John Baez: Chaitlin’s Incompleteness Theory

Attention conservation notice: only of interest to computer science nerds. The web page discusses a number of topics, but the section on Chaitlin is all I’m really suggesting here.

So, amazingly complex things can be compressed into fairly little information. You can’t help but wonder: how complex can something be?

The answer: arbitrarily complex! At least that’s true if we’re talking about the Kolmogorov complexity of a string of bits: namely, the length of the shortest computer program that prints it out. Lots of long strings of bits can’t be compressed. You can’t print out most of them using short programs, since there aren’t enough short programs to go around.

Of course, we need to fix a computer language ahead of time, so this is well-defined. And we need to make sure the programs are written in binary, so the comparison is fair.

So, things can be arbitrarily complex. But here’s a more interesting question: how complex can we prove something to be?

The answer is one of the most astounding facts I know. It’s called Chaitin’s incompleteness theorem. It says, very roughly:

There’s a number L such that we can’t prove the Kolmogorov complexity of any specific string of bits is more than L.

Source: surprises