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. This episode is sponsored by Auduble.

We often wonder where all the ancient alien civilizations are, and if they might not exist,

but could the reason be something as simple as a vital element being scarce?

So we had a big new discovery recently that we found phosphine gas on Venus, a possible biosignial for life, and while this episode was written before that and this focused principally

on what the scarcity of phosphorus might mean for looking for alien life, it's a bit too

important and relevant of a discovery not to address, and so we'll begin to it at the end

of the episode as an addition.

Our regular viewers know that one of our favorite topics, and indeed the topic that

inspired me to start the channel in the first place, is the Formy Paradox. This is the great

looming question in our so far fruitless search for other life forms in the galaxy. Why,

when the universe is so vast and old and life can form spontaneously from base molecules

and involving ascension beings like we did, have we not detected any clear signs of life

anywhere, let alone

galactic civilizations?

The answer is that so far we don't know why, but we have come up with a number of theories

as to what might make it more rare and difficult than we thought for life to form or

for intelligence to arise, what forces might just occasionally kill our life off and

start the process

over, and what errors in judgment might lead civilizations to destroy themselves not very

...