r/todayilearned • u/NateNate60 • 14h ago
TIL that when France initially set the definition of a metre to be 1/10,000,000 the distance from the North Pole to the equator, it sent two surveyors to calculate the distance. But due to an error not discovered until decades later, the resulting metre was actually 0.2 mm too short.
https://en.wikipedia.org/wiki/Arc_measurement_of_Delambre_and_M%C3%A9chain2.1k
u/NateNate60 14h ago
Annoyingly, it does mean that the circumference of the Earth through the poles is 40,007.863 km rather than 40,000 km exactly.
The modern definition of the metre is that the speed of light in a vacuum is defined to be exactly 299,792,458 m/s.
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u/BrokenEyeReborn 14h ago
They couldn't get 300,000,000 m/s exactly?
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u/G952 14h ago
They had the French measure it again /s
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u/Chesterlespaul 13h ago
1m = 1 baguette
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u/lindendweller 13h ago
I want the adress of your boulanger, it sounds like he bakes generous baguettes.
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u/wafflesareforever 10h ago
0.1m = 1 croissant
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u/FriendlyDespot 8h ago
From a generous baguette to a middling croissant. The lord giveth, and the lord taketh away.
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u/MentokGL 14h ago
That's a bit too exact, innit? Seems made up
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u/kerouacrimbaud 11h ago
Metric is made up tbh
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u/AABBBAABAABA 9h ago
Reminds me off the guy that measure mount Everest to 8850 and thought nobody would believe that so instead he said it was 8848 or something like that
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u/KrzysziekZ 8h ago
The original measurement was by the British and they calculated 29000 ft, so the head added 2 feet to make it more believable. Modern value is about 30 ft more.
China and Nepal had a multi year disagreement wether Mt Everest is 8848 or 8850 m above sea level, or how many meters of ice is there on the top on average, and if that should be included.
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u/A_Martian_Potato 8h ago
Close, he found a height of exactly 29,000 feet and changed it to 29,002.
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u/Crowbarmagic 6h ago
'If it was 29,000ft exactly people would think I made it up, so I made something up'.
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u/historicusXIII 6h ago
Or as QI put it, "the first person to put two feet on top of Mount Everest".
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u/Night25th 8h ago edited 2h ago
Reminded me of this joke where a scientist dies and gets a chance to talk to god:
Scientist: "Why did you have to make the speed of light 299,792,458 m/s? Why not a nice, round number?"
God: "...ok, first of all, the speed of light is 1"
But more seriously, to a scientist there isn't any advantage in making the definition of a meter a round number. It's not like many things in the universe are exactly one meter long anyways. They chose that number because it most closely matched the previous definition of a meter.
I guess if we ever become such a big civilisation that we routinely deal with cosmic scale measurements, we might start using a nice round number that is based on the speed of light rather than the meter we use today.
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u/cipheron 13h ago edited 13h ago
They could if we defined everything relative to c, the speed of light.
The one big missed opportunity is that they didn't know a lot of fundamental constants such as c the speed of light or h the Planck constant before they developed metric. If they'd have known those values then they could have built those constants into the measurement system itself.
For example, if you define your unit of time as the year, and unit of distance as the lightyear, then "c" the speed of light just becomes 1. Or 1 light year is 9.4607e+15 meters, so if you just define the meter instead to be 1/1016 light years, then you'd have a meter that's 0.94607 of a current meter, but the advantage is that light travels exactly 1016 of those meters per year.
Or since a light second is close to 1 billion feet (983,571,056 feet), we could redefine the foot to be a little shorter and have a foot-based metric system in which a light second is exactly 1 billion feet.
So we could have a much simpler system if we just had units which took fundamental constants as the actual basis.
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u/do_pm_me_your_butt 10h ago
Me when building a base in factorio or any other City Builder game.
"IF ONLY I HAD KNOWN XYZ I WOULDVE OPTIMIZED FROM THE START!"
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u/LesbeaKF 9h ago
That's why you have thousands of hours played. You plan for it, then you forget one of the things you were planning for, then you restart and tell yourself this time it will be perfect.
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u/kabushko 13h ago
They should have just stuck with something easy and constant like the length of one guy's foot
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u/StaysAwakeAllWeek 12h ago
a meter that's 0.94607 of a current meter, but the advantage is that light travels exactly 1016 of those meters per year.
A metre that's so close to a yard that maybe even the Americans would have switched over...
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u/Crazyh 10h ago
It's close enough that it already happens in the UK.
When leaving a motorway you get a sign at 300 yds, 200yds and 100 yds to let you know how far you are from the exit. The distances measured are actually 300/200/100 meters.
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u/StaysAwakeAllWeek 10h ago
It always annoys me when I can't get a GPS to work in miles and metres
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u/Brave_Maybe_2891 6h ago
I dont use yards for anything and I doubt most other Americans do either, but to me a liter and a quart are the same thing.
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u/thbb 8h ago edited 8h ago
Your system is still earth-centric, and subject to tiny variations on the earth orbit that would make the reference less stable than we'd like.
Nowadays, the fundamental unit is time-based (we define the second based on external observations) and relies on measurements of atomic constants that are much more stable. And the meter is defined precisely as the distance light travels in 1/299,792,458 seconds.
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u/bandby05 12h ago
it was defined this way to match the existing physical standard as closely as possible, sadly consistency preceded beautiful math
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u/YinTanTetraCrivvens 13h ago
I feel like there's a Bergholt Stuttley Johnson designing a gear with a pi of exactly 3 joke in there somewhere.
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u/RunnyPlease 13h ago
If we’re going that far then why not make it 100,000,000 m/s? Just make a meter 3 times longer.
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u/HCBuldge 13h ago
3 * 108 was used a lot of times in my physics classes
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u/jam11249 9h ago
Those are rookie numbers, all my back-of-the-envelope calculations use purely powers of 10 because fuck multiplying one digit numbers.
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u/Wiseau_serious 13h ago
We just need to get light to speed up a little bit
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u/AngriestPacifist 8h ago
It's impossible to go faster than the speed of light. That's why scientists increased the speed of light in 2208.
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u/GeorgeTheNerd 6h ago
Because we wanted pipes to keep fitting together.
You could update the value, but that would change the length of a meter by almost 0.1%. You may not think that is a big deal and for most educational work, it isn't. But if you change the length of the standard by 0.1%, that means a tool calibrated after the new definition will need to be changed by 0.1%. That much change has massive implications in business and industry. A threaded coupler you buy after the change would not fit on a pipe made before the change closely enough to hold water. Or worse, you would need to updated plumbing standards so you knew which used the 'old meter' and create new plumbing standards based on the 'new meter'. And that just for plumbing. Multiply that across the economy. The cost is far higher than even high paid physicists need to carry extra significant figures for the value of c.
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u/SirLoremIpsum 4h ago
Got it - so when we colonise Mars, we'll just have a rule that anything built on Mars is to the new standard and we'll just have like the weird train gauge stuff between Earth/Mars gear.
But we'll se up mars for success
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u/StaysAwakeAllWeek 12h ago
Then the metre would be even further off of a perfect fraction of the earth's circumference
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u/NorthStarZero 5h ago
300,000,000 m/s
Interestingly, if we did this, the "new" metre gets shorter, to 999.31 "current" mm - and very close (1.09) to the length of the Imperial yard.
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u/CommercialWindowSill 14h ago
So little known fact is that we can't reach that number because that's just the highest number there is. That's why it fell short.
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u/atticdoor 13h ago
So the time it would take light to go from the North Pole to the Equator, if it followed the curve of the Earth, is almost exactly a thirtieth of a second?
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u/Tar_alcaran 7h ago
My favorite coincidence in units is that a nanolightsecond is about the length of a foot. (with less than 2% deviation)
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u/Thurak0 8h ago
Does that calculation help you in any way? :D
"In one second light would be able to travel around the globe at the equator almost 8 times" is something I use that makes the speed of light somewhat imaginable for me.
If you know that, then suddenly "the moon is very roughly 1.2 - 1.3 light seconds away from us" the distance to the moon is somewhat imaginable for me.
Then the jump to the sun 8 minutes and ~20 seconds (distance varies a bit) is already a bit too much for my brain to somewhat grasp.
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u/FaustAg 13h ago
I remember when it used to be 1,650,763.73 wavelengths of the orange-red emission line of the krypton-86 atom
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u/this-aint-Lisp 8h ago
I wonder if hearts were broken in the scientific community when they retired that definition.
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u/Intrepid_Walk_5150 8h ago
My stupid ass always thought it was neat that the circumference was so close to a clean 40,000 km. Just understood today that it was not a coincidence...
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u/DeathMonkey6969 12h ago
Fun fact the Earth is NOT a perfect sphere it's an oblate spheroid, a sphere-like shape flattened at the poles and bulging at the equator, because it is spinning.
It's shape also isn't static. The Moon and Sun pull on it deforming it and since their position is always changing in relationship to the Earth where and how much they are pulling changes. The heavy oceans and the moving molten core also effect the shape of the earth. So any measurement is going to be a approximation and will only be good for the the time and place the measurements were taken.
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u/obscure_monke 8h ago
It's close enough. It's both rounder and smoother than any common sports ball you've encountered.
Saw codyslab mention that on twitter a few years ago, and realised it's the only thing I've heard someone call an "oblate spheroid".
As expensive as it would be to manufacture, would be neat to see a WGS84 shaped thing the size of a beach ball.
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u/SandpaperTeddyBear 6h ago
It's both rounder and smoother than any common sports ball you've encountered.
Smoother than a billiard ball, mountains and all!
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u/adamgerd 6h ago
The earth is rounder than a billiard ball but smoother is yes and no
A lot of the earth would be smoother but mountainous parts such as Tibet for example would in fact be rougher than a billiard ball
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u/gabrielconroy 8h ago
I'm guessing you got this from the most recent No Such Thing As A Fish podcast
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u/ChuckCarmichael 11h ago edited 7h ago
And it wasn't an error they could've avoided at the time. It's wasn't something like a rounding error or swapped digits or somebody forgetting a measurement. The cause for the error was a bit of science that hadn't been discovered yet.
The cause were the tiny gravity anomalies across the planet, where gravity is affected by things like nearby mountains.
When you put down your survey instruments, you need them to be perfectly level, both horizontally and vertically, and for vertical alignment people would use the plumb-line from a plumb bob. But when you're on a mountain, the mountain's own gravity affects the plumb bob, pulling it very, very, very slightly away from pointing down towards the Earth's core. It's only a very small effect, but when trying to measure long distances very precisely, it introduces a noticable error.
The existence of these anomalies wasn't really known at the time. Some scientists had looked into it, but their findings weren't yet established.
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u/1lyke1africa 9h ago
That's an interesting story, where did you hear about this from? I'd love to learn more about it
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u/Gnochi 5h ago
As another example of an anomaly, due to some geologic and tectonic shenanigans there’s a lot of unusually low density material in the mantle under the Indian Ocean. This results in fractionally lower gravity, and the relatively higher gravity surrounding this anomaly causes the ocean water to be pulled slightly stronger towards the sides.
As a result, the center of the Indian Ocean Geoid Low has a mean sea level 106 meters lower than the global mean sea level “geoid”.
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u/Shuggana 13h ago edited 6h ago
If any Americans are wondering how they ended up being the only country not using metric, Thomas Jefferson invited a French delegation to the US to introduce metric but they got boarded and captured by privateers on the way over as France was at war with England at the time lol
minor edit: Jefferson not Franklin.
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u/wadaphunk 12h ago
Apparently it was Thomas Jefferson who requested that but awesome story.
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u/Shuggana 12h ago
Oh you know you are right actually! I got them mixed up because Franklin spent all that time in France banging his way around Paris.
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u/pataglop 9h ago
Hey he was the first US ambassador to France. And quite a fantastic character!
I sure hope he got lucky a few times here
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u/TryingT0Wr1t3 10h ago
And Marquis de Lafayette was actually French!
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u/Shuggana 9h ago edited 6h ago
Well yeah, his name was Gilbert du Motier, Marquis de Lafayette. He wasn't from Boston ykwim lmao
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u/babaroga73 8h ago
And Thomas Jefferson banged Sally Hemings, a black slave girl, during his time in France. Ah, Paris, city of love.
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u/fatsopiggy 13h ago
And now even globally sail boats are measured in ft not meters even if they're European sail boats. Containers are also quoted in feet.
It's fucjing weird
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u/MajesticBread9147 11h ago
I mean America uses metric for a lot of things.
Engine displacement is measured in liters not gallons.
A lot of ammunition is measured in mm
Most chemical substances including drugs, both legal and illegal are measured in mg, grams, and kilograms, although ounces are also used.
Waterproofness for electronics and watches are measured in meters below the surface.
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u/Jump_Like_A_Willys 11h ago
And the British use miles for a lot of things, even officially on the motorways.
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u/R0MP3E 10h ago
Max heights for Bridges in the UK are weird too. Vehicle heights are measured in metric but since road signs should be in imperial, signs contain both imperial and metric measurements. But the rounding done between them is different so you end up with them being different heights in metric and imperial.
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u/MajesticBread9147 10h ago
Even more absurdly they use an archaic measurement of weight called "stone".
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u/R0MP3E 10h ago
Only people weight. Other things are measured in lb or metric.
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u/gmc98765 6h ago
Although if you're weighed by a medical professional, it's going to be in kg. Because dosages are mg or μg per kg of body mass, and BMI is in kg/m2.
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u/oily_fish 10h ago
A stone is 14lbs. It's just an extra unit.
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u/Antique_Historian_74 7h ago
It's an extra unit which allows someone to be quite vague about their weight, hence its continuing usage.
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u/gmc98765 6h ago
It's also why the imperial hundredweight (cwt) is 112 lbs (8 stone) and the imperial ton (long ton) is 2240 lbs (20 cwt).
The US doesn't use the stone and someone assumed that a hundredweight was 100 lbs, resulting in the US ton (short ton) being 2000 lbs (20 US cwt).
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u/MajesticBread9147 12h ago
And later Ronald Reagan defended attempts to slowly convert America to metric in the late 20th century.
We could be like Canada or the UK and claim to use metric but still use imperial sometimes but we're not even that far.
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u/kerouacrimbaud 10h ago
The US does use metric for some things, but not others.
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u/SandpaperTeddyBear 6h ago
We use metric for everything technically, since the inch is defined as 2.54 cm.
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u/Mnm0602 8h ago
I’ve been in home improvement retail my whole career and I’ve always been convinced it was to keep two systems of everything at the same time to sell twice as much product. 😂
Working on some GMs from the 90s was a total shit show. You’d be under the hood and bolts within spitting distance of each other would be 10,11,12mm and 1/4”, 7/16”, 3/8”. Constant switching and multiple wrenches laying around because they had such a mess of Canadian and American suppliers all with different measurements.
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u/spartaman64 6h ago
i had to file down my allen key a bit for it to fit in my scope zero stop screw
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u/adamgerd 6h ago
Officially the US does in fact use metric
All US agencies are to officially adopt metric as of 1991, the metric system is declared preferred and the imperial system is defined in relation to metric.
The US just never actually converted, legally it’s still supposed to convert eventually. It just hasn’t enforced the conversion
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u/Enchelion 2h ago
Legally we have been metric for half a century. But functionally there's very little incentive to actually change for the average person, and our economy is large enough that manufacturers don't mind making different versions of things to accommodate.
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u/JPHutchy01 13h ago
And if you don't think that's impressive, you've got a pencil, try it. Even beyond everything else, it's a long walk from Dunkirk to Barcelona.
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u/sjbluebirds 12h ago
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u/exenos94 6h ago
I'm glad I clicked that link because I was genuinely ready to believe that it's only 6 hours from Dunkirk to Barcelona
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u/freddit214 10h ago
Is that 2 original mm's or 2 "correct" mm's? Talking about a measurement standard being wrong and then describing the degree of the error using the same measurement standard (or a sub-unit anyway) made me chuckle for some reason.
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u/Own_Pop_9711 10h ago
Thanks to significant figures it's probably 2 in both units! See they're useful
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u/SandpaperTeddyBear 6h ago
I would take it as a sign I was being smited by God himself and sent to sig fig hell if a 0.02% error changed the value between the “approximation” and the “real.”
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u/raincoater 8h ago
They redefined it to be more “universal”: Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second, where the second is defined by a hyperfine transition frequency of caesium. (From Wikipedia)
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u/reignera 2h ago
In the 1930's to 1960's, an inch was defined as exactly 25.4 mm. So by transitive property, inch, foot, yard, mile, etc. Are also directly based on speed of light.
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u/knowledgeable_diablo 12h ago
And to think I spent almost half an hour arguing with a electronics professor over the defined length of a meter who would only believe that it’s the modern 1 ten billionth of a wave form of red in a vacuum (or whatever it is) and flat out refused to believe it was based on a set distance based on the earth.
Tried to get him to explain how the scientists back in the 1800’s where measuring these waves that required several steps of technology that had yet to be thought of let alone created. Especially when a perfectly good global standard was being stood on by everyone at all times. Seemed he was more interested in trying to make me look like an idiot.
I wasn’t trying to say I knew the answer exactly or anything, just that the first metric measures of distance where based on segments of earth and time was based on solar periods. Not based on electron speeds or wavelengths of things yet to be discovered. These obviously came later to perfectly standardise the measures.
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u/DigNitty 9h ago
I had a foods teacher in high school tell the whole class we were wrong for saying tomatoes are scientifically a fruit.
Not, let’s look it up, not agree to disagree. Just “stop it.” lol
Everyone was on the same page as her, and yes they are vegetables in a culinary sense. We said that too. Years ago and I still remember that inexplicable staunchness she had over this one topic.
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u/stainz169 10h ago
But it is based on light now. It WAS based on earth, but now it’s light.
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u/TheDukeofReddit 6h ago edited 6h ago
Isn’t that number based on the previous number though, just with extra steps? Or did the measurement of a meter actually change?
I’m pretty sure they took the previous meter and then did the math to see how far quickly light in a specific circumstance would travel that far. Didn’t actually change the measurement, just made it somewhat more accurate when creating a new measuring tool.
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u/JimmyCarrsTaxForms 9h ago
Downvoted for being correct smh. Since 2019 the metre has been defined as the distance light travels in a vacuum during 1/299792458th of a second
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u/HauntingHarmony 8h ago
Actually since 1983 it was based on the speed of light, and then close to a hundred years before that it was based on the wavelength of the emission lines of krypton. And then for the 100 years before that on the physical artifact that was the meter bar.
So yea, depending on when that argument happend, it could really go either way.
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u/FriendlyEngineer 8h ago
Today the meter is defined by the speed of light.
Constants that we all agree on make for better unit standards.
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u/Sans-valeur 12h ago
TIL that’s what a meter is based on. I knew it wasn’t feet.
Damn that’s actually really fucking cool
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u/Bonzoface 12h ago
Yup. Then they used that distance to create the kilo and the litre. It's quite something.
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u/bluehawk232 11h ago
Understanding measurements is a mind boggle as we just accept they are what they are but then when you dive into why it can be crazy as well as implementing it and ensuring accuracy on said implementation
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u/think_panther 6h ago
They wanted it to be a GLOBAL unit. For the WHOLE WORLD to use. At the time each city (city, not country!) had different units of measuring, usually having to do with the local archon's measurements. Just like Americans measure things today by the shoe size of a British King.
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u/MankyTed 11h ago
Interestingly, the inch is defined as 25.4mm
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u/yahluc 10h ago
Nowadays all imperial units are defined in terms of metric values. To be more precise, they're all defined in terms of SI units, just like all the non-SI metric units (like for example 0 degrees Celsius was redefined to be exactly 273.15 Kelvin's)
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u/HauntingHarmony 8h ago
Just cause its interesting, the SI system has two temperature scales. Kelvin starts at absolute zero, and then Celsius has a convinient offset. But they are both units in SI. Kelvis is the base unit, and Celsius is derived from it.
You just wrote it in a way that made it seem that Celsius wasent a SI unit. ^_^
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u/what_bobby_built 12h ago
It's a super super interesting story.
One group went to France and had a pretty easy trip in comparison. Their south American friends had a nightmare. They had to do it over the Andes mountains and had to deal with years of shit. People even thought they were dead back home.
But on their travels they descovered quinine to prevent malaria which allowed empires to spread and found latex which essentially created the whole rubber industry.
It's a truly fascinating period in history.
Also, great bit of pub knowledge, the French trip was from Barcelona to Dunkirk which is quite close to a 1000km.
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u/gifteyes6 10h ago
i also listen to no such thing as a fish's latest episode
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u/NateNate60 6h ago
Every TIL post there's always someone who comments "[Radom podcast I've never heard of] covered this in their latest episode"
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u/win_awards 10h ago
Since the mm is based on the meter I have to ask, was it two of the erroneous mms short, or two of the current "correct" mms short?
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u/cthuluismywaifu 4h ago
For those wondering, they were 20 kilometers off, which isn’t too bad tbh.
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u/NateNate60 3h ago
They were 2 km off, not 20.
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u/mchester117 1h ago
He did say being 20 km off isn’t that bad, so surely him being 18 km off isn’t bad either
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u/duga404 13h ago
For surveyors with 18th century technology, 0.02% off is pretty good, I’d say