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.
Same currencies are possible in regions that are economically similar. Like USA and Somalia can not have a same currency but USA and Britain can do so.
And there is a currency that is used all over the world too, Thats US Dollar. So there can not be one specific answer to your question thats why it is an interesting debate !