As with Rome, the limitation is often communication and transportation.
You’d have a hard time even keeping Mars part of unified empire with Earth given our current technology level. We simply can’t move things back and forth easily enough until we figure out fusion reactors (or some other power source) to a much higher level than we currently have.
Any sort of empire spanning more than a single solar system would require faster than light travel and communications.
Libra@lemmy.ml 2 days ago
I’ve heard it said before that the limitation on empire size is about 2 weeks. That is to say, if it takes longer than 2 weeks to get a message from the capital to the frontier it causes instability. So, it’s more about time than absolute physical size.
davidgro@lemmy.world 2 days ago
Assuming no FTL and centered at Earth (or the sun) that puts the max distance roughly a little past the low estimate for where the Oort cloud begins.
(Wolfram Alpha says 14 light days is 2424 AU and the cloud has inner edge estimates from 2000 to 5000 AU