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.

Welcome to the SFIA-i Paradox Great Filter series.

This one began as a spin-off of our looks at the Fermi Paradox, the big question of where

all the aliens seem to be hiding, and is rather the twin of our alien civilization series,

so as I decided it was time to start cleaning

up and organizing our audio-only versions of these episodes, it seemed appropriate to start

with the two of them.

Way back when I first started offering our episodes as audio-only, I decided I'd do some introductions

to the existing series and playlists, but I've gotten rather out of the habit

of doing that, or indeed of adding episodes to the playlist here, and after recently

adding our live stream audio recordings last week as a new playlist, I figured I should

set some time aside to get back in that habit.

As I said, our great filter series is essentially one of the twin spin-offs of our Fermi Paradox

series.

Where Fermi Paradox solutions go, you basically always have two fundamental camps, one that focuses

more on why we are not seen alien civilizations, or at least not admitting they exist,

which is very psychological and motivation-based,

and others that have more to do with the basic physical laws and scientific concepts.

They tend to offer us a reason why life, or at least intelligent life, might be rather

...