Not signed in (Sign In)

Start a new discussion

Not signed in

Want to take part in these discussions? Sign in if you have an account, or apply for one below

  • Sign in using OpenID

Site Tag Cloud

2-categories 2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry bundles calculus categorical categories category category-theory chern-weil-theory cohesion cohesive-homotopy-type-theory cohomology colimits combinatorics complex-geometry computable-mathematics computer-science constructive cosmology deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry differential-topology digraphs duality elliptic-cohomology enriched fibration finite foundations functional-analysis functor galois-theory gauge-theory gebra geometric-quantization geometry graph graphs gravity grothendieck group group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory homological homological-algebra homotopy homotopy-theory homotopy-type-theory index-theory integration integration-theory k-theory lie-theory limit limits linear linear-algebra locale localization logic manifolds mathematics measure-theory modal modal-logic model model-category-theory monads monoidal monoidal-category-theory morphism motives motivic-cohomology natural nlab noncommutative noncommutative-geometry number-theory of operads operator operator-algebra order-theory pages pasting philosophy physics pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory string string-theory subobject superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topology topos topos-theory type type-theory universal variational-calculus

Vanilla 1.1.10 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to nForum
If you want to take part in these discussions either sign in now (if you have an account), apply for one now (if you don't).
    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeJul 25th 2011

    I am splitting off Gelfand duality from Gelfand spectrum. Want to state the actual equivalence theorem here. But just a moment…

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeJul 25th 2011

    …now with statement of the theorem…

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeJul 25th 2011

    …and now the statement of the non-unital version should even be correct ;-). I have also expanded a bit more.

    • CommentRowNumber4.
    • CommentAuthorzskoda
    • CommentTimeJul 25th 2011
    • (edited Jul 25th 2011)

    Well is this desired? I mean the non-unitality is geometrically about the noncompact case, i.e. for locally compact Hausdorff. I see quoted some theorem on pointed slice category, this is a known trick (I learned it from a short discussion of Maszczyk with Janelidze in Warszawa), but it is really useful to have rather the standard Gel’fand duality for locally compact Hausdorff spaces with function spaces of functions vanishing at infinity. For that case, one has to be careful with morphisms.

    • CommentRowNumber5.
    • CommentAuthorTodd_Trimble
    • CommentTimeNov 12th 2014

    Qiaochu Yuan points out here that Gelfand duality as stated in the nLab here is not correct. I checked out Gelfand duality and the mistake is repeated in the Idea section, but does not reappear in the more formal statements and proofs below.

    Particularly, corollary 1 which states a contravariant equivalence between pointed compact Hausdorff spaces and non-unital commutative C *C^\ast-algebras is certainly (and clearly) correct. I’m guessing the mistake was thinking the category of pointed compact Hausdorff spaces is equivalent to the category of locally compact Hausdorff spaces and proper continuous maps. Yes, the one-point compactification does give a functor from LCHLCH (and proper maps) to */CH\ast/CH, and this functor is faithful and essentially surjective, but it isn’t full since it doesn’t hit any map that sends more than one point to the basepoint at infinity. Maybe we could identify the category of pointed CH spaces with the category of LCH spaces and partial proper maps with open domain, but I haven’t thought that through to the end.

    I don’t know how far this mistake has propagated through the nLab. I’m guessing not too far.

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeNov 12th 2014
    • (edited Nov 12th 2014)

    Thanks for the alert, that’s probably my bad. Sorry.

    I have removed the wrong statement and added (for the moment) a remark that with due care on the morphisms there is the desired generalization, with a pointer to (for the moment) the note Brandenburg 07.

    Should be expanded…

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeJul 22nd 2018
    • (edited Jul 22nd 2018)

    added pointer to Johnstone 82 and added remark that this discusses Gelfand duality with real-valued function algebras.

    I am looking for a reference that makes explicit first the general adjunction between topological spaces and (star-)algebras, and then obtains Gelfand duality as the fixed point equivalence of this adjunction. I see lots of chat about this perspective, but what’s a citable reference that spells it out?

    diff, v20, current

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeJul 22nd 2018

    added pointer to Negropontis 71. I suppose, historically, that’s the origin of category-theoretic discussion of Gelfand duality?

    diff, v21, current

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeJul 22nd 2018
    • (edited Jul 22nd 2018)

    added pointer to Porst-Tholen 91, section 4-c for Gelfand duality as the center of an adjunction between general (compactly generated Hausdorff) topological spaces and general (topological) complex algebras

    diff, v22, current

    • CommentRowNumber10.
    • CommentAuthorzskoda
    • CommentTimeJul 23rd 2018
    • (edited Jul 23rd 2018)

    8: clicking on doi for Negropontis did not work because the doi has brackets inside what does not work with our markup syntax. So I redone the link with writing html directly. Clicking on doi now works.

    I’d also like to mention the old unpublished observation of Joel W. Robbin that the set theoretic version of Gel’fand-Neimark duality holds iff we assume set theory satisfying the axiom of existence of measurable cardinals. Nowdays there are wider generalizations of this result.

    • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeJul 23rd 2018


    • CommentRowNumber12.
    • CommentAuthorDmitri Pavlov
    • CommentTimeMay 22nd 2020

    Added precise statements for two different nonunital versions.

    diff, v29, current

    • CommentRowNumber13.
    • CommentAuthorDmitri Pavlov
    • CommentTimeNov 20th 2020

    Added the original reference.

    diff, v30, current

  1. The previous version used “*-homomorphisms”, which only appears as “-homomorphisms” on the page. I replaced the * with *\ast so that this will appear as intended.


    diff, v31, current

Add your comments
  • Please log in or leave your comment as a "guest post". If commenting as a "guest", please include your name in the message as a courtesy. Note: only certain categories allow guest posts.
  • To produce a hyperlink to an nLab entry, simply put double square brackets around its name, e.g. [[category]]. To use (La)TeX mathematics in your post, make sure Markdown+Itex is selected below and put your mathematics between dollar signs as usual. Only a subset of the usual TeX math commands are accepted: see here for a list.

  • (Help)