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

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

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

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

We sometimes consider that life might be so rare that we have the whole galaxy of

trillions of worlds all to ourselves, and yet the cosmos is made of billions and billions

of galaxies, so aliens would surely still be common on the grander scale, but what if

humanity is truly alone in the universe?

From the earliest days of the show, we've talked about humanity's future in a way that tend

to assume we have the galaxy to ourselves, and we often discussed a future in which aliens

are a rarity, and maybe so rare we might claim this whole galaxy, and built telescopes

fueled by entire stars, before we even spotted the signs of a distant civilization

a billion light years away.

This is a concept that, like colonizing the moon or Mars, is so critical to the show's

discussions that it probably needs updated, but beyond that, it's a giant topic no single

episode can ever cover with lots of implications. Indeed, I never have covered the case where

humanity is genuinely the first civilization in the universe, period, not just our local sector.

That is a very different case than aliens just being rare in terms of how civilization

is going to act and view things if it gets out on the galactic scene and just never sees

anyone else. So I thought today we would explore the reasoning for us being ultra rare or even

unique, along with how it might impact the worldview, or galaxy view, of our universe.

It can seem like that when I talk about having the whole galaxy to ourselves, nearly a

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