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 ad-free, plus hours of bonus content,

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

We estimate the sun might have risen over Earth 1,659 billion, 330,000,750,000 times,

and will likely rise as many times again or more before the sun consumes our world.

And yet many more worlds will live on after ours,

most not coalescing for trillions of years after Earth is but a memory,

what will that last planet be like, that last sunset, and will anyone be left to see it?

To all good things there comes an end, and as much as we all like sequels to a good story,

there's no denying that even the most compelling tales tend to get boring after a time.

Perhaps that's so for all planets or the universe itself, but after trillions of sunsets, it does not seem that

the tail of Earth has grown tiresome yet.

Truth be told, we don't know how many times the sun will rise and set on this world.

The days used to be faster back in the primordial era of Earth.

Our orbital dance with our moon has slowed in tempo over the eons, and will keep doing so as time goes on.

Stars form and then die, and from their ashes are new worlds born, are our new sons.

To the best of our knowledge, this process began about 13.5 billion years ago, roughly thrice

the Earth's age, and our current models suggest

that all galaxy will still have nebulae, pockets of gas dense enough for stars to form from,

for some time between 10 to 100 trillion years from now. We believe the last stars will be examples

of blue dwarfs, stars which aren't known to exist anywhere in the

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