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.

The sun is not eternal, is a a ticking clock, and someday our time runs out.

Stars are born, they live, and they die, and if we want to survive, we must learn to outlive our own.

It is easy to imagine the earth as eternal, with the sun rising each morning as it always

has, but strongly reminds us that stars are mortal.

Our sun was born about 4.6 billion years ago, and, like all stars, it has a natural lifetime.

On the cosmic clock, we are halfway through its story, with roughly

another 5 billion years before it swells into a red giant and eventually fades into a white

dwarf. Yet for humanity, the deadline is far sooner. In just a billion years or so, the sun's

gradual brightening will push Earth into a runaway

greenhouse, boiling our oceans and stripping our planet of its habitability.

Long before the Sun's final flare, Earth will no longer be the lush home it is today.

And as we'll see today, there are any number of natural disasters or artificial man-made

accidents that might accelerate this timeline.

And so the question becomes, what does humanity do about it? Do we try to preserve Earth

itself, move it farther from the sun? Do we adapt to a frozen world if our planet just

alone as a rogue? Do we abandon the cradle and scatter into the stars? Or do we seize the tools

of stellar engineering,

lifting fuel from our star and even killing new suns to take its place?

Today we'll explore these options, how civilizations might survive the death of their star,

...