# [FOM] irrational conjectures

Harvey Friedman friedman at math.ohio-state.edu
Sat Mar 14 04:35:50 EDT 2009

```On Mar 11, 2009, at 10:52 AM, Timothy Y. Chow wrote:

> Harvey Friedman wrote:
>> WILD CONJECTURE. There exists a positive integer n < 2^1000 such that
>> the statement sin(2^[n]) > 0 can be proved using (commonly studied)
>> large cardinals using at most 2^20 symbols, but cannot be proved in
>> ZFC
>> using at most 2^2^2^20 symbols.
>
> Obviously, one can take any unsolved problem and formulate a similar
> wild conjecture.  But is there any particular reason to believe that
> large cardinals are lurking here?

Note that sin(2^[n]) > 0 can be proved in extremely weak fragments of
arithmetic, no matter what n is.

Saying that "there exists n < 2^1000" radically distinguishes it from
just routinely taking any open statement A, and asserting that A has a
proof using large cardinals with at most 2^20 symbols, but not in ZFC
using at most 2^2^2^20 symbols.

There is a kind of systematic idea here, coming out of my experience
with Boolean Relation Theory. There, I look at reasonably natural
*collections* of statements, much more natural than any individual one
in the collection, and show that only one statement in the collection
is independent of ZFC. Thus the overwhelming majority are decided in
ZFC.

>
>
> In the past you have remarked that after proving several instances
> of the
> wild-conjecture template, you started to develop a "feel" for when
> there
> was a large cardinal.  Can you articulate that feeling in more detail?
> Failing that, can you give some examples of "TAME CONJECTURES"?
> That is,
> take some unsolved problem X, and make the
>
> TAME CONJECTURE.  Either X is not provable even using large cardinals,
> or X is provable in ZFC.
>
> Are there any TAME CONJECTURES that you believe with roughly the same
> conviction as you believe your WILD CONJECTURES?
>
>

I have thought some about finding a proposed single reasonably
concrete sentence which I think is likely NOT to be solved using large
cardinals. But I don't have a good candidate for this. So I guess the

Of course, we know that there exists a Turing machine such that the
halting problem for it, is independent of large cardinals - assuming
that we envision a finite or even r.e. set of large cardinal axioms.

In fact, we can say that among the TMs of size at most n, at least one
has a halting problem is independent of ZFC. But it is not clear to me
roughly how small we can make n for this purpose.

In fact, I have never seen a decent n offered with the claim that
there is a TM of size n whose halting problem is independent of ZFC.

Harvey Friedman

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