Have always wonder which currency would the world accept if only one currency was to be used. Maybe the dollar?, don't think so, The British won't tolerate that.
Cryptocurrency?. Maybe. Until the advent of cryptocurrency, I never thought that would be possible but it seems possible.
The world is not too far from a unified currency.
Not going to happen, it is just a dream because as know governments get a great deal of power from their own fiat currencies, this is why the Euro was such a bad idea, to think that a single currency can be the national currency of several countries when each one of them has different needs was complete madness and they are paying the price of that mistake.
There has always been a currency that is the most dominant even way before globalization became a thing in the modern world, but there is never going to be only one world currency and if it happened then we will have a lot of things to worry about as most likely there will be only one government at that point.