32 ms·
International System of Units overhauled in historic vote
- adamnemecek 8y agoThe Wikipedia entry is pretty informative https://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_base_units https://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_ba...
- nudgeee 8y agoVeritasium did a great video [0] on this leading up to the vote. [0] https://youtu.be/c_e1wITe_ig https://youtu.be/c_e1wITe_ig
- ThetaOneOne 8y agoI wish he would spend a bit more time exsplining were some of the constants come from, although that would probably make the video a bit weaker overall. Wasting time on such information.
- delecti 8y agoHe's probably done videos on many of them already.
- garmaine 8y agoThis is massive news.
- artie_effim 8y agoI see what you did there...
- redial 8y agoThe went to great lengths working on this announcement.
- garmaine 8y agoNo they didn’t, the lengths stayed the same!
- xvilka 8y agoToo bad US doesn't use them.
- tdcbfdct3 8y agoThe US measurements system is defined in SI units. So one pound is now defined by Planck's constant.
- throwaway2048 8y agoIt does actually, US measurements are legally defined in terms of metric units. https://en.wikipedia.org/wiki/United_States_customary_units https://en.wikipedia.org/wiki/United_States_customary_units
- piano 8y agoThey really should cut the middle man. What surprised me reading that wiki page is that apparently the metric system was opposed in the US based on religious reasons. That is mind-boggling.
- umanwizard 8y agoIs there any compelling reason why the US should switch to the metric system for daily use? Metric is already used universally in science and engineering, which seem to be the main fields in which consistency across countries matters. I completely agree that in physics, chemistry, engineering, medicine, etc., it is important to use standard units. But what harm is it doing in practice if in everyday life, Americans say things like "I weigh 180 lbs" instead of 81 kg? The argument that the metric system makes unit conversions easier (e.g., the fact that it's immediately obvious how many meters are in 20 km, but not how many feet are in 12 miles) is true, but not very compelling to me. I virtually never find myself wanting to do these conversions in a non-scientific or non-engineering context, and on the very rare occasions where I need to, I can always look them up on Google. A good comparison is degrees Celsius, which are just as arbitrary/unscientific (the standard metric unit is the Kelvin). Somehow people around the world get along fine using Celsius.
- xaduha 8y ago> a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant – the fundamental constant of quantum physics. I thought they did that long time ago.
- keketi 8y agoI wonder how much the cylinder will auction for.
- adrianmonk 8y agoAt least there will be no disagreement about the shipping weight on the auction listing.
- Devagamster 8y agoThe real question is how many boxes will the fulfilment center place the kg in. If Amazon is anything to go by my money is on 3
- reaperducer 8y agoOT, but this! I recently ordered a picture frame from Amazon. It came in its packaging box, which was placed in a box by the manufacturer. That box was put in another box by Amazon and shrink wrapped to a large piece of cardboard, which was then put inside yet another box. On the surface, it seems crazy, but Amazon did manage to get it to me undamaged.
- toast0 8y agoMy wife recently ordered five storage boxes. They arrived in two packages on the same day. One package neatly fit four of the boxes. The other package was large enough for five, and contained one storage box and a excessive amount of packing material. Not an Amazon purchase, so it must be an industry issue.
- 8y ago
- imhoguy 8y agoI curiously wonder on what ground the future overhauls will happen. ToE? https://en.wikipedia.org/wiki/Theory_of_everything https://en.wikipedia.org/wiki/Theory_of_everything
- stickfigure 8y agoOn the rare chance that anyone here missed today's XKCD: https://xkcd.com/2073/ https://xkcd.com/2073/
- mbigras 8y agoThank you for linking this, just made my day!
- 3pt14159 8y agoThis is probably the dumbest thing I'll type on HN. In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?
- deleted 8y ago[deleted]
- AstralStorm 8y agoFor the same reason count is not a mass. Avogadro constant is a count relating number of specified atoms to mass.
- 3pt14159 8y agoIsn't this something essentially tautological though? When we discuss the mass of a neutron and we say "one neutron weighs one u" then we discuss the mass of an electron and we say "one electron is 5.4858×10−4 u" and "one proton is 1.0072764 u" then we add them up and say "one hydrogen atom is 1.00794 u while one helium atom is 4.002602" (forgetting some complications for a moment) are we not just summing likes? Or is it just that since mass is defined in Planck and time / distance terms that we need to relate it to counts of things? Theres a gap there I don't understand. Can we not just say "we measured a proton's mass and it is u"? Am I making a jump there?
- jjjensen90 8y agoIn my opinion it is because a mole is a numerical amount of atoms vs the mass of the substance, so it makes reactions, formulas, and measurements easier to determine. Avogadro's number is useful just as a baseline to use (number of carbon-12 atoms in 12 grams of carbon-12), like there are 12 inches in a foot or 100 centimeters in a meter...
- out_of_protocol 8y ago... except if you take 6 two-inches you'll see something different than 12 one-inches. Our universe is weird. Defect of mass and stuff
- bostonpete 8y agoI get that this is a significant milestone but this seems extremely overstated: "the new changes will have wide-reaching impact in science, technology, trade, health and the environment, among many other sectors." Am I missing something?
- microcolonel 8y agoI don't know about trade, but kilo standards were deviating by tens of micrograms from eachother, some things are sold at prices which warrant accounting for those micrograms, so a completely stable international definition seems helpful. Certain types of scientific instrument will need to be recalibrated to meet the new definitions.
- jbay808 8y agoIs there any scale in the world that can measure a kilogram to within the accuracy of a microgram? And if you buy a kilogram of something and they accidentally short you by a few micrograms, haven't you only overpaid by a few parts per billion? Even on a billion dollar order you've only overpaid by a few dollars...
- zamadatix 8y agoFor your first question some Kibble balances have accuracy parts per billion in measurement of the kilogram. For your second question, agreed - no trade deals care about the accuracy of the new kilogram vs old.
- gus_massa 8y agoI agree that nobody cares for this level of precision in comercial trade, but as a thought experiment ... According to the first result in Google https://brightside.me/wonder-curiosities/the-16-most-expensive-materials-in-the-world-188955/ https://brightside.me/wonder-curiosities/the-16-most-expensi... > 1. Antimatter — $62.5 trillion per gram > 2. Californium — $25-27 million per gram So the difference is a few dollars per milligram of antimatter, and less than a cent per kilogram of Californium. From https://en.wikipedia.org/wiki/United_States_Bullion_Depository https://en.wikipedia.org/wiki/United_States_Bullion_Deposito... > As of November 2017, Fort Knox holdings are 4,582 metric tons (147.3 million oz. troy), with a market value of over $100 billion. So the difference is a few hundred dollars.
- yholio 8y agoThe actual text of the resolution, for those with low tolerance for dumbed-down PR releases: https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN.pdf https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN...
- FiveSquared 8y agoI have low tolerance for long ass papers ;)
- geekone 8y agoBut it's only three pages long :(
- bunderbunder 8y agoIn a large font, and with enormous margins, no less.
- FiveSquared 8y agoSorry man, I thought it would be like GDPR lol
- ZainRiz 8y agoIsn't that just toilet paper? (long ass-papers)
- nathancahill 8y agoOne of the OG xkcd's: https://www.xkcd.com/37/ https://www.xkcd.com/37/
- metaos 8y agoConstants aren't and variables don't, in my experience!
- orblivion 8y agoI guess the next redefinition will happen if and when there's detectable drift in "fundamental" constants?
- reaperducer 8y agoI guess the next redefinition will happen if and when there's detectable drift in "fundamental" constants? And until then, all the metric fanbois will constantly tell you that metric is superior to imperial because its measurements are immutable. Until suddenly they are.
- nafey 8y agoAs opposed imperial constants? How is a foot standardized anyway? I suspect most manufactures rely on SI metrics for that.
- tialaramex 8y agoThere are no other standards. Metrology is expensive and doing it over again would offer no benefit whatsoever. All prior standards in widespread use were abandoned during the 20th century in favour of defining the relevant units in terms of SI units. Specifically the international yard equals 0.9144 meters and the international pound equals 0.45359237 kilograms There literally isn't another definition, in the US when you say "100 yards" the only legal meaning that has is 91.44 metres, which is whatever CGPM / BIPM says it is.
- ska 8y agoFoot is defined as 0.3048 meters, you can't get away from the SI definitions.
- redial 8y agoI've never heard anyone claim that as the reason for its superiority. Metric is superior because it makes sense as a system.
- 8y ago
- SethTro 8y agoThe Doubleclicks write a song about the IPK, the international prototype kilogram, and how it must feel about this. https://youtu.be/VHd4HPmz5aE https://youtu.be/VHd4HPmz5aE
- ballenf 8y agoHas a "metric" version of time ever been proposed? Seems odd to me that we're "ok" with divisions of 12 for time but not length. I guess for science seconds are basically the only measure of time that usually matters?
- bluGill 8y agoMetric had time from the start. However it was work 4 days, 1 day weekend. However the loss of personal time was very unpopular so it never caught on. I'm not sure why a metric hour didn't catch on.
- gugagore 8y agoI think I'm missing the joke. Mind explaining it?
- bluGill 8y agoNo joke, except I was referring to decmial time not metric time. https://en.wikipedia.org/wiki/Metric_time https://en.wikipedia.org/wiki/Metric_time https://en.wikipedia.org/wiki/Decimal_time https://en.wikipedia.org/wiki/Decimal_time a 7 day week gives two days weekends every 5 days, so you quickly lose personal time on the 4 day week.
- snazz 8y agoSeconds are the metric unit of time if I understand it correctly. It doesn’t make any sense to say “kiloseconds” or something like that because days are the time that the sun is up (ish), months are roughly based on moon cycles, and years are approximately the time it takes us to go around the sun. It’s also historical and pretty hard to change the basic units of time.
- semi-extrinsic 8y agoFWIW, while scientists don't usually use kiloseconds, it's pretty common to see 1.437e4 seconds, rather than 3h 43min 20sec, used as units in time series etc. Similarly one uses milliseconds, femtoseconds, and soforth.
- JohnJamesRambo 8y agoI read the uk address and was afraid they had voted to leave the metric system, as some sort of Brexit associated madness.
- onetimemanytime 8y agoif civilization fails....how we are going to measure these things? Or then, we'll have bigger problems so who cares
- 24gttghh 8y agoSo...How many Planck's is one Kilogram then? >The mass of the international prototype of the kilogram m(K) is equal to 1 kg within a relative standard uncertainty equal to that of the recommended value of h at the time this Resolution was adopted, namely 1.0 × 10-8 and that in the future its value will be determined experimentally, Is the Planck simply the most standard deviation the kilogram can stray from now?
- zamadatix 8y agoThis wikipedia section breaks down the new definition nicely https://en.wikipedia.org/wiki/Redefinition_of_SI_base_units#Kilogram https://en.wikipedia.org/wiki/Redefinition_of_SI_base_units#...
- 24gttghh 8y agoIt is still not apparent to me. Is a kilogram of something now it's joules x seconds or something? Does the kilogram now vary depending on what the kilogram is of? Like, is a kilogram of Iron a different mass from a kilogram of Aluminum? >The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs. So mass is now some sort of length times a given elapsed time?
- conbandit 8y agoI believe it means something like: Given the definition of metre and the definition of second, the kilogram is whatever value that makes the Planck constant h precisely 6.62607015×10−34 kg m^2 s^(-1).
- 24gttghh 8y agoBut isn't that a bit of a recursive definition? What might one use as the value of kg in that example?
- gwbas1c 8y agoI can imagine that in 100-200 years we'll have to adjust some unit because our understanding of some constant was just slightly wrong.
- Koshkin 8y agoAccording to the new definitions, some of the fundamental constants can no longer be wrong. We could even have defined them as 1 (which is what physicists have been doing for a long time already.)
- anticensor 8y agoIf you do that, magnitudes of resulting units will either be huge or very tiny, depending on the composition of fundamental constants in said measure. The constants are very carefully chosen to match old units.
- OscarCunningham 8y agoThere are some theories of physics that imply that the value of "constants" like the speed of light actually vary slightly over long distances or times. This would be very inconvenient for the new system if it turned out to be true.
- pfbtgom 8y agoHow would you use the new definition to calibrate instruments? My current understanding is that there is a lineage of artifacts calibrated against another artifact until one of those was calibrated against the one true artifact. So how would NIST or another certifying source say that my 1kg standard is 1kg +/- tolerance? Is it anyone with a kibble balance can now certify calibrations? How do you know your kibble balance is as accurate as the next guy's kibble balance? https://www.nist.gov/si-redefinition/kilogram-kibble-balance https://www.nist.gov/si-redefinition/kilogram-kibble-balance Edit: Found some information explaining this from NIST: https://www.nist.gov/si-redefinition/kilogram-disseminating-new-kilogram https://www.nist.gov/si-redefinition/kilogram-disseminating-...
- jonah 8y agoDon't miss the video for the DIY Lego watt balance. https://www.nist.gov/si-redefinition/nist-do-it-yourself-kibble-balance-made-lego-bricks https://www.nist.gov/si-redefinition/nist-do-it-yourself-kib...
- simcop2387 8y agoEssentially this brings it one more step away from using another artifact for calibrating things. Instead this lets us define the kilogram against what we believe are universal constants, in this case properties about the electromagnetic force. It's much simpler to understand looking at it with a watt balance, even though it's not going to be as precise or accurate as a kibble balance [1]. Basically now anyone with access to a kibble balance and the right set of numbers/information can make an exact 1kg object. [1] https://www.youtube.com/watch?v=ewQkE8t0xgQ https://www.youtube.com/watch?v=ewQkE8t0xgQ
- coder543 8y agoI'm pretty sure a watt balance and a Kibble balance are the same thing. Regardless, that YouTube video is so good! I was just about to post the same link.
- mjevans 8y agoOr potentially more usefully, ascertain an accurate measurement of how closely a given measuring device is to the target to calibrate it's use in actual measurements (outside of the expensive validation mechanisms).
- rubenhak 8y agoFinally there is order in units for science community. Hopefully such transformation will come to US one day.
- clord 8y agoThe US units are defined in terms of SI since the Mendenhall Order[0], so they also benefit from this change. [0]: https://en.wikipedia.org/wiki/Mendenhall_Order https://en.wikipedia.org/wiki/Mendenhall_Order
- kevin_thibedeau 8y agoIt wasn't until 1959 that the yard was metricized. This still affects precision machinery manufactured before the changeover.
- clord 8y agoIt was metricized with all the rest before that. What happened in 59 was harmonization with other countries including Canada, who had a different agreement on the metric yard. The older american definition was 1 yard = 3600/3937 meter. The international metric yard is exactly 0.9144m. (A difference of 0.002mm)
- Digit-Al 8y agoCan anyone tell this poor ignoramus whether the kg is getting heavier or lighter - and how much by (approximately, I know it's not going to be an exact figure given the reason they are changing it)?
- artimaeis 8y agoThe mass of the kilogram is remaining the same. These changes don't affect the "size" of any of the units. > "[...] the size of these units will not change (a kilogram will still be a kilogram) [...]"
- tzs 8y ago> These changes don't affect the "size" of any of the units. The size of electrical units is changing slightly. According to this BIPM document [1]: "The transition from the 1990 convention to the revised SI will result in small changes to all disseminated electrical units. For the vast majority of measurement users, no action need be taken as the volt will change by about 0.1 parts per million and the ohm will change by even less. Practitioners working at the highest level of accuracy may need to adjust the values of their standards and review their measurement uncertainty budgets". [1] https://www.bipm.org/utils/common/pdf/SI-statement.pdf https://www.bipm.org/utils/common/pdf/SI-statement.pdf
- shittyadmin 8y agoThis doesn't impact the actual weight of a kg. What this impacts is how the kg is defined, no longer does it rely on a physical kg. It used to literally be defined as the mass of "IPK" - the international prototype kilogram. https://en.wikipedia.org/wiki/Kilogram#International_prototype_kilogram https://en.wikipedia.org/wiki/Kilogram#International_prototy... This switch now defines it in terms of the force equivalent of the energy exerted by a single photon - if my understanding is correct. Theoretically a more scientifically sound way of keeping 1 kg a constant permanently.
- cco 8y agoThat doesn't make sense to me, the definition has changed. The IPK was 1 kg and the copies of it were all slightly heavier or lighter, for argument let's say IPK1 was 1.1 kg and IPK2 was 0.9 kg. Now that we have a constant for the mass of 1 kg, all of those IPK's will now have a new mass relative to the new definition. Unless the new definition was based on the current IPK and set its mass as of today as the standard, and that standard now will be unchanging?
- sandov 8y ago>The definition of the kilogram for more than 130 years, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant Maybe I interpreted it wrong (non-native English speaker), but does it say that the Kilogram will be equal to the Planck constant? Shouldn't it be that the definition of the Kg will be based on the Planck constant? >Although the size of these units will not change (a kilogram will still be a kilogram) Are our current measurements of the IPK that exact so the old kg is exactly equal to the new Kg? How can they measeure it with 0 error?. It doesn't make any sense to me.
- biotech 8y agoIt's not just you, the wording is a bit weird. Yes, they are trying to say that the definition of the kg will be based on the Planck constant. Further down, the article says: "The kilogram – will be defined by the Planck constant (h)."
- m1el 8y ago> but does it say that the Kilogram will be equal to the Planck constant? No, this statement means that Kilogram will give up its place as a fundamental unit to Planck constant. Earlier, Kilogram was used as a fundamental unit, defined by a physical object. Not anymore. The kilogram will be defined by Planck constant. Namely, m = E/c^2 = hf/c^2. > How can they measeure it with 0 error? We can't, all measurements have errors. But we can measure things better than a physical object, which has changed with time. So we only have to measure Plank constant with precision higher than variation of physical object's mass for the purpose of replacing the definition of mass.
- ashwinikd 8y agoI guess it means that we are fixing the value of the Planck constant and deriving measure of kilogram from it. Given the measure of second and metre, a kilogram is the mass so that the value of plank constant is observed to be exactly 6.626x10^−34.
- turdnagel 8y agoSo there was a definition of a kilogram based on an actual physical thing with an arbitrary amount of mass. Does this new definition essentially try to approximate that mass as close as possible? What is the margin of error there? I would love to know this for a second as well, although I don't know what we used to measure a second before we locked it to the vibrations of a cesium atom.
- bcoates 8y agoThe Earth?
- tialaramex 8y agoYes. In two ways. First, the assumption was that the Earth's rotational period was 86400 seconds. Mechanical clocks had given us no reason to doubt this was so. By the mid-20th century quartz timers were able to discern that the Earth has longer and shorter days, as numerous factors cause the spin to speed up or slow down. Instead of a single day the second was taken to be one 86400th part of an average day over the whole year. A few decades later the availability of atomic clocks made this seem silly and we uncoupled the second from the variably spinning Earth. The completely arbitrary seeming atomic clock definition of a second was basically chosen to be indistinguishable from our last guess at the "averaged over a year" second.
- tehaugmenter 8y agoVery cool explanation of the math as well as the concept behind the standard: https://www.youtube.com/watch?v=Oo0jm1PPRuo https://www.youtube.com/watch?v=Oo0jm1PPRuo
- yeukhon 8y agoSo now packages relying on older values would have to be updated, right? In that case, wow, all those ancient - but usable FORTRAN/C code. Correct me if I am wrong.
- delecti 8y agoIdeally the weight of a kilogram defined by the new definition should be identical to the weight of the old physical "the kilogram" object. The goal of this isn't to change how much a kilogram weighs, it's just to change how it's defined. For a comparison, it used to be that we measured the speed of light as being 299,792,458 meters/second. Since then, we have defined the meter to be 1/299,792,458 of the distance that light travels in one second. An object that was 1 meter long before is still 1 meter long, but the way we communicate how long a meter is has gone from "it's how long this particular stick in France is" to a precise definition based on fundamental properties of the universe.
- sk_hazratali 8y agoThe actual text of the resolution, for those with low tolerance for dumbed-down PR releases: https://marketcapcoin.blogspot.com/2018/11/tron-price-prediction.html https://marketcapcoin.blogspot.com/2018/11/tron-price-predic...
- kibwen 8y agoSee, the US wasn't being stubborn in not adopting metric, it was just waiting patiently for it to progress from beta to 1.0. :) (Fun fact: all the US customary units have been officially defined in terms of their metric counterparts since 1893: https://www.nist.gov/sites/default/files/documents/pml/wmd/metric/1136a.pdf https://www.nist.gov/sites/default/files/documents/pml/wmd/m...)
- Waterluvian 8y agoSo it's fair to rib my American friends with the fact that Imperial is implemented using metric?
- beloch 8y agoI like to commend my American friends for their undying loyalty to the memory of the Empire. U.S. customary units are derived from units that helped the British conquer the world, but even the British themselves have shamelessly abandoned them for the units of a filthy, monarch-less republic. It's good to see that Americans still subconsciously yearn for the firm ruling hand of their rightful Queen. Note: Americans hate it when I do this.
- BigChiefSmokem 8y agoOur King wears no clothes. We desperately could use a Queen and some manners right about now.
- combatentropy 8y agoIt just doesn't have the same ring to it. "He won't move an inch," or "He won't move a centimeter." "She won't quit until she's six feet under," or "She won't quit until she's two meters under." "I'll go the whole nine yards," or "I'll go the whole nine meters." "You can see for miles and miles," or "You can see for kilometers and kilometers."
- smolsky 8y ago
- winwares 8y agoThe redefinition of the kilogram marks the end of artefacts used to define our measurement units.
- ggm 8y agoNever understood why the reference weight was one and not a maintained average over several or tens. This could have included aperiodic less used reference weights stored differently, different washing cycles &c. I know several bipm participant nations had clones but they were always understood to be daughter weights. Level surfaces (for instance) used to be made as triplets and never pairs: pairs can form lenses. Not that a kibble balance definition isn't better: I just don't understand why the kg definition was a Singleton and not statistically satisfied.
- kderbyma 8y agoDecay would be exponentially greater with more weights. Causing a larger decrease over time.
- ggm 8y agoExcept some kg reference weights gain weight. The washing regime ablates, but the metal matrix is porus at the atomic level (I am told) and so they accrete. Therefore there would be gains and loses. Not just losses
- iharhajster 8y agoFor an engineer it's quite an anventure throughout your career discovering how many "languages" people speak: imperial, metric, IEC, ANSI, metric thread, NPT thread, all the units and industrial standards. And still foreign ISS parts mate in orbit on their first date. Or ITER parts fit toghether in plant. That's electrifying and inspiring.
- snowy100 8y agohek Na
- snowy100 8y agohek Na!
- edoo 8y agoThe US didn't adopt the metric system because it was considered blasphemous since the French used it. I'm not joking. We got screwed by a bunch of demagogues.
- gnopgnip 8y agoThe US officially adopted the metric system in 1975 with the Metric Conversion Act.
- edoo 8y agoThe act does not require the US to use metric in any capacity. It is optional. If it did kids would not be taught using the imperial system.
- slededit 8y agoThe US uses customary measures. Imperial is the old UK system. It has some important differences like the size of a gallon - and perhaps most importantly if you like beer: the size of a pint.
- gnopgnip 8y agoThere are a lot of situations in the US where using dual measurements, or just using metric is required, like food labeling. Using customary units is optional in many cases
- pouetpouet 8y agoMoreover the US signed the Convention du mètre [0] in 1878. By law all US customary units are based on SI units since 1883 [1] [0] https://en.wikipedia.org/wiki/Metre_Convention https://en.wikipedia.org/wiki/Metre_Convention [1] https://en.wikipedia.org/wiki/Mendenhall_Order https://en.wikipedia.org/wiki/Mendenhall_Order
- gorn 8y agoRecently I have been thinking about if any of our units makes sense in cosmic perspective. Let's take speed of light for example. It's approximately 300000 km/s. But then what is a second? It's 1/60 of a minute which is 1/60 of an hour which is 1/24 of a day(and so it goes) and all those numbers are arbitrary. A day doesn't make any sense outside our planet anyway, I doubt that there is another celestial body in the universe that takes the same time to complete a rotation. Period of some natural phenomena (like atomic electron transition) sounds better as a unit but it's a really tiny period of time so we have to scale it to make it practical for us. We will use decimal numeral system to do that, another arbitrary choice. What if we had 12 fingers or 8? This can be extended to all kinds of measurements so I wonder if any of this would make sense to another civilization. What would a cosmic system of units would like? Any reading about this would be greatly appreciated.
- carljoseph 8y agoThe definition of a second isn't based on the Earth's motion, but some natural phenomena like you recommended. "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." [1] [1] https://www.scientificamerican.com/article/how-does-one-arrive-at-th/ https://www.scientificamerican.com/article/how-does-one-arri...
- saagarjha 8y agoOf course, that definition was made to make our current definition of the second continue to work.
- gnopgnip 8y ago"The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom."
- Ono-Sendai 8y agoYes I think you're mostly correct, it's all pretty arbitrary. An alien civilisation is going to need units of length, time, speed, mass, energy etc.. Speed has an obvious unit which is the speed of light (in a vacuum), which seems to be the same everywhere. All the others are a bit more arbitrary I guess.
- LTL_FTC 8y agoMy poor textbooks! Welp, I guess there will be some great bargains next year.
- ajb1 8y agoSomething I've considered recently is the case of estimating heighth (or any length) in customary vs. metric. In the US, if I'm describing someone, perhaps to a police officer, I can fairly easily conceptualize the difference between 5ft, 5ft 6in, 6ft, or even smaller degrees of difference. Though I'm certain this is likely just a result of me having grown up with the customary system, it seems like it would be more difficult (or at least more tedious) to estimate the heighth of a person using meters, given that most humans are in the 1.5-1.8m range (by my estimation). Especially when looking only at one gender, the range of possible heights is quite small in meters, requiring more precision to describe. For example, I can reliably understand and visualize the difference between 5'0" and 5'4". I'm curious for those in the rest of the world - can you meaningfully visualize the difference between 1.5m and 1.6m? Or perhaps 1.55m and 1.58m?
- stephen_g 8y agoIf you use appropriate units, sure. Height of people is commonly measured in centimetres, not metres. Yes, one can easily estimate 150, 155, 160 etc. to within ten centimetres or so.
- hamilyon2 8y agoWell, sure we can. It is a matter of practice, like everything else
- llukas 8y agoThis is only due to you being used to certain units. I was raised in EU using Celsius scale and can relate to full scale. In US I can relate only to 70-80 range as this is what I consciously experienced (ie. adjusting air conditioning). I still need to convert Fahrenheit to Celsius for anything outside of that range. Also imperial sucks utterly as metric allows almost seamless exchange of mass measurements with volume for of pretty much anything in the kitchen (1g of water is roughly 1cm^3, almost everything we eat is very close in density to water).
- tempodox 8y agoWelcome news. Of course the U.S. will continue to be be the leader of the 3rd world by measuring in Royal Hangnails, Princely Bladders and Regal Farts.
- pulverizer 8y agoAbout metric vs imperial. We all adopted 10 based numbering. That puts any system not 10 based at disadvantage.
- zzo38computer 8y agoThe old definition of kilogram (with IPK) is no good, so it is very good that they are correcting it. Of course you can still use imperial and other units in whatever context they are useful, and so SI units can also be used in the context where they are useful. But still I am glad they change it, because the old definition of kilogram is no good.
- Millennium 8y agoThe main problem with imperial units is that it isn't a system. It's a hodgepodge of pieces of different historical systems, many of which made a lot of sense in their original context, but the context has been stripped from them and they've been mashed together with completely unrelated systems. A base-12 system would actually have some advantages, but very few of the imperial units are actually defined in terms of base-12, so it doesn't qualify.