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 wonder where all the vast and ancient alien civilizations are, but could it be that

they've migrated far away in space or time, or even journey beyond all cosmos?

The Fermi paradox is all about asking where all the aliens are, and one option is they

may originate all over the place, but tend to migrate to places more favorable for their civilizations.

This might be densely packed star clusters, or even migration to the vastly larger and denser

galactic core, or it might go the other way, out to the

galactic rim, home of scattered stars or ancient globular clusters, and home to civilizations

wishing to utilize the coldness of empty space far from stars or hiding to the end of time.

Perhaps they flee in time, too, to earlier times in our universe, or to that cold time at the end of time. Perhaps they flee in time too, to earlier times in our universe

or to that cold time at the end, or they may migrate to other universes or even more fertile

dimensions or layers of reality. And far from us, they may not be easy for us to see or

have any desire to reach out to us, figuring we'll eventually

migrate their way one day too, if we overcome the challenges need to become an interstellar

species. We'll be exploring all those options today as we contemplate the effects migration

...