[jonathanstrange]

Right now I rather believe in the Great Filter. If you look at e.g. Climate Change and the current war mongering including unprecedented nuclear threats, it's hard to imagine the current technical civilization is long-term survivable. During the next 500 years we will get delayed genetic weapons that can eradicate all of mankind, intelligent killer robots, probably even weapons that can destroy a whole solar system, in combination with exhausting all of Earth's natural resources. I used to be more positive but looking at our own behavior and judging that most intelligent life might evolve from former predators and technology involves heavy resource exploitation, the Great Filter seems quite credible.

It's also worth noting that long-term space survivability seems to be extremely hard to achieve, we haven't even managed to create long-term sustainable fully closed biospheres yet.

[closedloop129]

Why would you need a biosphere? You need processes that turn energy into nutrients. Those processes can be entirely chemical or cell-culture based.