I' ll take bitcoin as an example.
Is it mandatory that the value of all bitcoins is equal to the value of the world economy?
Can this value be archived before all the bitcoins are mined?
When I buy bitcoin someone will take my dollars.
So how can we technically replace all dollars with the bitcoins?
In the end will there always be someone with only dollars in their pockets or am i wrong?
A currency is just a debt title. Someone gets a service from you and "writes" you a debt title. then you take that and aquire something from someone else. BTC can replace that with some advantages - It´s decentralized and not inflationary. However it has to overcome it´s scalability problems. Moreover it should be more stable, price wise and fungible to become a real currency for everyday use.