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.nebula.t.v.t.v. And use my code, Isaac Arthur.

When our ambassador to the aliens of the D Denal party system found out he was invited to be the guest of honor at their annual feast, he told his alien colleagues he was very nervous trying to come up with a good speech.

Thankfully they assured the ambassador that he needn't worry about it and they merely wanted

to have him there for dinner as a man of wisdom and good taste.

I generally tend to fall into the category of being skeptical that there are any alien civilizations

within our own galaxy, and probably even our small corner of the universe.

A lot of the reason for that comes down to try to think through how a given alien civilization

would act if they arrived on the galactic scene ahead of us, and also considering this

in light of various concepts for alien behavior folks in science fiction have come up with.

Frequently these are high concepts scenarios like what if life evolved on a world with no sun

or two sons, or tweaking existing traits to a greater extreme, like the warrior culture

of the Cleons from Star Trek,

or a science and logic devoted cultural like the Vulcans. A lot of times the behavior

seems to break down on examination or suggest unexpected pathways the behavior should seem

to almost inevitably lead to, frequently counterindicating such a species could really exist,

or if it does, should

generally act as what we call a loud alien, the kind we absolutely expect to see on the

galactic stage if they arrived before we did, and which seem rather absent.

The biology and psychology of aliens is hard to contemplate beyond presumably being

...