The development of string theory has led to some surprising results. There are only a few possibilities to formulate self-consistent theories of fundamental strings, and in all of them, space has nine, not three dimensions. At first glance, this appears to be a decisive drawback - after all, doesn't space as we know it have no more than three dimensions? However, on further consideration, it turns out to be an advantage. String theorists know ways to describe "curled-up" dimensions which are irrelevant for everyday life, but are crucial for explaining the way the particle content of the standard model of particle physics (see table on the left) arises from string oscillations.