My Favorite Strange Number: Ω

[Symmetry]

And oddly enough, one of my favorite numbers is the Ω of S=k*ln(Ω) fame.

http://en.wikipedia.org/wiki/Microcanonical_ensemble

[sehugg]

Different but related -- The busy beaver game and the Σ function:

http://en.wikipedia.org/wiki/Busy_beaver

[JonnieCache]

This is discussed in the following google Tech Talk, "Incompleteness: a personal perspective" from Cristian Claude

http://www.youtube.com/watch?v=tYjmiT422yQ

He discusses, amongst other things, the work done on computing this uncomputable number, and why that isn't a contradiction. I think one of the people involved is in the audience.

[ced]

I don't understand how omega can be be incompressible. Compression, from the information theory perspective, allows me to send the string

  Digits #10000 to #100000 of the decimal representation of omega.

which any competent human could "decompress" into the corresponding digit sequence (inasmuch as it's computable)

[andrewcooke]

you're right that the isolated assertion is not at all sensible, but the wider context is that you are considering all possible algorithms and the sequences that they generate, and looking for some way of compressing as many of those as possible. you should read one of chaitin's books for a better idea (they're generally "accessible", but at some point you just give up trying to make complete sense of it all...)

in other words, you are choosing your compression for one particular algorithm (the one that generates omega - you could go further and say it's 1 for omega and 0 for everything else). this is a common problem in arguments about compressibility (if we're only trying to compress beethoven's ninth then i can do that in one bit too) - you have to be talking in an "average" or statistical sense for things to be useful.

having said that, the exact nature of what they're saying is still not clear to me (ie it's not clear exactly how the details of the argument work out, or how this eventually ties back to http://en.wikipedia.org/wiki/Shannons_source_coding_theorem).

[gjm11]

The bit in parentheses is why your argument doesn't show that omega isn't incompressible: it very emphatically isn't computable.

[Natsu]

That's not quite fair because you have to include the size of your decompression routine with the description.

Also, there's the whole "not computable" part.

[khafra]

When he says "compress," he means "losslessly." A compression which doesn't actually allow you to compute any of the original data is pretty lossy.

[kzrdude]

The link to Calude's paper in the article is broken, it is this: http://www.cs.auckland.ac.nz/~cristian/Calude361_370.pdf

[doodyhead]

The Halting Problem theoretically defines the limits of computation, but has anyone in a pragmatic, everyday coding situation actually reached that limit? In the practical sense I've never seen it have any bearing. Perhaps the problems I'm working on are too mundane.

[khafra]

I had just remarked, the other day, that people obsessed with Chaitin's Omega are much more interesting than people obsessed with Pi.