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posted by janrinok on Friday November 29 2019, @11:21PM   Printer-friendly
from the learning-can-still-be-fun dept.

Arthur T Knackerbracket has found the following story:

I remember first learning as a student that some infinities are bigger than others. For some sets of numbers, it was easy to see how. The set of integers is infinite, and the set of real numbers is infinite, and it seemed immediately clear that there are fewer integers than reals. Demonstrations and proofs of the fact were cool, but I already knew what they showed me.

Other relationships between infinities were not so easy to grok. Consider: There are an infinite numbers of points on a sheet of paper. There are an infinite numbers of points on a wall. These infinities are equal to one another. But how? Mathematician Yuri Manin demonstrates how:

I explained this to my grandson, that there are as many points in a sheet of paper as there are on the wall of the room. "Take the sheet of paper, and hold it so that it blocks your view of the wall completely. The paper hides the wall from your sight. Now if a beam of light comes out of every point on the wall and lands in your eye, it must pass through the sheet of paper. Each point on the wall corresponds to a point on the sheet of paper, so there must be the same number of each."

I remember reading that explanation in school and feeling both amazed and enlightened. What sorcery is this? So simple, so beautiful. Informal proofs of this sort made me want to learn more mathematics.

Manin told the story quoted above in an interview a decade or so ago with Mikhail Gelfand, We Do Not Choose Mathematics as Our Profession, It Chooses Us. It was a good read throughout and reminded me again how I came to enjoy math.


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  • (Score: 2) by FatPhil on Saturday November 30 2019, @02:46PM (4 children)

    by FatPhil (863) <reversethis-{if.fdsa} {ta} {tnelyos-cp}> on Saturday November 30 2019, @02:46PM (#926390) Homepage
    Your mathematics is flawed. One of the definitions of an infinity is something that is equal to a subset of itself. All you need is for equal to mean "can be put into one-to-one correspondence with each other", which is perfectly useful in the universe of discourse. Water fountains are not in the universe of discourse, so are irrelevant.
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  • (Score: 2) by barbara hudson on Saturday November 30 2019, @07:17PM (3 children)

    by barbara hudson (6443) <barbara.Jane.hudson@icloud.com> on Saturday November 30 2019, @07:17PM (#926504) Journal

    And I say the definition is flawed because it is arbitrary, and thought experiments (see my two infinite universes example) show it is flawed.

    Saying something is just because doesn't work. The fact that too many people accept logical contradictions when it comes to infinities shows just how fucked up/useless the definition is.

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    • (Score: 2) by FatPhil on Saturday November 30 2019, @08:24PM (2 children)

      by FatPhil (863) <reversethis-{if.fdsa} {ta} {tnelyos-cp}> on Saturday November 30 2019, @08:24PM (#926534) Homepage
      All I'm hearing is "I don't understand it, therefore it's wrong". Mathematicians do not accept logical contradictions. You don't understand it, therefore you're wrong, sorry.
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      • (Score: 2) by barbara hudson on Saturday November 30 2019, @10:18PM (1 child)

        by barbara hudson (6443) <barbara.Jane.hudson@icloud.com> on Saturday November 30 2019, @10:18PM (#926564) Journal

        What you are espousing most certainly leads to logical contradictions. We have two choices. Either a mathematics system that says infinity + infinity = infinity (which you side with), that when applied to the universe (where there may or may not be infinities), requires the violation of the laws of conservation, or infinity + infinity = bigger infinity, where the laws of conservation still work.

        Dark matter and dark energy changed everything. I didn't like it, but I accept it. Because I can see how ideas need to evolve when faced with new information.

        Once half the current mathematicians die off, we'll be able to see new ideas enter the field.

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        • (Score: 2) by FatPhil on Saturday November 30 2019, @11:38PM

          by FatPhil (863) <reversethis-{if.fdsa} {ta} {tnelyos-cp}> on Saturday November 30 2019, @11:38PM (#926582) Homepage
          > infinity + infinity = infinity (which you side with)

          Depends which infinities you're talking about. You're out of your depth, quit digging.
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