Qiaochu_Yuan comments on Open Thread, April 15-30, 2013 - Less Wrong

4 Post author: diegocaleiro 15 April 2013 07:57PM

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Comment author: Qiaochu_Yuan 16 April 2013 06:57:23AM *  8 points [-]

I mean if you localize a ring at zero you get the zero ring. Equivalently, the unique ring in which zero is invertible is the zero ring. (Some textbooks will tell you that you can't localize at zero. They are haters who don't like the zero ring for some reason.)

Comment author: [deleted] 16 April 2013 07:50:24PM 0 points [-]

BTW, how comes the ring with one element isn't usually considered a field?

Comment author: Qiaochu_Yuan 16 April 2013 08:03:07PM 6 points [-]

The theorems work out nicer if you don't. A field should be a ring with exactly two ideals (the zero ideal and the unit deal), and the zero ring has one ideal.

Comment author: Oscar_Cunningham 16 April 2013 10:52:50PM *  2 points [-]

Ah, so it's for exactly the same reason that 1 isn't prime.

Comment author: Qiaochu_Yuan 17 April 2013 12:17:33AM 5 points [-]

Yes, more or less. On nLab this phenomenon is called too simple to be simple.

Comment author: Oscar_Cunningham 16 April 2013 10:51:39PM *  1 point [-]

We often want the field without zero to form a multiplicative group, and this isn't the case in the ring with one element (because the empty set lacks an identity and hence isn't a group). Indeed we could take the definition of a field to be

A ring such that the non-zero elements form a multiplicative group.

and this is fairly elegant.