I read an interesting book called Count to a Trillion.
Astronomers detected an antimatter star a mere 50 light–years from Earth, and the US launched an unmanned mission to go there and learn what it could. Luckily the probe was programmed to transmit its findings multiple times, because the first few transmissions were missed; terrorists had launched a bioweapon that nearly caused an extinction event. Eventually Europe recovered enough to be paying attention. Appended like a footnote to the end of the probe’s transmission of everything it found were pictures of the writing covering the surface of the only moon of the only planet in the system, a gas giant.
The Europeans launched a manned mission a few decades later. One token American, the inventor of the suspended animation technique the crew would be using, was invited along. They went, they learned quite a lot from the Monument, they harvested a quite a lot of antimatter, and then they returned.
What they could decode from the Monument was mostly mathematics. A large portion of it was proofs for various theorems of [cliometrics](https://en.wikipedia.org/wiki/Cliometrics), or quantitative history. With a proper understanding of the mathematics, anyone can predict and even control the evolution of any complex system. It could be a computer program, a network, an organism, an ecology, a society, or all of the above at once. The other interesting bit of math was a complete proof of a system for calculating the value of a trade, given the distance between the participants and their relative level of technology and intelligence. It proves that profitable trade is possible between distant star systems, provided both sides know enough. Proper use of the system allows both sides to know the profit of any trade in advance, meaning no prior coordination need be required. Any two parties can use it to launch trade missions that take millennia to arrive knowing that the other side will already have made the same calculations and be expecting the mission.
The rest of what they decode is astronomy and history. The Monument records that a group of aliens in the dwarf galaxy M3 claim ownership and responsibility for the whole galaxy. Through several layers of delegation they are organizing the creation of life here in the Milky Way. In particular, any and all life arising near the antimatter star was seeded by an intelligence inhabiting a globular cluster 1000 light–years away. Therefore humans owe that intelligence a huge debt and must repay it, effectively making everyone on Earth a slave. As soon as they detect anyone tampering with the antimatter star they are instructed to send a mission to deracinate the planet, carry away whatever life they find, and use it to colonize other star systems. This mission cannot not be sent quickly, as we’re expected to be quite primitive and thus not worth spending very much on, but it will arrive in ~11,000 years whether anyone likes it or not. The crew of the ship then depart for Earth.
When they got back to Earth they found that the whole world was strange. Hundreds of years have past, all the countries are different, and their homes are gone. They end up using some of the antimatter as weapons, defeating the militaries of the world and declaring themselves ruler of all. Between their military power, their knowledge of cliometrics (primitive though it is at this point), and the vast riches of the antimatter that they brought with them, they manage to live in some style.
The main character (the token American from before) and his fiance discover one additional proof of importance: any form of life can be elevated above their boss if they can prove themselves more capable of long–term thinking. All you have to do is engage in really long–term trade. They decide that they should make Humanity equal to their boss’s boss’s boss’s boss, the intelligence at the dwarf galaxy M3, by sending a mission there and back. It’ll take 77,000 years but as long as Humanity survives that long and doesn’t forget about them then Humanity will be vindicated and will no longer be enslaved to anyone. They plan to depart the day after their wedding. They spend the night after their wedding in a disused hotel thousands of miles above the Pacific ocean in the middle of a space elevator.
Alas, that night the main character’s rival calls him out for a duel. He agrees and meets the guy at the base of the elevator. But the duel is a trap; his rival cheats and the space elevator is severed. He is buried under the rubble, wounded but alive, as his wife makes her way up to the ship. She can’t turn the ship around and come back for him and so must continue the mission without him. He decides that one night with his wife is not enough and has to find a way to live on Earth for the next 77,000 years or so until she gets back. Cue sequels.
So there you go. Love seems like a pretty good answer to me, but technically any sufficiently long–term motivation would suffice. I’m sure that you could imagine some, if you put your mind to it.
