6 ms·

New Geometric Perspective Cracks Old Problem About Rectangles

59 points by exanimo_sai 6y ago

thaumasiotes 6y ago
Wait a minute. > It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. > Their final proof — showing the predicted rectangles do indeed exist — transports the problem into an entirely new geometric setting. There, the stubborn question yields easily. > The rectangular peg problem is a close offshoot of a question posed by the German mathematician Otto Toeplitz in 1911. He predicted that any closed curve contains four points that can be connected to form a square. His “square peg problem” remains unsolved. How can the square problem possibly remain unsolved if the article is celebrating a proof that you can find the corners of a rectangle of any proportion in any closed curve. What if I choose the proportion "length = 1 times width"?
thaumasiotes 6y ago
> It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. > Their final proof — showing the predicted rectangles do indeed exist — transports the problem into an entirely new geometric setting. There, the stubborn question yields easily. Except that the article then contradicts itself by saying how they haven't actually proved this. They proved it for smooth closed curves, not for any closed curves. This is a really bizarre article. They seem like they want to describe the math. But they can't bring themselves to do it in a way that might be helpful. They're just waving words around. And then there's this: > it’s possible to rotate the Möbius strip in four-dimensional space so that you only change one of the coordinates in each point’s four-coordinate address — like changing the street numbers of all the houses on a block, but leaving the street name, city and state unchanged. (For a more geometric example, think about how holding a block in front of you and shifting it to the right only changes its x coordinates, not the y and z coordinates.) You can certainly translate a space along an axis without affecting its coordinates along other axes. But that's not a rotation.
- danharaj 6y ago
  > While locked down due to COVID-19, Joshua Greene and Andrew Lobb figured out how to prove a version of the “rectangular peg problem.” Emphasis mine.
  - thaumasiotes 6y ago
    The text you quote is not even part of the article. But it is related to text that precedes my quote: > One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. > “The problem is so easy to state and so easy to understand, but it’s really hard,” said Elizabeth Denne of Washington and Lee University. > It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. Emphasis mine. The article explicitly describes the problem they solved, only to later point out that they actually solved a different problem.
    - danharaj 6y ago
      Oh my god here, is the same qualification near the top of the article. > One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. On every Quanta article there's always someone welching about some gotcha they think they've found that just demonstrates how trash Quanta's popularizations of mathematical topics is. But whenever I read the article in question it always turns out that the writers and editors over there somehow manage to thread the needle in making their material accessible without being mathematically inaccurate. Vague, yes, but that's why they link to the research in question because it's a pop article not a journal publication. You edited your comment to add another objection. It is equally insubstantial unless you dug through the paper yourself and demonstrated that the transformation applied could not reasonably be called a rotation.
      - thaumasiotes 6y ago
        > Oh my god here, is the same qualification near the top of the article. >> One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. Did you read past the first sentence of my comment? > You edited your comment to add another objection. It is equally insubstantial unless you dug through the paper yourself and demonstrated that the transformation applied could not reasonably be called a rotation. I disagree. The article strongly implies that the transformation applied could be called a rotation, and I see no particular reason to doubt that. ("The Möbius strip can be rotated by any angle between 0 and 360 degrees, and he proved that one-third of those rotations yield an intersection between the original and the rotated copy.") But I very much object to the article's idea that I should help myself think about a rotation that only changes point values along a single dimension by visualizing an entirely unrelated transformation. How is that supposed to help?
kmill 6y ago
Here's a nice 3blue1brown video about the easier version of the inscribed rectangle problem, that some inscribed rectangle exists: https://www.youtube.com/watch?v=AmgkSdhK4K8 https://www.youtube.com/watch?v=AmgkSdhK4K8 And I remember thinking this was a nice overview of some aspects of the "square peg problem" (the Toeplitz conjecture): https://www.ams.org/notices/201404/rnoti-p346.pdf https://www.ams.org/notices/201404/rnoti-p346.pdf
ajuc 6y ago
I've seen the trick with describing rectangles as middlepoint, diagonal length and angle used in solving an interview questions, it was great. https://youtu.be/EuPSibuIKIg https://youtu.be/EuPSibuIKIg

59 points by exanimo_sai 6y ago

Wait a minute. > It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. > Their final proof — showing the predicted rectangles do indeed exist — transports the problem into an entirely new geometric setting. There, the stubborn question yields easily. > The rectangular peg problem is a close offshoot of a question posed by the German mathematician Otto Toeplitz in 1911. He predicted that any closed curve contains four points that can be connected to form a square. His “square peg problem” remains unsolved. How can the square problem possibly remain unsolved if the article is celebrating a proof that you can find the corners of a rectangle of any proportion in any closed curve. What if I choose the proportion "length = 1 times width"?

thaumasiotes 6y ago

> It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. > Their final proof — showing the predicted rectangles do indeed exist — transports the problem into an entirely new geometric setting. There, the stubborn question yields easily. Except that the article then contradicts itself by saying how they haven't actually proved this. They proved it for smooth closed curves, not for any closed curves. This is a really bizarre article. They seem like they want to describe the math. But they can't bring themselves to do it in a way that might be helpful. They're just waving words around. And then there's this: > it’s possible to rotate the Möbius strip in four-dimensional space so that you only change one of the coordinates in each point’s four-coordinate address — like changing the street numbers of all the houses on a block, but leaving the street name, city and state unchanged. (For a more geometric example, think about how holding a block in front of you and shifting it to the right only changes its x coordinates, not the y and z coordinates.) You can certainly translate a space along an axis without affecting its coordinates along other axes. But that's not a rotation.

danharaj 6y ago
> While locked down due to COVID-19, Joshua Greene and Andrew Lobb figured out how to prove a version of the “rectangular peg problem.” Emphasis mine.
- thaumasiotes 6y ago
  The text you quote is not even part of the article. But it is related to text that precedes my quote: > One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. > “The problem is so easy to state and so easy to understand, but it’s really hard,” said Elizabeth Denne of Washington and Lee University. > It starts with a closed loop — any kind of curvy path that ends where it starts. The problem Greene and Lobb worked on predicts, basically, that every such path contains sets of four points that form the vertices of rectangles of any desired proportion. Emphasis mine. The article explicitly describes the problem they solved, only to later point out that they actually solved a different problem.
  - danharaj 6y ago
    Oh my god here, is the same qualification near the top of the article. > One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. On every Quanta article there's always someone welching about some gotcha they think they've found that just demonstrates how trash Quanta's popularizations of mathematical topics is. But whenever I read the article in question it always turns out that the writers and editors over there somehow manage to thread the needle in making their material accessible without being mathematically inaccurate. Vague, yes, but that's why they link to the research in question because it's a pop article not a journal publication. You edited your comment to add another objection. It is equally insubstantial unless you dug through the paper yourself and demonstrated that the transformation applied could not reasonably be called a rotation.
    - thaumasiotes 6y ago
      > Oh my god here, is the same qualification near the top of the article. >> One of the problems the two friends looked at was a version of a century-old unsolved question in geometry. Did you read past the first sentence of my comment? > You edited your comment to add another objection. It is equally insubstantial unless you dug through the paper yourself and demonstrated that the transformation applied could not reasonably be called a rotation. I disagree. The article strongly implies that the transformation applied could be called a rotation, and I see no particular reason to doubt that. ("The Möbius strip can be rotated by any angle between 0 and 360 degrees, and he proved that one-third of those rotations yield an intersection between the original and the rotated copy.") But I very much object to the article's idea that I should help myself think about a rotation that only changes point values along a single dimension by visualizing an entirely unrelated transformation. How is that supposed to help?

kmill 6y ago

Here's a nice 3blue1brown video about the easier version of the inscribed rectangle problem, that some inscribed rectangle exists: https://www.youtube.com/watch?v=AmgkSdhK4K8 https://www.youtube.com/watch?v=AmgkSdhK4K8 And I remember thinking this was a nice overview of some aspects of the "square peg problem" (the Toeplitz conjecture): https://www.ams.org/notices/201404/rnoti-p346.pdf https://www.ams.org/notices/201404/rnoti-p346.pdf

ajuc 6y ago

I've seen the trick with describing rectangles as middlepoint, diagonal length and angle used in solving an interview questions, it was great. https://youtu.be/EuPSibuIKIg https://youtu.be/EuPSibuIKIg