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.

Spacecraft may one day be so common that everyone has flown on one, with thousands of

new spaceships being built every year in manufacturers dwarfing the enormous facilities

we build planes and sea-going vessels in.

Building a spaceship is an enormous undertaking.

They tend to cost as much as an aircraft carrier, even though the crew and cargo are in a space

about the size of a small boat or modest yacht.

They require precision manufacturing unlike any other vehicle, and yet, one day their manufacture might

be as a routine as that of an automobile. Emphasis on routine, not simple, as there's

nothing simple about the modern car, and I would not expect that to be true of personal

spaceships either, but in many ways a spaceship can be simpler than a terrestrial vehicle.

Space is mostly empty, with few obstacles or shifts to the road surface or air density to

require constant course corrections.

Today we'll be examining a lot of the different paths for the future of building ships,

and we'll be looking at everything from simple asteroid mining ships,

produced in a low-tech future, to cases where all the real work was done on the software

and design end, and someone just spills some self-replicator robots on a spare asteroid,

and they replicate and spawn ships out of it, or maybe even grow them quasi-biologically.

And as we'll see, even in these high-tech

...