A single world currency may come to exist within our generation. This mean having one form of fiat money that is unanimously agreed on having value by all people in the world, some what like the USA dollar or Bitcoin, much needed as humanity progresses towards absolute globalization. Although the negative of one single global currency is monopoly, I believe that its advantages outweigh its demerits because of simplification and equality.
As with many aspects of economics, having a single system of money can pose certain dangers to society such as corruption and conflict resulting from monopolizing the monetary exchange. Having a homogenous form of money worldwide makes it vulnerable to abuse because those in power of managing money could take advantages on international scale. I still clearly remember the global crisis of 2008 caused by the abuse of the USA dollar which led to an international catastrophe for banks in many countries. Nevertheless, the overall potential of a world currency is greater than its negative.
Undoubtedly, the benefit of having the same money used by all eight billion people on earth are easier transactions and greater equality. This means that humanity could not only get rid of a complex foreign exchange system, the forex which in itself is cumbersome and costly, but all humans could be rewarded similarly for service and products that are identical around the globe. I strongly believe that having one form of international currency like bitcoin and rewarding a doctor in India the same amount as a physician in the USA which work one step closer to a fair in global society.
Conclusively, the single world currency may lead to globalization of the world and society, there is equality and reduce risk of corruption or abuse of money, although, the monopoly in currency may have a jeopardizing effect on many sectors.