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Can someone please explain to me what topology is?

  1. Dec 25, 2004 #1
    Can someone please explain to me what topology is?
    thanks
     
  2. jcsd
  3. Dec 25, 2004 #2
    For these types of inquiries, I refer to google and wikipedia.

    An intuitive explanation can be found here.
     
  4. Dec 26, 2004 #3

    mathwonk

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    it is the study of the geometry of continuity. do you know what continuity means?

    if so can you see that, from the point of view of continuity, a circle and a line are different, but a circle and a square are the same? and a line and a half circle are the same?
     
  5. Dec 26, 2004 #4
    Similarly, a human is topologically equivalent to a torus when he plugs his nose. :smile:
     
    Last edited: Dec 26, 2004
  6. Dec 26, 2004 #5
    i appreciate it.
    My grandpa said it was like geometry shapes curved on spheres, like rubber geometry. And you deal with dimensions. Is this true?
     
  7. Dec 26, 2004 #6
    ya topology is also nicknamed "rubber-sheet geometry" because if you imagine everything as being made out of rubber you could stretch/compress it into other shapes "homeomorphic" (similar-shape) to the one you start with. a topologist is someone who can't tell the difference between a doughnut & a coffee cup
     
    Last edited: Dec 26, 2004
  8. Dec 27, 2004 #7
    the coffee cup must have a handle , if it doesnt any topologist can differentiate it from a doughnut :rolleyes:

    -- AI
     
  9. Dec 27, 2004 #8

    matt grime

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    what if it were an english doughnut? (no hole, jam in the middle, only calling it english to differentiate it from more familiar to some items).
     
  10. Dec 27, 2004 #9
    we have something like this, and it's called "sufgania" (this is how you pronounce it in hebrew), but it's too much fattening, beware!!! :surprised
     
  11. Dec 27, 2004 #10
    When does one usually take topology? In college?
     
  12. Dec 27, 2004 #11
    I took it (point-set topology) second term of my second year (right after real analysis). I don't ever recall seeing algebraic topology before final year, though I could be mistaken.
     
  13. Dec 27, 2004 #12

    matt grime

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    Depends where you are. Proper topology is taught in the 2nd/3rd year of a good university (undergrad) in the UK. or the 4th year of some, and is possibly taught at US at 4th year level at a good university (eg chicago) though it is more often left to a grad school level.
     
  14. Dec 27, 2004 #13

    arildno

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    No, then we are topologically equivalent to a DOUBLE torus.

    (You've forgotten the big chute connecting your (open) mouth and ass)
     
  15. Dec 27, 2004 #14

    dextercioby

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    That reminds me of a picture and a small discussion in "A Brief History of Time" by Hawking.He gave a reasonable explanation why a dog could not exist in 2 dimensions :tongue2: .I believe it could be said for every living organism with a digestive tractum.

    Daniel.
     
  16. Dec 27, 2004 #15
    Why couldn't a dog exist in 2d ?

    it just so happens we live in 3d ? nobody knows why ?

    roger
     
  17. Dec 27, 2004 #16

    dextercioby

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    For it to exist in 2D,it must have another internal structure,i.e. the absence of the digestive tractum.Only holes that do not communicate.If it had a digestive tractum,then the dog would be made up of 2 independent areas (like 2 disjoint sets/domains) and therefore it would have to be made up of 2 independent halves of a dog.It would be just like in that sadistic joke.

    Daniel.
     
  18. Dec 28, 2004 #17

    mathwonk

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    the first encounter with topology occurs when one first has a proper definition of continuity, which may occur in the first year of calculus. the first theorem may be something like: "an increasing sequence of real numbers has a (finite) real limit if and only if the sequence is bounded above".

    topology has already begun to appear in the definition of continuity, if one has the concept of a "neighborhood" in the definition. i.e. a neighborhood of a point p, is a set of reals which contains an interval of form (p-e,p+e), for some positive e. then a function defined on the reals is continuous at p, if for every neighborhood V of f(p), there is a neighborhood U of p, such that f(U) is contained in V. This definition of continuity uses only topological properties.

    once we have continuity we can define homeomorphism. i.e. two sets are homeomorphic if there are mutually inverse mappings between them, both continuous. then topology is the study of properties which are the same for any two homeomorphic sets. for example in the reals, a set S is homeomorphic to an open interval T if and only if S is also an open interval.
     
  19. Dec 28, 2004 #18
    I don't understand. A torus has one hole in it. If you plug your nose, the only hole in your body is this very 'chute' you speak of. To be a double torus, there would have to be two holes. What is the other hole?
     
  20. Dec 28, 2004 #19
    your arm is a handle isn't it? it would be attached to your shoulder at 1 end, & your nose at the other end, and that makes a handle. so there's one hole between your arm & body, and that other hole
     
  21. Dec 28, 2004 #20

    mathwonk

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    it seems rather obvious there are at least 9 orifices in the average male body.
     
    Last edited: Dec 28, 2004
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