It's definitely possible for a certain cryptocurrency to attain this level of adoption. Is it guaranteed though? Definitely not. Who knows? The sort of "global currency" probably wouldn't even be decentralized, probably something like PayPal. Also, who knows? If it we're to be a decentralized cryptocurrency, it might not even be bitcoin. It's just pretty early to say for sure.

Well one currency in a  one world is really didnt exist or not done through rather,I think this things is really hard to happen because we are really living in a differrent country with a differrent rule and in a different ways of law .We are living in a one world with a different country and with a different government tahtvis why i really didnt believe that one world one currency didnt really exist .

according to the variety of crypto currency on the web it will not be the only one, but crypto currency will make paper mony go away

I don't believe in it. Bitcoin won't be a worldwide currency due to several reasons:
1) It costs hell a lot, so newbies will hardly invest in it;
2) It's still not accepted everywhere:
3) It has some disadvantages comparing to altcoins (like missing altcoin support, etc.) that slow down the development of infrastructure.

I believe this is the plan.

i think it isbecause bitcoin is have a potential to grow in entire world so i think it is possible to become a currency to the world that's the impact of bitcoin in the future. for being a high quality exchange coin it is become a number one currnce in the future.

Utterly impossible. First of all, the world is composed of too many countries with different government, culture, tradition, currency and economic status. In order for the world to become one and to agree in only one kind of currency, they have to have a united agreement to change these differences. However, looking at the economic status of every countries, it is impossible. Just try imagining how the Third World countries will tie up with the First world countries in terms of its economy, in order to adopt whatever currency will be decided upon.

It is impossible to whole world. Different set of peoples are available in the world in every people to use Bitcoin is not possible. But Bitcoin will grow up not completely. In our world few of the peoples are only used in cryptocurrency. Because cryptocurrency has many drawbacks in the world. It is not a physical money this is main drawback. when it will create a physical currency that time we should consider this currency is a only one.

If US had introduced bitcoin instead of satoshi nakamoto then there was a chance. But now there is no chance that bitcoin will be the only single digital currency in the world. There are many altcoins popping up and also with added features. Bitcoin has gone way far for people that it is not even possible to earn some bitcoins anymore.

In my own view, cryptocurrency lead by Bitcoin and Ethereum is poised to be more popular as years go by but I don't believe that we can achieve a world currency system because of this. There are so many factors and variables involved and I also believe that the idea of 'one world one currency' will not be that beneficial actually to humanity. Just look at the fragile situation right now in Europe years after they adopted the Euro...it is not working well because not all economies are on the same level; each economy has its own strength and weaknesses and these things are reflected in the national currency you take that away and something will not be working at the end. Now, let's look at cryptocurrency. Bitcoin right now has myriad of problems all because just like any man-made innovation it can never be perfect as long as it is still manned by human beings with our human nature. I mean the technology and the capacity for innovations are there but politicking is taking the initiatives away. Decentralization has its own limits and when human nature sets in there would always be humps and bumps along the way.