How Long Is A Piece Of String?

I, and possibly many others, have a liking for this phrase. It is a great non-sequitur. When people ask 'How long will the job take?' and the one being questioned chooses not to be tied to an exact answer, it is guaranteed to bring the conversation to an abrupt halt when used as a reply.

But this week, BBC's Horizon decided to produce an entire programme on this very subject, and sent off Alan Davies to find a definitive answer. ( For those of you puzzled by the name - he is an actor, comedian and well loved panellist on Steven Fry's QI (Question of Intelligence) quiz.)

Alan went to an ironmonger's shop, and persuaded them to sell him a random length of string, which he cut from their enormous roll. It measured 32cm when stretched against their counter's inbuilt rule.

This could have been the shortest programme the BBC ever broadcast.

However, once the scientists got involved, the result was an hour's worth of fascinating television. It soon became clear, accuracy depends on the method being used - so therefore, does the answer! A Professor got Alan to measure a length of coastline on a map, first with a straight rule, then with his piece of string, finally with a map-measuring device. Three methods each giving a different answer. We were soon into the realm of fractals, as Alan and the Professor drew triangles, in ever decreasing size but ever increasing in number, on the damp sand of a Cornish beach.

From here on the programme took on a science fiction aura, as viewers were shown examples of various standard weights and measures. They started with ancient cubits, then moved all the way through the centuries to an extremely expensive, one metre bar of platinum and iridium. This is kept at a constant temperature to ensure its length remains stable, thus providing a perfect standard metre to use as a comparison.

But there are now far more sophisticated ways of measuring length - by using lasers. A metal marker was held in turn at each end of Alan's string, as a robotic sensor marked these points, before giving an extremely accurate reading. It was marginally short of the 32cm, as the string had by now begun to fray, and Alan had held the markers slightly in from the end as a result! Finally, we saw the most accurate and up to date equipment of all, which uses the speed of light to determine length. According to this, Alan's piece of string equalled three billionths of a second…

From speed of light, we were next embroiled in the mind blowing field of quantum mechanics, where objects are theoretically said to be in several places at once. The length of Alan's string was becoming ever more complex to ascertain. By the end of the programme, as far as my overloaded brain circuitry could understand, it ended in a black hole with a length which stretched to infinity. I think I'll stick with the thirty two centimetre version, thank you, or maybe simply keep to the original question, 'How long is a piece of string?'.