In many ways a satnav is a miraculous device. A network of US military satellites more than 10,000 miles above the surface of the Earth, each broadcasting a signal with little more power than a 100-watt light bulb, allows a device in your satnav or mobile phone to triangulate your location on the ground to within seven yards or so. The system is so finely tuned that the clocks aboard the satellites must be calibrated to run 38 microseconds a day slower than Earth time to correct for the effects of general and special relativity. This allows your phone to know your location and, after factoring in real-time traffic information, to calculate the quickest route to any destination with an astonishing degree of precision.
And yet, after all that, I still ignore the advice from my satnav quite a lot.
A few weeks ago, for instance, I had to drive to Gatwick to catch a flight. The satnav told me to take the M25. I ignored it, and instinctively took the A25 instead. (On the way home, by contrast, I was happy to follow my satnav’s advice slavishly.) Why was this?
Actually, I didn’t know at first — my decision to take the slower A25 was instinctive, not consciously reasoned. But, on reflection, I now realise that my instincts were right and my satnav was wrong. Gut Feeling 1, Silicon 0.
This is because the nature of the two journeys was totally different. On the way home, I simply wanted to get home by the quickest expected route — and so the satnav’s thoughts coincided with my own. On the way out, however, I did not want the fastest route: I needed the route which was least likely to cause me to miss my plane.
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