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 ad-free, plus hours of bonus content,

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

What if the universe is not silent because no one is speaking, but because something

is silencing them?

We often imagine the universe is a grand cathedral of stars, ancient and serene, a place where

life should arise again and again, filling the dark with

uncounted civilizations.

Yet, when we listen, really listen, the cosmos answers us with an unnerving silence.

No beacon, no megastructures, no friendly wave across the void, just the quiet home of galaxies

turning the night.

And that silence forces an uncomfortable question.

Well, the universe is not quiet because no one is out there, but because something has

made it quiet.

Today, we begin a two-part exploration of that unsettling idea.

In this episode, we will confront one of the most frightening answers to the

Fermi paradox, that ancient self-replicating machines may roam the Milky Way, hunting down

emerging civilizations, and sterilizing the stars. Next time, we'll look at the alternative,

civilizations that are not dead, but deliberately hiding the dark all around us, and why their

strategy may ultimately fail.

But first comes the metaphysically darker path, the Berserker hypothesis, and possibly

...