What concepts or facts do you know from math that is mind blowing, awesome, or simply fascinating?

Here are some I would like to share:

  • Gödel’s incompleteness theorems: There are some problems in math so difficult that it can never be solved no matter how much time you put into it.
  • Halting problem: It is impossible to write a program that can figure out whether or not any input program loops forever or finishes running. (Undecidablity)

The Busy Beaver function

Now this is the mind blowing one. What is the largest non-infinite number you know? Graham’s Number? TREE(3)? TREE(TREE(3))? This one will beat it easily.

  • The Busy Beaver function produces the fastest growing number that is theoretically possible. These numbers are so large we don’t even know if you can compute the function to get the value even with an infinitely powerful PC.
  • In fact, just the mere act of being able to compute the value would mean solving the hardest problems in mathematics.
  • Σ(1) = 1
  • Σ(4) = 13
  • Σ(6) > 101010101010101010101010101010 (10s are stacked on each other)
  • Σ(17) > Graham’s Number
  • Σ(27) If you can compute this function the Goldbach conjecture is false.
  • Σ(744) If you can compute this function the Riemann hypothesis is false.

Sources:

  • dbaner@lemmy.world
    82·
    1 year ago

    The infinite sum of all the natural numbers 1+2+3+… is a divergent series. But it can also be shown to be equivalent to -1/12. This result is actually used in quantum field theory.

    • yewler@lemmygrad.ml
      2·
      1 year ago

      It can’t be shown to be equivalent to -1/12. The sum definitely just simply goes to infinity. However, if you use some specific nonstandard definitions, you can squeeze out -1/12.

      What I think is interesting is how many choices of nonstandard definitions you can use to “prove” this result. I can recall 3 just right off the top of my head. However, as these are nonstandard definitions, one can’t really say that the sum is -1/12 without specifying which logical system you are operating in, because the default system makes it simply untrue.

      It’s like saying that 2+2=0. Sure, you can define the + sign to be some nonstandard function, but unless I describe that function to you, I can’t just simply tell you 2+2=0, because you’d just assume the standard definition of +, in which 2+2 definitely isn’t 0.

    • MüThyme@lemmy.world
      2·
      1 year ago

      I don’t suppose you know the exact application in QFT? I assume it’s used for some renormalization scheme?