Eugine_Nier comments on Multiverse and complexity of [laws of] the observed universe - Less Wrong

0 Post author: HoverHell 09 December 2010 04:06AM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (16)

You are viewing a single comment's thread.

Comment author: Eugine_Nier 09 December 2010 06:19:43AM 3 points [-]

Given multiverse hypothesis (universes with different physical constants / laws), the number of universes with infinitely large set of laws is much larger (both being infinite, though) than number of universes with finite sets of laws.

The question is not which set is larger, which is in any case almost meaningless since both are infinite, but which set has larger probability measure.

Comment author: jsalvatier 09 December 2010 07:44:24AM 4 points [-]

I do think it's meaningful to talk about different sizes of infinity (for example, countable vs. uncountable), but probability measure is probably more relevant.

Comment author: Sniffnoy 09 December 2010 08:56:26AM 2 points [-]

To expand on that point - what you are refer to there as "different sizes of infinity" are different cardinalities of sets. As you note, what sorts of infinities you have to use depends on what you are trying to measure; raw cardinalities are rarely the right notion of size, here we want to think in a measure-theoretic context. But it's worth noting that for measuring other things different systems of infinite numbers must be used; cardinalities and "infinities" should not be identified.

Comment author: HoverHell 10 December 2010 04:36:49AM 0 points [-]

Yes. I initially implicitly assumed uniform distribution (i.e. used it as default without any information to prefer some different particular one).

But what meaningful probability measures might be in this case? (Besides a point described few comments below [http://lesswrong.com/r/discussion/lw/393/multiverse_and_complexity_of_laws_of_the_observed/33li?c=1])

Comment author: orthonormal 15 December 2010 10:33:07PM 1 point [-]

In some cases, there's no way to define a uniform distribution (i.e. over the integers), so you've got to do something else.

Comment author: jsalvatier 15 December 2010 10:40:22PM 0 points [-]

Huh, can you define an improper uniform distribution over the integers like you can occasionally for the real line? Or does that always lead to an improper posterior?