18 ms·
The kilo is losing weight, changing all of science
- omegant 13y agoInteresting, anybody knows something tath weights something similar to the variation registered at the standar kilo? Like a virus or so.. On a side note it must be a slow day to get this news at the middle of the front page with 3 votes in one hour..
- gus_massa 13y agoThe difference is 25 or 50 micrograms. It’s muuuch heavier than a virus. The milligram weigh sets (1 milligram = 1000 microgram) are/were standard equipment in a chemistry lab (Now, if you are lucky, you get an electronic balance.) The smaller weights are only a small tin of 1 milligram. See the images in the middle of this page: http://www.ebay.com/itm/STAINLESS-STEEL-MILLIGRAM-WEIGHT-SET-100-g-TO-1-mg-/330539476607 http://www.ebay.com/itm/STAINLESS-STEEL-MILLIGRAM-WEIGHT-SET... I found a microgram weight set in Internet. (But I haven’t seen any of them in real life) http://cn.mt.com/cn/zh/home/products/Laboratory_Weighing_Solutions/Weights/microgram_weights.html http://cn.mt.com/cn/zh/home/products/Laboratory_Weighing_Sol... . These weights are only a small piece of thin wire, and you must handle them with a special tool because the fingers are too dirty. The smaller weight is 50 micrograms, that is approximately the variation between the kilo prototypes.
- speeder 13y agoThere is another competing proposal for solution that the article does not mention. It is define kilo as a specific number of Silicon-28 atoms, that have a well known mass. The laboratory with that proposal made the most perfect sphere ever, in attempt to allow measurements.
- ArikBe 13y ago^This. It's well explained in this YT video: https://www.youtube.com/watch?v=ZMByI4s-D-Y https://www.youtube.com/watch?v=ZMByI4s-D-Y
- Osmium 13y agoA side-benefit of this project (The Avogadro Project) is that there are a load of interesting things you can do with almost-pure Silicon-28, e.g. see http://www.nist.gov/pml/div684/enriched-silicon-project.cfm http://www.nist.gov/pml/div684/enriched-silicon-project.cfm (and more besides: there was a really interesting paper I saw recently which irritatingly I can't find now)
- philsnow 13y agoThat is really cool ... is that _aluminum foil_ wrapped around a hose in one of the pictures ? I wrapped an unshielded 12 foot vga cable in aluminum foil once and it greatly (subjectively) improved the video quality.
- nraynaud 13y agoI completely agree, It's time to start counting atoms/molecules of something (being careful with isotopes). Integer numbers are very good for "perfect" (well, very good) abstract definitions. And it would also really prolong the French Revolution spirit in the sense that this unit would become so universal that you don't need a physical reference anymore, like what we could achieve with the other base units (like second then meter).
- xentronium 13y agoKinda off topic: How is this good news for dieters? New kilo is lighter than old one, thus making all new measurements bigger in absolute numbers. Besides, can't they recreate a "canonical kilo" with the required measurements?
- martin-adams 13y agoIt's because dieters measure their progress in kilos lost. So if it's lighter, they can lose more kilos for the same effort.
- ewzimm 13y agoThose dieters who measure fifty millionths of a gram in weight loss have bigger problems.
- vesinisa 13y agoValid point, but your starting mass also increases. Then there's also that if the measurement changes, the results can become pretty bizarre. Say, you are on a diet for one month. At the start of the month, the kilo prototype weights 1 skg and at the end 1 ekg = 0.9 skg. You measure yourself at the start of the diet, and get that you weight 100 skg. You use some very precise diet-fu to draft a program that should see you losing 5 skg during the month. And lo and behold, you manage to stick to the program and loose exactly 5 skg. But at the end of the month, when you measure yourself against the now-lighter prototype, you get that you now weight 106 ekg. So, you actually achieved your target and lost 5 kilos, but meanwhile ended up with 6 kilos more body mass than before the diet! (Disclaimer: real changes in the prototype mass are of course way, way smaller.)
- legierski 13y agoI always thought 1 litre of water equals 1 kilogram. And as we know how long 1m is from nature, why don't they use 10cm x 10cm x 10cm of water at a specified temperature as a prototype of kilogram?
- deleted 13y ago[deleted]
- swinglock 13y agoClose, but apparently not. > One litre of liquid water has a mass of almost exactly one kilogram https://en.wikipedia.org/wiki/Litre https://en.wikipedia.org/wiki/Litre
- stan_rogers 13y agoThat was the original definition. Things change over the course of a couple of hundred years or so, though, and the imprecision of that definition was noticed early on.
- ajasmin 13y agoWhere does the imprecision come from exactly? Can't we derive the kilogram from the number of hydrogen and oxygen atoms in a litre of water at an uniform temperature?
- jjoonathan 13y agoBut then your definition depends on the definition of temperature (energy/entropy) which in turn depends on the definition of mass. You might say "make all measurements at the triple point" but then you are still stuck with the problem of dealing with thermal fluctuations and structural variation (liquids have uniform structure only in a weak statistical sense) in addition to the practical problem of ensuring uniform composition at the triple point. This idea doesn't work for benchtop measurements (How do you determine that you have 1 mole of H2O? By measuring it's mass!) and it doesn't make sense for high-precision measurements where you need to provide a mechanism to allow the experimenter to make the error arbitrarily small. One of the leading proposals for the 2014 redefinition is very similar in spirit, though: defining Avagadro's number to be an actual number rather than a derived quantity (effectively this uses Carbon 12 as the mass standard). Another proposal is to define Planck's constant. I can't comment on the measurability of this one, but it would probably make people studying atomic physics happy because they like to use units that set most common constants to one, and the redefinition would make more of these implicit factors of 1 defined, rather than measured quantities.
- deleted 13y ago[deleted]
- alan 13y agoCould the fact that the other kilogram weights are being moved around maybe affect their weight? Like they're more exposed to chemical disturbance? Some form of tiny relativistic effect?
- ronaldx 13y agoThe IPK being 2nd lightest out of 12 on the given graph is not statistically significant: even before accounting for post-hoc analysis. The even distribution suggests (to my eye) that this is as likely random as by some systematic effect.
- blahedo 13y agoIt's third lightest---there's an outlier that's way lower. But, again just from eyeballing, it looks like there's two clusters, one that has tracked with the IPK and one that is now heavier than the IPK. Based only on that, it strikes me as more likely that some of the national copies have gained mass(/weight), due to storage conditions or whatever, while others have kept their same weight. Of course this "doesn't matter" in that whatever the mechanism, it's still a problem for the science!
- ronaldx 13y ago> It's third lightest---there's an outlier that's way lower. wow, good spot, thanks :) Although it could be a problem for science, somehow it's nice that we can get a sense of margin of error by this method.
- jsonmez 13y agono matter how much we think we know about the universe, we still don't know sh#*!
- rmrfrmrf 13y agoI'm not a physicist, but it's irritating to me that this article is using weight and mass interchangeably. I doubt they'd ever allow this, but the "simple" solution is to bring the weight aboard the ISS and capture its mass on an inertial balance.
- ISL 13y agoNobody can build a kilogram-scale inertial balance of sufficient absolute precision. If we knew how, we'd be doing it. Also, the ISS is a tricky place to work for a precision measurement. It's electrically, seismically, and gravitationally noisy (and huge gradients). Precision gravitational measurements are generally carried out in dedicated spacecraft with careful attention to those concerns, if they can't be done on the ground.
- rmrfrmrf 13y agoServes me right for acting like a know-it-all. Kinda glad I did, though, because you gave me a lot of good information. Thanks!
- CamperBob2 13y agoMost people don't realize that the gravity on ISS is almost as strong as it is on the surface of the Earth. They're continuously falling toward Earth, going just fast enough to miss the ground.
- ronaldx 13y agoGravitational acceleration is approx 10% less? Based on the radius of the earth and the radial distance of the ISS. Some nice discussion: http://physics.stackexchange.com/questions/29929/gravity-on-the-international-space-station http://physics.stackexchange.com/questions/29929/gravity-on-...
- clubhi 13y agoThe simple solution involves space travel?
- ye 13y agoThe correct way to define a kilogram would be N number of molecules of Carbon (pick your favorite isotope) at relative speed = 0.
- berntb 13y agoWhich type of C molecules? I think you want to say "X mol of Y. Weight measured in a vacuum, which necessitates an Y with very low evaporation."? Since it isn't done like that, I assume it isn't easy to find an Y which is both easy to measure exactly and to keep pure. (I have a smattering of organic chemistry but no inorganic, so any more opinions from me would be without value.) Edit: Other people here talk about Si. We can keep that clean, at least (see electronics).
- yk 13y agoThey try it, the problem is that you can compare mass better than you can count molecules. So one of the approaches is, to manufacture a Si sphere as perfect as possible and calculate the mass from the radius and the properties of Si crystals. As far as I know, this had no practical results, except cool photos of strangely rendered looking spheres. [1] http://www.theepochtimes.com/n2/images/stories/large/2011/03/27/10301_big_2.jpg http://www.theepochtimes.com/n2/images/stories/large/2011/03... [2] http://www.ptb.de/cms/en/themenrundgaenge/hueterindereinheiten/das-si/avogadro.html http://www.ptb.de/cms/en/themenrundgaenge/hueterindereinheit...
- shocks 13y agoI believe they've been trying to do this with silicon.
- Zenst 13y agoI often wonder why they don't make a set of scales with a electro magnet at one end that attracts one end of a balance and you place the weight on the other end and adjust the strength of the magnet until you get a balance and from there can measure out that same weight. Now would need very well pression made electro magnet and balance. Though idealy the ability to measure out a fixed amout of atoms of element and wheigh that and work out the relationship of how many atoms of element X is needed for a kilo. Well until then it is one of the last area's of measurment that history still firmly has its teeth into. Was nice TV show in the UK not long ago that covered the whole area of weights and measures from the science and history of them comming about. One of the better science shows. http://www.bbc.co.uk/programmes/b02xgf5d http://www.bbc.co.uk/programmes/b02xgf5d "Deep underground in a vault beneath Paris lives the most important lump of metal in the world - Le Grand K. Created in the 19th century, it's the world's master kilogramme, the weight on which every other weight is based. But there is a problem with Le Grand K - it is losing weight. Professor Marcus du Sautoy explores the history of this strange object and the astonishing modern day race to replace it."
- ISL 13y agoYou've described a Watt balance and the Avogadro project.
- EGreg 13y ago"Weirdly, it’s not even known if the IPK is getting lighter, or if the national prototypes are getting heavier — but either way, something is causing these kilos to change weight, by around 50 micrograms every 100 years." Well they COULD always do that thing with the water where they heat it to 4 degrees celcius and measure its volume and weight. Then they'd know which it is. That said, there's a nice video on this: http://youtube.com/watch?v=ZMByI4s-D-Y http://youtube.com/watch?v=ZMByI4s-D-Y
- deleted 13y ago[deleted]
- fragsworth 13y ago> measure its volume and weight Except they'd have to measure its weight (mass), which is in... Kg...
- emhs 13y agoWell, they're using the static, known density at 4 degrees Celsius to produce water with a known mass, and then test what the measurement of that mass comes to. Basically they're using a known mass of water as a calibration aid. But I don't know that this level of precision could compete with the efforts underway.
- EGreg 13y agoExactly. They'd COMPARE it to the existing physical object used as the reference for the kg. Assuming water allover the world hasnt changed its properties over the last few centuries they'd know whether it became heavier or lighter.
- yetanotherphd 13y agoAccording to the video, that process is a way to measure Plank's constant (indirectly), which is precisely what they refer to in the article.
- xenophonf 13y agoYeah, that's actually a lot more difficult than you make it sound. See, for instance, http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Wate....
- leeoniya 13y agofascinating article, circa 2011. http://www.wired.com/magazine/2011/09/ff_kilogram/all/1 http://www.wired.com/magazine/2011/09/ff_kilogram/all/1
- mistercow 13y agoIt has always bugged me that scientists consider this obviously terrible kludge of a standardization method acceptable. A civilizaton looking back 20,000 years from now and translating our scientific literature would be able to figure out what we meant by "second" by measuring the decay of a cesium 133 atom. But a kilogram (or any unit derived therefrom)? Sorry, the prototype is at the bottom of a crater. You can't miss it - it's the size of a whole golf ball, after all.
- scott_s 13y agoThey consider it "acceptable" because no one has implemented a better solution. They are not happy with it, but it's the least-bad solution.
- ISL 13y agoYour concern is at the heart of the effort to redefine the kilo. Everyone wants to link it to fundamental constants. The trouble is that the IPK is still more reliable than our measurements of Planck's constant and Avogadro's number. The meter was an artifact until measurements of the speed of light surpassed the prototype. The situation here is the same. If the world ended and all of the distributed artifacts were lost, you could use existing measurements of fundamental constants to redefine the kilo at slightly worse precision.
- scotchmi_st 13y agoI'm not sure I understand: surely we can just say that one kilo is a certain number of carbon 12 atoms, and have done? Would seem sensible to me.
- logicallee 13y agoOK - how many?
- Leszek 13y agoPresumably 6.0221413 * 10^23 * 1000 / 12 = 5.0184511 * 10^25
- mdturnerphys 13y agoIt's a standard, yes, but it's really hard to reproduce.
- deleted 13y ago[deleted]
- PeterisP 13y agoIn order to make practical use of that (i.e., calibrate a weight-measurement-tool) you need to be able to somehow make an artifact with that certain number of carbon 12 atoms, or measure the count of atoms with a sufficient accuracy.
- CoryG89 13y agoWow, is it surprising to anyone else that a 1.54 inch tall/wide cylinder of 90% Platinum / 10% Iridium would weigh a kilo (2.2 pounds)?
- smcl 13y agoYes, you're not the only one. I've never owned or held anything platinum but I still didn't expect such a small amount to weigh so much
- Aloha 13y agoI've always wondered why the KG was not defined as a certain volume of Water at Sea Level.
- jtjuyjuy 13y agoIt has been defined in the past as the mass of 1L of demineralized water at a specific temperature. Much less precise.
- grecy 13y agoHow do you define the unit used to measure the volume?
- jevinskie 13y agoBy using the well defined meter.
- grecy 13y agoRemind me again what that's defined as?
- nknighthb 13y agoPer http://www.bipm.org/en/CGPM/db/17/1/ http://www.bipm.org/en/CGPM/db/17/1/ "The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second."
- rpearl 13y agogrecy, the meter is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. A 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.
- n0mad01 13y agomaybe it's because the original kilo is a curiosity and therefore was passed through thousands of hands (maybe someone even dropped it?) the last 100 years? this surely can have a "losing weight" effect.
- KaiserPro 13y agoAs they cost billions to produce, they've held securely since they've been made.
- KaiserPro 13y ago90% platinum and 10% iridium for its virtual immunity to oxidization, and because it’s extremely hard-wearing well thats bollocks. Platinum is hilariously soft. There are a few issues, one is radioactivity. There are radioactive impurities that as they decay loose weight. Second, its postulated that there is a build up of trace amounts of mercury on the IPK due to environmental factors. thirdly, they are not cleaned anymore. they used to be cleaned with shammy leather.
- tlb 13y agoPure platinum is soft and malleable, but the heat-treated alloy can be as hard as stainless steel. https://en.wikipedia.org/wiki/Platinum-iridium_alloy https://en.wikipedia.org/wiki/Platinum-iridium_alloy
- cantrevealname 13y agoOK, here's a wacky theory about why this is happening: The article says that the kilogram copies are brought to Paris to be compared. Therefore the copies are undergoing significant acceleration (e.g., transported on airplanes or trains) while the original in Paris remains stationary. From the stationary kilogram's point of view, all of the other kilograms had undergone relativistic mass increases during the time of their travel. Suppose a tiny amount of this mass increase is somehow actually retained when all the transported kilograms are brought to the same frame of reference (i.e., when the airplanes land in Paris). What's a simple way to disprove this idea?
- sp332 13y agoThe "mass" gained from motion is really just the extra energy. When the energy is removed from the point of view of the stationary kilogram, all the extra "mass" is gone too.
- fragsworth 13y agoRight, in other words, you only have extra mass during the time that you are at a higher velocity.
- sp332 13y agoAnd, specifically, you only have "extra" mass from the viewpoint of someone traveling at a different speed or direction. From your own frame of reference, your mass never changes.
- cantrevealname 13y agoYes I know that. That's why I said if the mass were "somehow actually retained". I'm positing that the some of the extra energy somehow becomes real mass. Yes, this is not how special relativity works. That's why I said "wacky theory". But is there a simple and obvious way to falsify this?
- krisoft 13y ago
- muuh-gnu 13y agoCan somebody explain to me why an SI unit has the "kilo" prefix already in it, making other SI prefixes unusable with it? 1 kJ = 1000 standard units of energy. 1 kg = 1 unit of mass. Was this just an unfortunate historical accident? But if the too that much care to make a unit system that makes intuitive sense, why would they let in such an annoying exception? Why didnt they just make "gram" the standard unit or just made up another name?
- stormbrew 13y agoOther SI units can and obviously are used with it. Micrograms, milligrams, and grams are really commonly used. I'm not sure why they chose to do it this way, but it definitely doesn't really have any bearing on how it's used.
- knappador 13y agoThe order of magnitude chosen to calibrate the metric on doesn't change the prefix magnitude. 1 kJ = 1000J 1 kg = 1000g Adjusting prefixes puts the units on the order of magnitude where they are easy to write in typical domain problems. For a heat-capacity and heat-transfer problem, I might end up with J/kg or kJ/kg being convenient, while for expressing the specific energy of jet fuel, I'll use MJ/kg because it's 39. In the case of the kg, I'll bet that 1g was simply too small for the tools of the time to make an accurate model that was reproducible to the desired accuracy. For all I know, the weights were die-cast from the same melt, and the effect of scratches gets reduced as the surface-area/volume ratio goes down.
- samatman 13y agoBecause the margin of error on a weighing device is typically constant. Therefore, a better gramme could be established by weighing a kilogramme and dividing by 1000. This is also why an STP ml of water (used to) weigh a gramme, btw.
- EdiX 13y agoIt was a bad decision by french revolutionaries: http://www.bipm.org/en/si/history-si/name_kg.html http://www.bipm.org/en/si/history-si/name_kg.html However all the standard prefixes still apply normally, ie you will have milligrams (mg) that are 1/1000000 of 1kg.
- kunai 13y agoFor anyone interested in the Planck and Avogadro projects to redefine the kilo, this video is an imperative watch: https://www.youtube.com/watch?v=ZMByI4s-D-Y https://www.youtube.com/watch?v=ZMByI4s-D-Y
- velodrome 13y agoThe scientific community is working on the replacement: Known as the Avogadro Project, the plan is to bring together enough atoms of one substance – silicon – to make a kilo. Attention has focused on silicon because: - its characteristics are very well understood - a single crystal of the right size can be grown - its atomic structure is extremely uniform - its widespread use in the computer industry means it can be obtained with relative ease at high purity and resonable cost. A spherical shape was chosen because a sphere has no edges that might get damaged and only one dimension has to be measured in order to calculate its volume. --- http://www.csiro.au/content/ps35k http://www.csiro.au/content/ps35k http://www.youtube.com/watch?v=ZMByI4s-D-Y http://www.youtube.com/watch?v=ZMByI4s-D-Y
- Shish2k 13y ago> A spherical shape was chosen because a sphere has no edges that might get damaged and only one dimension has to be measured in order to calculate its volume. Surely every dimension needs to be checked, to ensure that it's a perfect sphere? (Which I assume is harder than checking a cuboid has six flat sides joined at right angles)
- ISL 13y agoIf you build an apparatus for measuring a sphere's diameter, it's possible to measure it in any orientation. If their test mass were cylindrical, they'd need the ability to measure both the diameter and the length to the requisite precision. I believe it is in this sense that 'dimension' was used.
- ISL 13y agoThe Avogadro project isn't the only horse in this race. The electromechanical approach, known as a Watt balance, is underway in several national standards labs around the world.
- harigov 13y agoIf they made 40 copies of the prototype, they know exactly how to make it - don't they? Why can't they make one more?
- PeterisP 13y agoThey can make a copy by adjusting its weight against an etalon weight (cutting to the "same size" wouldn't be nearly as accurate as the current differences) - so they can make one more kilo-as-it-is-right-now, but they can't magically make one more of kilo-as-it-was-in-1879 unless they get a time machine.
- NAFV_P 13y agoOriginally the meter was defined as the distance around the Earth, perpendicular to the equator, divided by 40 million. The French spent a while triangulating the French countryside from North to South to calculate the Earth's curvature. Unfortunately it was assumed that the earth was a prolate spheroid, when actually it is oblate. This is one of the reasons it was reformulated. The East India Company triangulated most of the length of India, but it was tremendously expensive. http://en.wikipedia.org/wiki/Great_Trigonometric_Survey http://en.wikipedia.org/wiki/Great_Trigonometric_Survey
- mmanfrin 13y agoDoesn't 1cc of water (at 4C) == 1 gram? Why not use 1000cc of water as the measurement for the kilo?
- heydenberk 13y ago1 cc of water is very nearly 1 gram, but not exactly. A few centuries ago, they were definitionally the same; now they're merely very similar.
- skj 13y ago> This is a problem, because the weight of the IPK is the kilo. A kilogram is not a unit of weight, but a unit of mass.
- D9u 13y agoSince gold is allegedly the most inert element, why wasn't the the prototype made of gold?
- maxerickson 13y agoPlatinum is less reactive than gold.
- pontifier 13y agoWe just need more mass surveillance on those kilograms... Kidding aside, can we please define the kilogram already?