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I do not understand where the value of the bitcoin comes from.
In old times people were trading in gold or silver. They began to deposit the gold coins in banks and started to trade with these deposit certificates. The deposit certificates became paper money. Then the convertibility of paper money for gold was abandoned, but the paper money had its momentum so it remains in use today.
But how did bitcoin get its momentum? I understand that to get bitcoins, you need to compute some cryptographical puzzles, so the amount of bitcoins is proportional to the computational time spent. But is this computaitonal time spent usefully as in industry, or is it just spent for the sake of gathering the bitcoins?