[FOM] Arithmetical soundness of ZFC

[Timothy Y. Chow]

Harvey Friedman <friedman at math.ohio-state.edu> wrote:
> WHAT WOULD EVIDENCE OF THE NON ARITHMETICAL SOUNDNESS OF ZFC LOOK LIKE?

One example would be a proof of "ZFC is inconsistent" in ZFC.

Actually, what I think is more interesting is Nik Weaver's implicit 
suggestion that a random sentence in the first-order language of 
arithmetic is undecidable in PA.  Is there any way to make this precise?

Tim