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 add free, plus hours of bonus content,

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

We often look out into the galaxy and wonder where all the civilizations are, but could it

be that we don't see them because they've all chosen to exist in fortress star systems

surrounded by despoiled deserts of their own making.

When we look up the night sky and see thousands of stars, it naturally raised the question

of if any of those might be home to other peoples, distant kindred of ours, spiritually

if not genetically.

When we found out the galaxy is so much bigger than even what

we see, and itself is but a pinprick in the universe, it's natural to ask the question

of why we don't see other alien civilizations. This is what we call the forming paradox,

the seeming contradiction between our observations of how big an ancient our universe is, how full of

life all planet it is, and how absent the rest of the universe seems to be of that life.

The universe is throwing the ultimate silent party, and Earth didn't get the memo, either

that or invitation got lost in the cosmic mail.

One option that we explored a couple

months back is that life is quite common, and it just rarely gets very complex. Only for a

fraction of the time Earth has had life on it has had any real plants or animals, so perhaps

we are an anomaly and the universe is full of worlds that are full of slime

and algae and not much else.

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