蘑菇短视频

Which are the world鈥檚 biggest cities, and what are their populations? Two simple questions that we discover are surprisingly difficult to answer. Plus, has the world got heavier or lighter since the industrial revolution? It鈥檚 a question posed by a More or Less listener that got us wondering, too. Dr Chris Smith, part of a group of Cambridge University researchers, known as the Naked Scientists, reckons he鈥檚 worked out the answer. This programme was originally broadcast on the 蘑菇短视频 World Service.