Where does unification collide?

In physics, unification is the joining of forces once thought separate into a single framework that describes them with the same laws. Maxwell's 1865 A dynamical theory of the electromagnetic field gave the first such joining, showing that electricity and magnetism are two aspects of one electromagnetic field and that light is a wave in it. The program continued with Weinberg's 1967 A model of leptons and Georgi and Glashow's 1974 Unity of all elementary-particle forces, which merged the electromagnetic and weak interactions and then proposed one framework that would include the strong force as well. Here the word names the combining of distinct physical forces, not the matching of logical terms or the merging of grammatical descriptions.[1][2][3]

Unit

One combined description of two or more fundamental forces under shared laws

Recovery means

Not applicable

Measured by

Tested by predictions the joined theory makes that the separate theories do not, such as new particles or interaction rates

In logic and computer science, unification is the operation of finding a substitution of variables that makes two symbolic expressions identical. Robinson's 1965 A machine-oriented logic based on the resolution principle introduced the unification algorithm as the central step of automated theorem proving. It computes the most general substitution that makes the expressions match, or reports that none exists, and it now underlies logic programming languages and the type inference done by compilers. Here the word names an equation-solving step over symbols, not the joining of physical forces or the merging of grammatical descriptions.[4]

Unit

One most-general substitution that makes two expressions identical, or a report that none exists

Recovery means

Not applicable

Measured by

Judged by whether the computed substitution makes the expressions equal and is the most general one that does so

In linguistics, unification is the operation that combines two sets of feature descriptions into one, keeping every piece of information from both when they do not conflict and failing when they do. Kay's 1979 Functional grammar introduced this operation as the engine of functional unification grammar, and Shieber's 1986 An introduction to unification-based approaches to grammar drew the resulting family of formalisms together. A grammar built this way states what features each phrase must carry, and unification merges the descriptions of its parts into a consistent whole. Here the word names the merging of feature structures in a grammar, not the joining of physical forces or the term matching of a theorem prover.[5][6]

Unit

One merged feature structure combining two consistent descriptions

Recovery means

Not applicable

Measured by

Judged by whether the merged structure preserves all consistent features and fails exactly when features conflict