Hm. I tend to think that it's not impossible, but simply very impractical. Outside of the very nearest neighbouring systems, any interstellar colony would inst

Hm. I tend to think that it's not impossible, but simply very impractical. Outside of the very nearest neighbouring systems, any interstellar colony would instantly become an isolated new civilisation. There's simply no plausible way for interstellar trade or even just meaningful communication. All a colony at say, 82 Eridani - a sun-like star about 20 ly from Earth, would have a two-way communication time of 40 years. Even digital "goods" aren't worth exchanging if it takes 20 years to send them and another 20 years to receive any kind of payment. At a very optimistic 30% lightspeed, ships would take 67 years to get there. This means no one can make the journey within a single human lifetime, unless the lifespan is dramatically increased or some form of hibernation technology is used. In any case, colonists would be completely removed from Earth and all that effort pretty much requires a suitable target planet to be present. Without radical genetic changes, humans wouldn't be able to thrive and survive on a Super Earth or in poisonous atmospheres. So another factor would be spending tens of thousands of years and unfathomable amounts of energy terraforming planets or changing the human genome beyond recognition. The same issues would apply to extra-terrestrial intelligences as well, which is why I don't think interstellar colonisation would even be all that desirable in the first place. First you have to find a suitable host star. Next you need to find a matching planet. Then you need to scout potential candidates (likely using automated probes), which would take about a century even for just the nearest stars... While all this is certainly doable, it's really not all that attractive given that you instantly "lose" the colony anyway simply due to the distances involved.