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 add-free, plus hours of bonus content,

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

When we imagine the end of worlds, we usually think of mushroom clouds,

but there may be far stranger ways to end everything, in fire and paradox.

When we envision doomsday, we usually picture of nukes exploding over cities,

fireballs in the sky,

and the grim ticking of a nuclear clock edging closer to midnight.

Nuclear weapons are the archetype of humanity's self-made apocalypse, and before them I don't

think we dreamed of human-generated apocalypses as even possible.

Inevitarily they were the effect of angry gods or the slow erosion

of time. But once the idea arrived, it blossomed like a mushroom cloud, and science fiction

was not content to stop there. The human imagination has conjured up planet-busters,

star killers, and weapons that don't just kill bodies, but tear apart the

very fabric of time, space, and causality. In today's episode, we'll be looking at these

ultimate weapons, both the terrifyingly plausible and the fantastically impossible, from

doomsday devices that could wipe out a planet to ontological weapons that could unmake you

retroactively, erasing you from history itself. We'll ask how realistic they are and what sort of

science and technologies might let them exist. And, if all that sounds like fun, grab a drink and a

snack, give those like, subscribe, and notification buttons a smack,

and let's dive into the apocalypse.

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