11 - Estimates of Expansion Timescales

Summary

Introduction

‘I see that the valleys are thick with people and even the uplands are becoming crowded. I have selected a star and beneath that star there is a land that will provide us with a peaceful home.’

Ru, Traditional Founder of Aitutaki in the Cook Islands (Buck, 1938)

An important corollary of the question ‘Where are they?’ is the question ‘Could they have gotten here yet?’ If we imagine a spacefaring civilization arisen a billion years ago and a thousand parsecs from Earth, what are the odds that the descendants of that civilization would have established settlements in the solar system before now? The answer, I believe, is that, if such a civilization had arisen and if interstellar travel is practical at a small percentage of light speed, it is virtually certain that the solar system would have been settled by non-natives long ago. Unless we discover that interstellar travel is impractical, I conclude that we are probably alone in the Galaxy.

We know nothing of any extraterrestrial civilization. If we assume that some have existed, it is also reasonable to assume that at least some would be as inquisitive and as eager for adventure as humanity (Hart, 1975; Jones, 1985). It would take but one such species to fill the Galaxy.

Humanity has a history of expansion into available areas on Earth. If we examine our past, we can estimate how long it might be before humanity would expand throughout the Galaxy.