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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This episode is sponsored by Auduble.

One of the greatest constraints on human civilization has been the need to travel

outward to new horizons, to find fertile land to gather and farm from.

What if the solution is to go upward, not outward?

So today we're taking a look at vertical farming, asking what it is and what the opportunities

and challenges are in developing it, and if it can ever become practical.

Now discussion of vertical farming almost always involves discussion of other farming techniques,

typically greenhouses, soilless farming, hydroponics, aquapotics, aeroponics, and other controlled

environment agriculture, and so we will discuss those today briefly too, but vertical farming

itself is the concept of growing farms in vertical stacks, multiple levels, or of just

taking far more advantage of height in farm layout. As an example, in a future of low gravity space farming, up and down aren't much harder

to work with than left and right or forward and back, whereas you usually want to optimize

maximum internal volume per external surface area on space habitats, keeping them compact,

so you would be a lot more likely to see farmed

volumes rather than farmed areas, so to speak.

Now the biggest hurdle of vertical farming is cost, it's outrageously expensive to build up

or even to build it all, compared to raw, cleared land, mostly we'll get into current

exceptions today and expected future ones. This is also why vertical farming is almost always discussed in tandem with controlled

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