NEW HAVEN – You might think that we have been living in a post-bubble world since the collapse in 2006 of the biggest-ever worldwide real-estate bubble and the end of a major worldwide stock-market bubble the following year. But talk of bubbles keeps reappearing – new or continuing housing bubbles in many countries, a new global stock-market bubble, a long-term bond-market bubble in the United States and other countries, an oil-price bubble, a gold bubble, and so on.