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 brought to you by Brilliant.

Probably two of the most common and important questions in astronomy are what black holes are and what dark matter is,

but many wonder if dark matter and black holes are the same thing.

Others suggest black holes might be the key to finally shedding some

light on dark matter.

What are black holes? What is dark matter? And do they have anything to do with each other?

The simple answer is yes, they are very related, we're just not sure how much. And today we're going

to talk about both the notion that mysterious dark matter might be composed of black holes,

and the newer idea that we might be able to use black holes to learn more about dark matter.

One thing both have in common is they are seemingly invisible except by their gravitational

effect on the outside universe.

And that's probably a good place to begin for the entire subject, because until the last

couple of decades, there was real doubt about if Blackhors actually existed, and many

folks still wonder if Dark Man herself is just some measuring error.

Both concepts are similar in age to the term

galaxy coming to mean one of many giant clusters of stars dating to the early 20th century,

and are very much intrinsically connected to that early understanding of our universe, being vastly

bigger and distinct from our galaxy. We had some suspicions about black horses of possibility even before Einstein predicted them

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