I woke up migrainey this morning. Not as bad as some people get migraines, but bad by my standards. Like, it hurt to go from my bedroom, which has black blinds and mostly muted colours, to my bathroom, which has meadow-green blinds and a lot of shiny white tile. Chills and mild nausea and angry, angry sinuses on top of the piercing headache.

While I was lying in bed trying to rehydrate and brace myself to go and find my paracetamol, I remembered how, as a child, I would sit hunched at breakfast, bowing my head to look into the shadows under the table because the light in the kitchen was too bright. My parents told me it was just that my eyes needed time to adapt to the brightness after sleeping in the dark for a night (it wasn't, I've always had problems with strong light, and the radio blaring the miseries of BBC morning news certainly didn't help either).

My dad might even have explained to me how irises work, I think I remember something like that. But I also remember a few years later seeing videos of pupils dilating and contracting with changes in light and not being able to understand why, if the iris muscles could react so quickly, it took me ten minutes or more in the morning to be able to look up in rooms with the light on. The answer is probably neurological, what I experience with bright light is very consistent with descriptions autistic people have given me of their hypersensitivities, but that's not really what I want to write about rn.

I'm pretty sure I can remember the first time I fell in love with a city. My tastes aren't particularly unusual: I was on a school trip to New York in the winter of 2004. At night the city breathed great plumes of steam from street vents, and by day the sky above the boat ride to Ellis Island (not the statue of liberty, I don't think the trip budget stretched to that) was the merciless grey of a steel security fence. It was bitterly cold. On our last day there, it snowed in the morning and I saw a Greenwich Village punk sweeping the doorstep of their shop, and then we walked onto Broadway and got hit full-barrel by the wind like an explosion of icy teeth. I was on a film noir kick at the time and bought a long coat - not quite a trench coat, because I'm a useless shopper - in a department store in lower Manhattan. I still have the coat, though it's basically unwearable these days.

(warnings after the jump: discussion of 9/11, discussion of COVID/2020, assorted queer sex/dysphoria stuff)

Google says the average depth of the Pacific Ocean is about 4000m. With a surface area of 165 million square kilometres, that gives it a total volume of roughly six hundred and sixty million cubic kilometres.

The Burj Khalifa is the world's tallest building, at around 830m tall, but as best I can tell the top 230m of that aren't really spaces for human use (this is based on it having 163 floors with a listed purpose on Wikipedia and the highest sky deck being on the 148th floor at 555m for an average of 3.75m per floor, putting floor 163 around 610m up).

I'm taking that as a marker for how high we could possibly build living space above local ground level.

The total land surface area of the earth is around 153 million square kilometres (30% of total surface area at 510 million square kilometres). If we approximate the habitable volume of the earth as a 600m layer over all of that, it gives around 92 million cubic kilometres.

(This is actually a pretty significant overestimate. The highest-above-sea-level permanent settlements on earth are a little over 5000m above sea level, so we can't build Burj Khalifas anywhere above 4400m and expect to get the full use out of them. I can't think of a quick way to estimate how much of the earth's land surface area is above 4400m, but it's not a trivial fraction).

The upshot of this is that the 'approximate habitable volume of the earth' would fit into the Pacific ocean about 7 times.