By Sue Halpern
If you wanted to make a lot of money, quickly, you could not have done much better than to have bought bitcoin in September, 2017. At the time, the cryptocurrency was trading at just under four thousand dollars; three months later, it topped out at more than nineteen thousand dollars. Bitcoin’s volatility (it is nowdiscouraged merchants from accepting it for payment. A vender can never be sure how much a bitcoin will be worth by the time a transaction has cleared. The Bitcoin network is structured in such a way that it can process only seven transactions per second. (By contrast, Visa, the credit-card company, processed a hundred and seventy-five billion payments in the last year, which works out to about fifty-five hundred transactions a second.) At the height of Bitcoin’s popularity, in late 2018, there was so much activity on the network that it could take as much asa week for a transaction to go through—in that amount of time, its value could have changed by thousands of dollars.