## Gödel's Incompleteness Theorem

Wim Hordijk recently sent us a digital postcard from Vienna, where he had traced the steps of the eminent mathematician Kurt Gödel. Here is what he discovered.

Will sophisticated algorithms one day replace mathematicians?

*A*and its negation

*not A*to both be true. How can this be, and be coherent? What does it all mean?

In the 1930s the logician Kurt Gödel showed that if you set out proper rules for mathematics, you lose the ability to decide whether certain statements are true or false. This is rather shocking and you may wonder why Gödel's result hasn't wiped out mathematics once and for all. The answer is that, initially at least, the unprovable statements logicians came up with were quite contrived. But are they about to enter mainstream mathematics?

Many people like mathematics because it gives definite answers. Things are either true or false, and true things seem true in a very fundamental way. But it's not quite like that. You can actually build different versions of maths in which statements are true or false depending on your preference. So is maths just a game in which we choose the rules to suit our purpose? Or is there a "correct" set of rules to use? We find out with the mathematician Hugh Woodin.

**Runner up in the general public category**. Great minds spark controversy. This is something you'd expect to hear about a great philosopher or artist, but not about a mathematician. Get ready to bin your stereotypes as

**Rebecca Morris**describes some controversial ideas of the great mathematician David Hilbert.

*incompleteness theorem*in 1931, the mathematical community was stunned: using maths he had proved that there are limits to what maths can prove. This put an end to the hope that all of maths could one day be unified in one elegant theory and had very real implications for computer science.

**John W Dawson**describes Gödel's brilliant work and troubled life.

**Gregory Chaitin**explains why he thinks that Gödel's incompleteness theorem is only the tip of the iceberg, and why mathematics is far too complex ever to be described by a single theory.

**Jon Walthoe**explains the tricks involved and how great thinkers like Pythagoras, Newton and Gödel tackled the problems.