Reply #28: just a whole lot of assumptions there

[qazplm]

1. a space faring civilization is a stable civilization. Disease, internal conflict, accidents, even conflicts with other space-faring civilizations could result in your consistent pattern of doubling not taking hold.

2. Every colony will produce another colony/the home-world will continually send out new colonists. All sorts of reasons why that wouldn't be true. Religious or other dogmatic reasons might cause some colonies not to ever spawn another colony. It might also cause the original home-world to cease sending out more colonies. Heck a home-world could send out it's first colony, and then be taken out by a Gamma Ray Burst, or Super Volcano, or Asteroid/Comet impact, or huge CME, etc.

3. We aren't the first/most advanced intelligent life-form in the galaxy, or one of the first. No evidence one way or the other, we have no idea how long it takes. Certainly odds are it requires a second-generation star or later to get the heavier elements necessary, we think, for complex life to take hold and certainly for technology to reach the level of interplanetary flight.

4. When we were "discovered," we were habitable/appealing. You only have to go back to early human times to see a glacial, cold period where we almost went extinct because of the world climate. There have been plenty of times in our planet's history where it's not been appealing to live here. A civilization could have come by at the wrong time, said, eh, not worth it, and left.

5. That if they did colonize a planet, they would ignore the indigenous life. Let's assume you are right, and a civilization would have already come here, why does it then follow that they'd have colonized? Perhaps they saw intelligent, but non-advanced life, and somewhat like the Prime Directive, simply went somewhere else so as not to get involved. Perhaps that's too naive but I suspect that even we would at least have that conversation if we were to come across another less advanced civilization sometime in the future.

Just a ton of assumptions in your somewhat glibly confident statement. There are a lot of reasons why "they" may not currently be here, and none of them require that "they" not exist.