Maybe all reals can be listed?

Click For Summary
SUMMARY

This discussion centers on the impossibility of listing all real numbers, primarily through the lens of Cantor's diagonal argument. Participants explore various methods of constructing lists of real numbers, including binary trees and mirroring techniques, ultimately concluding that no single list can encompass all reals. The diagonalization argument is reaffirmed as a valid proof by contradiction, demonstrating that any proposed list of real numbers will always omit at least one number. The conversation emphasizes the need for new arguments to further understand the limitations of listing real numbers.

PREREQUISITES
  • Understanding of Cantor's diagonal argument
  • Familiarity with binary trees and their construction
  • Knowledge of mathematical proof techniques, particularly proof by contradiction
  • Basic concepts of real numbers and their properties
NEXT STEPS
  • Study the implications of Cantor's diagonal argument in set theory
  • Explore advanced topics in real analysis, focusing on uncountability
  • Research alternative proofs regarding the listing of real numbers
  • Investigate the concept of dimensional flooding in mathematical contexts
USEFUL FOR

Mathematicians, computer scientists, and students of mathematics interested in set theory, real analysis, and the foundations of mathematics.

  • #31
There is no mathematical term "closed list".
There are sets closed in some topology, but that is unrelated to the topic here.
 
Physics news on Phys.org
  • #32
??

There are an infinite number of diagonals in a list. For every coordinate, the are 4 diagonals, in an infinite list, there are an infinite number of coordinates.

Ok, name it what you want then *shrug* It's obviously pertinent that there are "closed lists" in real number list representation, particularly when the topic talks about diagonalization, which is what we're discussing. You blankly stated that Cantor proved once and for all, that diagonalization proved uncountability. That's not true, there are "closed lists". I just proved one right in front of you, why do I need a source for it to be proven to you?

Additionally, "closed lists" have been found for lists of irrationals, though the lists were shown to not be complete.

The open question is whether the incompleteness is inherent or whether it's a sequence problem?

Like I explained before, if you list all the counting numbers first, you can't list all the rationals "next", because the counting numbers go forever. BUT! You can interpolate them (called scattering) and if you scatter them, you can make a whole list of the rationals… to do this, the sequence has to be very precise. When adding irrationals, obviously, the only way to include them is to interpolate them with the rationals, because, again, the new list of all rationals goes on forever, and you can't tack the irrationals at "the end".

Cantor could have just run into a sequencing problem, and considered it a proof. We already know lists can be constructed that contain their diagonals - so the question isn't in my mind, resolved. You can argue dimensional flooding, and I can come back and say you have a sequencing problem… but to do this, I have to solve, not just state, the scattering sequence that proves the dimensional flooding can be listed - at least in order to prove you wrong.

In saying this, it is extremely easy to see dimensional flooding from a sequencing error, and assume it can't be done, when all it really is, is a sequencing error.
 
  • #33
You keep using words in ways different from their usual meaning, together with expressions apparently invented by you, and when asked what you mean you don't explain it. A discussion cannot work that way. I closed the thread.
 

Similar threads

  • · Replies 43 ·
2
Replies
43
Views
6K
  • · Replies 62 ·
3
Replies
62
Views
10K
  • · Replies 55 ·
2
Replies
55
Views
8K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 86 ·
3
Replies
86
Views
9K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
4
Views
2K