The last time the oil price lost all sense of gravity, as it threatens to again with the price of Brent crude now well north of $100 a barrel, it helped tip the world economy into the deepest recession since the 1930s. Is history about to repeat itself? Much depends on developments in the Middle East, but things are once more looking perilous. By adding to energy costs, the effect of high oil prices is to reduce the amount of money for spending on other things, thereby undermining aggregate demand in the wider economy. Eventually a tipping point is reached...