This is the January 2017 edition of the Gwern.net newsletter; previous, December 2016/2016 in review (archives). This is a collation of links and summary of major changes, overlapping with my Changelog; brought to you by my donors on Patreon.
Site Reliability Engineering: How Google Runs Production Systems (not a book whose principles I ever expect to apply as intended, but it is fascinating to read about the technical problems & capabilities at Google-scale, the clever solutions applying rarefied computer science techniques, and the war stories about how things can go wrong. Inspired a little by it, I added a number of tests to my Gwern.net sync script.)
The Anubis Gates, Tim Powers (a delicious time-travel adventure, full of London color drawing on London labour and the London poor; a cyclopaedia of the condition and earnings of those that will work, those that cannot work, and those that will not work, et al 1851 ; ultimately, the elements don’t come together in as deep a package as Declare and I am a little disappointed that Powers doesn’t pull off nearly as subtle a ‘secret history’ as he does in that—while I hoped that things like the Dancing Monkeys or Ashbless were historically real, it turns out that Powers had to make them up. But still a fun reread.
On a side note: in The Anubis Gates, magic is associated with the moon and normality with the earth & sun & Christianity; practitioners are pained and weakened by the touch of the earth and the growth of Christianity, which protects against & destroys magic (and so by the 1800s setting, magic has become almost useless), and gradually lose weight & float as they gravitate towards the moon. The wizened leader of the magicians is so many millennia old and steeped in magic that he would fall towards the moon, and must live in a domed building while upside down lest he fall to the moon like other magicians, rotating around the dome as the moon moves. Given this Chekhov’s gun, it is not surprising that eventually he does fall out of the dome and falls into the sky, presumably to his doom. What happens to him? The character sits around and moves normally while upside down, and neither bounces nor struggles to move; this suggests that an equivalent of Earth gravity now pulls him to the moon (or if we assume the Earth continues to pull, twice Earth gravity, never mind that the moon is much smaller—this is magic). After falling out of the dome, he will start accelerating upwards at ~9.8 m/s2; as there is air resistance, he will soon hit terminal velocity, which for a human is ~54m/s, so after ~6s, he will stop accelerating and then begin accelerating slowly as the air thins out & offers less resistance, increasing by ~1% every 160 meters.
Logically, one would expect him to impact the Moon at some extraordinary velocity as there will be effectively no terminal velocity for his body once out of the earth’s atmosphere, but he will have died long before of thirst, hypothermia, or hypoxia (in increasing order of speed) and probably well before he hits the Armstrong limit of 19000m. At the Armstrong limit, even the water on one’s tongue boils. In any case, the magician will be moving so fast that 19000m is trivial and will be reached within ~5.8 minutes, leaving little time for starvation/thirst/hypothermia; by this point, he will have previously lapsed into unconsciousness and be suffering from cerebral hypoxia, yielding brain death within 5–10 minutes. So in general, we can safely assume that less than 10 minutes after falling out of the dome, the magician is dead from hypoxia accelerated by hypothermia. But the body will keep on going. How long does it take to reach the Moon? The moon is on average 384400000 meters away, but the body will keep accelerating once it gets past the bulk of the earth’s atmosphere; assuming no more terminal velocity after 500 seconds, the body will reach the average distance of the moon after ~9351s or ~2.6h, traveling at something like 86795m/s or 86km⁄s. (Strictly speaking, he might miss the moon and have to spiral around, or might even never impact, but I can’t calculate the orbital mechanics there.) Being a wizened and now desiccated/frozen body, it probably doesn’t weigh anywhere over 50kg, but will still pack a major punch with a kinetic energy of
0.2*50*(86795^2)joules or 7.5 megajoules (for comparison 1 ton of TNT is ~4.2 GJ).