Humanity has always looked to expand its horizons. It started on foot, traveling across land to hunt and forage for food. Soon it became horses to venture ever further, and ships to cross the seas. Eventually, humankind developed flight, and their world began to feel small. So they looked to the stars.
Soon after taking flight for the first time, humans reached the moon. Then other planets in their solar system. Then finally, beyond. However, humans were fundamentally limited by the speed of light, a physical constant that constrained their travel. It took human explorers over 5 years in a spaceship to reach the nearest star, Proxima Centauri.
They were nothing if not determined, however. Humanity began building ever-bigger spaceships for ever-longer journeys, eventually culminating in the “Generation Ships”, massive starships the size of the Earth’s moon designed to ferry hundreds of thousands of travelers across the stars as they grow old, die, and have children to continue their journey. Several generations of people lived their entire lives on these ships, knowing that one day their descendants would reach their ultimate destination.
Then, thousands of years later, inhabitants of the Generation Ship “GSS Orion” stumbled across a structure of unknown origin. They knew it couldn’t be human-made, since theirs was the first ship sent out to this distant region of space. They rerouted their ship to orbit a nearby star and investigated.
The structure was a giant golden ring with a rippling, silvery fluid stretching across it. Objects that passed through the ring and its fluid did not appear on the other side. Through rigorous analysis, the citizens of GSS Orion determined that this ring was a mode of transportation. Objects that went through it were sent somewhere, but they were unable to determine where. Eventually, they sent explorers through, using smaller ships designed for just a few individuals. These ships were laden with sensors, recording equipment, and communications devices. They never returned, and the GSS Orion never received a signal from the explorers’ communications devices. Wherever they were being sent, it was far enough away that lightspeed signals weren’t reaching them within a lifespan.
Over hundreds of years, the inhabitants of the GSS Orion studied and replicated the technology of the ring, and used it to develop copies of the ring. They called these structures Gates, while the original is named the Progenitor Gate.
In order for a Gate to be active, it needs to have a paired Gate at a separate location. There does not seem to be a limit to the distance between a pair of Gates. This indicates that the Progenitor Gate does have a paired Gate somewhere else in the universe that remains active.
Humanity had a new renaissance. Generation Ships that had landed and settled on disparate planets across the Milky Way were gradually connected to the Gate Network, and civilizations separated by thousands of lightyears could now travel to each others’ homeworlds in a matter of minutes. Faster-than-light communication was developed using directional small-scale Gate technology, allowing worlds to communicate without sending ships through a Gate.
It has been tens of thousands of years since the GSS Orion discovered and replicated the Progenitor Gate. Humanity has explored much of the Milky Way. Explorers are constantly pushing out to the frontier to expand the Gate Network. The average solar system has hundreds of Gates to various destinations. Every so often, due to bravery, stupidity, curiosity, or some combination, people fly ships through the Progenitor Gate in an attempt to uncover one of the biggest mysteries of the universe. No one has ever returned.