Suppose $\kappa$I understand the motivation behind measurable cardinals is to ask the question: "is there any set large enough to admit a measurable cardinal. Then $\kappa$non-trivial measure on all of its subsets?"
Hence, it's also admitsworthwhile to ask the question "is there any real-closed field large enough to admit a $[0,1]$non-valuedtrivial 'Lebesgue' measure on all of its subsets?" Here's one way to formulate this question precisely:
First, let $\Bbb R^*$ be our real-closed field, noting that it can be non-Archimedean.
NowSecond, let's construct a hyperreal fieldgeneralize our notion of cardinality"measure." Given some $\kappa$$\Bbb R^*$, and look at the closed hyperreal intervallet $[0,1]^*$$\Bbb R^{**}$ be a strictly larger real-closed field. Then the $[0,1]$ valuedwe will allow our measure on $\kappa$ can be extended$\Bbb R^*$ to this hyperreal intervaltake values in $\Bbb R^{**}$.
Is there a wayNow, we want to do this which is translationfind real-invariantclosed fields $\Bbb R^*$ and $\Bbb R^{**}$, and furthermorea function $\mu: 2^{\Bbb R^*} \to \Bbb R^{**}$ which resembles the Lebesgue measure on the ordinary real unit interval, but withobeys the property that every subset is measurable?following:
- For all $S \subseteq \Bbb R^*$, $\mu(S) \geq 0$.
- $\mu(\emptyset) = 0$.
- Countable additivity of pairwise disjoint sets.
- $\mu([0,1]^*) = 1^{**}$.
- $\mu$ is a complete measure.
- $\mu$ is translation-invariant.
I'm leaving the notion of "resembles" deliberately vague hereNow, as I feel there might be more than one satisfactory way to do this that's inhere are the spirit of my question.questions:
I'm also interested in the answer in which a hyperreal $[0,1]^*$-valued measure is permitted, if that makes anything easier.
- Can this measure space exist?
- If so, then what relationship does this measure space have with the concept of a measurable cardinal?