Is NxN Truly Equivalent to N When Using Gaussian Integers?

  • Context: Graduate 
  • Thread starter Thread starter cragar
  • Start date Start date
  • Tags Tags
    Proof
Click For Summary

Discussion Overview

The discussion revolves around the equivalence of the set of natural numbers (N) and the Cartesian product of natural numbers with itself (NxN) using Gaussian integers. Participants explore the implications of mappings between these sets and the cardinality of N and NxN.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes a mapping using Gaussian integers to show that NxN is equivalent to N, citing specific examples of products of Gaussian integers.
  • Another participant points out a flaw in the mapping, noting that pairs (x,y) and (y,x) are mapped to the same integer, suggesting a lack of injectivity.
  • A third participant questions whether the original intention was to map from N to NxN instead of the other way around, highlighting a potential misunderstanding in the mapping direction.
  • Several participants assert that NxN is not equivalent to N, stating that NxN has the same cardinality as the set of rational numbers, and that the proposed mapping appears to be one-to-one but not onto.
  • One participant reiterates that while NxN is not equivalent to N, they also mention that N is equivalent to NxN, indicating a contradiction in the discussion.

Areas of Agreement / Disagreement

Participants generally disagree on the equivalence of N and NxN, with multiple competing views presented regarding the nature of the mappings and cardinalities involved. The discussion remains unresolved.

Contextual Notes

There are limitations in the assumptions made about the mappings and the definitions of equivalence and cardinality that are not fully explored or resolved in the discussion.

cragar
Messages
2,546
Reaction score
3
I thought of a way to use Gaussian integers to show that NxN~N
We look at (1+i)(1-i) and this corresponds to the coordinate (1,1)
then (1+2i)(1-2i)-->(1,2) then (1+3i)(1-3i)-->(1,3)... and you keep doing this, so we have injected NxN into N.
 
Mathematics news on Phys.org
actually there is a problem with this (x,y) and (y,x) get mapped to the same integer
 
It looks to me like your mapping goes from N to N x N. Is that what you intended? (1 + i)(1 - i) = 1 - i2 = 1 + 1 = 2. So here the integer 2 is mapped to (1, 1). Did you mean for it to go the other way?
 
The fundamental problem is that N x N is NOT equivalent to N, it has the same cardinality as the set of rational numbers. It appears that your assignment is "one-to-one" but not "onto".
 
HallsofIvy said:
The fundamental problem is that N x N is NOT equivalent to N, it has the same cardinality as the set of rational numbers. It appears that your assignment is "one-to-one" but not "onto".

But ##\mathbb{N}## is equivalent to ##\mathbb{N}\times\mathbb{N}##...
 
HallsofIvy said:
The fundamental problem is that N x N is NOT equivalent to N, it has the same cardinality as the set of rational numbers. It appears that your assignment is "one-to-one" but not "onto".
The rationals and the naturals do have the same cardinality.
 

Similar threads

Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 105 ·
4
Replies
105
Views
11K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 55 ·
2
Replies
55
Views
7K
  • · Replies 12 ·
Replies
12
Views
3K
Replies
17
Views
3K