Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

When your home doesn't want you anymore, the stars might be your only refuge, and your

greatest challenge.

One of the most common topics on this show is space colonization, heading out to settle

strange new worlds under alien suns. But part of

that conversation is asking not just about the technical aspects of how to journey to a new world,

build settlements, and tear from that planet, or forge that space habitat. It is also about the

motivations and forces in play, causing people to settle

in space. But what happens when the urge to leave is not entirely your choice, when exile,

not exploration, is the driving force behind colonization? And could this end up being the primary

motivation for settlement? On the one hand, there are a lot of inherent human psychological factors that press us to explore and colonize new places.

Evolution tends to produce creatures that grow, explore, and expand, and humanity as a whole has a strong tendency to look over that next horizon,

pioneer of the frontier, and build new homes and civilizations,

humanity's restless spirit has always been its compass,

pointing toward uncharted horizons and untold challenges.

Our willingness to tackle and overcome these challenges is part of what makes us great.

On the other hand, space is unimaginably vast, and the times and energies involved in traveling

to these new frontiers are beyond merely huge.

I don't doubt that we will settle this solar system, but the distance to the nearest star

...