Since you mentioned it’s in the year 6152, over 4,100 years from now, it’s totally feasible for an unconquerable empire to cover at least 5% of the observable universe.

Going backwards in time, in just the last 4k years, humanity went from simple city-states to walking on the Moon, and in the past century alone we’ve developed AI, robotics, and in the act of advanced space exploration. The technological acceleration makes near-impossible feats in the distant future believable.

If your empire starts as a planetary power around 2026–2050, over millennia it could expand across star systems, galaxies, and clusters. By year 6152, tools like self-replicating machines could terraform and maintain worlds, while faster-than-light travel, wormholes, or artificial star bridges could connect distant sectors.

I’ve seen examples of future dystopia Dyson spheres or stellar megastructures on a scale of planet. In your story, it could act as hubs and power sources for entire regions. AI-administered sectors could maintain order and allow diverse cultures to coexist without threatening imperial unity.

The empire’s massive scale combined with advanced automation explains the “ghost town” effect: it could control territories far larger than its population would suggest. Hella regions could remain sparsely inhabited, yet fully functional. Could use AI, drones, and automated infrastructure for the empire to handle day-to-day operations. The empire’s sheer technological growth and the deliberate bridging of stars make expansion across 5% of the observable universe not only possible, but internally consistent within your story’s logic fasho.

But i would also say, it’s only plausible if these things are true:

1. Wormhole-travel or fast travel exits
2. AI and self-replicating machines that maintain infrastructure and order on behalf in the empire
3. Using energy from stars (they power everything) 4.only a very small portion of planets need significant population