Wasn't it Tony Sivori who wrote:

Mike Williams wrote:

The numbers of a star-travelling technological species may only be
limited by the amount of real estate they occupy. It's possible that
some civilisations may have managed to artificially limit their
populations, but it only takes one star-travelling species to have
failed to inhibit their biological imperative to reproduce, and they'll
occupy every inch of real estate in the galaxy in less than a hundred
million years.

That assumes that they will have technology capable of transporting
significant numbers to suitably hospitable planets, that said technology
never meets obstacles exceeding its limits (like distance and time in
transit), and that it will always have a base capable of maintaining it.

They don't need to transport significant numbers at any one time between
the stars. 

That is a lot of ifs. And even if it were to happen, it would be a lot of
effort. It would almost certainly be easier to compete locally for real
estate.

The problem with exponential population growth is that no finite amount
of real estate will be enough.

Let's suppose that there's a civilisation whose numbers double every 50
years, and they have a technology that's capable of sending out 10
spaceships carrying two people each to the 10 nearest stars, with enough
technology to get a colony started.

A couple arrive and start breeding. After 50 years there's 4 aliens on
each new planet. After 100 years there's 8. After 500 years there's
1024. After 1000 years there's over a million. After 2000 years there's
over a trillion and the planet is getting a bit crowded, so each planet
builds 10 spaceships and send them off to the next nearest set of
uninhabited planets. 

So after 2000 years there's 100 new colonies.

Another 2000 years later, these second generation colonies are getting
crowded and they each send of 10 spaceships to the next nearest set of
uninhabited planets.

So after 4000 years there's 1000 new colonies.

After 6000 years there's 10000 new colonies.

After a while this pattern breaks down because there aren't enough
nearby uninhabited planets. Terraforming all the material in each
colonised solar system helps slightly, but doesn't affect the overall
picture. So by about 20000 years the picture you end up with is
something like a sphere of stars where every possible inch of real
estate is occupied, that's expanding at close to the maximum speed that
their starships can achieve. If that speed is 0.1% of light speed, they
fill the whole galaxy in about a hundred million years.

So why aren't they here?

-- 
Mike Williams
Gentleman of Leisure