Sewing-Machine comments on Harry Potter and the Methods of Rationality discussion thread, part 8 - Less Wrong

8 Post author: Unnamed 25 August 2011 02:17AM

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Comment author: Eliezer_Yudkowsky 07 September 2011 04:08:11PM 1 point [-]

This makes it sound like believing in an uncountable ordinal is equivalent to AC, which would make things easier - lots of mathematicians reject AC. But you might not need AC to assert the existence of a well-ordering of the reals as opposed to any set, and others have claimed that weaker systems than ZF assert a first uncountable ordinal. My own skepticism wasn't so much the existence of any well-ordering of the reals (though I'm willing to believe that no such exists), my skepticism was about the perfect, canonical well-ordering implied by there being an uncountable ordinal onto whose elements all the countable ordinals are mapped and ordered. Of course that could easily be equivalent to the existence of any well-ordering of the reals.

Comment author: TobyBartels 11 September 2011 09:43:48PM 3 points [-]

This makes it sound like believing in an uncountable ordinal is equivalent to AC

Since I found the other replies insufficiently stark here, let me just say that it is not. The details are in this subthread.