To put myself in the clear, I came across this old comment because I was looking through Doug S’s old posts (because I was idly curious). I replied to your comment because I’m ridiculously pedantic, a virtue in mathematics. I haven’t downvoted any of your comments and I harbor no feelings of antipathy towards you. Eliezer’s a big boy and he can take care of himself.
Now, back to the math debate! I don’t think it’s legitimate to conflate countable sets with sets with finite information content. Here are two counter examples. 1. The set of busy beaver numbers (a subset of the naturals). 2. The digits of Chaitin’s Omega [make an ordered pair of (digit, position) to represent these] (see http://en.wikipedia.org/wiki/Chaitin%27s_constant). It’s been proved that these sets can’t be constructed with any algorithm.
“The set of busy beaver numbers” communicates, points to, refers to, picks out, a concept in natural language that we can both talk about. It has finite information content (a finite sequence of ascii characters suffices to communicate it). An analogous sentence in a sufficiently formal language would still have finite information content.
Note that a description, even if it is finite, is not necessarily in the form that you might desire. Transforming the description “the sequence of the first ten natural numbers” into the format “{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}” is easy, but the analogous transformation of “the first 10 busy beaver numbers” is very difficult if not impossible.
As nshepperd points out, an element of a countable set necessarily has finite information content (you can pick it out by providing an integer—“the fifth one” or whatever), while generic elements of uncountable sets cannot be picked out with finite information.
I think the finite information content comes from being an element of a countable set. Like every other real number, the digits of Chaitin’s constant themselves form a countable set (a sequence), while that set is a member of the uncountable R. Similarly, the busy beaver set is a subset of N, and drawn from the uncountable set 2^N.
Countable sets are useful (or rather, uncountable ones are inconvenient) because you can set up a normalized probability distribution over their contents. But… the set {Chaitin’s Constant} is countable (it has one element) but I still can’t get Omega’s digits. So there still seems to be a bit of mystery here.
To put myself in the clear, I came across this old comment because I was looking through Doug S’s old posts (because I was idly curious). I replied to your comment because I’m ridiculously pedantic, a virtue in mathematics. I haven’t downvoted any of your comments and I harbor no feelings of antipathy towards you. Eliezer’s a big boy and he can take care of himself.
Now, back to the math debate! I don’t think it’s legitimate to conflate countable sets with sets with finite information content. Here are two counter examples. 1. The set of busy beaver numbers (a subset of the naturals). 2. The digits of Chaitin’s Omega [make an ordered pair of (digit, position) to represent these] (see http://en.wikipedia.org/wiki/Chaitin%27s_constant). It’s been proved that these sets can’t be constructed with any algorithm.
“The set of busy beaver numbers” communicates, points to, refers to, picks out, a concept in natural language that we can both talk about. It has finite information content (a finite sequence of ascii characters suffices to communicate it). An analogous sentence in a sufficiently formal language would still have finite information content.
Note that a description, even if it is finite, is not necessarily in the form that you might desire. Transforming the description “the sequence of the first ten natural numbers” into the format “{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}” is easy, but the analogous transformation of “the first 10 busy beaver numbers” is very difficult if not impossible.
As nshepperd points out, an element of a countable set necessarily has finite information content (you can pick it out by providing an integer—“the fifth one” or whatever), while generic elements of uncountable sets cannot be picked out with finite information.
I think the finite information content comes from being an element of a countable set. Like every other real number, the digits of Chaitin’s constant themselves form a countable set (a sequence), while that set is a member of the uncountable R. Similarly, the busy beaver set is a subset of N, and drawn from the uncountable set 2^N.
Countable sets are useful (or rather, uncountable ones are inconvenient) because you can set up a normalized probability distribution over their contents. But… the set {Chaitin’s Constant} is countable (it has one element) but I still can’t get Omega’s digits. So there still seems to be a bit of mystery here.