Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content,

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

This episode is sponsored by Audible.

However often the universe gives birth to life, intelligence, and civilization, some civilization

had to be the first, and that lonely, first to the party civilization, looking around

wondering, where is everyone, might very well be us.

Looking out the immensity of the universe with its billions of galaxies, each billions of years old and containing billions of stars and planets, it's kind of difficult to imagine

we are all that is, the only place with life on it, and yet in the century or so since we

started getting a grasp on

how big the universe is and searching it for signs of life, we've come up with no strong

evidence of any other civilization.

This we call the Fermi paradox, the seeming contradiction of just how big and old the universe

is and how devoid of life it is, or at least of intelligent life making its presence

detectable.

Many explanations have been offered over the years, but one of the most common is that

life just isn't that common, or at least rarely manages to reach our current level, and

it would need to be further along a pathway to space colonization or energy abundance for us

to be able to see or hear them.

We've discussed this possible solution and the reasons for it in our great filter series,

all the various factors that might filter out candidates at various steps from newly

...