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5:23 AM
This question was for a very long time at the top of unanswered questions:
163
Q: Ultrafilters and automorphisms of the complex field

Simon ThomasIt is well-known that it is consistent with $ZF$ that the only automorphisms of the complex field $\mathbb{C}$ are the identity map and complex conjugation. For example, we have that $\vert\operatorname{Aut}(\mathbb{C})| = 2$ in $L(\mathbb{R})$. But suppose that we are given a nonprincipal ultraf...

It was also explicitly mentioned in this meta thread:
14
A: MO-Hard Questions

Andrés E. CaicedoSimon Thomas asked in Ultrafilters and automorphisms of the complex field whether the existence of non-principal ultrafilters (over the natural numbers) suffices to imply the existence of a nontrivial automorphism of the complex field $\mathbb C$. In set theoretic terms, the question is whe...

Recently, an answer was posted and it is not accepted. (I do not know enough to be able to judge the correctness of the answer.)
8
A: Ultrafilters and automorphisms of the complex field

Paul LarsonIt seems not. It was shown by Di Prisco and Todorcevic (and reproved later by at least three sets of authors) that if sufficiently large cardinals exist (e.g., a proper class of Woodin cardinals), then after forcing with $\mathcal{P}(\omega)/\mathrm{Fin}$ (the infinite subsets of $\omega$, orde...

 

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