What is Topology: Definition and 808 Discussions

In mathematics, topology (from the Greek words τόπος, 'place, location', and λόγος, 'study') 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 holes, opening holes, tearing, gluing, or passing through itself.
A topological space is a set endowed with a structure, called a topology, which allows defining continuous deformation of subspaces, and, more generally, all kinds of continuity. Euclidean spaces, and, more generally, metric spaces are examples of a topological space, as any distance or metric defines a topology. The deformations that are considered in topology are homeomorphisms and homotopies. A property that is invariant under such deformations is a topological property. Basic examples of topological properties are: the dimension, which allows distinguishing between a line and a surface; compactness, which allows distinguishing between a line and a circle; connectedness, which allows distinguishing a circle from two non-intersecting circles.
The ideas underlying topology go back to Gottfried Leibniz, who in the 17th century envisioned the geometria situs and analysis situs. Leonhard Euler's Seven Bridges of Königsberg problem and polyhedron formula are arguably the field's first theorems. The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological space was developed.

View More On Wikipedia.org
  1. I

    Is R with the cofinite topology path connected?

    u is the usual topology, cf is the cofinite topology. yes proof: pick a and b in (R,cf) ((0,1),u) ~ ((a,b),u). then the identity on (a,b) is continuous is because (R,cf) \subset (R,u). map 0->a and 1->b. the fn is continuous at the end points because no subset of the image is open in...
  2. P

    Topology Q: Curved Space w/out Higher Dimensions?

    Hi, does it make sense to posit a curved (hall of mirrors type) space without higher dimensions? In other words, if I say we live in a 3 dimensional torus shaped universe, does that statement necessarily entail there's at least a 4 dimensional overall hyperspace? Or can I have a torus curved...
  3. O

    Understanding Topology: Metric Spaces, Open Balls, and Intersection Proofs

    So I'm trying to teach myself some topology, and the first thing I noticed, was that a metric space is a topological space under the topology of all open balls.. But then, consider the intersection of two open balls, can someone prove to me that the result is another open ball? Or do they...
  4. M

    Solve Connected Set Closure: Show Not Disconnected

    I'm struggling with something that I suspect is very basic. How do I should that the closure of a connected set is connected? I think I need to somehow show that it is not disconnected, but that's where I'm stuck. Thanks
  5. J

    Topology Question:Connected Components

    Hi, I have a conceptual question. In a project I am working on, we are dealing with \Re^{n} (with the usual topology), and I am working on characterizing some objects. In particular, I am dealing with the intersection of two simply connected open sets (that do not have any sort of...
  6. N

    Topology of Curved Space: Understanding Distance on a Positively Curved Sphere

    [SOLVED] Topology of curved space Homework Statement The distance between a point (r, theta) and a nearby point (r + dr, theta + d\theta) on a positively curved sphere is given by ds^2 = dr^2 + R^2 \sin ^2 (r/R)d\theta ^2 NOTE: I mean that ds^2 = (ds^2). My question is - how do I...
  7. H

    Real Analysis vs Differential Geometry vs Topology

    I would just like to know which of these math courses is best suited for physics. I have taken advanced calculus and linear algebra, so I've seen most of the proofs one typically sees in an intro analysis course (ie. epsilon delta etc.). I intend to do work with a lot of Quantum Field Theory...
  8. J

    Topology Question: Continuous Functions and Simply Connected Subsets

    Hi, I have a question that I'm not sure about. If f:A->C is continuous and B is a subset of C that is simply connected, is f(^-1)(B) necessarily connected or simply connected for that matter? Since the spaces are not necessarily homeomorphic I cannot consider it a topological invariant...
  9. U

    Topology Questions: Isham's Modern Differential Geometry for Physicists

    I'm a physics student and I'm trying to work my way through Isham's Modern differential geometry for physicists. I guess the first question would be what you guys think of this book, does it cover all the necessary stuff (it's my preparation for general relativity)? Sadly I'm already having...
  10. K

    Convex Subsets of Ordered Sets: Interval or Ray in Topology?

    Homework Statement Let X be an ordered set. If Y is a proper subset of X that is convex in X, does it follow that Y is an interval or a ray in X? The Attempt at a Solution I considered it to be yes. Since in the ordinary situation, the assertion is obviously valid: check out the...
  11. M

    Does Every Topology Have a Minimal Subset Basis?

    I can't seem to find this result in any of my textbooks. Given any basis B for a topology T on X, is there a minimal subset M of B that also is a basis for T (in the sense that any proper subset of M is not a basis for T)? If so, is Zorn's Lemma needed to prove this? Is the same true of...
  12. J

    Topology: homeomorphism between quotient spaces

    I posted this earlier and thought I solved it using a certain definition, which now I think is wrong, so I'm posting this again: Show that the quotient spaces R^2, R^2/D^2, R^2/I, and R^2/A are homeomorphic where D^2 is the closed ball of radius 1, centered at the origin. I is the closed...
  13. J

    TOPOLOGY: homeomorphism between quotient spaces

    Show the following spaces are homeomorphic: \mathbb{R}^2, \mathbb{R}^2/I, \mathbb{R}^2/D^2. Note: D^2 is the closed ball of radius 1 centered at the origin. I is the closed interval [0,1] in \mathbb{R}. THEOREM: It is enough to find a surjective, continuous map f:X\rightarrow Y to show that...
  14. M

    Conflicting statements from two topology textbooks

    Conflicting statements from topology textbooks Definitions: A point p is a limit point of A iff all open sets containing p intersects A-{p}. Let A' denote the set of all limit points of A. So far, so good. Cullen's topology book (1968) states that (A U B)' = A' U B'. I read her proof...
  15. T

    Is the Sum of Two Closed Sets in R^n Always Closed?

    Let A, B in R^n be closed sets. Does A+B = {x+y| x in A and y in B} have to be closed? Here is what I've tried. Let x be in A^c and y in B^c which are both open since A & B are closed. So for each x in A^c there exists epsilon(a)>0 s.t. x in D(x, epsilon(a) is subset of A^c. For each y...
  16. J

    Topology: Nested, Compact, Connected Sets

    [SOLVED] Topology: Nested, Compact, Connected Sets 1. Assumptions: X is a Hausdorff space. {K_n} is a family of nested, compact, nonempty, connected sets. Two parts: Show the intersection of all K_n is nonempty and connected. That the intersection is nonempty: I modeled my proof after the...
  17. J

    Topology: Questions & Answers on Algorithms, Homeomorphisms & More

    I was wondering about topology. a) Is there an algorithm for the number of topologies on finite sets? b) If two spaces are homeomorphic, are intersections of opens sent to intersections of opens? Are unions of opens sent to unions of opens? I tried to find an algorithm in the first part, and...
  18. quasar987

    Hausdorffness of the product topology

    [SOLVED] Hausdorffness of the product topology Is it me, or is the product of an infinite number of Hausdorff spaces never Hausdorff? Recall that the product topology on \Pi_{i\in I}X_i has for a basis the products of open sets \Pi_{i\in I}O_i where all but finitely many of those O_i are...
  19. J

    Topology Questions: Proving Existence and Comparison of Topologies

    Homework Statement 1. given a set X and a collection of subsets S, prove there exists a smallest topology containing S 2. Prove, on R, the topology containing all intervals of the from [a,b) is a topology finer than the euclidean topology, and that the topologies containing the intervals of...
  20. K

    What is the biggest unsolved problem in topology

    What is the biggest unsolved problem in topology
  21. MathematicalPhysicist

    Does Convergence in Open-Compact Topology Ensure Pointwise Convergence?

    Let C(X,Y) be the continuous functions space between the topological spaces X,Y, with the open-compact topology. prove that if the sequence {f_n} of C(X,Y) converges to f0 in C(X,Y) then for every point x in X the sequence {f_n(x)} in Y converges to f0(x). here's what I did, let x be in X and...
  22. J

    When is a Collection of Finite or Countable Subsets a Topology?

    [SOLVED] very basic topology questions Homework Statement Let X be a set and T be the collection of X and all finite subsets of X. When is T a topology? Let T' be the collection of X and all countable subsets of X, when is T' a topology? The Attempt at a Solution it's clear the empty set...
  23. J

    In topology: homeomorphism v. monotone function

    1. Let f:\mathbb{R}\rightarrow\mathbb{R} be a bijection. Prove that f is a homeomorphism iff f is a monotone function. I think I have it one way (if f is monotone, it is a homeomorphism), but I'm stuck on the other way (if f is a homeomorphism, then it is monotone). I tried to prove...
  24. M

    Please help me identify this topology book

    I have photocopied pages of a advanced-looking point-set topology textbook, but I don't know the name of the book or the author. It has 427 pages (the last index page is p.427), and based on its references, it was written no earlier than 1966, and probably no later than 1975. I've attached a...
  25. M

    I'm going to prove every single theorem in topology

    I've started studying point-set topology a month ago and I'm hooked! I guess one reason is because each question is proof-based, abstract, and non-calculational, which is what I like. I've decided to take on the project of proving every single theorem in topology (that is found in textbooks)...
  26. R

    How Can I Prove These Topology Statements?

    Hello I have a proof that I need to try to work out but I'm not really getting too far and need help if you could at all. The question is Let A and B be two subsets of a metric space X. Prove that: Int(A)\bigcupInt(B)\subseteqInt(A\bigcupB) and Int(A)\bigcapInt(B) = Int(A\bigcapB) I...
  27. S

    What is the proof of the theorem on limit points in topology?

    I'm having some trouble understanding the distinction between closed sets, open sets, and those which are neither when the set itself involves there not being a finite boundary. For example, the set { |z - 4| >= |z| : z is complex}. This turns out to be the inequality 2>= Re(z). On the right...
  28. J

    Does Alan Hatcher's Topology book Work on 'Experimental' PDF Readers?

    Does anyone here have one of these book readers? I want to know how good the 'experimental' PDF support is. For instance, will it display Alan Hatcher's Topology book?
  29. M

    What are the basics of differential topology?

    I was just wondering if anyone had a decent website explaining some of the basic terminology of differential topology. Specifically, I'm having a bit of trouble understanding charts and atlases and how one defines a smooth manifold in an arbitrary setting (i.e., not necessarily embedded in R^n)
  30. J

    Limit in closure, topology stuff

    Let A\subset X be a subset of some topological space. If x\in\overline{A}\backslash A, does there exist a sequence x_n\in A so that x_n\to x? In fact I already believe, that such sequence does not exist in general, but I'm just making sure. Is there any standard counter examples? I haven't seen...
  31. M

    Is a Closed Graph of a Function on a Closed Interval Indicative of Continuity?

    Homework Statement All right, so this appeared on my final. The intervals are in the reals: If f : [a, b] -> [c, d] , and the graph of f is closed, is f continuous? Homework Equations The Attempt at a Solution Well, my gut reaction is no, just because it seems like a fairly...
  32. B

    Topology Question (Normal Spaces)

    Not sure where to put a question about topology, but I'll try here. I'm trying to show that a certain topology for the Real line is not normal. The topology in question has no disjoint open sets (they are all nested) and therefore, no disjoint closed sets. If a topology has no disjoint...
  33. MathematicalPhysicist

    Is U-A Open and A-U Closed in Topological Spaces?

    just want to see if i got these: 1.let U be open in X and A closed in X then U-A is open in X and A-U is closed in X. 2. if A is closed in X and B is closed in Y then AxB is closed in XxY. my proof: 1. A'=X-A which is open in X X-(A-U)=Xn(A'U U)=A'U(U) but this is a union of open sets...
  34. Z

    Topology of closed timelike curves (CTC)

    For less than BH_h, deep in gravitational potential well, with very extreme curvature, might one have a future light cone tipping over sufficiently to become spacelike and then wrap around to join up (glued) to past light cone? This is like a closed timelike curve, which can not be shrunk to a...
  35. E

    How useful is topology in theoretical physics?

    How useful is topology in theoretical physics? By topology, I mean the contents of Munkres book, Hausdorff spaces, homeomorphisms, etc. It seems to me like topology is totally a mathematical construct since the idea of an "open set" in an abstract space seems to have no "physical" meaning...
  36. Z

    Topology outside vs inside black hole

    If topology of a manifold were invariant (or not), what specifically would topology of a patch of such manifold in neighborhood (outside) of such BH, suggest?
  37. MathematicalPhysicist

    Proving Equality of Subspace Topologies: A Topological Lemma Approach

    Well it's not homewrok cause i don't need to hand this question in, this is why i decided to put it here. (that, and there isn't a topology forum per se, perhaps it's suited to point set topology so the set theory forum may suit it). Now to the question: Show that if Y is a subspace of X...
  38. E

    What is the inherited topology of a line in RlxR and RlxRl?

    Homework Statement If L is a straight line in the plane, describe the topology L inherits as a subspace of RlxR and as a subspace of RlxRl in each case it is a familiar topology.(Rl= lower limit topology) The Attempt at a Solution RlxR topology is the union of intervals...
  39. P

    Algebraic topology for dummies?

    I am looking for the most basic but rigorous to some extent book on Algebraic topology out there.
  40. JasonRox

    Unique Partition of Evenly Covered Sets in Algebraic Topology

    Note: I have many questions and will keep posting new ones as they come up. To find the questions simply scroll down to look for bold segments. Feel free to contribute any other comments relevant to the questions or the topic itself. Here it is... Let p:E->B be continuous and surjective...
  41. E

    Topology: Show Equivalence of T and T' on R^2

    Homework Statement I am asked to show that T=[particular point topology on R^2 ((0,0) being the particular point)] is equal to T'=[topology on R^2 from taking the product of R in the particular point topology (0 being particular point) with itself]. The Attempt at a Solution I'm...
  42. P

    Exploring the Universe's Topology: Insights from a New Study | Space.com"

    Hi, I've read this article (http://www.space.com/scienceastronomy/mystery_monday_040524.html), which says: "In the new study, researchers examined primordial radiation imprinted on the cosmos. Among their conclusions is that it is less likely that there is some crazy cosmic "hall of mirrors"...
  43. JasonRox

    Surjectivity of Induced Homomorphism in Algebraic Topology

    I'm totally stuck on these two. The first is... Let A be a subset of X; suppose r:X->A is a continuous map from X to A such that r(a)=a for each a e A. If a_0 e A, show that... r* : Pi_1(X,a_0) -> Pi_1(A,a_0) ...is surjective. Note: Pi_1 is the first homotopy group and r* is the...
  44. P

    Torus Excluding Disc: Boundary of RP^2 X RP^2

    Homework Statement What is the torus excluding a disc homeomorphic to? What is the boundary of a torus (excluding a disc)?The Attempt at a Solution RP^2 X RP^2? As a guess.
  45. M

    Topology: Bijection with Open intervals

    Good Morning, I am trying to prove that any 2 open intervals (a,b) and (c,d) are equivalent. Show that f(x) = ((d-c)/(b-a))*(x-a)+c is one-to-one and onto (c,d). a,b,c,d belong to the set of Real numbers with a<b and c<d. Let f: (a,b)->(c,d) be a linear function which i graphed to help me...
  46. E

    Continuous functions in topology

    Homework Statement In topology, a f: X -> Y is continuous when U is open in Y implies that f^{-1}(U) is open in X Doesn't that mean that a continuous function must be surjective i.e. it must span all of Y since every point y in Y is in an open set and that open set must have a pre-image...
  47. N

    Comparing Finite Complement and (-inf,a) Topologies: Are T_3 and T_5 Comparable?

    I need to show if the finite complement topology,T_3, and the topology having all sets (-inf,a) = {x|x<a} as basis ,T_5, are comparable. I've shown that T_3 is not strictly finer than T_5. But I'm not sure about other case. I need help.
  48. R

    Is Every Infinite Set Countable? Understanding Finite vs. Infinite in Topology

    Homework Statement I always get confused between countably many vs. uncountable. I suppose if one can index the points of a set , then it is countable. 1)So, anything that is finitie is countable. Anything that is infinite is also countable? Then what is uncountable, something that...
  49. 1

    Uses of Topology: Learn What It Can Do

    I am not a math student but I have read some basic stuff about topology just because it sounded interesting, and I was wondering if people could name some uses of it, because it does not seem to have very many. Also on a related question, how often are new branches of mathematics "invented"...
  50. N

    Queer questions about topology

    Many abstract mathematical concepts have their intuitive correspondences or geometrical meanings. such as differentiable is corresponding to "smooth", determinant is corresponding to "volumn",homolgy group is corresponding to "hole". 1.The question is whether "exact" and "exact sequence" have...
Back
Top