Slow aliens: Realistic scale

Here's an idea that I've been toying with. The aliens are real, they are here and they dominate at least a part of our galaxy.

How did they overcome the vast distances and why haven't we noticed? Same reason. This alien race is s-l-o-w. Their life span is orders of magnitude longer than ours. (Their metabolism is slower in a similar manner) So they can explore, conquer and colonize one solar system after another without FTL. What's a hundred year journey to a fifty thousand old person?

Now my question is about scale. As I said, these aliens now dominate a part of our galaxy, so they must be "slow" enough to manage an empire at least five thousand light years across without FTL tech. They also must be so slow that we haven't noticed them yet (we might have detected them, but we mistook their actions for geological/astronomical events) At the same time I don't want to make them too slow. Otherwise they couldn't realistically have developed in our galaxy's lifespan, and we would also never notice them making the story less interesting.

So:

• How much slower than us do they have to be to become a local galactic superpower given that communication is limited by c and travel by fractions of c? (Hand waved propulsion for now)
• Where is the sweet spot where the are just fast enough for us to realize they exist and are coming?

Some clarification after excellent comments:

The effect I'm after is that the alien precence becomes obvious once you take a (long) step back. (Wait a minute, the continental drift isn't random?) If this concept turns into a story it will be around a somehow balanced conflict between us (who can do small-scale things quickly) and them (who can do large-scale things slowly)

posted over 7 years ago

Guran‭

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