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A model category is a category equipped with notions of weak equivalences, fibrations and cofibrations allowing to run arguments similar to those of classical homotopy theory.

73 votes

Do we still need model categories?

Here are some rough analogies: Model Category :: $(\infty, 1)$-category Basis :: Vector space Local coordinates :: Manifold I especially like the last one. When you do, say, differential geometry …
Chris Schommer-Pries's user avatar
49 votes

What are surprising examples of Model Categories?

The category of sets admits precisely nine model category structures, no more no less. I learned this fact from Tom Goodwillie's comments on a different MO question. It always shocks people when I m …
Chris Schommer-Pries's user avatar
25 votes
4 answers
3k views

A Peculiar Model Structure on Simplicial Sets?

I'm wondering if there is a Quillen model structure on the category of simplicial sets which generalizes the usual model structure, but where every simplicial set is fibrant? I want to use this to do …
Chris Schommer-Pries's user avatar
20 votes
2 answers
1k views

How many model categories have the same weak equivalences?

There are many situations which arise where one might consider different Model categories with the same underlying category. For example in (left) Bousfield localization you start with a model categor …
Chris Schommer-Pries's user avatar
19 votes
4 answers
3k views

What are the fibrant objects in the injective model structure?

If C is a small category, we can consider the category of simplicial presheaves on C. This is a model category in two natural ways which are compatible with the usual model structure on simplicial set …
Chris Schommer-Pries's user avatar
18 votes
1 answer
2k views

A Model Category of Segal Spaces?

So in Julie Bergner's work on $(\infty, 1)$-categories arXiv:0610239, she considers several model categories which model $(\infty, 1)$-categories, which are known to be equivalent. I'm guessing that t …
Chris Schommer-Pries's user avatar
16 votes
Accepted

Derived categories and homotopy categories

Yes. The former is a special case of the latter. There is a model category structure on the category of (say bounded) chain complexes of objects in your given abelian category. The weak equivalences a …
Chris Schommer-Pries's user avatar
11 votes
Accepted

Is the simplicial nerve a localization?

This is not true. Here is a counter example. We let $\mathcal{C}_*$ be the following simplicial category. It has two objects 0 and 1. Their only endomorphisms are the identity. There are no morphisms …
Chris Schommer-Pries's user avatar
10 votes
3 answers
1k views

When is the projective model structure cartesian? When is the internal hom invariant?

If M is a sufficiently nice model category and D is a small category then there are two natural model structures we can impose on the functor category $Fun(D,M)$ where the weak equivalences are the le …
Chris Schommer-Pries's user avatar
8 votes
0 answers
315 views

A model category for E-infty algebras in a non-monoidal model category?

Given a suitable nice symmetric monoidal category $C$, symmetric monoidally enriched, tensored, and cotensored over a symmetric monoidal category $S$, and an operad $\mathcal{O}$ in $S$, we can consid …
Chris Schommer-Pries's user avatar
4 votes
Accepted

Is a left Bousfield localization of simplicial presheaves a locally cartesian closed model c...

Section 2 of this paper of Rezk addresses exactly the question of when the localization by S yields a Cartesian model category. For that the relevant property is that that if you take the product of a …
Chris Schommer-Pries's user avatar