I also think that there is no solution to this problem unless you find something what every person on this planet can only do once.
The question is also what you want to achieve with this. Do you just want to give every person one coin, nevertheless what they already own, or do you want a fair distribution of wealth?
The only possible solution posted so far ist from McKane
People get onto a spaceship, and fly to Mars.
Every person leaving the ship gets 1 coin.
Ship goes back to Earth to get more people. Rinse and repeat.
But I would skip the last point, that the ship goes back to earth to prevent replay attacks.
The spaceship should not be able to return to earth.
Next point: No one who enters the spaceship is allowed to take anything with him what could have value.
Even if there would be a solution to distribute exactly one coin to each person on earth (or mars), this would not change anything as long as there are other currencies and other valuable things owned by the people.
This one coin will not make any difference to the current distribution of wealth, if the old value remains. Hence no one should be allowed to take anything with them to the spaceship. But this is actually also mostly impossible as people are corrupt, can be bribed etc.
Next point: if however we manage to distribute exactly one coin to each person, it would not take long until we have the same situation as now.
And the reason for this is, that all people are different.
Such a system can only work if all people have the same ideals, the same morals, the same knowledge, are not greedy and all want the same things and so on. But this is an illusion.
There are always people who are smarter than other people and gain an advantage over people who are not as smart.
There are always people who want to have more than other people.
Even people who won the lottery but are unable to handle money correctly, will lose it again after some time. There are more than enough examples where this actually happened.
This means, a fairly distributed wealth is not possible for humanity.
I can think of a world completely without money, where somehow everyone can get the things he want ("want" not "need"!).
The only way you can achieve this is by connecting everybody to a virtual world where things you want can be created instantly and harm to other people does not have an effect to them physically.
Let me close this post with a quote:
Did you know that the first Matrix was designed to be a perfect human world? Where none suffered, where everyone would be happy. It was a disaster. No one would accept the program. Entire crops were lost. Some believed we lacked the programming language to describe your perfect world. But I believe that, as a species, human beings define their reality through suffering and misery. The perfect world was a dream that your primitive cerebrum kept trying to wake up from. Which is why the Matrix was redesigned to this: the peak of your civilization.