But is there an adaptation of one world currency? Can Bitcoin or other cryptocurrencies be a substitute for money in the future?
I doubt if we will have one world currency. Many countries will refuse the idea of a single world currency. Instead, I guess many countries have their own digital currencies as China does with Digital Yuan currency. Regarding Bitcoin or other crypto coins, they are possible to be the world currencies, but they seem not to substitute the national currencies of each country in the world.
Governments will not allow it too since it's decentralized that they have no control much more if it's centralised since there are different countries who will manage or will manipulate it. They might allow BTC or other altcoins but not to the point they will all accept or allowed a one crypto currency only without them being able to control it.