# Did Paul Cohen settle the Continuum Hypothesis?

1. Jan 12, 2010

### SW VandeCarr

Did Paul Cohen "settle" the Continuum Hypothesis?

Paul Cohen proved the Continuum Hypothesis is independent of ZFC and concluded that it's truth or falseness is undecidable (1963). Is this still the case today? These links suggest there is still interest in proving or disproving it.

http://www.gauge-institute.org/cantor/HilbertFirstProblem.pdf

http://www.ams.org/notices/200106/fea-woodin.pdf

EDIT: I'm suspicious of the the first link. I can't find out much about the Gauge Institute except that it's located in St Paul,MN and I don't think this paper proves anything, but I'm not a mathematician.

Last edited: Jan 12, 2010
2. Jan 12, 2010

### CRGreathouse

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

The CH is independent of ZFC; this is forever true.

The first link is crackpottery. The second article seems a good summary of the state of affairs; it certainly doesn't contradict Cohen's result.

3. Jan 15, 2010

### SW VandeCarr

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

Here's Part II of Woodin's paper. He seems to believe that the problem is decidable without resolving all instances of the GHC, utilizing the Large Cardinal Axioms (as part of a well ordered hierarchy) and the Axiom of Projective Determinacy along with ZFC (although he seems to think Choice no longer would be necessary) From what I could find, Woodin seems the be major (credible) investigator re the decidability of CH.

http://www.ams.org/notices/200107/fea-woodin.pdf

Last edited: Jan 15, 2010
4. Jan 15, 2010

### Hurkyl

Staff Emeritus
Re: Did Paul Cohen "settle" the Continuum Hypothesis?

Whether or not ZFC+Large Cardinals+Axiom of Projective Determinacy can prove the CH has no bearing whatsoever on whether or not ZFC can prove CH.

Investigating what can be proven from additional hypotheses is an interesting thing that set theorists may do, but that doesn't change what can or cannot be proven from ZFC alone.

Oh, I just noticed:
That sounds like a misstatement -- where did "truth" or "falseness" come from?

5. Jan 15, 2010

### SW VandeCarr

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

I don't think I indicated it did. No one is questioning the independence of CH and ZFC, but Woodin is attempting to use ZF along with some new axioms as a basis for deciding the status of CH.

The point was never argued. I couldn't find anything in the Wooden papers that said ZFC was sufficient to decide CH. The whole of the two papers, as far as I can surmise, try to make a case for the new axiomatic system he's working on. He seems quite aware of the difficulties but remains cautiously optimistic. Clearly such a new system must be consistent with ZFC. As I said ZF is included in the system he's developing but indicates at the end of his second paper that C may not be needed given the new axioms.

Poor choice of words. Just should have said the provability of CH.

Last edited: Jan 15, 2010
6. Feb 19, 2010

### srijithju

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

I would like to ask from where did the axioms of ZFC come from in the first place ?

Why is it that you consider the axioms of ZFC relevant , but adding a few more axioms to ZFC , just an exercise for set theorists ?

I am not a mathematician , and have very limited knowledge of mathematics , so what I maybe saying maybe complete rubbish , but as far as by understanding goes , ZFC is just a set of axioms that lead to a 'consistent' theory . If by adding any number of axioms , I still am able to generate a 'consistent' theory , then what reason would be left for someone to favour ZFC from this other new theory ?

In the above paragraph , my usage of the word theory might be inappropriate , but I do not know what is the right word that should be used.

7. Feb 19, 2010

### Hurkyl

Staff Emeritus
Re: Did Paul Cohen "settle" the Continuum Hypothesis?

They were brought up in the opening post.

Also, ZFC is the conventional "standard" -- unless someone says otherwise, we should assume if they refer to set theory, they mean at least ZF, and usually C as well.

8. Feb 19, 2010

### CRGreathouse

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

ZFC + "CRGreathouse is emperor of the world" is consistent if and only if ZFC is consistent... but I haven't been able to get people to adopt that axiom system for some reason.

9. Feb 19, 2010

### JSuarez

Re: Did Paul Cohen "settle" the Continuum Hypothesis?

Actually, ZFC is a set of axioms that lead to a theory that we believe to be consistent. Consistency can only be proved in a stronger theory, and so on...