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.

We often think that one day the world will come to an end and humanity with it, and possibly

with us causing it, but what that era might be like

depends a lot on why humanity went away.

There are many ways for how humanity might cease to exist on Earth, and so we all picked

six basic scenarios to examine, which I think convert over to most other cases reasonably

well.

Those will be, one, an extinction level natural catastrophe.

Two, mass destruction by us nuking ourselves or dystopian industrial scenarios.

3. A super plague. 4. Artificial intelligence kills us off. 5. Aliens come by and kill us off.

And 6. Humanity abandons Earth.

And after we go through those, we'll talk about scenarios for afterwards in a more general

sense, like asking if some other critter might evolve to replace us as intelligent players,

and if so, if they might just be the first in a series of doomed civilizations to arise.

We are assuming we're their first such civilization on Earth, though we examine the scenario

that we might not be the first in our episode The Cylirian Hypothesis, as well as our episode

Cyclic Apocalypse.

We'll move pretty quickly through our first two cases as they are well-known examples,

but also cases where it's very unlikely humanity could be destroyed without leaving the planet

...