We keep finding space stations, and we don't know why yet.
Most are in orbit around planets, but plenty more are orbiting moons, stars, the odd black hole, or just floating in deep space.
Their age varies, some are so old that just getting close enough to dock makes them shatter like glass, others are so recently constructed that the lights are still on and the reactors are still fueled. All are empty of any life or robots smarter than a roomba.
The ones orbiting planets are orbiting dead worlds, or living worlds where nothing on them is smart enough to launch a space station.
The stations in deep space are weirder. The most information came from the one by Epsilon Eridani. A massive installation, it had docking rings for hundreds of vessels, all empty. It was in remarkable shape for how old it was (from the unrepaired micrometeorite impacts, we estimate it has been abandoned for about 3000 years), so we were able to access a lot of information from its main computer. We found the coordinates of several home planets, and visited them all. All were dead, empty, or in one case, simply missing. The star was still there, the other uninhabitable planets mentioned in the databanks were there, but their homeworld? Gone. No debris or expanding gas cloud, it's just missing.
And that's the thing: if we found space stations along with abandoned ruins of ground-based installations, that'd make sense. If we met dozens of living races, amongst a few empty satellites of long dead races, that'd also be expected. But this is all the evidence we're not alone in the universe we've found.
We've sent probes to over half the stars in this galaxy and visited hundreds in crewed spacecraft, but the empty space stations are the only evidence of alien life. Every planet is either a sterile husk, a gas giant, or a vibrant living world with nothing smarter than a giraffe living on it. Oh, there's strange life forms of every kind! But none of them seem sapient, certainly not sapient enough to build a space station.
Where is everyone? We've been asking that question since we first understood the Drake Equation and the Fermi paradox, but the question has taken on a new form as we've gone to the stars and found endless empty houses in the sky.
It's the difference between looking at an empty desert and walking through an abandoned city. In both cases, there's a silent emptiness, but in the latter case, it seems to contain a sinister element. This place is empty, but it shouldn't be. Something made it empty, and we haven't found out why yet.
We keep looking, and keep listening to the echoes of our own footsteps in the silent habitats.
