A lot of thought has gone into this area. I think the parameters of this simulation are too conservative, which is perhaps the point. Several issues: 1. Speeds

A lot of thought has gone into this area. I think the parameters of this simulation are too conservative, which is perhaps the point. Several issues: 1. Speeds are likely to be much higher. We largely rely on chemical propulsion plus gravity slingshots. For a sufficiently advanced civilization you're likely to concentrate a star's power to provide significant outward propulsion (and braking!) without the mass concerns of carrying reaction mass; 2. Once you've built one of those starships, it will likely continue on its journey after stopping at a new system to colonize and resupply. It's not clear to me if the simulation assumes this. Given the time frame of 1B years it seems not; 3. Stars in the Milky Way rotate at different speeds. Like in a few hundred thousand years we'll have a new closest neighbour for awhile. This potentially increases spread as the colonized systems drift further away extending their reach over time; 4. The simulation just looked like a collection of stars rather than, say, a spiral arm galaxy. So a realistic timeline is closer to 10M years than 1B years. I'm firmly in the camp that believes the speed of light is a hard limit. FTL drives and variants (eg wormholes) just seem to be wishful thinking by people who don't understand function domains (eg negative mass). Assuming that, a galaxy-spanning civilization is unlikely to be a civilization in the sense we understand it given that it might take you >1M years to cross from one side to the other. That's not really a problem for detecting such civilizations as the source of detection isn't likely to be EM transmissions (as the SETI program began looking for). Instead, it's likely to be the IR signatures of Dyson swarms. Short version: in space, the only way to cool down ultimately is to radiate that heat away into space. That radiation is completely dependent on the temperature of the object radiating heat. For any normal range temperature that's firmly in the IR range. So, if a star has a Dysown Swarm, it'll shine incredibly brightly as an IR source with a very low amount of visible light. Can you spot one such star? Possibly not. But an entire galaxy? You're likely to be able to see that from 1M+ LY away, easily. Given the small amount of time this would take to eventuate, in cosmological terms at least, the reason we haven't been able to detect any highly-advanced civilizations within our light cone is quite simple: there aren't any.