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topology In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ...
, a branch of mathematics, the loop space Ω''X'' of a pointed
topological space In mathematics, a topological space is, roughly speaking, a geometrical space in which closeness is defined but cannot necessarily be measured by a numeric distance. More specifically, a topological space is a set whose elements are called po ...
''X'' is the space of (based) loops in ''X'', i.e.
continuous Continuity or continuous may refer to: Mathematics * Continuity (mathematics), the opposing concept to discreteness; common examples include ** Continuous probability distribution or random variable in probability and statistics ** Continuous ...
pointed maps from the pointed
circle A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. Equivalently, it is the curve traced out by a point that moves in a plane so that its distance from a given point is con ...
''S''1 to ''X'', equipped with the
compact-open topology In mathematics, the compact-open topology is a topology defined on the set of continuous maps between two topological spaces. The compact-open topology is one of the commonly used topologies on function spaces, and is applied in homotopy theory and ...
. Two loops can be multiplied by
concatenation In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenat ...
. With this operation, the loop space is an ''A''-space. That is, the multiplication is homotopy-coherently associative. The
set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...
of
path component In topology and related branches of mathematics, a connected space is a topological space that cannot be represented as the union of two or more disjoint non-empty open subsets. Connectedness is one of the principal topological properties ...
s of Ω''X'', i.e. the set of based-homotopy equivalence classes of based loops in ''X'', is a
group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...
, the fundamental group ''π''1(''X''). The iterated loop spaces of ''X'' are formed by applying Ω a number of times. There is an analogous construction for topological spaces without basepoint. The free loop space of a topological space ''X'' is the space of maps from the circle ''S''1 to ''X'' with the compact-open topology. The free loop space of ''X'' is often denoted by \mathcalX. As a
functor In mathematics, specifically category theory, a functor is a mapping between categories. Functors were first considered in algebraic topology, where algebraic objects (such as the fundamental group) are associated to topological spaces, and m ...
, the free loop space construction is
right adjoint In mathematics, specifically category theory, adjunction is a relationship that two functors may exhibit, intuitively corresponding to a weak form of equivalence between two related categories. Two functors that stand in this relationship are kno ...
to cartesian product with the circle, while the loop space construction is right adjoint to the
reduced suspension In topology, a branch of mathematics, the suspension of a topological space ''X'' is intuitively obtained by stretching ''X'' into a cylinder and then collapsing both end faces to points. One views ''X'' as "suspended" between these end points. The ...
. This adjunction accounts for much of the importance of loop spaces in stable homotopy theory. (A related phenomenon in
computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (includi ...
is currying, where the cartesian product is adjoint to the
hom functor In mathematics, specifically in category theory, hom-sets (i.e. sets of morphisms between objects) give rise to important functors to the category of sets. These functors are called hom-functors and have numerous applications in category theory and ...
.) Informally this is referred to as
Eckmann–Hilton duality In the mathematical disciplines of algebraic topology and homotopy theory, Eckmann–Hilton duality in its most basic form, consists of taking a given diagram for a particular concept and reversing the direction of all arrows, much as in ca ...
.


Eckmann–Hilton duality

The loop space is dual to the
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
of the same space; this duality is sometimes called
Eckmann–Hilton duality In the mathematical disciplines of algebraic topology and homotopy theory, Eckmann–Hilton duality in its most basic form, consists of taking a given diagram for a particular concept and reversing the direction of all arrows, much as in ca ...
. The basic observation is that : Sigma Z,X\approxeq , \Omega X/math> where ,B/math> is the set of homotopy classes of maps A \rightarrow B, and \Sigma A is the suspension of A, and \approxeq denotes the
natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
homeomorphism In the mathematical field of topology, a homeomorphism, topological isomorphism, or bicontinuous function is a bijective and continuous function between topological spaces that has a continuous inverse function. Homeomorphisms are the isomor ...
. This homeomorphism is essentially that of currying, modulo the quotients needed to convert the products to reduced products. In general,
, B The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline o ...
/math> does not have a group structure for arbitrary spaces A and B. However, it can be shown that Sigma Z,X/math> and , \Omega X/math> do have natural group structures when Z and X are pointed, and the aforementioned isomorphism is of those groups. ''(See chapter 8, section 2)'' Thus, setting Z = S^ (the k-1 sphere) gives the relationship :\pi_k(X) \approxeq \pi_(\Omega X). This follows since the homotopy group is defined as \pi_k(X)= ^k,X/math> and the spheres can be obtained via suspensions of each-other, i.e. S^k=\Sigma S^.Topospaces wiki – Loop space of a based topological space
/ref>


See also

*
Eilenberg–MacLane space In mathematics, specifically algebraic topology, an Eilenberg–MacLane space Saunders Mac Lane originally spelt his name "MacLane" (without a space), and co-published the papers establishing the notion of Eilenberg–MacLane spaces under this name ...
*
Free loop "Free Loop (One Night Stand)" (titled as "Free Loop" on ''Daniel Powter'') is a song written by Canadian singer Daniel Powter. It was his second single and the follow-up to his successful song, " Bad Day". In the United Kingdom, WEA failed to r ...
* Fundamental group * Gray's conjecture *
List of topologies The following is a list of named topologies or topological spaces, many of which are counterexamples in topology and related branches of mathematics. This is not a list of properties that a topology or topological space might possess; for that, ...
*
Loop group In mathematics, a loop group is a group of loops in a topological group ''G'' with multiplication defined pointwise. Definition In its most general form a loop group is a group of continuous mappings from a manifold to a topological group . ...
*
Path (topology) In mathematics, a path in a topological space X is a continuous function from the closed unit interval , 1/math> into X. Paths play an important role in the fields of topology and mathematical analysis. For example, a topological space for ...
*
Quasigroup In mathematics, especially in abstract algebra, a quasigroup is an algebraic structure resembling a group in the sense that " division" is always possible. Quasigroups differ from groups mainly in that they need not be associative and need not have ...
*
Spectrum (topology) In algebraic topology, a branch of mathematics, a spectrum is an object representing a generalized cohomology theory. Every such cohomology theory is representable, as follows from Brown's representability theorem. This means that, given a cohomolo ...
*
Path space (algebraic topology) In algebraic topology, a branch of mathematics, the path space PX of a based space (X, *) is the space that consists of all maps f from the interval I = , 1/math> to ''X'' such that f(0) = *, called paths.Martin FranklandMath 527 - Homotopy Theory ...


References

* *{{Citation , last1=May , first1=J. Peter , author1-link=J. Peter May , title=The Geometry of Iterated Loop Spaces , series=Lecture Notes in Mathematics , url=http://www.math.uchicago.edu/~may/BOOKSMaster.html , publisher=
Springer-Verlag Springer Science+Business Media, commonly known as Springer, is a German multinational publishing company of books, e-books and peer-reviewed journals in science, humanities, technical and medical (STM) publishing. Originally founded in 1842 ...
, location=Berlin, New York , isbn=978-3-540-05904-2 , doi=10.1007/BFb0067491 , mr=0420610 , year=1972, volume=271 Topology Homotopy theory Topological spaces