Does ZFC Imply the Power Set of Naturals?

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Discussion Overview

The discussion revolves around whether Zermelo-Fraenkel set theory with the Axiom of Choice (ZFC) implies the existence of the power set of the natural numbers. Participants explore the axioms of ZFC and their implications for the existence of sets, particularly focusing on the natural numbers and their power set.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that standard formulations of ZFC imply the existence of the power set of the natural numbers based on the empty set axiom, pairing axiom, and the power set axiom.
  • Another participant challenges this by stating that the existence of the empty set and pairing axiom alone does not guarantee the existence of the natural numbers, emphasizing the need for the axiom of infinity to establish their existence.
  • A follow-up question is posed regarding whether the axioms of Infinity, Empty-Set, and Pairing are jointly sufficient and individually necessary for the existence of P(N).
  • Another participant reiterates the previous point about the necessity of the power set axiom in this context.
  • One participant notes that the power set of the natural numbers may vary across different models, suggesting that some models may contain only certain subsets of the power set.
  • It is mentioned that while variations in the natural numbers across models are possible, they are less common.

Areas of Agreement / Disagreement

Participants express differing views on the sufficiency of certain axioms for establishing the existence of the power set of the natural numbers, indicating that multiple competing views remain in the discussion.

Contextual Notes

There are unresolved questions regarding the dependence of the existence of the natural numbers on specific axioms and the implications of different models on the nature of the power set.

mpitluk
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Is it true that for every standard formulation T of ZFC, T ⊢ the power set of {naturals}?

After all, the empty set axiom and the pairing axiom are in T, and so we get N. Then by the power set axiom we get P(N).
 
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The existence of the empty set and the pairing axiom does not give us the existence of the natural numbers. Indeed: all natural numbers may exist that way, but perhaps they will not be contained in a set!
For the existence of a set of natural numbers, ZFC has included a special axioms that gives us that: the existence of an infinite set. Together with that, we can prove that the natural numbers exist. And by the power set axiom, also P(N) exists. So the answer to your question is yes.
 


So Infinity, Empty-Set and Pairing are jointly sufficient and individually necessary for P(N)?
 


mpitluk said:
So Infinity, Empty-Set and Pairing are jointly sufficient and individually necessary for P(N)?

And the power set axiom, of course.
 


Whoops. Right, thanks.
 


One thing to note here is that the power set P(\mathbb{N}) might not be the same in all models, some may contain only some of the subsets.

(indeed, it's also possible to create models where \mathbb{N} is different, but that's much less common)
 

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