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.t.v.t.v.

And use my code, Isaac Arthur.

The Fermi paradox asks a simple question with a complicated answer. slash Isaac Arthur, and use my code, Isaac Arthur.

The Fermi Paradox asks a simple question with a complicated answer.

If the universe is so vast and old, and life seems likely to emerge, then where is everybody?

It's a mystery we've explored meantime times on this show, sometimes seriously, sometimes speculatively, and occasionally with a bit

of a laugh. There are dozens of proposed explanations ranging from the sobering to the

downright strange. We even did a three-hour compendium of them, which is still a short summary,

and today I'll be sharing five that I find especially compelling, and seven that frankly

I could do without. Or at least, I wish they were less popular because their reasoning

or evidence leaves a lot to be desired, and if they sound great at first.

I know in most top five or top ten lists you're supposed to save your number 1 pick for last

to keep folks watching, but in this case I think we need to start with the number 1 on both

ends, because they're essentially the default answers to the Fermi Paradox, and honestly,

I haven't ranked the rest all that precisely anyway.

Since I have got more explanations I dislike than I like, let's start there,

with what's arguably the original Fermi Paradox solution.

And that's the idea that space is just too big to colonize.

As the Hitchhiker's Guide to the Galaxy puts it, space is big, really big.

...