The Vacuum
The space between stars is not empty the way a room is empty. It is empty the way a probability is empty. A single hydrogen atom per cubic meter. A dust grain the size of a bacterium floating across a volume larger than the Earth. The vacuum is a clarity so absolute that it becomes its own kind of density. Light travels through it without scattering, without losing focus, carrying information across billions of years unchanged.
This clarity is a problem for observation. The atmosphere that keeps humans alive also keeps them blind. It scatters the light, warps it, adds noise. The stars twinkle because the air is turbulent. In space, the stars do not twinkle. They are fixed points of absolute brightness. The clarity is overwhelming. Telescopes in orbit must be shielded from the clarity, filtered, coded, because raw vacuum provides too much information. The eye evolved in fog. The vacuum offers no purchase for evolution.
The vacuum is also a graveyard. Molecules that escaped atmospheres, dust from exploded stars, the thin exhaust of rockets; all of it still there, traveling at the speed of whatever launched it, never slowing, never stopping, because there is no friction to stop it. The clarity of space is full of ghosts. They are too small to see. The vacuum keeps them in perfect preservation.