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0 pointskragen2y ago0 comments

guilty as charged. it gets worse, though: meters are originally based on the size of the earth, but humboldt's expedition (?) fucked up the measurement and now we're stuck with a meter that's significantly too short, nominally defined as the distance light travels in 9192631770/299792458 cycles of the hyperfine transition radiation frequency of cesium-133. you probably think this is a goddamned joke but it's not

i ask you, what the fuck kind of number is 9192631770? is that a hexadecimal encoding of linus torvalds's first child's birthdate? no, it's just a random fucking number derived from the sumerian base 60 numbering system and the average rotational speed of the earth in the 20th century. the kelvin has a similarly filthy history; it's when the thermal energy changes by 1.380649e-23 joules, because that makes the triple point of water come out to 273.16 kelvins. so now we have to preserve those numbers for all eternity like they're the fucking holy writ of the priestesses at delphi in order to interpret scientific papers from the 19th and 20th century. (and don't get me started on the motherfucking calendar. jesus jumping blue christ.)

you will be pleased to learn about https://en.wikipedia.org/wiki/Natural_units (which i used in https://dercuano.github.io/notes/2017-sap-allocation.html because i'm uncreative) and https://en.wikipedia.org/wiki/Duodecimal#Systematic_Dozenal_...

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7 comments · 4 top-level

nuancebydefault2y ago· 2 in thread

You probably know all this, but it is fun to write. Units are parts of models. Used Models were the best in class, at the time they were derived or adopted. Models are wrong and get replaced by less wrong models over time.

That said I think meters and Kelvins are doing their job just fine even for use with rocket science. I'm glad I learned the SI units at school, they reduced the number of constants a lot in physical formulas.

kragenOP2y ago

yeah, but there are still a lot of constants even with the si units, which is because they predate the discoveries of many of the constants. more constants generally means more arithmetic operations you can accidentally leave out of your program and constants you can get wrong. this was a bigger concern in the slide-rule era, but the humans are still infallible, so it hasn't gone away entirely

i don't think it makes sense to describe miles or meters or stoney lengths as 'wrong' or 'right'; you can express the fitzgerald contraction or orbital speed or whatever equally well with any of the three, but one of them simplifies the fitzgerald contraction somewhat

fnordpiglet2y ago

I think a key tho in a measurement unit that’s desirable is its relationship to something consistent everywhere in the universe, such that the reference unit is reproducible by anyone. This doesn’t matter much day to day but as a system we should converge to one that anyone anywhere can agree how long a distance may be without a mutually agreed upon calibration but can calibrate without access any specific reference unit. The triple point of water is always what it is, and a colony on mars without easy access to something locked in a room in Paris or whatever can create their own reference measurements from whole cloth and they’ll be the same as the colony at Alpha Centauri now and in 20,000 years.

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cyberax2y ago· 1 in thread

> guilty as charged. it gets worse, though: meters are originally based on the size of the earth, but humboldt's expedition (?) fucked up the measurement and now we're stuck with a meter that's significantly too short

Uhm, a kilometer is supposed to be 1/40000-th of the Earth's meridional (i.e. from South to North poles) circumference. The modern value is 40008km, so the official meter is juuuust about 0.02% shorter than it should be.

kragenOP2y ago

i think it was a ten thousandth of the distance from the north pole to the equator through paris, disregarding the southern hemisphere, which was more difficult to survey. i've been looking for a precise number for how far that distance actually turned out to be, but i haven't been able to find it; i would be delighted if you could!

whether 0.02% sounds ridiculously good or ridiculously bad depends on your frame of reference

https://en.wikipedia.org/wiki/History_of_the_metre#History_o... says that the original mètre des archives in 01799 was machined to within 50μm, which is 0.005%, four times smaller than the error in delambre and méchain's computation. so even at the time that was a pretty large error. since then the measurement uncertainty of the meter has improved by five more orders of magnitude, to about 0.1 part per billion. 0.02% is 200 parts per million, or 200000 parts per billion, which is a lot more than 0.1

kragenOP2y ago

it wasn't humboldt's expedition https://en.wikipedia.org/wiki/Alexander_von_Humboldt#Spanish... which had nothing to do with the decades-earlier meter-measuring expedition https://en.wikipedia.org/wiki/French_Geodesic_Mission_to_the... (except for being inspired by it) and the contemporary calculations of the paris meridian https://en.wikipedia.org/wiki/History_of_the_metre#M%C3%A8tr...

lupusreal2y ago

It all gets the job done, no reason to let any of it bother you.

j / k navigate · click thread line to collapse

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7 comments · 4 top-level

nuancebydefault2y ago· 2 in thread

kragenOP2y ago

fnordpiglet2y ago

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cyberax2y ago· 1 in thread

kragenOP2y ago

whether 0.02% sounds ridiculously good or ridiculously bad depends on your frame of reference

kragenOP2y ago

lupusreal2y ago

It all gets the job done, no reason to let any of it bother you.

j / k navigate · click thread line to collapse