So this thread spawned a little conversation between me and my coworker. Let's say we identify a star that has some large planets surrounding it (I think we've discovered about 300 extrasolar planets so far), and one of them appears to have something within the habitable zone of that star
Wiki said:
Currently Gliese 581 d, the third planet of the red dwarf star Gliese 581 (approximately 20 light years from Earth), appears to be the best example yet discovered of a possible terrestrial exoplanet that orbits close to the habitable zone surrounding its star.
So let's say we decide to pack up the family and hit the road:
With our current technology we can probably get around 150,000 MPH (Helios pulled off a solar slingshot that was able to get up to that speed). That will put us at
one light year in approximately 4467.2 years, or 223.6 generations.
Let's assume we can efficiently transport the materials and people to space and build a large enough ship, or basically a extra-terrestrial housing complex, to hold a thousand families (we don’t want any crossbreeding), complete with shopping malls and entertainment. Let’s say this is a space version of the
John Hancock Center in Chicago (345m tall, 1.45 billion cubic meters).
Let's assume we have deflectors and collectors that are able to process iron ore and other minerals that we can intercept from space dust and other stuff, and we can expand our ship to continue being able to support the growing population.
Let’s assume we have rules in place to maintain a population growth rate of 0.3%/year (eg ½ of China’s). After 4467.2 years that gives us a population of about 2.5 billion people.
We are living a happy life. We have plenty of work to do and opportunity for expansion. We live out our days in comfy flats. We keep going and going and expanding our ship.
After our first light year of travel, our ship has grown to 3.6 × 10^15 cubic meters, or about twice as large as our moon.
We gave up and didn’t bother to figure out the numbers after another nineteen light years distance, especially since our math is probably off anyway.
So when we get there 85,000 years later, we could have a ship around the size of Jupiter traveling 150,000 miles per hour. It would probably be a good idea to camp out outside of their solar system and use shuttles to visit their planets. Of course, their scientists have already discovered us and may be starting to send probes themselves. So, realistically, we could have smaller vessels visiting them, interacting with their cows and such. But I don't think we'd travel that far and not say "oh hai!!" to everyone on the planet.