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 ad-free, plus hours of bonus content,

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

Many believe aliens have contacted us, others that they soon will, and if they have,

or if they do, if the ball is in all court, what should our next move be?

Folks coming into today's video might be wondering if the title is implying we have

already been contacted by aliens and asking what we should do, or if we are talking about

a hypothetical case, where they show up and say hello in a very clear and undebatable way.

And the answer is yes, as we will be discussing both scenarios, and for our hypothetical,

we will assume that the well-known Navy UFOs turned out to be aliens.

As channel regulars know, I am pretty skeptical about aliens coming and visiting us, but not, because I think

it would be unlikely they would if they were nearby and could. Rather, I tend to assume there

are no intelligent alien civilizations in our galaxy, or even our wider region of the cosmos.

I tend to assume that if you can travel the galaxy in a practical fashion,

you can also colonize it,

and so on billion-year timelines of evolution and galactic formation,

someone who arrived earlier on the scene than us by even just a million years

already colonized everything. Thus we would see them

easily, even though they were nice enough to leave our planet B. It's also why I tend to

assume if we bump into anyone, while they may not be peaceful, they probably are not going

to be genocidal thugs coming to wipe us out, because it's

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