Humanity is not what it used to be.
Fourty thousand years ago. That is when humanity left its shores. Earth was our home and our shining beacon, a great example, no... the
only example of a successful civilization this galaxy had ever seen. We were the first in space, the first to overcome the troubles that led all others into extinction. In those days, mankind looked to the stars as an absolute destiny, one last, final frontier with no bounds.
It is now possible for humans to live several centuries, if they so choose. Our pasttimes include building cities for lesser species, classifying alien biology, and terraforming barren worlds. There are at most 20,000 humans on a world, any more and they start having to share natural resources with each other. Most don't interact with more than a dozen other humans in their lives aside from their vat-grown successor. They prefer to talk to AI's usually, and within a lifetime it is possible to learn every subject of math, biology, physics, engineering, and literature. Humans are fairly independent these days.
But there is one rule that is universally never broken, and that is: "Never uplift another species." Some see this rule as an example of the human desire for dominance and power, while others see it as justified. To them, the human condition is a curse. Once you know everything, there is no purpose anymore, nowhere to go further. Humanity has progressed as far as it can go. Science has stagnated, and everyone knows that once you learn everything, you will never again have that sense of discovery. Though it is in a sense true that one can re-learn things after getting rusty over the years, that sense of learning something new is never again there, at least after the first few cycles.
Humans usually self-terminate before their 200th year.
Hence, the
Discovery Project.
It has become a custom in the stellar systems neighboring Sagittarius to dive into the supermassive black hole at the center of the Milky Way, rather than to self-terminate. It is considered a wasteful practice by some, but for others it is a dream come true, and some are willing to cross lightyears for it, without FTL.
Some have taken advantage of this trend by equipping black-hole-divers' vessels with incomplete faster-than-light Warp Drives, requiring nothing but exotic matter to complete. Because exotic matter cannot be found in our universe, FTL has been a dream long abandoned. However, if black-hole-divers were to enter the antiverse of a black hole and acquire exotic matter, it would theoretically be possible to travel back through the black hole and into our universe again. So far there has not been any tangible success... but these people have nothing left to lose anyhow.
The hope is that somewhere beyond the event horizon lies a breakthrough, something which will allow humans to progress further once again. Something to lift humans up out of stagnation.