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 would our world be like if life persisted after humanity was gone?

Sometimes we contemplate an end to humanity but not to our world, and 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 pick

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.

2. Mass destruction by us nukeying 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 there

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's cyclic apocalypses.

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