Table of Contents
Abstract
Purpose: This paper introduces and rigorously proves the Simplicity-Expressive Power Principle (SEPP). It establishes a single, quantitative information-theoretic principle from which the classical limitative results of Gödel, Turing, and Chaitin can be seen as immediate consequences, thereby offering a deep and unified explanation for the limits of formal reasoning.
Methods: The methodology is twofold. First, a formal development within algorithmic information theory is used to define a system's "Expressive Power" and prove the main theorem, SEPP. Second, this formal result is used as the rigorous foundation for a philosophical argument that reframes the limits of reason as a law of complexity conservation.
Results: The main theorem is
Conclusion: SEPP is a fundamental law of information for formal systems. This result supports a constructivist model of mathematics, offers a potential re-framing of the puzzle of the "unreasonable effectiveness" of mathematics, and has broad implications for formal epistemology and the philosophy of physics.
Introduction
A single, quantitative principle governs the limits of formal reasoning: the Simplicity-Expressive Power Principle (SEPP). In conceptual terms, SEPP states that a formal system’s capacity to describe complex phenomena is strictly bounded by the complexity of its own axioms. This principle provides a unified framework for understanding why all formal systems are inherently constrained, revealing that the limits of reason are not arbitrary but follow from a fundamental law linking a system's simplicity to its expressive reach.
Contribution and Relation to Prior Work
The foundational concepts of algorithmic information theory (AIT) have long been used to analyze the limits of formal systems (Li and Vit´anyi 2008;Calude 2002;Yanosky 2013). Key historical concepts include Solomonoff's theory of inductive inference (Solomonoff 1964), Levin's search algorithm (Levin 1973), and Chaitin's Omega number (Chaitin 1987). These landmark theories primarily address questions of prediction, problem-solving, and a system's introspective limits—what it can know about its own computational processes.
This paper builds on this foundation but is fundamentally different in its purpose and scope. SEPP is a principle of extrospective description. Its central question is not about prediction or internal problem-solving, but about a system's capacity to describe and ground knowledge of external phenomena.
The critical insight is that while the Complexity-Entropy bound (
The contribution of this work is thus threefold:
- We introduce Expressive Power,
, a new measure designed specifically to quantify a system's maximum descriptive reach. - We frame the relationship between this power and the system's simplicity as a fundamental law, SEPP.
- We demonstrate that this single, extrospective law is a powerful unifying source from which the classical, introspective limitative theorems of Gödel, Turing, and Chaitin can be derived as necessary corollaries, and from which new insights can be generated.
This unifying and generative power demonstrates that SEPP is not merely a repackaging of known bounds, but a new and more general law of informational economics for formal systems.
Formalizing Simplicity and Expressive Power
The simplicity of a system
On the Definition of Expressive Power
The central definition of this paper is that of Expressive Power,
First, we model phenomena with probability distributions, and we measure their informational content using Shannon entropy. This is not an arbitrary choice; Shannon entropy is the canonical, rigorously justified measure of information for a probabilistic source in information theory. Any principle aiming to quantify descriptive power must engage with it.
Second, we demand the strongest possible epistemic standard: certification via formal proof. A system only truly "knows" or "describes" that which it can prove. Any weaker standard, such as mere consistency, would fail to capture the system's actual deductive reach. Our goal is not to measure a system's day-to-day "usefulness," but to find its ultimate informational limit. To find this hard limit, we must demand this strongest standard of knowledge.
A potential objection is that this definition is so strong that the expressive power of powerful real-world theories like ZFC might be quite low. This objection correctly identifies the definition's strength but mistakes its purpose. The principle
Definition 2.1 (Expressive Power). The expressive power of a formal system
Definition 2.2 (Certification). A consistent R.E. system
Remark 2.3 (On the Strength of the Certification Condition). One might consider weaker epistemic standards for a system's descriptive capacity. For example, a system could be said to "model" a distribution if it could merely prove the distribution's entropy value, or if it could certify the probabilities of some but not all outcomes. However, such definitions, while potentially useful for measuring practical applicability, are insufficient for establishing a fundamental, law-like boundary. To find the absolute, hard limit on a system's ability to ground knowledge, we must demand the strongest, most rigorous standard: the provable certification of every possible outcome. The strength of the definition is thus a necessary feature for the principle to have the force of a fundamental law.
Remark 2.4 (Relation to Chaitin's
Theorem 2.5 (Simplicity-Expressive Power Principle (SEPP)). For any consistent, recursively enumerable (R.E.) formal system , the following inequality holds:
Remark 2.6 (On the Constant
Remark 2.7 (An Intuitive Example of SEPP). Consider a trivial formal system,
- Simplicity: The description of this single axiom is a short string, so its simplicity
is a small constant. - Expressive Power:
certifies the distribution where and otherwise. The Shannon entropy of this distribution is . This is the richest distribution it can certify, so . - The Principle Holds: The inequality
is clearly true. To describe richer phenomena (distributions with entropy ), a system would require more complex axioms.
Consequences of SEPP: Generation and Unification
This section demonstrates SEPP's dual role. The proofs in this section are presented as concise logical arguments, with technical lemmas detailed in the Appendix.
A Generative Consequence
Corollary 3.1 (Principle of Diminishing Algorithmic Returns). Let
Proof This result follows from applying SEPP to both
A Unifying Consequence
The following derivations are not intended to replace the original, constructive proofs of the limitative theorems. Rather, their purpose is explanatory and unifying. In the same way that conservation laws in physics (e.g., conservation of energy) provide a high-level, unifying explanation for disparate phenomena without replacing the detailed mechanical derivations, SEPP provides a single, high-level informational principle that explains why these disparate logical limitations must exist. The goal is to show that they are all necessary consequences of the same fundamental mismatch between a finite axiomatic complexity and an infinite descriptive demand.
Corollary 3.2 (Gödel's First Incompleteness Theorem (Gödel 1931)). Any consistent R.E. system
Proof Assume
Corollary 3.3 (Undecidability of the Halting Problem (Turing 1936)). There is no algorithm that decides the halting problem.
Proof Assume a halting decider exists. A formal system
Corollary 3.4 (Chaitin's Incompleteness Theorem). For any consistent R.E. system
Proof As rigorously proven in the Appendix, if a system could prove that strings have arbitrarily high complexity, its expressive power would necessarily be infinite. This would mean
Philosophical Contribution and Conclusion
This paper has introduced, proven, and demonstrated the consequences of the Simplicity-Expressive Power Principle. The dual results establish SEPP as a fundamental law of information for formal systems. The depth of this unification lies in its explanatory power: it reframes the limits of reason, shifting the paradigm from one of logical paradox to one of complexity conservation.
This perspective provides a powerful formal basis for a constructivist model of mathematics. The limits of reason are not arbitrary flaws but are a direct, quantifiable consequence of building knowledge from a finite axiomatic base. SEPP formally explains Gödelian incompleteness—the inability of a theory to prove all truths about its domain. But the history of mathematics reveals a second, related struggle with what might be termed incompleteness of domain: the inability of a domain to furnish the objects needed to solve its own problems. The extension from the natural numbers to the integers to solve simple subtraction is a classic case. In both instances, the path forward is the same: the injection of genuinely novel information, be it a new axiom or a new type of object. While a Platonist position remains coherent, SEPP supports a more parsimonious alternative, suggesting that mathematics is better modeled as a verb than a noun: an ongoing process of construction against these dual limits, forever bounded by the complexity of its own starting points.
Furthermore, this constructivist model offers a potential resolution to the long-standing puzzle of the "unreasonable effectiveness of mathematics" in the physical sciences. The mystery of why our physical world conforms to abstract mathematical laws is most potent from a Platonist perspective. A constructivist viewpoint, however, reframes the question: we invent and select mathematical tools precisely because they are effective at modeling the observed regularities of the universe. The effectiveness is not a miracle, but a result of targeted design. The Simplicity-Expressive Power Principle then explains why this effectiveness is not "unreasonable" but is, in fact, bounded and necessarily incomplete. Our most powerful physical theories, from General Relativity to the Standard Model, are formal systems
In conclusion, SEPP is a fundamental law of information for formal systems. Its primary contribution is to provide a unified, quantitative explanation for the limits of reason, shifting the paradigm from one of logical paradox to one of complexity conservation. This perspective provides a powerful formal basis for a constructivist model of mathematics and offers a new, information-theoretic lens on the relationship between formal systems and the world they are built to describe. It establishes that any attempt at a "perfect" description is doomed not by self-reference, but by the simple and inexorable laws of informational economics.
Remark 4.1 (A Speculative Parallel to Physics). The law of bounds on formal description established by SEPP resonates with similar informational limits found in fundamental physics. The trade-off between a system's Simplicity (
Declarations
Funding Not applicable.
Conflict of interest The author has no conflicts of interest to declare.
Availability of data and material Not applicable.
References
- Calude CS (2002) Information and Randomness: An Algorithmic Perspective, 2nd edn. Springer-Verlag, Berlin, Heidelberg
- Chaitin GJ (1987) Algorithmic Information Theory. Cambridge University Press, Cambridge
- Gödel K (1931) Über formal unentscheidbare sätze der principia mathematica und verwandter systeme i. Monatshefte für Mathematik und Physik 38:173–198
- Levin LA (1973) Universal sequential search problems. Problemy Peredachi Informatsii 9(3):115–116. In Russian. English translation in Problems of Information Transmission, 9(3):265–266
- Li M, Vitányi PMB (2008) An Introduction to Kolmogorov Complexity and Its Applications, 3rd edn. Springer, New York
- Shoenfield JR (1967) Mathematical Logic. Addison-Wesley, Reading, MA
- Solomonoff RJ (1964) A formal theory of inductive inference. Part I. Information and Control 7(1):1–22
- Turing AM (1937) On computable numbers, with an application to the entscheidungsproblem. Proceedings of the London Mathematical Society s2-42(1):230–265
- Yanofsky NS (2013) The Outer Limits of Reason: What Science, Mathematics, and Logic Cannot Tell Us. The MIT Press, Cambridge, MA
Technical Appendix: Formal Proofs and Derivations
This appendix provides the fully detailed definitions and proofs referenced in the main body.
AIT Preliminaries
We assume a standard prefix-free universal Turing machine
Definition A.1 (Kolmogorov Complexity). The prefix-free Kolmogorov complexity
Definition A.2 (Shannon Entropy). Let
By convention,
Proposition A.3 (Chain Rule for Complexity (Li and Vit´anyi)).
Proposition A.4 (Complexity-Entropy Bound (Li and Vit´anyi)). For any lower semi-computable probability distribution
Full Proof of the Simplicity-Expressive Power Principle
Lemma A.5 If a consistent R.E. system
Proof A program can be written that, given a description of
Theorem A.6 (SEPP, Restated). For any consistent R.E. system ,
Proof Let
Proofs of Corollaries
Proof of Corollary 3.1 (Diminishing Returns) Let
Lemma A.7 If a consistent R.E. system
Proof To prove this, we explicitly construct, for any integer
- Construction of
: Let . This set is infinite but not recursively enumerable. Let be the first strings in in lexicographical order. Define the distribution to be uniform over this set of strings: for and otherwise. - Properties of
: The entropy of this distribution is . The distribution is lower semi-computable because one can approximate from above, and thereby enumerate the set of strings whose complexity is known to be greater than . - Certification by a Complete System: For each
, the statement " is in the support of " is true. This statement is equivalent to the claim that a specific Turing machine (one that searches for and lists the first strings with complexity ) eventually halts and includes in its output. The assertion of a specific Turing machine's halting is a canonical sentence in the language of arithmetic. By Shoenfield's absoluteness theorem (Shoenfield 1967), sentences are absolute, meaning if they are true in the standard model of arithmetic, they are provable in any complete axiomatization of arithmetic. Since these statements are true by construction, a complete system must prove them. - Specifically, for each
in the support of , must prove the sentence . This is precisely the condition for certification. - Conclusion: Since we can construct such a distribution
with entropy for any arbitrary integer , and a complete system would certify every one of them, the set of entropies of distributions certified by is unbounded. Therefore, by definition, .
Lemma A.8 The existence of a halting decider implies the existence of a formal system
Proof Let
- Constructing the System: Construct the system
by adding to Peano Arithmetic (PA) an axiom schema that formalizes the statement "program on input halts if and only if ". - Violation of Chaitin's Theorem: A halting decider allows for the computation of the Kolmogorov complexity
for any string . The procedure is as follows: to find , enumerate all programs in increasing order of length. For each program, run it and use the oracle to determine if it halts. The first program that halts with output is the shortest, and its length is . - This means that for any integer
, the system can compute a string such that , and can formally prove that its complexity is indeed greater than . For example, it can prove the theorem . - Implication for Expressive Power: By Proposition A.9 (proven next), a system that can prove
for arbitrarily large must have infinite expressive power. - Conclusion: Since
can prove theorems of this form for any , it follows that .
Proposition A.9 If a consistent R.E. system
Proof Suppose
- Construction of
: Write a program that enumerates all theorems of . Let be the set of the first distinct strings for which the program finds a proof of a theorem of the form . Since the premise is that such proofs exist for any , this search will terminate. Define the distribution to be uniform over this set: for and otherwise. - Properties of
: The entropy of this distribution is . The distribution is lower semi-computable because its support set is recursively enumerable by construction. - Certification by F: By its very construction, for each
, can prove that is in the support of . can also prove the size of the set is . From this, it can prove the lower bound for each . This is the condition for certification. - Conclusion: Since we can perform this construction for any arbitrarily large integer
, it follows that for any , there exists a distribution with entropy that certifies. The set of entropies of distributions certified by is therefore unbounded. By definition, .