsystem can simultaneously reconstruct the complete global state from its own accessible data and evolve under an autonomous unitary law, once genuinely (entangling-ly) coupled to the rest of the system (§8) - a consequence of purification non-uniqueness (Hughston-Jozsa-Wootters) and the non-unitary character of open marginal dynamics, requiring no assumption beyond a generic (non-fine-tuned) boundary coupling. The two failures named in that theorem arise from the same physical mechanism - entanglement across the observer's own boundary - but are shown not to be strictly the same fact, only generically co-occurring. Thermalization of coarse blocks (Calabrese-Cardy growth to a Page-value plateau) is real, established physics, distinct from all of the above, and is presented (§9) together with the timescale τ*(ℓ) it requires, and its role as the only available justification for treating the system's effective Hamiltonian Ĥeff as possessing a meaningful temperature Tc, given that the axioms admit no literal external bath. A note on generality. QGCF does not require a literal discrete graph. (QGCF3) is stated as a disjunction: a discrete, graph-based realization (QGCF3a), giving the sharper results of §8.2 and §8.6.2 exactly; or a continuum realization with only a locality/metric structure (QGCF3b), giving the standard, approximately-causal Lieb-Robinson bound instead. Everything else in this document §5-§7, §8.3-§8.6.1, §9 - depends only on finite-dimensionality and unitarity (QGCF1-QGCF2), or on (QGCF4)'s boundedness/genericity, and holds identically under either branch of (QGCF3).
The Generalized No-Chaos TheoremBounded Complexity Growth at Any Fixed Coarse-GrainingWithin the Quantum Gravity Consistency Framework (QGCF) - any finite-dimensional, closed, unitarily evolving system satisfying (QGCF1)-(QGCF4) - three logically distinct results are established. First, ontic chaos is impossible in three senses: spectral quasiperiodicity, Poincaré recurrence, and exact vanishing of the asymptotic quantum Lyapunov exponent λL (§5). Second, dynamical (Lyapunov/0-1-test) chaos at any FIXED coarse-graining scale ℓ is also impossible, unconditionally - a direct corollary of the same almost-periodicity that gives λL=0 (§7); the one established quantum-chaos diagnostic that survives this obstruction is level (spectral) statistics, checked preliminarily against a non-integrable/integrable benchmark pair (§7.3). Third, and logically independent of the first two: no observer realized as a proper subsystem can simultaneously reconstruct the complete global state from its own accessible data and evolve under an autonomous unitary law, once genuinely (entangling-ly) coupled to the rest of the system (§8) - a consequence of purification non-uniqueness (Hughston-Jozsa-Wootters) and the non-unitary character of open marginal dynamics, requiring no assumption beyond a generic (non-fine-tuned) boundary coupling. The two failures named in that theorem arise from the same physical mechanism - entanglement across the observer's own boundary - but are shown not to be strictly the same fact, only generically co-occurring. Thermalization of coarse blocks (Calabrese-Cardy growth to a Page-value plateau) is real, established physics, distinct from all of the above, and is presented (§9) together with the timescale τ*(ℓ) it requires, and its role as the only available justification for treating the system's effective Hamiltonian Ĥeff as possessing a meaningful temperature Tc, given that the axioms admit no literal external bath. A note on generality. QGCF does not require a literal discrete graph. (QGCF3) is stated as a disjunction: a discrete, graph-based realization (QGCF3a), giving the sharper results of §8.2 and §8.6.2 exactly; or a continuum realization with only a locality/metric structure (QGCF3b), giving the standard, approximately-causal Lieb-Robinson bound instead. Everything else in this document §5-§7, §8.3-§8.6.1, §9 - depends only on finite-dimensionality and unitarity (QGCF1-QGCF2), or on (QGCF4)'s boundedness/genericity, and holds identically under either branch of (QGCF3).
Recently, several approaches to solving linear systems on a quantum computer have been formulated in terms of the quantum adiabatic theorem for a continuously varying Hamiltonian.Such approaches have enabled near-linear scaling in the condition number κ of the linear system, without requiring a complicated variable-time amplitude amplification procedure.However, the most efficient of those procedures is still asymptotically suboptimal by a factor of log(κ).Here, we prove a rigorous form of the adiabatic theorem that bounds the error in terms of the spectral gap for intrinsically discrete-time evolutions.In combination with the qubitized quantum walk, our discrete adiabatic theorem gives a speed-up for all adiabatic algorithms.Here, we use this combination to develop a quantum algorithm for solving linear systems that is asymptotically optimal, in the sense that the complexity is strictly linear in κ, matching a known lower bound on the complexity.Our O[κ log(1/ )] complexity is also optimal in terms of the combined scaling in κ and the precision .Compared to existing suboptimal methods, our algorithm is simpler and easier to implement.Moreover, we determine the constant factors in the algorithm, which would be suitable for determining the complexity in terms of gate counts for specific applications.