Money is saved up work. Physics calls that energy and the unit is watts. So could we swap money for watts? No, money is slightly more than just energy. It's intelligently directed energy. And energy can't be converted into intelligence. Except now it can.

In Ian Banks Culture they have no concept of money at all. Everything is abundant so nothing has a price. However, certain works of art can be treated as scarce and when that happens they reinvent money. The mark of a great work of art when they say "we reinvented money for this".

Is Ian Banks right or will watts remain in use? I think watts will be used since energy can be transmuted into matter and vis versa. So if you want to own a planet or a comet you could purchase it at it's energy value. If it's in a desirable location then you might pay somewatt more than it's energy value. If it's a long way from the nearest black hole you might pay less than it's energy value to account for the cost of transporting it to be converted into energy.