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.

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In the deep, empty, immensity of inner style of space, some few people may find a home

far from an east star to call their own.

Space is big, really big, really, really big. We live on the thin surface of a rock far more immense than all of our civilizations and ecosystems

combined, and yet it is nothing but a pale blue dot, as seen by the Voyager 1 probe,

when it was 40 times as far from Earth as Earth is from our Sun. This distance is often

called the edge of our solar system, and all of our major planets all the way out to Neptune,

and all of their moons and the asteroid belt are inside this volume.

That pale blue dot on which we all but a thin skin around the rock and magma below is

insignificant compared to this volume, which is 50 trillion trillion times larger.

This is the same as a single grain of sand compared to our entire planet.

Inside this fast, empty expanse of space, we have our eight major planets,

over 100 moons and dwarf planets, and millions of minor planets and asteroids.

One day, this volume, trillions of trillions of times larger than our entire world,

will see each of those millions of minor planets colonized or re-shaped into vast habitats and megastructures.

Civilizations beyond our ability to meaningfully count will arise inside this expanse, in our solar system,

...