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.tv slash Isaac Arthur and use my code, Isaac Arthur.

This episode is brought to you by Brilliant.

To all good and great things, there comes an end, but it can be a spectacular end when

it at last comes, and that end can be a long time off.

Tomorrow, September 17th, 2021, we will celebrate the seventh anniversary of SFIA's first

episode, Megastructures in Science and Science Fiction.

So this seems like a great time to return to what has become one of our favorite topics.

For those new to the channel, welcome, and while I realize the episode's title sounds

like the name of a heavy metal band, the megastructures we discuss on this show are, often

as not, entire artificial worlds, with as much or far more habitable space than the surface

of a planet.

The end of Earth is a popular topic of discussion in science and philosophy, and the topic

of a recent episode on this show, but in science fiction it's also common to contemplate

the end of alien worlds far from Earth, so given that it's likely most of future humanity

will live their lives on entirely artificial worlds, immense megastructural habitats, it's

also quite likely that deaths

of these worlds will be a far greater interest to future civilizations than will dying planets,

but I suppose contemplating either of their endings would also be an appropriate theme for a heavy metal album.

So our focus today is going to be on examining the ways these might die, and their stages in life,

...