2-category

Definition

A 2-category is a generalization of the concept of a category, which allows for morphisms between morphisms, known as 2-morphisms. In a 2-category, objects can have not only arrows (morphisms) that connect them, but also higher-dimensional arrows that relate those arrows to each other, making it a richer structure. This adds layers of relationships and transformations, which is particularly useful in the study of functors and natural transformations, as it helps to understand how these mappings behave in more complex ways.

5 Must Know Facts For Your Next Test

1. In a 2-category, there are three levels of structure: objects, morphisms (1-morphisms), and 2-morphisms that connect these morphisms.
2. Each 2-morphism has its own composition rules, allowing for more intricate interactions between morphisms compared to standard categories.
3. Examples of 2-categories include the category of categories itself, where the objects are categories, the 1-morphisms are functors, and the 2-morphisms are natural transformations.
4. 2-categories facilitate a deeper understanding of homotopy theory by allowing the study of paths and higher-dimensional analogs in topological spaces.
5. The concept of 2-categories is essential in advanced topics like higher category theory, which further extends the ideas found in traditional category theory.

Review Questions

• How does a 2-category differ from a standard category in terms of structure and relationships?
  • A 2-category differs from a standard category primarily by introducing an additional layer of relationships through 2-morphisms. While a standard category consists only of objects connected by morphisms, a 2-category includes morphisms that can relate these morphisms to one another. This added complexity allows for richer interactions and enables the exploration of concepts such as natural transformations in greater depth.
• Discuss how functors and natural transformations play a role in understanding 2-categories.
  • Functors serve as the primary mappings between categories within the context of 2-categories, allowing for the transformation of objects and morphisms. Natural transformations then provide a means to relate different functors while maintaining categorical structure. In this way, both functors and natural transformations become essential tools for navigating and analyzing the relationships in 2-categories, illustrating how multiple layers of connections can be understood through these mappings.
• Evaluate the significance of 2-categories in higher category theory and their impact on mathematical research.
  • The significance of 2-categories in higher category theory lies in their ability to encapsulate complex relationships that go beyond standard categorical frameworks. By incorporating multiple levels of morphisms, 2-categories enable mathematicians to investigate phenomena such as homotopy types and higher-dimensional structures. This contributes to ongoing research in topology and algebraic structures, leading to advancements that challenge traditional perspectives and deepen our understanding of mathematical concepts.

Related terms

Category: A mathematical structure consisting of objects and morphisms between them, where each morphism has a defined domain and codomain.

Functor: A mapping between categories that preserves the structure of categories, sending objects to objects and morphisms to morphisms.

Natural Transformation: A way of transforming one functor into another while respecting the structure of the categories involved, providing a bridge between different functors.