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.

We know the dangers of science and technology, and how they might mask

doomsday's as hidden treasures, but could the very quest for knowledge or the existence

of the conscious mind itself be a ticking time bomb waiting to wipe us out?

Once long ago, some human first looked up at the stars and wondered what they were,

and how vast that celestial sphere was, and if it might be home to other peoples or the gods

themselves, as we grew in knowledge, we began to realize just how immense and ancient the cosmos truly

were, and wondered if life might have arisen out on those distant and uncountable worlds.

Surely many are like our own pale blue dots, and such planets must number in the untold

billions, yet we see no ironclad signs of the mighty

empires that should dwell among the stars and be impossible to mistake for any natural phenomena.

This seeming paradox, an ancient and immense universe, and yet a quiet one, is known

as the Great Silence, or the Fermi paradox.

Many solutions are proposed, including that these aliens are indeed present and hide from us,

or we choose to ignore the evidence of them, but the largest collection of solutions revolve around

the idea that civilizations like ours either evolve very rarely, filtered out

by many challenges and conditions that make Earth rare, early filters on life emerging,

or middle filters that prevent the rise of complex, intelligent, or technological life.

The other side of that are what we call the late filters, those which our civilization

...