The Milky Way is only about 100K to 200K light years in diameter; the 2 million diameter includes hypothetical dark matter.[1] If it takes a thousand years on a

The Milky Way is only about 100K to 200K light years in diameter; the 2 million diameter includes hypothetical dark matter.[1] If it takes a thousand years on average to spread civilization out by another light year, that's as little as 100M years to spread from one side of the normal-matter galaxy to the other. That's less than 1% of the age of the Milky Way. Assuming exponential growth, an alien civilization could easily have populated the galaxy. Or heck, octopuses are pretty smart and have been around for 150 million years, if they were land animals and figured out fire they'd probably rule the galaxy already. [1] https://en.wikipedia.org/wiki/Milky_Way https://en.wikipedia.org/wiki/Milky_Way