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Poincaré Conjecture May Be Solved

Flamerule writes "The New York Times is now reporting that Dr. Grigori (Grisha) Perelman, of the Steklov Institute of Mathematics of the Russian Academy of Sciences in St. Petersburg, appears to have solved the famous Poincaré Conjecture, one of the Clay Institute's million-dollar Millennium Prize problems. I first noticed a short blurb about this at the MathWorld homepage last week, but Google searches have revealed almost nothing but the date and times of some of his lectures this month, including a packed session at MIT (photos), in which he reportedly presented material that proves the Conjecture. More specifically, the relevant material comes from a paper ("The entropy formula for the Ricci flow and its geometric applications") from last November, and a follow-up that was just released last month."

29 of 284 comments (clear)

  1. Cool. by Anonymous Coward · · Score: 3, Funny

    Only two years more of eating noodles before he's rich!

  2. What about the Dunwoody paper? by Glyndwr · · Score: 5, Interesting

    The link to mathworld.wolfram.com from the post says:

    In April 2002, M. J. Dunwoody produced a five-page paper that purports to prove the conjecture. However, according to the rules of the Clay Institute, the paper must survive two years of academic scrutiny before the prize can be collected.

    So, why the excitment about this later Perelman paper? Has the Dunwoody paper been debunked?

    --
    You win again, gravity!
    1. Re:What about the Dunwoody paper? by Darnit · · Score: 4, Informative

      Dunwoody

      It seems as if he missed a step and couldn't figure it out.

    2. Re:What about the Dunwoody paper? by rasafras · · Score: 5, Informative

      It doesn't appear that the paper will survive the two years...

      From the site:
      It is unclear as of this writing if Dunwoody's proof will last even a fraction of that duration.

      In fact, it appears that the purported proof has already been found lacking, judging by the facts that (1) the abstract begins, "We give a prospective [italics added] proof of the Poincaré Conjecture" and (2) the revised April 11 version of the preprint contains a small but significant change in title from "A Proof of the Poincaré Conjecture" to "A Proof of the Poincaré Conjecture?" In particular, a critical step in the paper appears to remain unproven, and Dunwoody himself does not see how to fill in the missing proof.

    3. Re:What about the Dunwoody paper? by King+Babar · · Score: 5, Informative
      So, why the excitment about this later Perelman paper? Has the Dunwoody paper been debunked?

      A gap or three in the proof were found within days, and a mathematician friend of mine reported that it didn't look like solutions to these problems were immediately forthcoming.

      The excitement about this paper comes from the fact that the guy who did the work has come up with impressive results in the past, builds on important and cutting edge work, and seems to have a really thorough command of the potential difficulties. (In other words, when he is asked questions about the tricky points, he immediately responds with what look like strong and well-thought-out answers.) For that matter, his work claims to prove a more general conjecture of which Poincare is a special case, and so this work could have more general significance to many other problems, even if there turns out to be a glitch or two in this iteration of the proof.

      It's a very hard problem, and this answer could be wrong, too. But there's a big difference between tossing a paper up on a preprint server and giving a lecture at MIT where nobody can (yet) touch you. :-)

      --

      Babar

    4. Re:What about the Dunwoody paper? by Eccles · · Score: 5, Funny

      So, why the excitment about this later Perelman paper? Has the Dunwoody paper been debunked?

      The part of the proof where it says "then a miracle occurs..." is being questioned by numerous mathematicians.

      --
      Ooh, a sarcasm detector. Oh, that's a real useful invention.
  3. Explanation by MaestroSartori · · Score: 5, Informative
    Shamelessly stolen from here:

    If we stretch a rubber band around the surface of an apple, then we can shrink it down to a point by moving it slowly, without tearing it and without allowing it to leave the surface. On the other hand, if we imagine that the same rubber band has somehow been stretched in the appropriate direction around a doughnut, then there is no way of shrinking it to a point without breaking either the rubber band or the doughnut. We say the surface of the apple is "simply connected," but that the surface of the doughnut is not. Poincaré, almost a hundred years ago, knew that a two dimensional sphere is essentially characterized by this property of simple connectivity, and asked the corresponding question for the three dimensional sphere (the set of points in four dimensional space at unit distance from the origin). This question turned out to be extraordinarily difficult, and mathematicians have been struggling with it ever since.


    Now, can someone tell me what practical applications there might be of this? Or is it strictly an abstract concept?
    1. Re:Explanation by jkramar · · Score: 4, Funny

      Silly people... this is TOPOLOGY! It's not meant for people to USE it! It's just for mathematicians to RUMINATE UPON!

      Has Fermat's Last Theorem actually been used in practical applications? I don't think so...

      --

      true && more || less
    2. Re:Explanation by Vann_v2 · · Score: 5, Insightful

      That's not really fair. There is a lot of mathematics that is useful, especially to scientists, but something like Fermat is just one of those mathematical problems which are interesting because 1) they look very simple, but 2) turn out to be maddeningly difficult to prove. To say Fermat, which is basically a mathematical problem akin to getting Linux running on your toaster, is indicative of the field of mathematics is unfair.

    3. Re:Explanation by CommieLib · · Score: 4, Funny

      Mmmmm...hypothetical donut...

      --
      If your bitterest enemies are people who hack the heads off civilians, then I would say you're doing something right.
    4. Re:Explanation by jalet · · Score: 5, Funny

      > Now, can someone tell me what practical
      > applications there might be of this?

      An application would be to make better doughnuts, I suppose.

      --
      Votez ecolo : Chiez dans l'urne !
    5. Re:Explanation by Enonu · · Score: 3, Funny

      How can you break the rubber band in order to get the doughnut to go to a point without breaking the doughnut too?

    6. Re:Explanation by Gleef · · Score: 3, Informative

      Some uses for topology:
      http://www22.pair.com/csdc/car/carhomep.htm

      Granted, none of this is stuff I would expect a gas station attendant to be playing with, but it's apparently increasingly important for researchers and engineers.

      --

      ----
      Open mind, insert foot.
  4. Google Partner Link by Anonymous Coward · · Score: 3, Informative

    For the lazy/paranoid.

  5. What's that conjecture again? by n3k5 · · Score: 4, Informative
    for the first time in ages, I'm looking forward to the discussion on this, in the hope that someone explains it in a manner I can understand
    The explanation in the article is not too bad; the Wikipedia contains a better explanation:
    [The Poincaré] conjecture is that every simply connected compact 3-manifold without boundary is homeomorphic to a 3-sphere.

    Loosely speaking, this means that every 3-dimensional object that has a set of sphere-like properties can be stretched or squeezed until it is a 3-sphere without breaking it. Note that a 3-sphere consists of all those points in 4-dimensional space R4 that have a distance of 1 from the origin.
    --
    but what do i know, i'm just a model.
    1. Re:What's that conjecture again? by Alsee · · Score: 5, Informative

      It's so simple when you put it in plain english ...
      [/sarcasm]


      Ok, try this:

      We long ago proved that an ordinary sphere is the only shape in 3 dimentions with no holes in it.

      Note that the "shape" is "made of clay". You are allowed to stretch it, squish it, and bend it all you want. You aren't allowed to cut it or put a hole in it. And you can't "meld" parts togther.

      A coffee cup is the same "shape" as a donut because you can smoothly "flow" the cup part into the handle and you get a donut.

      What they just proved is that a 4-dimentional sphere is the only shape with no holes in it.

      So what? Well if you have some wierd complex 4 dimentional "thing" and you know it doesn't have any holes in it then you now know it has to be equal to a sphere. It SEEMS obvious, but it was still important to prove. It is important for many other proofs.

      Better?

      -

      --
      - - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
  6. Re:Y'know by LordYUK · · Score: 4, Funny

    "...in the hope that someone explains it in a manner I can understand"

    You're new here, arent you?

    --
    This is my sig. Its pathetic.
  7. Now THATS Patience... by drgroove · · Score: 4, Interesting

    "Though his early work has earned him a reputation as a brilliant mathematician, Dr. Perelman spent the last eight years sequestered in Russia, not publishing."

    "However, according to the rules of the Clay Institute, the paper must survive two years of academic scrutiny before the prize can be collected."

    So, all told, Perelman is going to wait a total of 10 years from the time he started to work on the solution to the Conjecture, to the time where the scientific community lets him know if his answer is correct. Wow.

  8. Poincare Conjecture Solved Ages Ago by The+Real+Minister · · Score: 5, Funny
  9. Now I Understand... by masq · · Score: 5, Funny
    ... why we love talking about Linux so much - It's so damn USER-FRIENDLY compared to other geek pursuits!
    We present a monotonic expression for the Ricci flow, valid in all dimensions and without curvature assumptions. It is interpreted as an entropy for a certain canonical ensemble. Several geometric applications are given. In particular, (1) Ricci flow, considered on the space of riemannian metrics modulo diffeomorphism and scaling, has no nontrivial periodic orbits (that is, other than fixed points); (2) In a region, where singularity is forming in finite time, the injectivity radius is controlled by the curvature; (3) Ricci flow can not quickly turn an almost euclidean region into a very curved one, no matter what happens far away. We also verify several assertions related to Richard Hamilton's program for the proof of Thurston geometrization conjecture for closed three-manifolds, and give a sketch of an eclectic proof of this conjecture, making use of earlier results on collapsing with local lower curvature bound.
  10. sigh by danro · · Score: 5, Insightful

    Silly people... this is TOPOLOGY! It's not meant for people to USE it! It's just for mathematicians to RUMINATE UPON!
    Has Fermat's Last Theorem actually been used in practical applications? I don't think so...


    If everyone thought like you we'd still be living in caves.
    Just because practical applications aren't totally obvious for a layman (or even a matematician) doesn't mean this will never be of practical use.
    Even if no practical applications are ever found, this proof (if it survives peer review) may well pave the way for something else that is immensly useful.
    There's just no way to tell right now.

    --

    "First lesson," Jon said. "Stick them with the pointy end."
  11. Re:What is it ? (Translation to make it easier) by MarvinMouse · · Score: 5, Informative

    translation to make it easier.

    basically all the poincare conjecture says is that if you have a 3 dimensional figure which is closed (therefore, it it bounded (doesn't go off to infinity in either direction), and doesn't have any "holes" in it (like a donut)) then you can take every point and map it to a point in an equivalent sphere without losing continuity (therefore, everypoint will have the same "neighbourhood" of points as it had in the initial shape.)

    ie. You can map a cube into a sphere, or a dodecahedron, or a weird globlike thing that doesn't fold back on itself, or a whole piece of paper (without holes), or a pencil, or a lot of different figures.

    As well, this conjecture also handles figures with holes in them (like donuts), and maps them all to simpler figures.

    It's a very simple concept, but has been incredibly hard to prove, and what makes this conjecture even more frustrating is the fact that 1 and 2-dimensional forms of this conjecture were incredibly easy to prove, as well as 4 and up have been solved, and were reasonably easy as well. Yet for some reason the 3 dimensional version does not lend itself easily to a simple proof.

    Everyone generally believes this is true, but no one has been able to prove or disprove it.

    If proven, this is an important aspect of topology, because then we can map all n-dimensional figures to a simpler form (like a sphere) and know that the continuity and general structure of the figure will remain the same.

    --
    ~ kjrose
  12. Wait for it wait for it.... by I+Want+GNU! · · Score: 4, Insightful

    Mathematical rigor demands we see the proof first. One decade ago Wiles thought he solved Fermat's Last Theorem but a mistake was found and worked again for several months before ultimately solving it. Faulty proofs are made all the time. Until it undergoes peer review I will be very skeptical.

  13. Re:Donuts, apples, I'm hungry by override11 · · Score: 4, Funny

    Only a specific subset of 3-dimensional objects have holes or cavities that are facinating

    Women, right???

    --
    No I didnt spell check this post...
  14. Perl? by comet_11 · · Score: 5, Funny

    I swear that looks like perl.

    --
    By reading this comment, you immediately waive any and all rights regarding it.
  15. Actually, Perelman is claiming much more... by Anonymous Coward · · Score: 5, Informative
    Perelman isn't claiming just to have proved the Poincare Conjecture -- he's claiming to have proved the Thurston's Geometrization Conjecture, a much more general (and harder to explain) result. Basically, while the Poincare Conjecture just says things about 3-spheres (namely every "simply-connected" 3-manifold is a 3-sphere), the Geometrization Conjecture says that _any_ compact Riemannian 3-manifold is built in a specific way from a handful of basic building blocks (the important thing here is that you're not just considering the manifold structure, but the metric structure as well).

    Anyway, if true, this is kind of like Wiles proof of Fermat's Last Theorem -- proving an old conjecture by proving a more general (and more modern) one (in Wiles case, it was proving part of Taniyama-Shimura).

  16. Practical Applications? by lildogie · · Score: 3, Insightful

    > Now, can someone tell me what practical applications
    > there might be of this? Or is it strictly an abstract concept?

    Speaking as a layman, the practical application of these sorts of proofs is that you can use them to prove equivalent, more practical questions.

    One of the references in another comment explained that this conjecture has been proved for all other dimensions, and this 3-sphere seems to be a special case, as far as proof is concerned.

    If the Poincare' conjecture were proved, then the general case could be solved. After that, "simply" proving that another hard problem is equivalent to the Poincare' conjecture is enough to prove that other problem.

    Now, I've heard the problem described with a lasso instead of with a rubber band. I can imagine times when I'd really like to know when my lasso is going to close around something or if it's just going to slip off ;-)

  17. Re:Explanation and George Boole by SystematicPsycho · · Score: 4, Insightful

    Are you on a computer right now? Ever heard of a guy called George Boole? Does a "boolean" sound familiar? Well you see, this guy called George Boole he hated mathematicians so much he decided to invent this thing called Boolean Logic. You know the, 1 & 1 == 1, 1 || 0 == 0 stuff? As it turns out it was totally useless and that's what he intended, to invent something mathematically correct that is totally useless. So thanks to George Boole for accidentally inventing the foundation of computer architecture, logic gates and boolean logic - and he has something to do with you being on the computer right now. Indeed he is pissed off as he intended it to be useless.

    Give maths time and it will applicable to your everyday life. What has been going on for the past 3,000 years?

    --
    Analytic & algebraic topology of locally Euclidean meterization of infinitely differentiable Riemmanian manifold
  18. "Useless" mathematics that we use by Len · · Score: 4, Insightful

    100 years ago a proof of the difficulty of factoring large numbers might only have been interesting to mathematicians. Now that we use encryption based on the difficulty of factoring products of large primes, it's very important.

    Galois fields are used for checksum algorithms, something I'm sure Galois never thought of.

    Fourier transforms are used for image compression (JPEG).

    Who knows what Poincaré's topology might be used for in the future?