Energy is possibly the biggest barrier towards future space colonization. It is entirely possible that we discover some new source of energy that allows us to:

Energy is possibly the biggest barrier towards future space colonization. It is entirely possible that we discover some new source of energy that allows us to: 1. Send a sustainable human population out of the solar system; 2. Travel to an inhabitable planet which may be millions of light-years away; 3. Geo-engineer that planet to the extent that it can self-sustain a moderate human population. None of these steps is trivial. The pessimistic side of me thinks that we may actually never overcome any of these challenges.