What is Topology: Definition and 807 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.

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  1. Z

    Topology question: finite sets

    Homework Statement If A and B are finite, show that the set of all functions f: A --> B is finite. Homework Equations finite unions and finite caretesian products of finite sets are finite The Attempt at a Solution If f: A -> B is finite, then there exists m functions fm mapping to...
  2. S

    Product of compact sets compact in box topology?

    So Tychonoff theorem states products of compact sets are compact in the product topology. is this true for the box topology? counterexample?
  3. L

    Books on topology, geometry and physics

    Hi everyone, First my background, I'm a junior in physics and math. I've taken griffiths QM, EM (first semester only so far), mechanics and such. In terms of math, I've taken an applied algebra and linear algebra course. I've learned some GR from Sean Carroll's text and a short course in GR...
  4. U

    Topology question → What geometric figure?

    James came to a place where there was a bridge, supported by parabolic arcs. In the middle waving a transparent gelatinous substance in the form of spherical shell of exotic matter. He had come to " delighted well", a horizontal formation, which is much talk and little experienced. Slowly James...
  5. M

    Topology Q: Show f is Continuous in X with d and A

    hi all, i am studying from croom's introduction to topology book. i came across such a question. and i don't have a clue as to how to start . Let X be a metric space with metric d and A a non-empty subset of X. define f:X->IR by : f(x): d(x,A), x E X (x is an element of X) show that f is...
  6. R

    What are the best books on point set topology for undergraduate students?

    Hi! Can someone recommend some books on point set topology for undergraduates? I am going to use it this summer for preview and also during the fall because the instructor is not going to use a textbook. Thank you!
  7. J

    No problem, glad we could help! And welcome to the site! :)

    Let X be any infinite set. The countable closed topology is defined to be the topology having as its closed sets X and all countable subsets of X. Prove that this is indeed a topology on X. Any help would be greatly appreciated. Thanks!
  8. R

    Basic Topology- when doesn't the reflexive relation hold?

    Homework Statement When doesn't the reflexive relation hold? In order for aRb to be true, aRa must hold and the other two conditions. Homework Equations The Attempt at a Solution I am new to topology and am not really taking a course in topology. To me it looks like a is always equivalent to...
  9. T

    Topology - Interior of set - Rudin

    Homework Statement I am trying to solve part d of problem 9 in chapter 2 of Rudin's Principles of Mathematical Analysis. The problem is: Let E* denote the set of all interior points of a set E (in a metric space X). Prove the complement of E* is the closure of the complement of E. I will...
  10. L

    Topology Books for Beginners - John Milnor's Differentiable Viewpoint

    Hey guys, So my prof assigned John Milnor's book about topology from a differentiable viewpoint for out topology and geometry class. I was wondering if anyone had a book they could recommend as an introduction into topology because I don't think professor Milnor's book really is an...
  11. A

    Take Intro to Topology or Intro to Analysis?

    I'm about to take my higher upper division classes to complete my mathematics major. I've decided that I'd like to take either Intro to Topology or Intro to Analysis as my topics of choice, along with the required Linear Algebra course that most graduate schools are looking for in applicants...
  12. C

    Topology of Minkowski spacetime

    I recently Googled "spacetime topology" and found that the topology of Minkowski spacetime is generally described as that of an R4 manifold. This is not my field, but I'm surprised. Perhaps mathematically the (---+) "Lorentz signature" can be taken as a secondary characteristic of the...
  13. J

    Right Ray Topology: Excluded Set Topology

    Topology Excluded set << Original text of post restored by Mentors >>
  14. M

    The meaning of different in Munkres' Topology

    The meaning of "different" in Munkres' Topology Hi, I'm working on problem 20.8(b) (page 127f) in Munkres' "Topology", the problem is to show that four topologies are "different". Does different in this context mean that they are unequal - in which case one can contain the other, or...
  15. D

    Topology of flat spatime -metric?

    I am studying topology. There I learn that the open sets given by the metric can be used to define a topology, e.g. the usual metric topology on R^n given by the Euclidean metric. Now I try to understand the topology of (flat) spacetime. Is there a metric? The Lorentz 'metric' gives...
  16. D

    Is the Lorentz metric compatible with the topology of flat spacetime?

    Could someone clarify, and/or point me to some reference on: Lorentz metric is not really a metric in the sense of metric spaces of a topology course since it admits negative values. If I use it to define the usual open sphere about a point, that sphere includes the entire light-cone through...
  17. E

    Math books: group theory and topology

    Just want to ask for recommendations for good math books on 1) groups, modules, rings - all the basic algebra stuff but for a physicist 2) topological spaces, compactness, ... I need books for a theoretical physicist to read up on these topics so that I could study, say, algebraic...
  18. D

    Learn Topology: Resources for Beginners

    I want to learn topology but I can't find any good resources (except for thoughtspacezero on youtube, which got a bit difficult to understand after a few videos). Can you suggest some materials? Thanks in advance!
  19. T

    Is X Separable in a Totally Bounded Metric Space?

    Homework Statement Let (X,d) be a totally bounded metric space. Prove that X is separable Note: the definition of an epsilon-net in my book is this: A finite subset F of X is called an epsilon-net if for each x in X there is a p in F such that d(x,p) < epsilon The Attempt at a...
  20. T

    Compactness in Metrizable Spaces: Proving X is Compact with Bounded Metrics

    Homework Statement Let (X,T) be a metrizable space such that every metric that generates T is bounded. Prove that X is compact. The Attempt at a Solution I was thinking about this problem a bit before I headed off to work and wanted to get you guys' thoughts and/or ideas. At first I...
  21. C

    Is the Universe Infinite and Flat in Cosmology?

    Am i right in saying that consenses amongst the cosmological community is that the curvature of space is 0? So it is flat euclidean geometric space (I hope I am using correct terminology) which is neither +/- in curvature but exactly 0? Am I also right in saying that flat cosmological models...
  22. P

    Can Probability and Topology Combine for an Exciting Research Topic?

    I need to write a paper on something to do with (general) topology, and we are encouraged to try and relate it to something that we enjoy. I really like probability (at least basic probability + stochastic processes), and I'm wondering if someone might suggest topic(s) that might be of interest...
  23. J

    Relations between curvature and topology

    Hello, all, the most important results that I know in this topic is the Gauss-Bonnet Theorem (and hence the classification of compact orientable surfaces) and also the Poincare-Hopf index theorem. But there are still some fundamental problems I don't understand. For example, is the...
  24. Z

    Applying Algebraic Topology, Geometry to Nonabelian Gauge Theory

    I 've been reading about Homotopy , homology and abstract lie groups and diff.forms and I would like to see those beautiful ideas applied on a Nonabelian Gauge Theory . Any recommendations for a textbook that apply these ideas to gauge theory ? Text books on particle Physics and QFT do not...
  25. G

    [Topology] Accumulation points

    Homework Statement Given N = {1, 2, 3, ...} and En = {n, n+1, ...} (n in N) define a topology on N with T = {empty set, En} Determine the accumulation points of {4, 13, 28, 37}, find the closure of {7, 24, 47, 85} and {3, 6, 9, 12, ...}. Also determine the dense subsets of N. Homework...
  26. P

    Topology: Connectedness and continuous functions

    Could you please check the statement of the theorem and the proof? If the proof is more or less correct, can it be improved? Theorem Let be a topological space and be the discrete space. The space is connected if and only if for any continuous functions , the function is not onto...
  27. B

    Rainbow Spectrum Topology Map to Heightmap Grayscale.

    Hello, I am working with python's Image Library (PIL), Sympy, and Matlab. I have a topographical map of the earth, ( see 3d warehouse from google ). I am wondering if with an rgb matrix from a jpeg heightmap is traditionally the value of black and white ignored, because it seems that the...
  28. H

    Topology intervals on the real line proof

    Homework Statement a) Let I be a subset of the real line. Prove I is an interval if and only if it contains each point between any two of its points. b) Let Ia be a collection of intervals on the real line such that the intersection of the collection is nonempty. Show the union of the...
  29. T

    Classic Textbook Topology Question

    Homework Statement Prove that the topologist's comb is pathwise connected but not locally connected. Homework Equations For A = {1/n : n = 1,2,3...}, the topologist's comb (C) is defined as: C = (I X {0}) U ({0} X I) U (A X I) The Attempt at a Solution Consider the point p =...
  30. D

    Prove G is Closed: Continuous f, Hausdorff Y

    Let f: X \rightarrow Y be a function. The graph of f is a subset of X x Y given by G = {(x,f(x) | x \in X } . Show that if f is continuous and Y is Hausdorff, then G is closed in X x Y. Any tips on how to start? Is it saying that f: X \rightarrow Y = G ?
  31. F

    Proof of Topology: Compact Subsets in Open Sets

    If AxB is a compact subset of XxY contained in an open set W in XxY, then there exist open sets U in X and V in Y with AxB contained in UxV contained in W. Is this true for all spaces XxY? Or does it hold for only regular spaces?
  32. T

    Lower Limit Topology Clopen Sets

    Homework Statement Let T be the lower-limit topology on R. Is (R,T) connected? Prove your answer. The Attempt at a Solution Since there exists a proper subset V of R such that V is both open and closed (since all intervals of the form [a,b) are open and closed), then (R,T) is...
  33. Y

    Topology and the swartzschild solution - where is the mass?

    My professor and I were discussing the emergence of the Swartzschild solution from topological considerations, corresponding to the manipulations of a point singularity. He pointed out to me that mass nowhere enters into the considerations, and so classifying black holes according to mass is...
  34. P

    Recursive definition from Munkres Topology

    Hi all, just joined PF; I have a question about Munkres's Topology (2ed), Section 9 #7(c): Homework Statement Find a sequence A_1, A_2, \ldots of infinite sets, such that for each n \in \mathbb{Z_+}, the set A_{n+1} has greater cardinality than A_n. Homework Equations...
  35. T

    Topology: Homeomorphic Mapping

    Homework Statement Let X = [0,2 PI] x [0,2 PI] and let D be the partition of X that contains: -{(x,y)} when x =/= 0,2 PI and y =/= 0,2 PI -{(0,y),(2 PI,y)} for 0 <= y <= 2 PI -{(x,0),(x,2 PI)} for 0 <= x <= 2 PI Let U be the quotient topology on D induced by the natural map p: X ->...
  36. T

    What is a separable Hausdorff subspace and how can it be demonstrated?

    Homework Statement Give an example of a topological space (X,T) that is separable and Hausdorff, with a subspace (A,T_A) that is not separable. The Attempt at a Solution Let X = R and T be a topology on X whose basis elements are open intervals intersected with the rationals and...
  37. T

    .999 = 1, in descrete topology?

    When one is considering a the real numbers with the extension of an infinitesimal, implying that it is possible for a number to be the highest number lower than a number, would .999... then be the highest number less than 1? (Similar to *R, but I'm generalizing my hypothesis to include any...
  38. D

    Topology: Subset of A Continuous Function

    Homework Statement Let f be a real-valued function defined and continuous on the set of real numbers. Which of the following must be true of the set S={f(c):0<c<1}? I. S is a connected subset of the real numbers. II. S is an open subset of the real numbers. III. S is a bounded subset of the...
  39. T

    Topology: Proving non-separability

    Homework Statement Show that any countable subset of N with the discrete topology cannot be dense in N. Homework Equations Informally a set is dense if, for every point in X, the point is either in A or arbitrarily "close" to a member of A The Attempt at a Solution I was thinking...
  40. D

    Topology: two product space questions

    Greetings all, doing more problems for my test tomorrow. I'm not sure how to start these two.. 1.) I'm trying to show that if X and Y are Hausdorff spaces, then the product space X x Y is also Hausdorff. So, I know that I must have distinct x1 and x2 \in X, with disjoint neighborhoods U1...
  41. D

    Which sets are open and closed in a subspace?

    Here's two more question I'm working on in test prep. 2.) Let Y = [-1,1] have the standard topology. Which of the following sets are open in Y, and which are open in R. A= (1,1/2) \cup (-1/2,-1) B= (1,1/2] \cup [-1/2,-1) C= [1,1/2) \cup (-1/2,-1] D= [1,1/2] \cup [-1/2,-1] E= \cup...
  42. D

    Topology Questions (studying for test)

    Greetings all, I have a test upcoming next week and a lot of problems to solve. I asked in a previous thread whether or not I should just continue to adding to the thread and it seems the answer was yes. I appreciate any help! This is a tough subject. Anyways, the first one I'm working on. I...
  43. T

    Separable Hausdorff Spaces: Example with Non-Separable Subspace

    Homework Statement Give an example of a separable Hausdorff space (X,T) that has a subspace (A,T_A) that is not separable. Homework Equations A separable space is one that has a countable dense subset. The Attempt at a Solution Let (X,T) (i.e. the separable Hausdorff space) be...
  44. T

    Proving Homeomorphism between Topological Spaces (X,T) and (delta,U_delta)

    Homework Statement Let (X,T) be a topological space and let U denote the product topology on X x X. Let delta = {(x,y) in X x X : x = y} and let U_delta be the subspace topology on delta determined by U. Prove that (X,T) is homeomorphic to (delta,U_delta) The Attempt at a Solution...
  45. T

    What is an example of a separable Hausdorff space with a non-separable subspace?

    Homework Statement Give an example of a separable Hausdorff space (X,T) with a subspace (A,T_A) that is not separable. The Attempt at a Solution well since a separable space is one that is either finite or has a one-to-one correspondence with the natural numbers, the separable...
  46. M

    Topology Problem: Closure X Path-Connected?

    Hello, I have a question about topology. If X is a path-connected space then is it also true that closure X is path-connected? I think it's obvious, but I can't solve it clearly...
  47. P

    Infinite index set in product topology

    Homework Statement Let Y := \prod_{i \in I} X_i Now assume U_i \subset X_i to be open. If we take i to be infinite, \prod_{i \in I} X_i cannot be open. Why? Homework Equations The Attempt at a Solution I can't quite get my head around how to approach this problem. A...
  48. S

    Topology Help: Proving Open Sets in T[SUB]C for X and C Collection"

    let X be a set and C be a collection of subsets of X whose union equal X. let β[SUB]C the collection of all subsets of X that can be expressed as an intersection of finitely many of the sets from C. let T[SUB]C be the topology generated by the basis β[SUB]C. prove that every set in C is...
  49. E

    Topology - spaces, compactness

    Homework Statement Find a metric space and a closed, bounded subset in it which is not compact. Homework Equations N/A The Attempt at a Solution I know that a metric space is a space that has definition such that a point has a distance to any other point. However, I know a...
  50. B

    Topology: Continuous f such that f(u)>0 , prove ball around u exists such that

    Homework Statement Let O be an open subset of R^n and suppose f: O --> R is continuous. Suppose that u is a point in O at which f(u) > 0. Prove that there exists an open ball B centered at u such that f(v) > 1/2*f(u) for all v in B. Homework Equations f continuous means that for any {uk} in O...
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