[wruza]

Expansion is a property of k>1 reproduction. We could make a sustainable happy civilization even on this dirty planet, if not our biological drive to multiply and eat all gifted to us resources with time. My bets are not on climate ops or hunting-gathering for mature civilizations, but simply on k~=1, the simplest form of existence that brings more value with time instead of more size.

[jason-phillips]

In my opinion this comment brings the discussion full circle, from reasoning the difficulties of intergalactic travel back to the quandary of our home.

[GoblinSlayer]

Sustainable reproduction is what enables space travel, expansive species spend their time on infighting, they have no resources to fly anywhere, example: humankind. But even in case of humankind, our exponential reproduction is winding down over time. Irrespective of reproduction, a barbaric species won't be able to fly beyond moon.