Topology Definition and 816 Threads

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. nightingale123

    Topology: Determine whether a subset is a retract of R^2

    Homework Statement Let ##X=([1,\infty)\times\{0\})\cup(\cup_{n=1}^{\infty}\{n\}\times[0,1])## and ##Y=((0,\infty)\times\{0\})\cup(\cup_{n=1}^{\infty}\{n\}\times[0,1])## ##a)##Find subspaces of of the euclidean plane ##\mathbb{R}^2## which are homeomorphic to the compactification with one...
  2. Arman777

    I Topology of the Universe and infinities

    There are couple things that keep me questioning about the nature of the universe. Let me start from the begining. Big Bang happened and our universe was created, and from now on let us suppose that the universe is infinite in size. Later on, the universe expands and after a time we can see...
  3. poincare

    What Are the Prerequisites for Nakahara's Geometry, Topology and Physics?

    For anyone who is familiar with the book "Geometry, Topology and Physics" by Nakahara, what do you think are the mathematical and physics prerequisites for this book ?
  4. nightingale123

    Topology: Understanding open sets

    Homework Statement We define ##X=\mathbb{N}^2\cup\{(0,0)\}## and ##\tau## ( the family of open sets) like this ##U\in\tau\iff(0,0)\notin U\lor \exists N\ni : n\in\mathbb{N},n>N\implies(\{n\}\times\mathbb{N})\backslash U\text{ is finite}## ##a)## Show that ##\tau## satisfies that axioms for...
  5. nightingale123

    Finding homeomorphism between topological spaces

    Homework Statement show that the two topological spaces are homeomorphic. Homework Equations Two spaces are homeomorphic if there exists a continuous bijection with a continuous inverse between them The Attempt at a Solution I have tried proving that these two spaces are homeomorphic...
  6. M

    Mind reading of Cup Yacht Designer Herreshoff by Topology

    Homework Statement There was the times 100 years ago, N.Herreshoff was designing giant J Boats, America s Cup boats by only carving a wood piece in few hours ,without drawing calculating anything and builders were measuring the wooden half model and building a multi million dollar yacht wins...
  7. L

    A Can I change topology of the physical system smoothly?

    I am encountering this kind of problem in physics. The problem is like this: Some quantity ##A## is identified as a potential field of a ##U(1)## bundle on a space ##M## (usually a torus), because it transforms like this ##{A_j}(p) = {A_i}(p) + id\Lambda (p)## in the intersection between...
  8. FallenApple

    I Need to know the Topology on the Space of all Theories?

    So according to Dr. Frederic Schuller, we need to at least know the topology on the space of all theories in order to know that we are getting closer to the truth. I take that this is because we need to know the topology to establish that convergence is possible in the first place. How does this...
  9. L

    A Can I find a smooth vector field on the patches of a torus?

    I am looks at problems that use the line integrals ##\frac{i}{{2\pi }}\oint_C A ## over a closed loop to evaluate the Chern number ##\frac{i}{{2\pi }}\int_T F ## of a U(1) bundle on a torus . I am looking at two literatures, in the first one the torus is divided like this then the Chern number...
  10. dkotschessaa

    I Passed My Master's Qualifier - Dave K

    Holy bleeping bleepity bleep bleep! I now will have a Master's in mathematics - and a lot of extra time (for my family of course). -Dave K
  11. L

    A Integration along a loop in the base space of U(1) bundles

    Let ##P## be a ##U(1)## principal bundle over base space ##M##. In physics there are phenomenons related to a loop integration in ##M##, such as the Berry's phase ##\gamma = \oint_C A ## where ##C(t)## is a loop in ##M##, and ##A## is the gauge potential (pull back of connection one-form of...
  12. dextercioby

    I Continuity of the determinant function

    This is something I seek a proof of. Theorem: Let ## \mbox{det}:\mbox{Mat}_{n\times n}(\mathbb{R}) \rightarrow \mathbb{R}## be the determinant function assigned to a general nxn matrix with real entries. Prove this mapping is continuous. My attempt. Continuity must be judged in...
  13. ohwilleke

    I Geometry of GR v. Spin-2 Massless Graviton Interpretation

    In classical general relativity, gravity is simply a curvature of space-time. But, a quantum field theory for a massless spin-2 graviton has as its classical limit, general relativity. My question is about the topology of space-time in the hypothetical quantum field theory of a massless spin-2...
  14. Auto-Didact

    A Algebraic topology applied to Neuroscience

    Eugene Wigner once famously talked about the "unreasonable effectiveness of mathematics" in describing the natural world. Today again we are seeing this in action in particular with regard to the description of the biological brain from the perspective of neuroscience. Researchers from the Blue...
  15. A

    A Are all edge states topological?

    Hey am new to this forum but I have a question regarding topologically protected states.. Let's suppose we have a 1D gapped system divided two to distinct regions that have different periodicity or different properties and that at the centre, where the two regions 'meet' states appear in the...
  16. T

    Booster transformer topology for transmission application

    Hi, Regarding transmission line booster transformer topologies I'm curious as to what would happen over all the possible permutations. I refer you to the following: http://top10electrical.blogspot.com.au/2015/03/booster-transformer.html I presume that in real life the booster transformers...
  17. G

    Best Written High School Physics Text Books (SAT)

    Advanced Physics (Advanced Science) by Steve Adams & Jonathan Allday from OUP Oxford: and Physics (Collins Advanced Science) 3rd Edition by Kenneth Dobson from Collins Educational: http://www.amazon.com/dp/0007267495/?tag=pfamazon01-20 Does anyone know any of these books? I find them very...
  18. Oats

    Topology Willard's General Topology vs Dugundji's Topology

    Hello, I have read a fair chunk of Munkres' Topology book and took a short introductory course during undergraduate, but I would like to learn point-set topology a little better. I have quite a bit of mathematical maturity, so that isn't an issue for me. I had a larger list of potential books to...
  19. S

    Simple open set topology question

    Homework Statement [/B] Is {n} an open set?Homework Equations [/B] To use an example, for any n that is an integer, is {10} an open set, closet set, or neither?The Attempt at a Solution [/B] I say {10} is a closed set, because it has upper and lower bounds right at 10; in other words, it is...
  20. davidge

    I Math of Relativity: Topology Needed?

    How much of topology one needs to know to have a great knowledge of the math of Special and General Relativity? I'm asking this because I'm interested in really look at the theory of Relativity with the eyes of a mathematician. I suppose that just knowing what a manifold is or even what a...
  21. KennethK

    How to show simplicial complex is Hausdorff?

    Homework Statement Prove that any simplicial complex is Hausdorff. Homework EquationsThe Attempt at a Solution I have proved that for any finite simplicial complex, it is metrizable and hence Hausdorff. How to show the statement for infinite case?
  22. mr.tea

    Finding a Matrix to Connect Equivalence Classes in Quotient Space

    Homework Statement (part of a bigger question) For ##x,y \in \mathbb{R}^n##, write ##x \sim y \iff## there exists ##M \in GL(n,\mathbb{R})## such that ##x=My##. Show that the quotient space ##\mathbb{R}\small/ \sim## consists of two elements. Homework EquationsThe Attempt at a Solution Well...
  23. JuanC97

    I Understanding Co-vectors to Dual Spaces and Linear Functionals

    Hi, I'm trying to get a deeper understanding of some concepts required for my next semesters but, sadly, I've found there are lots of things that are quite similar to me and they are called with different names in multiple fields of mathematics so I'm getting confused rapidly and I'd appreciate...
  24. S

    I Definition of Topology - What Does {##U_\alpha | \alpha \in I##} Mean?

    Hello! I just started reading an introductory book about topology and I got a bit confused from the definition. One of the condition for a topological space is that if ##\tau## is a collection of subsets of X, we have {##U_\alpha | \alpha \in I##} implies ##\cup_{\alpha \in I} U_\alpha \in \tau...
  25. F

    Topology by Simmons Problem 1.3.3

    Homework Statement Let ##X## and ## Y## be non-empty sets, ##i## be the identity mapping, and ##f## a mapping of ##X## into ##Y##. Show the following a) ##f## is one-to-one ##~\Leftrightarrow~## there exists a mapping ##g## of ##Y## into ##X## such that ##gf=i_X## b) ##f## is onto...
  26. F

    Topology by Simmons Problem 1.2.1

    Homework Statement If ##\bf{A}## ##= \{A_i\}## and ##\bf{B}## ##= \{B_j\}## are two classes of sets such that ##\bf{A} \subseteq \bf{B}##, show that ##\cap_j B_j \subseteq \cap_i A_i## and ##\cup_i A_i \subseteq \cup_j B_j## Homework EquationsThe Attempt at a Solution Since ##\bf{A} \subseteq...
  27. D

    Shim Inductor in Phase Shifted Full Bridge topology

    What is the purpose of the shim inductor and how exactly does it function in PSFB topology? I noticed that I had dramatically improved efficiency when I added a shim inductor to my circuit, not too sure how or why this works though.
  28. mr.tea

    Topology Self-Study Topology for Scientists

    Hi, I would like to receive suggestions regarding (general) topology textbook for self-study. I have background in real analysis, linear and abstract algebra. I am not afraid of a challenging book. Thank you!
  29. sa1988

    "Show B is closed if and only if...." (More Topology....)

    Homework Statement Let ##A## be a subspace of a topological space ##X##, and let ##B\subset A##. Show that ##B## is closed if and only if there exists a closed subset ##C \subset X## such that ##B = C \cap A## Homework EquationsThe Attempt at a Solution So I've started by just drawing the...
  30. sa1988

    Determine all of the open sets in given product topology

    Homework Statement ##X = \{1,2,3\}## , ##\sigma = \big\{\emptyset , \{1,2\}, \{1,2,3\} \big\}##, topology ##\{X, \sigma\}## ##Y = \{4,5\}## , ##\tau = \big\{\emptyset , \{4\}, \{4,5\} \big\}##, topology ##\{Y, \tau\}## ##Z = \{2,3\} \subset X## Find all the open sets in the subspace topology...
  31. B

    Coarsest Topology With Respect to which Functions are Continuous

    Homework Statement See attached picture.Homework EquationsThe Attempt at a Solution At the moment, I am dealing with part (a). What I am perplexed by is the ordering of the parts. If the subbasis in part (b) does indeed generate this coarsest topology, why wouldn't showing this be included in...
  32. sa1988

    Are the following subsets open in the standard topology?

    Homework Statement Determine whether the following subsets are open in the standard topology: a) ##(0,1)## b) ##[0,1)## c) ##(0,\infty)## d) ##\{x \in (0,1) : \forall n \in \mathbb{Z}^{+}## ##, x \not= \frac{1}{n}\} ## Homework EquationsThe Attempt at a Solution a) ##(0,1)## is open because...
  33. B

    Dictionary Order Topology on ##\mathbb{R}^2## Metrizable?

    Homework Statement I am trying to show that there exists a metric on ##\mathbb{R}^2## that induces the dictionary order topology on the plane. Homework EquationsThe Attempt at a Solution If I recall correctly, vertical intervals in the plane form basis elements for the dictionary order...
  34. C

    Is Set S Open in R3? A Proof by Using Open Discs

    Homework Statement I have a set I = {x from R3 : x1<1 v x1>3 v x2<0 x x3>-1} Homework Equations Open disc B (x,r) (sqrt (x-x0)^2 + (y-y0)^2) < r The Attempt at a Solution I have done, for example by x1<1, that let r = 1-x1 Then sqrt ((x-x1)^2 + (y-y1)^2) < sqrt (x-x1)^2) < r = 1-x1 So |x-x1|...
  35. Alfreds9

    Finding the acoustic point in a valley

    Hello, I have a practical problem, I'd like to find the "best" spot to hear sounds in a valley (forgive me if "acoustic point" isn't an appropriate term, I just couldn't come up with anything better and scrolling an acoustics text didn't help), or at least a non-blind spot (one which instead...
  36. C

    How to prove a set is a bounded set?

    1. I have to show that S1 = {x ∈ R2 : x1 ≥ 0,x2 ≥ 0,x1 + x2 = 2} is a bounded set.2. So I have to show that sqrt(x1^2+x2^2)<M for all (x1,x2) in S1.3. I have said that M>0 and we have 0<=x1<=2 and 0<=x2<=2. And x2 = 2-x1 We can fill in sqrt(x1^2 + (2-x1)^2) = sqrt (0^2 + (2-0)^2) = 2 < M = 3...
  37. T

    I Interior and closure in non-Euclidean topology

    Hello everyone, I was wondering if someone could assist me with the following problem: Let T be the topology on R generated by the topological basis B: B = {{0}, (a,b], [c,d)} a < b </ 0 0 </ c < d Compute the interior and closure of the set A: A = (−3, −2] ∪ (−1, 0) ∪ (0, 1) ∪ (2, 3) I...
  38. T

    I Understanding the product topology

    I am having some trouble visualising the following problem and I hope someone will be able to help me: Let (X, dx) and (Y,dy) be metric spaces and consider their product topology X x Y (T1) and the topology T2 induced by the metric d((x1,y1),(x2,y2)) = max(dx(x1,x2),dy(y1,y2)) so the maximum of...
  39. V

    A Question about Berry phase in 1D polyacetylene

    Hi. I'm taking a look at some lectures by Charles Kane, and he uses this simple model of polyacetylene (1D chain of atoms with alternating bonds which give alternating hopping amplitudes) [view attached image]. There are two types of polyacetylene topologically inequivalent. They both give the...
  40. L

    A A question about split short exact sequence

    I am looking at a statement that, for a short exact sequence of Abelian groups ##0 \to A\mathop \to \limits^f B\mathop \to \limits^g C \to 0## if ##C## is a free abelian group then this short exact sequence is split I cannot figured out why, can anybody help?
  41. B

    Proving a Certain Set is Closed in the Uniform Topology

    Homework Statement Let ##Q = \{(x_1,x_2,...,) \in \mathbb{R}^\omega ~|~ \lim x_n = 0 \}##. I would like to show this set is closed in the uniform topology, which is generated by the metric ##\rho(x,y) = \sup d(x_i,y_i)##, where ##d## is the standard bounded metric on ##\mathbb{R}##. Homework...
  42. Lucas SV

    I Metrics which generate topologies

    Given a topological space ##(\chi, \tau)##, do mathematicians study the set of all metric functions ##d: \chi\times\chi \rightarrow [0,\infty)## that generate the topology ##\tau##? Maybe they would endow this set with additional structure too. Are there resources on this? Thanks
  43. B

    Convergence of a Sequence in a Finer Topology

    Homework Statement Clearly if a sequence of points ##\{x_n\}## in some space ##X## with some topology, then the sequence will also converge when ##X## is endowed with any coarser topology. I suspect this doesn't hold for endowment of ##X## with a finer topology, since a finer topology amounts...
  44. F

    Butterworth filter via Cauer topology

    Hi all. I would like to ask some explanation regarding how to obtain L and C values for a butterworth filter using the first Cauer topology. I will consider a normalized low pass filter. (Link added by Mentor) https://en.wikipedia.org/wiki/Butterworth_filter What I don't understand is this...
  45. C

    I What chapters of Munkres Topology are essential?

    I would like to know which chapters in Munkres Topology textbook are essential for a physicist. My background in topology is limited to the topology in baby Rudin, Kreyzig's functional, and handwavy topology in intro GR books. I feel like the entire book isn't necessary, but I could be mistaken.
  46. GEOPHILE2

    A Handlebody and Knot composed of polygons

    Has anyone seen any literature related to the construction of topological structures with geometric composition as seen below?
  47. GEOPHILE2

    Is it appropriate to share personal content on this platform?

    Hi, I'm a new member and not sure if it is ok to post a link to my blog or youtube channel. So I thought I would ask first before doing so. Is that ok or should I do it someplace else?
  48. M

    I Does global topology lead to a preferred frame in SR?

    According to this author, http://www.math.uic.edu/undergraduate/mathclub/talks/Weeks_AMM2001.pdf, a locally Minkowski spacetime with a nontrivial global topology may have a preferred inertial frame, in the sense that hypersurfaces of constant time can only be defined using particular time...
  49. I

    Proving that three closed orbits must contain a fixed point

    A smooth vector field on the phase plane is known to have exactly three closed orbit. Two of the cycles, C1 and C2 lie inside the third cycle C3. However C1 does not lie inside C2, nor vice-versa. What is the configuration of the orbits? Show that there must be at least one fixed point bounded...
  50. V

    I Can a CW complex exist without being a Hausdorff space?

    I am with a query about cw complex. I was thinking if is possible exist a cw complex without being of Hausdorff space. Because i was thinking that when you do a cell decomposition of a space (without being of Hausdorff) you do not obtain a 0-cell. If can exist a cw complex with space without...
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