What is Topological: Definition and 264 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. Greg Bernhardt

    Topology Introduction to Topological Manifolds by John Lee

    Author: John M. Lee Title: Introduction to Topological Manifolds Amazon Link: https://www.amazon.com/dp/1441979395/?tag=pfamazon01-20 Prerequisities: Real Analysis course involving epsilon-delta and preferebly metric spaces, group theory Level: Grad students Table of Contents: Preface...
  2. L

    A question about multiresolution analysis (from a topological point of view)

    Hi, I have a problem understanding something This is a snapshot of a book I am reading Point no. 2 concerns me, because it looks to me like it contradicts itself, with "this or this" The first part says \sum_{j}V_j = \mathbb{L^2(R)} which, to me, looks completely equivavalent...
  3. S

    Proving Inverse Function Continuity: A Topological Challenge

    Homework Statement Prove that if the inverse of a function between topological spaces maps base sets to base sets, then the function is continuous. Homework Equations I have no idea. The Attempt at a Solution I seriously have no idea. This is for my analysis course, and I'm not...
  4. TrickyDicky

    Aharonov-Bohm topological explanation

    In trying to get the Aharonov-effect right I've found something that I'm not sure how to sort out. Briefly put my understanding of the effect is that it shows something that cannot be explained by classical physics in the sense that makes observable a classical EM global gauge transformation...
  5. C

    Exploring the Topological Cross Section in Experimental Quantum Physics

    Hello, I've found in some of the articles on experimental quantum physics the term "Topological cross section" Now I'm trying to understand what is it and in particular what the difference between topological and differential cross section? Thanks in advance for suggestions on any reading...
  6. F

    Spin Orbit Coupling leading to topological insulator behaviour

    Hi I am studying how the spin orbit interaction in certain materials can lead to topological insulator effects and realize it has something to do with the effects of the SOC on the band structure of the material (Bi2Se3), possibly due to the inversion of the valence and conduction band but I...
  7. marellasunny

    What is Topological Equivalence in Functions and Dynamical Systems?

    It would be helpful if someone could please explain topological equivalence of functions in simple words? I am working on dynamical systems and chaos theory.In the underlying material,topological equivalence has taken a more complex definition involving orbits.Please be kind enough to explain...
  8. S

    INverse of a function between topological spaces and continuity

    Homework Statement Prove that if the inverse of a function between topological spaces maps base sets to base sets, then the function is continuous. Homework Equations The Attempt at a Solution I really don't know how to do this. Wikipedia entry for 'base sets' redirects to Pokemon...
  9. A

    Could dark energy and expansion of space be just a topological effect?

    Sigh. My first post. I wrote rather long message here and as I tried posting it, "you need to login" - and it vanished. :( Anyways. I have no high physics/math education but still I consider myself enthusiasts. So be gentle! :) Consider the following "my way of filling sudokus", just thinking...
  10. H

    Lebesgue topological dimension

    Hi, I was reading the definition of dimension from the book: "Topology", Munkres, 2nd ed. Surely I don't understand, but I wonder how ℝ2 can have dimension 2. Take the open sets U_n=\{(x,y)\mid -\infty < x <\infty, n-1<y<n+1\} for every integer n. It covers the plane but its order is...
  11. G

    Topological Insulators and Inversion Symmetry

    Hi, I was curious if specific symmetries (or lack thereof) in crystal structure are necessary for the formation of topological insulators. Specifically, do we require that inversion symmetry (or inversion asymmetry) be present in the lattice in order to form the TI state? Thanks, Goalie33
  12. C

    Topological Phase: Definition & Examples

    Hi there! Can anybody tell me, if generically any system, which is solely described by a topological field theory, resides in a topological phase? I can't find any clear notion of topological phase. Only topological phase of matter, but I mean any kind of system. Thanks for your help.
  13. F

    Studying Topological QFT: A Guide

    Hello, Can anyone tell me how to go about studying Topological QFT. I am fine with QFT, Fibre bundles and currently doing Cohomology from Nakahara. Should i directly start with Witten's paper or are there any more elementary review papers? Thanks.
  14. A

    Changes in the internal structure during a Topological transform

    Changes in the internal structure during a "Topological transform" Is there any field of topology which deals with the changes in internal structure of an object when it undergoes topological transform? If I'm transforming a cube into a sphere, is there any 'field of topology' which analyze the...
  15. R

    Topological Insulators Explained: Quantum Hall Effect & More

    I'm sorry if this is in the incorrect section, but can someone please explain what topological insulators are, the quantum hall effect, how you make a topological insulator and anything else that is relevant to the topic. Thanks.
  16. Y

    What would be the pre-requisites to learn Topological Quantum Field Theory?

    Personally, I am interested in Topological Quantum Field Theory. And now I am battling against Quantum Field Theory. I am not sure how much Quantum Field Theory is needed to do Topological Quantum Field Theory. And I am not sure what should be the mathematical pre-requisites of Topological...
  17. P

    Topological sigma model, Euler Lagrange equations

    Homework Statement My question refers to the paper "Topological Sigma Models" by Edward Witten, which is available on the web after a quick google search. I am not allowed to include links in my posts, yet. I want to know how to get from equation (2.14) to (2.15). We consider a theory of maps...
  18. K

    Kitaev's Periodic Table (of Topological Insulators & SCs)

    Hi PF, I'm trying to come to grips with the work of Alexei Kitaev on applying notions from (topological) K-theory to the task of classifying phases of topological insulators and superconductors (paper here: http://arxiv.org/pdf/0901.2686v2.pdf). Despite having plenty of citations, I've yet to...
  19. M

    Prove: If (X; T1) and (Y; T2) are homeomorphic topological

    Hi, Prove: If (X; T1) and (Y; T2) are homeomorphism topological spaces and (X; T1) is disconnected then (Y; T2) is disconnected. I think I need some help with this proof Proof: Let (X, T1) be disconnected and let f be a homeomorphism. If f(X,T1) is disconnected then there exist two...
  20. marcus

    Loop Gravity as the Dynamics of Topological Defects

    There is a natural way to formulate Loop quantum geometry as the dynamics of line defects in a flat vacuum. Just under 2 months ago, I attended a 90 minute seminar talk on this at the UC Berkeley physics department. Unfortunately that talk is not online, but we do have an earlier talk given last...
  21. C

    Finite Dimensional Hausdorff Topological Space

    How do I prove that a Hausdorff topological space E is finite dimensional iff it admits a precompact neighborhood of zero?
  22. J

    A tiny topological claim in a larger proof of mine

    Homework Statement I'm writing a proof for my Real Analysis III class, and in one clause I claim that the intersection of my countably infinite set of intervals {En} where En=(1+1/2+1/3+1/4+...+1/n , ∞), has the property that the infinite intersection of all En's equals ∅ (This would be a...
  23. M

    Time reversal symmetry in Topological insulators of HgTe quantum Wells

    Hi everyone, While reading about the BHZ model used to describe HgTe quantum well topological insulators, I read at many places that the effective Hamiltonian (which is a 4 x 4 matrix) can be written in block diagonal form and the lower 2x2 block can be derived from upper 2x2 block as...
  24. M

    Does {1/n} n=1 to infinity converge? Why or why not? in a topological space

    hi, can someone please help me with this problem. Let T be the collection of all U subset R such that U is open using the usual metric on R.Then (R; T ) is a topological space. The topology T could also be described as all subsets U of R such that using the usual metric on R, R \ U is...
  25. S

    Prove that topological manifold homeomorphic to Euclidean subspace

    Homework Statement Show that every topological manifold is homeomorphic to some subspace of E^n, i.e., n-dimensional Euclidean space. Homework Equations A topological manifold is a Hausdorff space that are locally Euclidean, i.e., there's an n such that for each x, there's a neighborhood...
  26. F

    Topological Insulator: 100% Spin Polarization & Transport Properties

    Why is it so important to claim that the topologically protected surface states are 100% spin polarized. Is there any connection between the degree of polarization and for instance transport properties, like the absent backscattering of these states at impurities?
  27. conquest

    Glueing together normal topological spaces at a closed subset

    Hi all! My question is the following. Suppose we have two normal topological spaces X and Y and we have a continuous map from a closed subset A of X to Y. Then we can construct another topological space by "glueing together" X and Y at A and f(A). By taking the quotient space of the disjoint...
  28. S

    Proof about countable base of topological space

    Homework Statement Prove that if a topological space has a countable base, then all bases contain a subset which is a countable base Homework Equations A base is a subset of the topological space such that all open sets can be constructed from unions and finite intersections of open sets...
  29. B

    Is Boundedness Applicable to Topological Spaces?

    Is there such thing as a bounded topological space? Or does 'boundedness' only apply to metric spaces?
  30. I

    Defining Topological Spaces help

    Homework Statement Let ℝ be set of real numbers. Which of the following collection of subsets of ℝ defines a topology in ℝ. a) The empty set and all sets which contain closed interval [0,1] as a subset. b)R and all subsets of closed interval [0,1]. c)The empty set, ℝ and all sets...
  31. A

    How to prove that a topological space is non-hausdorff?

    Is there a method or an algorithm or a theorem or whatever that tells us a topological space is not a Hausdorff space?
  32. J

    Definition of a Topological Space

    Just a small (and, really, quite useless) little nugget here: In the definition of a topological space, we require that arbitrary unions and finite intersections of open sets are open. We also need that the whole space and the empty set are also open sets. However, this last condition is...
  33. atyy

    Is N = 4 gauge theory on S4 an effective description of topological gravity?

    It's often been hoped that gravity is topological, eg. Witten, Xu, Gu & Wen, Rovelli. Heckman & Verlinde make a new suggestion: http://arxiv.org/abs/1112.5210 Instantons, Twistors, and Emergent Gravity "The basic idea is to view N = 4 gauge theory on S4 as an effective low energy description of...
  34. R

    Topological dimension of the image of a smooth curve in a manifold

    Here is the situation I am concerned with - Consider a smooth curve g:[0,1] \to M where M is a topological manifold (I'd be happy to assume M smooth/finite dimensional if that helps). Let Im(g) be the image of [0,1] under the map g . Give Im(g) the subspace topology induced by...
  35. T

    Convexity and Topology: Are They Related?

    Hello! It's not really a homework problem, but it should be able to help me with something. I was just wondering: if two sets are Homeomoprh (topologically), and one of them is convex, does it mean that the other one is convex as well? Thanks a lot! Tomer.
  36. N

    What do topological insulators have to do with hall currents?

    Hello, So a topological insulator can induce a magnetic field when an electric charge is near to it (I can give a reference if necessary), but the thing is, the paper interprets the origin of this magnetic field as being the hall currents on the surface of the topological insulator. Now I...
  37. L

    Measurable spaces vs. topological spaces

    Dear All, It sounds a strange question, we know that the measure theory is the modern theory while the topological spaces is the classical analysis (roughly speaking). And measure theory solves some problems in the classical analysis. My first question is that right? Second, Is every...
  38. R

    A Question about Topological Connectivity

    I am not a Mathematician, and I've been pondering this idea for years. I will try to describe it intelligibly. Imagine a Ring. It has three "Inputs" and three "Outputs". Any of the three "Outputs" takes you to a different Ring with three Entrances and three Exits. You cannot return to the...
  39. F

    Cauchy sequence and topological problems

    [PLAIN]http://img805.imageshack.us/img805/1575/photo0138d.jpg Hi, on thursday, i have exam of advance calculus and i could not solve two problem in study sheet given by İnstructor. By 9 question, i prove by add an subtract XnY to |XnYn-XY| and i have found that |Xn(Yn-Y)+...
  40. S

    Is Discreteness A Topological Property?

    Is discreteness a topological property? Hey guys. I'm currently in an advanced calculus course (not topology), and the only mention of topological property in my text is that it's a property that is conserved under continuity. This section is just a brief primer on compact sets and...
  41. U

    Why topological insulators are topological?

    Hi, this is my first post here! I've been studying about topological insulators, but still I can't understand why this materials are called topological, I've read about topological analogy between the donut and the coffee mug and the smooth changes on the Hamiltonian, but I can't get the full...
  42. Fredrik

    Generalizations (from metric to topological spaces)

    This is kind of a weird question. I like to think about how I would explain things to other people, and I realized that I don't know a great way to explain in general how terms defined in the context of metric spaces are generalized to the context of topological spaces. It's not at all difficult...
  43. Z

    Difference between sigma algebra and topological space

    What is the difference between sigma algebra and topological space topological space?also what is the meaning of algebra on a set? the definitions are very similar except that in the case of sigma algebra the union is taken to include infinite number of sets .right?
  44. A

    Markov Random Topological Spaces

    The Markov chain, as you know, is a sequence of random variables with the property that any two terms of the sequence X and Y are conditionally independent given any other random variable Z that is between them. This sequence (which is in fact a family, indexed by the naturals) can and has been...
  45. Rasalhague

    Topological and neighbourhood bases

    I'm trying to follow a proof in this video, #20 in the ThoughtSpaceZero topology series. I get the first part, but have a problem with second part, which begins at 8:16. Let there by a topological space (X,T). Let x denote an arbitrary element of X. Definition 1. Topological base. A set B...
  46. A

    Topological classification of defects

    Please help somebody on this problem... When we topologically classify the defects in ordered media, we consider the character of the fundamental group of the associated order parameter space. To construct those groups, we circumscribe the line defects by circles and the point defects by...
  47. L

    Proving Compactness of a Topological Group Using Subgroups and Quotient Spaces

    Hello! Could anyone help me to resolve the impasse below? Th: Let G be a topological group and H subgroup of G. If H and G/H (quotient space of G by H) are compact, then G itself is compact. Proof: Since H is compact, the the natural mapping g of G onto G/H is a closed mapping...
  48. I

    How to show induced topological space

    I am beginning to read about the topology, I met a problem puzzled me for a while. If Y is a topological space, and X\subset Y, we can make the set X to be a topological space by defining the open set for it as U\cap X, where U is an open set of Y. I would like to show that this indeed...
  49. L

    Given Any Measurable Space, Is There Always a Topological Space Generating it?

    As well known, for any topological space (X,T), there is a smallest measurable space (X,M) such that T\subset M. We say that (X,M) is generated by (X,T). Right now, I was wondering whether the "reverse" is true: for any measurable space (X,M), there exists a finest topological space (X,T) such...
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