Driving along in the car the other day, my four-year-old son asked why things that were closer to us were moving faster than those further away. What should I tell him?Milton Inverdale, London, UKThanks for a vast number of answers to this question, many of which were probably more suited to undergraduate level than to a four-year-old. However, one notable group of wags insisted on sidestepping the answer at all costs.Among these was the inevitable "Ask your mother", from Tony Turner of Tuross Head, New South Wales, Australia.Stephen McIntosh of Hull, UK, suggested: "You are far too intelligent for a four-year-old... have a lolly."More encouraging was the answer from Dave Oldham of Northampton, UK, who offered: "If you can ask a question like that at four years of age it won't be many more years before you can explain it to me."And congratulations to Peter Gosling of Farnham, Surrey, UK, for his unashamedly literal view of the world. His advice was: "I think you should tell your son that it is illegal for him to be driving at four years old." - Ed