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.

This episode is sponsored by Brilliant.

When determining what the biggest threats to ourselves are, quite often, you only need to find

a mirror.

Doomsday scenarios for humanity are a common topic of discussion, and one we've looked at here on SFIA before too, but so often those doomsday scenarios really only apply

to her humanity exclusively on Earth and at all technological level or lower.

As we've noted before, while an asteroid impact like what probably killed the dinosaurs

is a terrifying scenario, it's only terrifying to a civilization lacking space travel.

To those with it, an asteroid approaching Earth is a cause for celebration, not worry, as

it represents a handy piece of matter we can mine or otherwise make use of without paying

the fuel bill to bring it here or pull it out of Earth's gravity well.

When you can detect and predict an asteroid coming near Earth years in advance, and when you've got a thriving

orbital economy, you're still going to race out to deal with the matter.

It's just that the race is to get to it early so you can nudge it into a good stable orbit

with the least fuel, and everyone can start suing each other over who has dibs on this

new mountain of money.

Natural disasters just aren't plausible threats to space-faring colonial civilizations,

not in a grand apocalyptic sense.

You don't have your whole population on just one world or even necessarily one star system.

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