A few weeks ago I had a long discussion about mathematics with someone. It's a not a subject I can claim any deep knowledge - other than the basics - it had simply arisen out of a long conversation that had free-wheeled almost over an entire day. Both of us were sharing a compartment on a train which had left Beijing early in the morning bound for Ulan Bataar, where we due to arrive the following day.

The conversation mirrored the contours of the landscape the train took us past: social, precise, exchanging names, whilst we passed through the orderly Chinese capital; then more relaxed and open, as the train negotiated the blurred interfaces between city and suburb, then suburb and countryside; finally becoming more extended and abstract, suiting the openness and simple vastness of the country the train was pulling us through.

No architectural blueprints exist for conversations, you don't design them; they happen. That's how we ended up debating mathematics. Not unexpected that we would touch on this however, my traveling companion for this particular journey was a retired French-Canadian maths teacher and an indefatigable, hard-core traveler to boot, who had sold up completely to travel for a year in Asia.

The point we had reached at this stage was Zero (the mathematical term and not in the sense that the conversation had been fully mined out), and she was recounting it's history. That's right, numbers have histories. Zero, apparently is a technical invention, it came after the others in the number range. It's there so we have something to express the concept of Nothing.

So many things are taken for granted that it's difficult to imagine how it would be without them. Take a world without zero for instance. No one would ever be millionaires and some birthdays would lose their emotional sting - no one would ever be Forty. Idiomatic language would be struggling: no more zeroing in, or out, and certainly no more "We invade at zero hour !" (we did, it's now going to be at twenty past). Picture trying to explain to someone what naught or blank meant, then try zilch and zip. The awfulness that Ground Zero evokes would be gone (Like millions elsewhere I wish we had never had to use this expression in it's current context).

Funny, I often wonder about a world where there's something missing that I enjoy - chocolate, coffee, especially. But these are things that I take active interest in, I look for them, I search for them. When it's a case of trying to imagine the absence of something so deeply embedded into human thinking as to be virtually invisible like zero, and which is part of our intellectual DNA, then that's much harder. We can't live without it.