Find out about these important results that destroyed a mathematical dream.

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?

Paraconsistent mathematics is a type of mathematics in which contradictions may be true.
In such a system it is perfectly possible for a statement *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.

When Kurt Gödel published his *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.

Kurt Gödel, who would have celebrated his 100th birthday next year, showed in 1931 that the power of maths to explain the world is limited: his famous incompleteness theorem proves mathematically that maths cannot prove everything. **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.

For millennia, puzzles and paradoxes have forced mathematicians to continually rethink their ideas of what proofs actually are. **Jon Walthoe** explains the tricks involved and how great thinkers like Pythagoras, Newton and Gödel tackled the problems.