Reply #23: Sense

[GreenStormCloud]

Assume that a space faring civilization is capable of taking a planet from freshly discovered to fully industrialized in 1,000 years. That would be a gross overestimate of the time needed, but it makes a convenient one. So from one home planet they would have two industrial planets in one millennium. Then that colony would establish a new colony as would the home planet also establish another one. Repeat each millennium. The number of industrialized planets doubles each millenium.

For a starting point, assume that the other planet has got there first by a mere one million years. In astronomical terms, that is nearly simultaneous. So the other planet has only 1,000 doublings. They would have colonized 2^1,000 planets. Yes, two raised to the 1,000th power.

By the 64th doubling, in a mere 64,000 years they will have colonized 9.2 quintillion (9,223,372,036,xxx,xxx,xxx)star systems.

When one considers the 300 billion stars in our galaxy, it is reasonable to conclude that if star travel were possible, somebody else would have already discovered it. And in somewhat less 40,000 years, they would be here.

If we allow a space faring civilization to colonize several planets at the same time, and to bring them up to independent civilization status in only a few centuries, then they get here rather quickly, as they fill the entire galaxy rather quickly.