At the start of 2017, a Bitcoin, one of a number of cryptocurrencies, cost less than US$1,000. Since then its value has increased more than tenfold to over US$15,000. Some say Bitcoin is the start of a revolution in finance. Other say it is yet another irrational speculative bubble driven by what John Maynard Keynes used to call 'animal spirits'. One of the major challenges facing Bitcoin in the long term is the extraordinary amount of energy it takes to maintain the Bitcoin network. Owen Bennett Jones asked the academic, Catherine Mulligan, and journalists, Frances Coppola and Jordan Pearson to explain why Bitcoin uses so much energy.

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