It's been exactly 20 years since those geniuses called theoretical physicists first promised the world a theory of everything (TOE) that would explain all natural phenomena on Earth and in heaven. The New York Times this week interviewed most of the key players to find out where these Einsteins have led us two decades on. The disappointing answer, I am sorry to report, is that we haven't got very far. But what really caught my eye about the Times' article is that a former Hongkonger apparently set it all in motion. In fact, Yau Shing-tung (pictured), a Chinese University graduate and Harvard-based mathematician, did one better: he first raised those physicists' hope for a TOE and then dashed it (That's something you don't do every day). TOE, first introduced in 1983, is properly called string theory, a mathematical labyrinth which teaches that particles are better thought of as wriggling strings than as points or waves. The ground-breaking work Professor Yau did in the late 1970s was so arcane few people around the world really understood it, but for a time, those in the know thought it held the key to TOE. The problem is something like this: string theory requires 10 dimensions to work but everyone knows we live in the three dimensions of space and one of time, as Albert Einstein has taught. Professor Yau provided a solution which proved the six extra dimensions could curl up like loops in a rolled-up carpet, so microscopically tiny as to have no impact on us but big enough for string-like particles to wriggle around. That made string theory viable and the theorists all went gaga over what are now called Yau-Calabi spaces, so celebrated even a stage play was named after them. Unfortunately, Professor Yau proved only one way to fold up these extra spaces. He soon discovered there are more ways, and a little later, a lot more ways to fold them up - the number of solutions now exceeds 10 to the power of 100 or 1 followed by one hundred zeros. Each solution provides a model for a possible universe with slightly varying laws of physics, and it's almost impossible to tell which model fits the one we live in. No wonder some physicists who don't share the string theorists' enthusiasm are questioning whether TOE will amount to 'TOA [theory of anything]' at all.