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A spaceship appeared near a lake one day. It sent out a series of images, on the left of those images was different sizes of cycles, in the middle was a triangle, on the right was different sizes of squares. Three shapes are connected by double-headed arrows.

Scientists, linguistics and basically everyone went to high school joined a huge discussion on the internet. The conclusion couldn’t be simpler: they want to trade. They will convert what they have to a currency, a triangle, and trade with us. This could mean our first entrance to a big society of the universe! The joy of the realization that we were not alone faded fast. The public quickly focused on debating what they wanted and what they could give us.

On the second part, there was no lack of fantasies. Militaries were dreaming about all kinds of alien weapons, Scientists were yearning for all kinds of answers, Engineers were hoping for all kinds of solutions, even children were imagining space toys. As for what they wanted, the situation was no better. All the digits we had so far of pi, the Euler’s equation, the set of numbers (3,4,5). It’s like Voyager Golden Records all over again.

But everyone agreed that the latter is probably most important for now. Two days after the landing, leaders across the world gathered on a meeting just to address one question: what a civilization so advanced as being able to space-travel could possibly want from us?

A renowned anthropologist gave the opening speech of the meeting. After a tedious tribute to the unity of humanity and endeavor and the rejoice of finally not being alone, he stated that since the universe is spare and limited by the speed of light, the communication is clogged. He then concluded that civilizations in the universe are in a situation that is not unlike tribesmen on an open market. The subtle difference being we were the actual tribesmen wielding stone axes, while they were literally aliens with laser guns. The good thing was that the aliens did not seem to know how primitive we were, or they would definitely not waste any time on us. The strategy was to try to come up with the best of what we had, so the alien would not look down on us. That way, we would be able to get the most from the only life form we know.

He looked at everyone in the room, saying “We are two tribesmen trying to trade. What tribesmen all want? Food? not necessarily. Tools? Maybe. The one thing that all tribesman want is not very different from what we want today. Shells. Or money in our case. “

“We and the space society, if there is one, are clearly not well communicated. Just like ancient human societies. Thus it is reasonable to assume that the space currency would much resemble shells or gold, but not coins and banknotes, let alone stocks or cryptocurrencies.” The audience smiled, for they remembered a few decades ago the hype of bitcoins. “Thus,” he continued “I would like to direct our discussion to what we have, much like shells or gold, that holds the properties of portability, stability, partibility and most importantly, scarcity even for a fairly advanced civilization?”

The next one on stage was an ambitious biologist. He expressed appreciation the anthropologist politely for his opening speech, and started straight to the point. “I agree with my former speaker. I think the most precious thing we have is time. Time is the one thing that is limited for any kind of civilization. What I propose is the crystallization of time: every living creatures on earth.” A series of gasps of disbelief burst from the audience, along with suppressed discussions. The biologist gestured the room to quiet down, “Please let me finish!” he continued, “For over 4.5 billion years live has evolved on earth. Every DNA contains endless failures and successes of every ancestor lied before us. This is an achievement that no one can take away, no one can find out without billions of years of billions of billions of lives died and thrived. This is the true gold that every civilization wants. Such DNA alone with chemical environment of every cell inside the creature, is also some kind of information, which is actually portable and stable is carefully stored.”

“And what exactly is this ‘storage’ you are talking about? How are you planning to give that to them? A sacrifice?” A voice shouted from the crowd. “Yes,” the biologist nodded gravely. “But we only need a small sample of living creatures. Maybe a few species would be enough for us to trade with them.” The biologist had clearly lost his confidence when he said the last sentence, for he had no idea how much a pair of frogs would value in the eyes of an alien. He was booed off stage before he could even finish the last sentence.

A philosopher later talked in a review of the meeting in a talk show, commented, “… (that) is absurd. If every civilization wants the result of evolution, they would have ended up killing each other to loot the so-called ‘crystallization of time’!”

A computer scientist took the floor, he spoke with a wide smile, “Our biologist friend has got a point, but what he is proposing is merely a solution to an NP problem. The NP problem is: what is the best form of life on earth? But lives on earth is not even close to perfection, the example being the recurrent laryngeal nerve and human retina just to name a few. And if such an imperfect solution is all they want, I would say that such civilization does not worth our time. In my opinion, if all a civilization wants is a solution to a problem, a solution to rule all solutions, that solution would be a polynomial solution to an NP-hard or NP-complete problem. That way, all NP problems would be reduced to P. Yet, all they need is one, all others are redundant. Apparently, such things are not a good candidate of space currency.”

“What I am proposing, is the raw power of computation. It is well established that there is a limit on how much computational power you can have inside a given volume of space. The most famous on being the Bekenstein bound, along with many other limits on processing speed , etc. , etc. So instead of giving them pure gold, we should be giving them the mining power of gold, so they could use that computational power to whatever they want. For practical use, I suggest we give them our best classical supercomputer.”

“If I may ask, sir, why not quantum computers?” Someone raised his hand and asked. “That’s a very good question.” said the computer scientist, “We are currently only able to use a few hundreds of qubits, which is a huge improvement over the last few years, but quantum computers are not the magic bullets to all NP problems. They are only good for solving BQP problems, which is only a small fraction of the vast ocean of NP problems. And when you consider how much raw computational power we already have on a classical computer, a quantum computer’s raw performance is not quite as satisfying. In other words, we need now a few thousands of qubits to achieve quantum supremacy.”

Many of the audience apparently agreed with the computer scientists and nodded in admiration of his insight. The next speaker decided not to go on stage, for he thought a perfect answer had come up and he was not able to add anything new to it. So did the one after him, and the one after that. The audience waited in awkward silence, and if no one was to come up the stage, the meeting would end unexpectedly on the third speech.

Finally, a mathematician cleared his throat and went up to the stage. He looked around everyone and started speaking in a trembling accent, much like Master Yoda from Star Wars. “That this is the answer I think not. If computation power that they seek, then they need what, is mere space. Nothing, our computational power is, compared to technologies such an advanced civilization might have. Of more use to them, an empty space is, than space cramped primitive machine that performs primary school arithmetic. Plenty of space in the vacuum, there is. So to earth why they bother coming? I believe not that time is what they seek. For trading would generate more time not. True though, much of the biologist talked is. Important, the crystallization of time is.”

Many elderly participants remembered Master Yoda and were amused, but their respect and deference for the mathematician’s wisdom held it back.

The mathematician continued, “Easy to be satisfied, stability, scarcity and portability are. Hard to find, partibility is. Granular the currency must be.” And then he signaled a young man to come up to the stage. The young man took over the microphone and said “What my professor is saying is that any solution to any NP problem, no matter how easy or how hard it is, is as good as any other. Such a solution would be a proof of invest of time, are hard to manifest, easy to verify, is intellectual thus perpetual and portable, and are granular.”

An economist asked eagerly, saying that such currency is “naturally universal”, but was concerned about bad money driving out good, for “the quality of an NP problem is bound to get cheaper and cheaper.” A question of how to avoid duplicates of such NP solutions was asked by another physicist.

The young man said slowly “Duplicates will not count as a valid currency. There should be a bank that keeps track of which civilization solved which problems. And unfortunately, this is like bitcoin, if any of you remember. The late-comer must put more effort into the mining as more and more easier problems have been solved. So this also addresses your question of bad money driving out good. It’s actually good money driving out bad, for there is no more bad currency. We think such solution will be beneficial to the entire group of civilizations. As more and more complicated problems are solved, the currency itself will ultimately be practical to actual problems in ‘day-to-day’ lives.” He bowed and went off the stage with the mathematician.

The meeting ended on the 4^th speech.

Soon everyone on earth started working on various NPC problems. A website was quickly founded for people to register their answers to avoid duplications. Almost everyone stopped working and were racking their brains to find and solve an NP problem. Although the mathematician’s claim was that any solution to any answer is equally good, an AI was set up to filter low-quality NP problems for obvious reasons. You cannot expect that coloring a 4-country map with four colors is equal to coloring the world map with four colors. Nor will coloring the world map with red yellow blue and green be a different NP problem than coloring with magenta scarlet indigo and cyan.

Two more days later, a team was dispatched to approach the spaceship, carrying a selected assortment of answers to NP problems in a hard drive. The process was broadcast live. The commentator said that although the hard drive was an outdated storage device, it is more reliable and the information was stored in an “obvious” and robust in arrays of directions of magnetization. When the team came near the spaceship, some kind of hatch opened. Everyone in front of a screen gasped. The leader carefully put the hard drive into the hatch. It closed. Everyone on earth held the breath. The world has never been so quiet ever since the dawn of humanity.

Suddenly the signal was interrupted and a message was shown on every screen on the planet with different languages, including sign languages, languages without words, and those were long extinct. “Congratulations! Any civilization that is capable of figuring out what the currency is, is eligible to join the united market of the galaxy. Welcome. We will meet again!”

The spaceship suddenly disappeared just like it came.

Afterthoughts:

I first thought of the similarity between computation power and gold. In my not-so-informed view of economics, gold is hard to mine, and owning gold means owning money. That, together with the idea of bitcoin giving miner salaries gave birth to this short fantasy. And the biologist part is a reflection of what I have been wondering about life and evolution itself. I could have written it better if I read more about complexity theories, but I will settle for this for now.

There are bound to be loopholes and other factual mistakes in this wild thought of mine. If you care to point it out, please leave a comment.