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 brought to you by World Anvil.

A new model suggests that nearly a quarter of the universe is now colonized by a few

thousand, graby, alien, mega-civilizations, each one controlling not just millions of worlds,

but millions of galaxies, and that humanity will likely join their number

shortly as the heir to quadrillions of stars and planets.

So just over a year ago, Robin Hansen, some colleagues released a paper in the Astrophysical

Journal titled, If Loud Aliens Explained Human EURliness, Quiet Aliens are also rare,

which will link in the description as well as a website GravyAilions.com.

And almost as soon as it came out, folks started asking if I'd do a video on this new

solution to the Fermi Paradox, and I joke that we'd already done several.

Grabby Aliens is a cool mathematical model, but we need to say from the outset that it is not a new Fermi

paradox solution. It is modeling a trio of variables we have some data on that are related

to civilizations getting out to the stars, and it seeks to show us that for any plausible value

of those variables, the only one that

makes sense is that alien civilizations don't pop up much, that the kind that remain fairly

quiet from observational standpoint aren't vastly more common than the big loud expansionist

ones, and that therefore humanity doesn't see any aliens because we are among the earliest.

It suggests there might not be any of what we would consider to be alien civilizations in this galaxy,

and that it's probably half a billion light years, if not more, much more, to the next high-tech alien civilization.

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