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,

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What if the galaxy is full of civilizations?

Not silent, not extinct, but deliberately unseen.

We often talk on this channel about the Great Silence as though it was some kind of cosmic

threat, the growl in the dark underbrush, the cold breath on the back of your neck,

that makes you wonder whether something predatory is out there. But silence is not only the

hallmark of the hunter. Silence can be deliberate, cultivated, and strategic. It can be the quiet

of a monastery, the hush of a deep library, or the veil drawn by someone who does not wish

to be seen. In our last episode, we explored the bleakest possibility that ancient machines

might have sterilized the galaxy, leaving only islands of surviving biospheres scattered throughout

the Milky Way. It's a nightmare vision, a galaxy patrolled by the relics of a long-dead civilization.

But that explanation for the Fermi paradox feels like cosmic horror, today's topic is more like

cosmic espionage, the idea that the galaxy may not only be full of life, but full of civilizations

that have chosen not to reveal themselves.

Empires that have gone dark, silent, and shadowed, dwelling in places we do not think to look.

...