Dr. Relic Hunter had seen dead civilizations before, but never one that had been murdered.
She floated in the observation bubble of the research vessel Chronos Deep, watching her team of xenoarchaeologists swarm over the ruins of Kepler-442b. From space, the planet looked diseased—vast swathes of geometric scarring where cities had been systematically erased, leaving only mathematical precision in destruction.
"Dating confirms it," her assistant, Artifact Seeker, reported through the comm. "The entire civilization was eliminated in a single rotation. Approximately twelve thousand years ago."
"Weapons signature?"
"That's just it, Dr. Hunter. There is none. No radiation, no exotic particles, no antimatter residue. It's as if someone simply... deleted them."
Relic frowned. In thirty years of excavating dead worlds, she'd catalogued civilizations that had destroyed themselves through war, environment collapse, transcendence, or simple ennui. But this was different. This was precise, surgical, intentional—and impossibly clean.
"I'm coming down," she decided. "Prep the temporal imager. If we can't find physical evidence, maybe we can find chronological echoes."
The surface of Kepler-442b was a graveyard of absence. Where cities should have stood, only perfectly flat plains remained. Where the planet's crust showed evidence of mining, the excavations had been filled with material that matched nothing in the local geology—as if someone had carefully erased all evidence of resource extraction.
"It's like someone cleaned up after killing them," Artifact mused, running his hands over a surface too smooth to be natural. "Who murders a civilization and then tidies up?"
The temporal imager revealed more mysteries. The device could read quantum echoes in matter, reconstructing shadows of the past. But when they activated it, the display showed only static at the moment of destruction—a perfect sphere of nothing expanding from a single point until it encompassed the planet.
"Information vacuum," Relic breathed. "Someone didn't just kill them—they erased the information of their existence. But they missed the echoes, the quantum shadows."
Working backwards from the sphere of erasure, they began to piece together the final days of Kepler-442b's inhabitants. The aliens—hulking crystalline beings that communicated through light—had been on the verge of something momentous. Their technology had reached a crucial threshold.
"Look at these equations," Artifact said, highlighting reconstructed mathematics from a research facility. "They were working on... is this zero-point energy extraction?"
Relic's blood ran cold. "Not just extraction. Weaponization. They were trying to turn vacuum energy into a weapon."
The pieces fell into place with horrifying clarity. The crystalline beings had discovered how to tap into the universe's fundamental energy, the quantum foam that underlies reality. But someone—or something—had stopped them before they could implement it.
"The Guardians," Relic whispered, invoking the name xenoarchaeologists used for the hypothetical ancient species that seemed to police dangerous technological development. "They're real."
They'd found hints before—civilizations that had mysteriously vanished just as they achieved certain technological milestones. Stars that had been artificially dimmed to prevent their planets from developing. Regions of space where physics itself had been subtly altered to make certain discoveries impossible.
"We need to go deeper," Relic decided. "If the Guardians cleaned this up, they might have missed something in the quantum substrate."
They deployed the deep archaeology equipment—devices that could read information fossilized in the quantum vacuum itself. And there, buried beneath layers of deliberate erasure, they found it.
A message. Not from the murdered civilization, but from their killers.
"THRESHOLD SPECIES IDENTIFIED. VACUUM ENERGY WEAPONIZATION ATTEMPTED. INTERVENTION SUCCESSFUL. TOTAL INFORMATION CLEANUP COMPLETED. TIMELINE PROTECTED."
"Timeline protected?" Artifact asked. "Protected from what?"
Relic was already pulling up her database of dead civilizations, cross-referencing with the technological thresholds they'd achieved before extinction. The pattern was clear once you knew what to look for. Every civilization that had come close to certain discoveries—vacuum energy weapons, causal loop generators, consciousness transfer at galactic scales—had been erased.
"They're not protecting the timeline from these civilizations," she realized. "They're protecting it from what these technologies would cause. Vacuum energy weapons could literally unravel spacetime. Causal loops could create paradoxes that retroactively prevent the universe from forming."
"So the Guardians are... what? Cosmic gardeners? Pruning dangerous branches from the tree of technological development?"
"More than that." Relic pulled up the quantum echo data, showing the moment of erasure. "Look at the precision. This isn't just advanced technology—this is technology that understands the deep structure of reality. The Guardians aren't just older than us. They're operating on a level that makes our physics look like cave paintings."
As they prepared to leave Kepler-442b, Relic couldn't shake a terrifying thought. Humanity was advancing rapidly. How long before they crossed one of the Guardian's thresholds? How long before Earth became another archaeological site, its people reduced to quantum echoes and careful notes in an alien database?
"What do we do with this information?" Artifact asked as they departed the murdered world. "If we report this, if humanity knows there are technological paths that lead to extinction..."
"We document everything," Relic said firmly. "That's what archaeologists do. We preserve the past, even when it's a warning. Especially when it's a warning."
She looked back at Kepler-442b, now just another point of light among billions. Somewhere in the galaxy, the Guardians continued their work, pruning civilizations that grew too dangerous. They'd been doing it for millions, perhaps billions of years—a cosmic filter that explained why the universe seemed so empty despite its age.
The Fermi Paradox had an answer, and it was terrifying in its simplicity: civilizations that developed certain technologies were erased so thoroughly that they might as well have never existed. The universe wasn't empty—it was carefully maintained.
As the Chronos Deep entered hyperspace, Relic began composing her report. She included everything—the evidence, the implications, the warning. Humanity deserved to know what lines not to cross, what research to avoid, what futures led to deletion.
But in her heart, she knew it might not matter. Curiosity was fundamental to intelligent life. Eventually, some human scientist would push too far, discover too much. And then Earth would join Kepler-442b in the catalog of archaeological sites, another dead world for future xenoarchaeologists to puzzle over.
The universe had gardeners, and they did not tolerate weeds.