The universe is slipping away from us. Faster than light, space presses outwards, trawling galaxies further and further, until the light from their stars is beyond our reach and they are dark forever after. The longer we wait, the less heaven remains.
Our future prospects depend upon reaching for those heavens. Stars are vast wells of energy. The amount of energy available to us determines our span here: with more energy, our future selves can enjoy a longer, more fruitful civilization. Enough energy, and we may outlast the sun. We may witness the Milky Way crash into Andromeda. We may watch as black holes devour swirls of red-hot dust, until even trace vapors are gone. To live so long, we need energy. We need mass.
Mass is energy in its most compact form. Our future selves will scramble to gather every clod we can. Even a single grain contains enough fuel to power a person for twenty millennia. We will grasp at every speck.
That is the goal of a star-faring civilization. No need to terraform, when orbiting O’Neill cylinders work just as well. Any sufficiently advanced people will launch von Neumann probes near light speed, aimed out at the edges of the cosmos. They will travel past hundreds of millions of galaxies, each with billions of stars, to the furthest point.
When the speed of these probes is insufficient, when the universe’s gaping expanse travels too fast to keep up, they will settle on comets and asteroids. There, they will engineer massive cargo ships. The goal is to grab hold of every planet and star, to capture dust along the journey home, to haul all the mass of the visible universe back to our origin. A ‘vast, wide-meshed net’ cast across the stars, nothing held-out.
So, we have an answer to the Fermi Paradox — “With such a large place, shouldn’t we see other people out there?” We do not see their Matrioshka Brains enveloping stars. We can’t spot the thermal signatures of Dyson Swarms. Because there aren’t any. An advanced civilization would pour all its available resources into the construction of a fleet of von Neumann probes, to sweep galactic dust homeward on a trillion-year voyage.
Other peoples may have arisen and flourished many millions of years ago. We would not notice. Their whole stuff is scattered across aeons of light. And, only as their bounty drags itself ashore will they wake to reap. Perhaps we are on the very edge of their span and we might glimpse a probe’s landing, grumbling, crunching through planetary crust. We may find it simpler to gather ourselves up, launching alongside our visitors’ vessels, heading to an alien home. Their knowledge would be immense in comparison. We may as well flock together, assured of that meeting-place in everlasting abundance. Their coming would leave nothing but darkness behind.