“The most dangerous weapon in the galaxy is money, Captain.”
– Duchess Satine Dryze in Star Wars: The Clone Wars
Let's say I zoomed up to Mars in SpaceX, and after a long, somewhat harrowing flight, I wanted a drink. If I walked into the first bar I saw and plunked down a dollar bill, a twenty-dollar bill, my Visa, or even flashed my bitcoin wallet (if I had one), I'm pretty sure the bartender would laugh at me. I could tell him all day long that this was legal tender where I'm from and highly respected by all countries on Earth, but why would he trust me, an alien from a far-off planet he knows nothing about? How could he verify that he would ever actually get paid through his planet's system, whatever it might be? Because this universe doesn't have a system in place for people to make transactions that transcend space and time, I would end up thirsty.
If money is so valuable, shouldn't we be able to easily, quickly, and clearly communicate its value to anyone, anywhere–even on Mars or in deep space?
It's a historic problem as well as a futuristic one, as civilizations on planet Earth made contact and had to figure out how to transact with each other. The point of this exercise is not that I believe there will be a near-term interaction with people from other planets; it is that I believe there is value exploring how we would communicate a common store of value that we would both trust.
From Star Trek to the Death Star
Money, or ...