Is the Banach-Tarski Paradox a Valid Refutation of the Axiom of Choice?

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Discussion Overview

The discussion centers on the Banach-Tarski Paradox and its relationship to the Axiom of Choice, exploring whether the paradox serves as a valid refutation of the axiom. Participants examine the implications of the paradox from mathematical, philosophical, and physical perspectives.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Meta-discussion

Main Points Raised

  • Some participants question if the Banach-Tarski Paradox can be considered a valid refutation of the Axiom of Choice, suggesting that surprise alone does not imply a disproof.
  • Others argue that the paradox contradicts naive intuition and has implications for physics, asserting that it arises directly from the Axiom of Choice and basic measure theory.
  • There is a viewpoint that acceptance of the Axiom of Choice is subjective, with some asserting its necessity for the existence of bases in vector spaces, despite leading to counterintuitive results.
  • One participant challenges the notion that the paradox contradicts physics, stating that the sets involved are not physical and that "outrage" over the result is unfounded.

Areas of Agreement / Disagreement

Participants express differing opinions on whether the Banach-Tarski Paradox undermines the Axiom of Choice, with no consensus reached on the implications for intuition or physics.

Contextual Notes

Some discussions reference the philosophical implications of the Axiom of Choice and related concepts, such as the axiom of constructibility and the continuum hypothesis, indicating a complex interplay of ideas without resolving the underlying mathematical or philosophical questions.

DeadWolfe
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Is this paradox a valid refutation/disproof of the axiom of choice?

I don't know very much about it myself, but I thought it might make an interesting topic.
 
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Only if you have reason to think the result is wrong, not just surprising.

The axioms generally used by mathematicians do not prove the result wrong, if that's what you're asking.
 
The point is that the result flies in the face, not only of naive intuition, but of physics. Since it only uses beginner measure theory plus the axiom of choice, it seems tht the outrage is directly due to the AoC.
 
Whether one chooses to accept the aciom of choice is largely personal preference. To many of us it is *obvious* that a vector space always has a basis. So we want it. It also leads to some weird stuff.

www.dpmmms.cam.ac.uk/~wtg10[/URL]

then follow the links to his lecture to the philosophical society, where he gives a couple of examples where the axiom of choice ought to be true and one where it isn't. I believe Devlin has a thought experiment in one of his monthly articles which indicates some of the subtlety too.

EDIT:

Acutally the Devlin thing is on the axiom of constuctibilty and the continuum hypothesis (how many real numbers are there) but it's fairly close to some of this stuff, and reasonably illuminating to the layman.
 
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"The point is that the result flies in the face, not only of naive intuition, but of physics. Since it only uses beginner measure theory plus the axiom of choice, it seems tht the outrage is directly due to the AoC."

"naive intuition" is just another name for "common experience" and one simply does not have common experience with the kind of sets used in the Banach-Tarski theorem. It does not "fly in the face" of physics since physics has nothing to do with this. The types of sets used are not in any sense "physical". I don't see any "outrage".
 

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