Worldline Collision Theory Memoria desactivada ChatGPT 4o User Summarize and explain: Self-Reference and Computational Complexity © 2001 by Christopher Michael Langan [This paper contains background information on the P?NP problem. Being the first part of a much longer work-in-progress, it is for introductory purposes only. If anyone finds any errors – and there are sure to be a few, given the time crunch under which this was written – kindly let me know. The bibliography can wait for a future installment (meanwhile, thanks to Stephen Cook, A.K. Dewdney and Robert Rogers).] Introduction: The Problematic Role of Self-Reference in Mathematics Self-reference is an ever-popular topic in recreational mathematics, where it is usually characterized as a pathological rarity that must be treated with great care in order to avoid vicious paradoxes like this statement is false. To some extent, this reflects the history of mathematics; scarcely had Bertrand Russell presented his eponymous paradox in set theory, namely "the set of all sets that do not include themselves as elements", than he proposed to outlaw it with a stupefyingly complex theory that boiled down to a blanket prohibition on self-inclusion and its semantic equivalent, self-reference. Since then, mathematicians have regarded themselves as having two choices with regard to self- reference: follow Russell’s prescription and avoid it, or use it (with great care) for the express purpose of extracting paradoxical inconsistencies from, and thereby disproving, certain especially problematic conjectures. Mathematical reasoning equates to the direct or indirect derivation of theorems from primitive axioms. Ordinarily, a mathematical conjecture is proven correct by direct (deductive or inductive) derivation within an axiomatic system, or by showing that its negation leads to a contradiction or an absurdity within the system; similarly, a conjecture is proven incorrect by either directly deriving its negation, finding a counterexample, or showing that it leads to a contradiction or an absurdity, again within a single axiomatic system. Where each of these maneuvers is confined to a formal axiomatic system, and where the symbols, formulae and rules of inference of a formal system are taken to refer only to each other, they unavoidably involve self-reference. Indeed, any algebraically closed language treated apart from external meaning is self-referential by definition, and so is any process relying on the properties of such a language. To the extent that mathematics consists of such languages, mathematical reasoning is such a process. It follows that mathematics as a whole is implicitly self-referential in nature. But certain limits are maintained nonetheless. For example, in order to avoid introducing a forbidden subjective component into what is supposed to be an objective enterprise (the quest for "absolute" mathematical truth), at no point is a mathematician ever supposed to be caught referring to himself or his own thought processes as part of a mathematical proof. Even when deliberately employing self-reference in proving a conjecture, the mathematician must punctiliously externalize and thereby objectivize it, hygienically confining it to a formula or abstract machine model. By confining self-reference to the object level of discourse, the mathematician hopes to ensure the noncircularity of a higher level of discourse from which the predicates true and false can be downwardly assigned with no troublesome rebound…a level hopefully inhabited by the mathematician himself. By avoiding self-reference on the "business" level of discourse, he hopes to avoid having his own reasoning falsified "from above" on the basis of what would otherwise be its circularity. In short, the trapper does not propose to be caught in his trap. Unfortunately, this is a philosophically dubious position. It begins to unravel as we approach the foundations of mathematics, where the object is to trace the roots and account for the very origins of mathematical reasoning. At this stage of explanation, it becomes impossible to avoid the realization that in order to be consistent, mathematics must possess a kind of algebraic closure, and to this extent must be globally self-referential. Concisely, closure equals self- containment with respect to a relation or predicate, and this equates to self- reference. E.g., the self-consistency of a system ultimately equates to the closure of that system with respect to consistency, and this describes a scenario in which every part of the system refers consistently to other parts of the system (and only thereto). At every internal point (mathematical datum) of the system mathematics, the following circularity applies: "mathematics refers consistently to mathematics". So mathematics is distributively self- referential, and if this makes it globally vulnerable to some kind of implacable "meta- mathematical" paradox, all we can do in response is learn to live with the danger. Fortunately, it turns out that we can reason our way out of such doubts…but only by admitting that self-reference is the name of the game. When a language self-refers, it stratifies or separates into levels, with reference flowing directionally from metalanguage to language. E.g., each the following statements – "this statement is about itself", "the subject of this statement is this statement", and "this formula x is a description of x" – is actually a statement and the object of a statement, with statement and object occupying the metalanguage and object levels respectively. The operative rule in such cases is that reference never flows upward from object to statement, but only downward (from metalanguage to object) or laterally (from object to object, by virtue of the expression of these objects within a higher-level metalanguage mediating their mutual influence). This stratification is very important from a proof-theoretic standpoint, as the following example shows. Theorem: "This statement is false" is false. Proof: If the statement in quotes is indeed false, then it is true. On the other hand, if it is true, then it is false. This is a contradiction. Since the quoted statement generates a contradiction, it is logically inconsistent and therefore false. (Q.E.D.) But wait! Unfortunately, if the quoted statement is false, then it is true (as stated in the proof). This would seem to contradict not only the overall statement including the quoted statement, i.e. the "theorem", but the proof as well…unless we have a rule saying that the statement in quotes can refer to neither the overall statement of which it is part, nor to the proof of the overall statement. In that case, it can invalidate only itself, which is exactly what it is taken to be doing, and can do so only within a metalanguage capable of expressing the reflexive self-invalidating relationship. It should be noted that technically, "this statement is false" is invalid on purely formal grounds; it is in fact a forbidden instance of self- reference. But since it is analogous to any statement that implies its own negation in an axiomatic context- and such statements are routinely dealt with in mathematics without immediate concern for their "bad syntax"- its clarity makes it valuable for illustrative purposes. In the above example, self- reference is confined to a formula that pronounces itself false. Because this formula refers negatively to its own veracity, it is a self-contained paradox attempting to double as its own falsifying metalanguage and thus possessing a whole new level of "falsehood". But aside from true or false, what else could a formula say about itself? Could it pronounce itself, say, unprovable? Let’s try it: "This formula is unprovable". If the given formula is in fact unprovable, then it is true (and therefore a theorem). But sadly, we cannot recognize it as such without a proof. On the other hand, suppose it is provable. Then it is false (because its provability contradicts what it states of itself) and yet true (because provable)! It seems that we still have the makings of a paradox…a statement that is "provably unprovable" and therefore absurd. ChatGPT Summary and Explanation: Self-Reference and Computational Complexity Christopher Michael Langan's paper, "Self-Reference and Computational Complexity," explores the significant role of self-reference in mathematics, particularly in the context of the P=NP problem. Self-Reference in Mathematics Historical Background: Self-reference often leads to paradoxes, such as "this statement is false." Bertrand Russell's paradox (the set of all sets that do not include themselves) led to the development of theories to avoid self-reference in set theory. Mathematicians typically avoid self-reference or use it carefully to disprove problematic conjectures. Mathematical Reasoning: Involves deriving theorems from axioms within a formal system. A formal system is inherently self-referential because its symbols and rules refer only to each other. Mathematics, therefore, is implicitly self-referential. Avoiding Self-Reference in Proofs: Mathematicians externalize self-reference to avoid subjectivity. They use formulas or abstract models to keep self-reference at the object level, ensuring non-circularity in higher-level discourse. Global Self-Reference: Mathematics must be algebraically closed and thus globally self-referential to be consistent. This leads to the realization that mathematics refers to itself consistently. Although this global self-referential nature could expose mathematics to paradoxes, it is an inherent characteristic. Stratification and Directionality in Self-Referential Systems: Self-referential statements stratify into levels, with reference flowing from metalanguage to language. Example: "This statement is false" creates a paradox because it is self-referential. Dealing with Paradoxes: Self-referential paradoxes, such as "This statement is false," are handled by confining self-reference within a metalanguage. Another example, "This formula is unprovable," also creates a paradox, illustrating the complexities of self-reference. Implications for Computational Complexity The paper sets the stage for a deeper exploration of the P=NP problem by highlighting the foundational role of self-reference in mathematical logic and reasoning. Understanding self-reference is crucial because it influences how we approach proofs and the inherent limitations of formal systems. User But what if we now introduce a distinction between levels of proof, calling one level the basic or "language" level and the other (higher) level the "metalanguage" level? Then we would have either a statement that can be metalinguistically proven to be linguistically unprovable, and thus recognizable as a theorem conveying valuable information about the limitations of the basic language, or a statement that cannot be metalinguistically proven to be linguistically unprovable, which, though uninformative, is at least not a paradox. Presto: self-reference without the possibility of paradox! In the year 1931, an Austrian mathematical logician named Kurt Godel actually performed this magic trick for the entertainment and edification of the mathematical world. Undecidability: the Power of Paradox As part of his Erlangen Program for 20th century mathematics, the eminent German mathematician David Hilbert had wanted to ascertain that mathematics is "complete" when formalized in a system like the predicate calculus…i.e., that all true theorems (and no false ones) can be proven. But after helpfully setting out to show that every true formula expressed in the predicate calculus is provable, Kurt Godel sadly arrived at a different conclusion. As it turns out, not even arithmetic is complete in this sense. In any consistent formal system containing arithmetic, there are true but unprovable statements. Although their truth can be directly apprehended, they cannot be formally derived from a finite set of axioms in a stepwise fashion. First, Godel posited axioms and rules of inference for deriving new true formulas from true formulas already in hand. These were just the axioms and rules of the first- order predicate calculus, comprising the logic of proof throughout the mathematical world. To these he adjoined the Peano postulates of standard arithmetic, a set of axioms and rules for the natural numbers. These consist of 6 basic axioms incorporating the equality symbol "=", 3 additional axioms to define the meaning of that symbol, and a rule of induction corresponding to the meta-level rule of inference adjoined to the six basic axioms of the predicate calculus. The predicate calculus and the Peano postulates, together comprising 15 axioms and 2 rules of inference, define a powerful and comprehensive system for the expression and proof of arithmetical truth. After defining his arithmetical system, Godel’s next step was to enable the formulation of self-referential statements within it. Because arithmetic refers to numbers, this meant assigning numbers to arithmetical formulae. He accomplished this by (1) assigning a natural number or "code number" Î {1,2,…,15} to each of the 15 distinct logical and arithmetical symbols employed in the system; (2) numbering the symbols in each formula from left to right with the consecutive prime "placeholder" numbers 2,3,5,7,…; (3) raising each prime placeholder number to a power equal to the code number of the symbol in that place; and (4) multiplying all of the resulting (large but computable) numbers together to get the Godel number of the formula (note that this procedure is reversible; given any Godel number, one may compute the expression it encodes by factoring it into a unique set of prime factors). In addition, Godel numbered proofs and partial derivations, i.e. deductive sequences of r consecutive formulae, with the products of r numbers 2 m ´ 3n ´ 5p ´ …, where the bases are the first r primes and the exponents m, n, p,… are the Godel numbers of the first, second, third,… formulae in the sequence. In this way, every arithmetical predicate expressible by a formula or sequence of formulae is Godel-numbered, including the predicate "is a proof of (some formula)" and "(this formula) cannot be proven" [equivalent formulations with universal and existential quantifiers: "for all numbers x, x is not the Godel number of a proof of (this formula)"; "there does not exist a number…that is the Godel number of a proof of (this formula)"]. It is important to realize that these predicates actually correspond to real numeric relationships "isomorphically hybridized" with logical relationships. The biological flavor of this terminology is not accidental, for the isomorphism guarantees that numeric relationships areheritable as their logical isomorphs are derived. When one logical formula is derived by substitution from another, they become numerically related in such a way that a distinctive numeric predicate of the Godel number of the ancestral formula is effectively inherited by the Godel number of the descendant formula. This maintains a basis for consistency, ensuring that the negation of the numeric predicate of a formula cannot be derived from the numeric predicate of the formula itself. ChatGPT Summary and Explanation: Self-Reference and Computational Complexity (Continuation) Levels of Proof and Godel's Incompleteness Theorem Levels of Proof: Introducing a distinction between levels of proof helps avoid paradoxes. A statement could be proven at a higher "metalanguage" level to be unprovable at the basic "language" level, providing valuable insights without paradox. Kurt Godel's work in 1931 demonstrated this principle effectively. Godel's Incompleteness Theorem: David Hilbert's Program: Hilbert aimed to prove that mathematics is complete, meaning all true statements can be formally proven. Godel's Conclusion: Godel proved that in any consistent formal system containing arithmetic, there are true statements that cannot be proven within the system. This implies that mathematics is inherently incomplete. Godel's Method: Formal System: Godel used the first-order predicate calculus and Peano postulates for arithmetic. The system includes 15 axioms and 2 rules of inference, defining a comprehensive framework for arithmetic. Encoding Formulas: Godel assigned natural numbers to arithmetical symbols and formulas, creating "Godel numbers". This coding system allows formulas to refer to themselves. Numbering Proofs: Proofs and derivations were encoded using products of prime numbers raised to powers representing the Godel numbers of the formulas. This process ensures that every formula and proof sequence can be uniquely represented by numbers. Self-Referential Statements in Arithmetic: Godel Numbering: Allows the creation of self-referential statements like "this formula cannot be proven". These statements can be expressed and manipulated arithmetically. Consistency and Isomorphism: Godel's system maintains consistency by ensuring that numeric relationships mirror logical relationships. The "isomorphically hybridized" relationship ensures that the numeric properties of formulas are preserved through logical derivations. Implications for Mathematics and Computational Complexity Undecidability: Godel's work demonstrates the power and limitation of self-reference. It highlights the existence of true but unprovable statements, challenging the notion of completeness in mathematics. Computational Complexity: Understanding self-reference is crucial in exploring problems like P=NP. The methods and insights from Godel's work provide foundational tools for analyzing the limits of formal systems and computational problems. By recognizing the stratification of proof levels and employing self-referential techniques, mathematicians can navigate the complexities of formal systems, enhancing our understanding of mathematical truth and computational complexity. User Let us be a bit more specific. Godel’s idea was to express the logical syntax of arithmetic, which is ordinarily formulated in terms of logical and arithmetical symbols, in terms of pure numeric relationships. To do this, the various logical relationships within and among syntactic formulae must be mirrored by numeric relationships among the (Godel-numeric) images of these formulae under Godel’s logic-to-number mapping. The key property that allows this mirroring to occur is called representability. An n-ary numeric relation R(x1,…,xn) is representable in the first-order Peano arithmetic N iff there is in N a formula A(a1,…,an) with n free variables such that for all natural numbers k1,…,kn, the following conditions hold: 1. If R(k1,…,kn) holds, then |--NA(k1,…,kn), i.e. A(k1,…,kn) is provable in N 2. If R(k1,…,kn) does not hold, then |--N~A(k1,…,kn) In this case, we say that A(a1,…,an) represents the numeric relation R. E.g., let R be the "less than" relation among natural numbers. Then R is representable in N because there is a formula x