A Range of values for ##2^{\aleph_0}##

Click For Summary
In models of ZFC where the Continuum Hypothesis (CH) does not hold, the value of 2^{\aleph_0} can vary significantly. Solovay's result indicates that for any uncountable cardinal \kappa, there exists a forcing extension where 2^{\aleph_0} equals \kappa. However, König's theorem restricts the values of 2^{\aleph_0}, stating it cannot be \aleph_{\omega}, \aleph_{\omega_1 + \omega}, or any cardinal with cofinality \omega. This highlights the complexity of cardinality in set theory under different models. Understanding these relationships is crucial for exploring the implications of the Continuum Hypothesis.
WWGD
Science Advisor
Homework Helper
Messages
7,742
Reaction score
12,942
TL;DR
Possible values of cardinality in different models of ZFC+ ~CH
Ok, so assume we have a model for ZFC where CH does not hold. What values may ##2^{\aleph_0}## assume over said models?
 
Physics news on Phys.org
According to Wikipedia,

A result of Solovay, proved shortly after Cohen's result on the independence of the continuum hypothesis, shows that in any model of ZFC, if ##\kappa## is a cardinal of uncountable cofinality, then there is a forcing extension in which ##2^{\aleph_0} = \kappa##. However, per König's theorem, it is not consistent to assume ##2^{\aleph _{0}}## is ##\aleph _{\omega }## or ##\aleph _{\omega _{1}+\omega }## or any cardinal with cofinality ##\omega##.
 
Excellent, Steven Daryl, thank you.
 
There is a nice little variation of the problem. The host says, after you have chosen the door, that you can change your guess, but to sweeten the deal, he says you can choose the two other doors, if you wish. This proposition is a no brainer, however before you are quick enough to accept it, the host opens one of the two doors and it is empty. In this version you really want to change your pick, but at the same time ask yourself is the host impartial and does that change anything. The host...

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 13 ·
Replies
13
Views
1K
Replies
27
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
Replies
16
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K