If the world uses a single currency, will the economy be more stable?
This is a very interesting question. The sovereign nations issue their own currencies and are taken for granted by many people, but few consider whether this is the economically optimal option.
Maybe it is hard to reach that all countries will have a single currency to use. Some countries does not acknowledged the use of other currency except of their old and usual medium of transaction because this old fiat money for them is a part of their history