back to article Holy moley! The amp, kelvin and kilogram will never be the same again

As incredible as it may seem, until this week the definitive measurement of a kilogram was a cylinder made of an alloy comprising 90 per cent platinum and 10 per cent iridium sat under a glass dome in a room in Paris. The cylinder is one of six official exact masses of one kilogram, and it has been that way since 1889: The …

  1. malle-herbert Silver badge
    Joke

    And as usual...

    There's always an appropriate xkcd...

    1. The Man Who Fell To Earth Silver badge
      Go

      "...using methods that can be replicated anywhere on the planet."

      Er, no.

      "...using methods that can be replicated anywhere in this Universe."

      FIFY

      1. Joe W

        Re: "...using methods that can be replicated anywhere on the planet."

        We-ell... Not anywhere, not anytime. There are measurements that suggest those constants are in fact not. Constant, that is (cannot remember which ones, though) . And I'm not taking about the first moments (big bang, inflation, etc).

        1. Charlie Clark Silver badge

          Re: "...using methods that can be replicated anywhere on the planet."

          There are measurements that suggest those constants are in fact not. Constant, that is (cannot remember which ones, though)

          There are some observations that suggest that Planck's constant ("h") might not be, er, constant in space and time. Time is sort of understandable, at least in the very early phases of the universe during expansion but I think the observations are of much more recent times. Came across this a few years ago so it could have been debunked or theorised away but it would not suprise me in the least if the universe didn't have quite a few more surprises for us.

      2. Charles 9 Silver badge

        Re: "...using methods that can be replicated anywhere on the planet."

        Incorrect fix. The second is still defined terestrially, and there's currently no way to change this because of the lack of any kind of absolute point of reference. Put it this way. The measurement of cesium oscillation can change depending on how high up one is on the planet (due to time dilation effects). That's why the qualification of using mean sea level on a theoretical geoid.

        1. The Man Who Fell To Earth Silver badge

          @Charles 9 Re: "...using methods that can be replicated anywhere on the planet."

          Wrong. Relativity, both General and Special, are the way they are precisely because of all clocks being local. Apparently Physics wasn't your "thing" in school.

        2. Spamfast Bronze badge

          Re: "...using methods that can be replicated anywhere on the planet."

          The measurement of cesium oscillation can change depending on how high up one is on the planet (due to time dilation effects).

          There is no absolute reference frame.

          But if we both use the same definition then we can agree that we're measuring the same thing.

          When we get different numbers for the same measurement, that gives us data about the difference between our reference frames, itself useful information.

        3. cosmogoblin

          Re: "...using methods that can be replicated anywhere on the planet."

          Not so. You simply define your local second, the second in your frame of reference, and adjust it appropriately for other frames of reference (inertial/gravitational).

          As long as your cesium atom and your experimental equipment are in the same frame of reference, you'll get the same value for the second as anybody else in the known Universe.

          There is a slight uncertainty due to the variation in gravitational field strength at different parts of the apparatus, but this in fact makes your measurement more precise and reliable if your experiment is in space, where the gravitational field gradient is minimal.

        4. rajivdx

          Re: "...using methods that can be replicated anywhere on the planet."

          Not true. The speed of light is fixed for all observers. This means that time dilation effects are not detectable to you if you are in the same frame of reference. This means that you will still measure 1 second correctly for your frame of reference using a Cesium clock whether you are in total void or on the surface or the earth or on the event horizon of a black hole.

      3. diodesign (Written by Reg staff) Silver badge

        "...using methods that can be replicated anywhere in this Universe."

        Well, yeeeeeah... our planet is in this universe, at least it was the last time I checked ;-)

        I kinda thought it would be presumptuous to say the constants would work everywhere in the universe. I expected a physics PhD to pop up and yell at us if we said "anywhere in the universe" because, I dunno, at least one of the constants used by the SI base units may not apply or change near black holes or other weird crap out there.

        I don't know if people realize how much of a tightrope it is writing for a fair number of readers, most of them experts in a technical field. We try to get everything right within a reasonable time frame.

        So anyway, that's why we thought "planet" would be a sensible non-offensive, non-triggering bounding box for boffins, seeing as humans aren't going much further into space for a while.

        C.

        1. Ken Moorhouse Silver badge

          Re: "...using methods that can be replicated anywhere in this Universe."

          The Kibble balancer wouldn't work in a weightless environment, for starters. The target kilogram, though anchored, would be floating around the lab.

          1. Tomato42 Silver badge

            Re: "...using methods that can be replicated anywhere in this Universe."

            > The target kilogram, though anchored, would be floating around the lab.

            it can also work in a mode in which the acceleration imparted on the object by the electric field is used to derive its mass

          2. cosmogoblin

            Re: "...using methods that can be replicated anywhere in this Universe."

            True enough, but there are other methods (currently, I think, even more ludicrously expensive).

            A lot of news outlets have been reporting that the kilogram is now defined in terms of the Kibble balance, which is completely missing the point. The kilogram is defined independently of any measuring equipment; you just need appropriate measuring equipment to effectively use that definition, and the Kibble balance is our best current equipment.

            The Kibble balance compares the weight of an object with the electrical power needed to lift that object, and therefore needs a known gravitational field strength. It would be possible to make a related device that instead of lifting an object, accelerated it in zero g; thus comparing the acceleration with electrical power, and determining its mass that way. Doing away with the need for gravity, I imagine this could be made more precise than the Kibble balance.

          3. DropBear Silver badge

            Re: "...using methods that can be replicated anywhere in this Universe."

            "The Kibble balancer wouldn't work in a weightless environment"

            That is not wrong, but it needs to be noted that on the other hand the balance would work just fine on the Moon or Mars - for any of those, including Earth, you also need a precise measurement of the local "g", measured using meters and seconds.

            The other thing to note is that while the Kibble balance was used to pin down a value as precise as possible for the Planck constant so that it results in our legacy kg being as close to the new definition as possible, once that is done one doesn't necessarily need to use a Kibble balance specifically to derive a reference kg from the Planck constant again - any apparatus linking the two units would suffice - weight may be gravity-dependent but mass isn't.

            And indeed, while the Kibble balance may be the most famous, other approached to define the kg starting from the same constant do exist - most well known probably being the Avogadro Project silicon sphere atom count.

      4. Spazturtle Silver badge

        Re: "...using methods that can be replicated anywhere on the planet."

        "...using methods that can be replicated anywhere in this Universe."

        If you have proof that the laws of physics are consistent throughout the universe please come and collect your Nobel prize.

    2. DonL

      Re: And as usual...

      "There's always an appropriate xkcd..."

      Perhaps it was part of the point of the joke, but the definition of the pound is actually linked to the kilogram:

      "Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms"

      https://en.m.wikipedia.org/wiki/Pound_(mass)

    3. RobThBay

      Re: And as usual...

      I was just about to post the same link. :) :)

    4. Adrian 4 Silver badge

      Re: And as usual...

      Given the way almost every unit is defined by its relationship to others, I think maybe this one is appropriate.

      I do hope they didn't just cut off the branch they were sitting on.

  2. Anonymous Coward
    Anonymous Coward

    Le Grand K's fate

    So what's going to happen to Le Grand K? Used as a paperweight? Melted down for souvenirs? Or put on show in a museum?

    1. Voyna i Mor Silver badge

      Re: Le Grand K's fate

      I think maybe I'll buy it. It's accurate enough for normal use and will save me my annual trip to Paris to recalibrate my kitchen scales.

      Incidentally the article is pretty damn good but I think it might need explaining that there is one arbitrary factor in all of this - the caesium atom wavelength which was chosen for stability and lack of fine structure, IIRC. The original metric system relied on two arbitrary numbers - the period of the Earth's rotation and its circumference - neither of which were in fact constant.

      1. Lars Silver badge
        Happy

        Re: Le Grand K's fate

        "the period of the Earth's rotation and its circumference - neither of which were in fact constant.".

        The period of the Earth's rotation, was a very funny thing to write and has nothing to do with the metre.

        The "assumed" distance from the equator to the pole was divided by 10.000.000.

        (the circumference 40.000 km).

        A glimpse into the British soul we find in this "On 20 May 1875 an international treaty known as the Convention du Mètre (Metre Convention) was signed by 17 states.".

        Britain was not among those 17 states.

        There used to be an absolutely marvellous account of Britain's indecisive journey towards the metric system, but I cannot find it any more, perhaps it was too revealing.

        https://en.wikipedia.org/wiki/History_of_the_metric_system

        1. Voyna i Mor Silver badge

          Re: Le Grand K's fate

          @Lars, I'm making allowance for the fact that English is obviously your second language, but this article is about the redefinition of units, not the redefinition of the metre.

          The old MKS system was based on several non-universal numbers but for everyday use the most important were [spoiler alert] the metre, kilogramme and second.

          As I noted, the metre was supposed to be a fraction (actually 1/40 000 000) of the Earth's circumference, which can't be stated with a very high accuracy.

          The second is based on the rotation period of the Earth, which also varies slightly.

          The kilogramme is 1/1000 the mass of a cubic metre of pure water at a particular temperature - highly impractical and so soon replaced by standard masses.

          So there was nothing "funny" about mentioning the period of the Earth's rotation because it defined one of the three basic units.

          In fact, using the way the metre is defined nowadays, you could derive the "old" metre from the "old" second by saying that the metre is the distance that a point on the equator at mean sea level moves in a certain time - to be exact 86400/40 000 000 seconds.

          1. Lars Silver badge
            Pint

            Re: Le Grand K's fate

            @Voyna i Mor

            Sorry for misunderstanding you. They did use the 10.000 km as the distance from the equator to the pole by simply saying it's 10.000 and thus 1m is what it is. The exact distance to the pole doesn't change that, it would be like pointing out that each feet is not exactly one foot.

            English is my third of four, but that had nothing to do with my mistake.

            Have beer on me.

            1. Alan Brown Silver badge

              Re: Le Grand K's fate

              "They did use the 10.000 km as the distance from the equator to the pole by simply saying it's 10.000 and thus 1m is what it is."

              For some reason the metre was defined as 1/10,000 of 1/4 of the circumferential arc a few times in history.

              The French innovation seemed to be defining it from pole to equator (of course that's going to be different from north pole vs south pole, oblate spheroid etc). Previous definitions were either at the equator or sliced at the latitude of the city of the civilisation which defined it - so the egyptian metre was slightly longer than the greek metre, etc (the ancients were perfectly well aware that the earth was round and had a pretty accurate idea of its size. Colombus' fallacy was that it was much smaller than it is and everyone thought he'd starve to death on the voyage, not fall off the edge. He nearly did starve too - and falsified ship's log records to make it seem as if the distance travelled was considerably less than reality in order to deceive his crew, because by his stated original calculations they should have reached Asia long before they hit the Carribean.)

              The roman mile was slightly different, being "1000 marching paces" and defined to allow for planning of rest breaks, etc.

          2. Alan Brown Silver badge

            Re: Le Grand K's fate

            "The old MKS system was based on several non-universal numbers but for everyday use the most important were [spoiler alert] the metre, kilogramme and second."

            Anyone who's had to calculate anything in rods, poles perches and chains (never mind gills, barrels, hogsheads, bushels and pecks) will have heaved a sigh of relief that most of the sane world switched to something that used common multipliers AND UNITS across the board.

    2. Will Godfrey Silver badge
      Unhappy

      Re: Le Grand K's fate

      It will be put in a museum with great fanfare, then as interest in it wanes, will be moved by degrees to less auspicious locations, until it is almost forgotten. There will be a brief resurgence of interest when it is stolen to order for some obscenely rich person's private collection.

      In tens of thousands of years time, archeologists in special protective gear will find it while searching though the highly radioactive remains of what appears to have been a fairly advanced civilisation. Recognising that it contains important metals that are in short supply it will be immediately taken to the Whole Earth Technology centre to be put to use.

      1. Michael Habel Silver badge

        Re: Le Grand K's fate

        In tens of thousands of years time, archeologists in special protective gear will find it while searching though the highly radioactive remains of what appears to have been a fairly advanced civilisation. Recognising that it contains important metals that are in short supply it will be immediately taken to the Whole Earth Technology centre to be put to use.

        I think you forgot to pin the blame of all this on both Brexit, and the Orange Man. Otherwise +1

        1. Anonymous Coward
          Anonymous Coward

          Re: Le Grand K's fate

          By "Orange Man" do you mean Mr. I. Paisley, or the equally damaging Tangerine Trumpet?

          Both, along with their followers and cults, have done severe harm to our cultures. The legacy of one is still a drag on the Brexit process and all it contains.

      2. HelpfulJohn

        Re: Le Grand K's fate

        Hmm, it won't work out that way.

        After the fall of the Wizards, when the wars of lightning and magics kill the Great Cities, the remnant species that were once Humans will eke out short, crude, barbaric lives in the rubble, for a while, until they evolve into other species.. Eventually, erosion and tectonics will delete all trace of Man from the planet, whether Life exists on it or not.

        There will never be any archeologists because no second wave of City Cultures can ever arise without cheap, easy to reach oil and coal to kick-start it and we've eaten all of those.

        The Fall of The Cities is the end of technology, the end of the Dream of Stars, the end of any hope of a Human Galaxy.

        There will be no one left to hear our songs or mourn our kings.

    3. Anonymous Coward
      Anonymous Coward

      Re: Le Grand K's fate

      "So what's going to happen to Le Grand K?"

      SAme as teh Berlin Wall when that became surplus to requirements(*) ... you'll be able to buy "chips from Le Grand kg" from a wide range of didgy street vendors all over Paris

      ---

      (*) also cf "splitners from the one true cross"

      1. Ken Moorhouse Silver badge

        Re: "So what's going to happen to Le Grand K?"

        There will be a slimmed-down version of it which they will call "Special K".

        1. This post has been deleted by its author

    4. DropBear Silver badge

      Re: Le Grand K's fate

      So what's going to happen to Le Grand K?

      Nothing much. Greengrocers won't suddenly sprout Kibble balances in the back rooms of their shops; you still need practical artefacts to calibrate stuff against, with the Grand K (and its copies around the world) continuing to sit at the top of that pyramid - it's just that instead of being exactly 1kg by definition it will now simply embody a reference kg with a measured and documented (tiny) error.

      1. HelpfulJohn

        Re: Le Grand K's fate

        "Greengrocers won't suddenly sprout Kibble balances in the back rooms of their shops;"

        No, not suddenly, but with a little more technological development it may be that carrying such a thing around in a pocket will be cheap and easy in ten years or so. Probably as part of a mobile computing and sensing device. We might even have a classy name for it ... "mobile phone", perhaps?

  3. Anonymous Coward
    Anonymous Coward

    Is there such a thing as a complete physical vacuum even in observable space?

    1. Def Silver badge

      No, but as far as the speed of light is concerned, you only need space to be devoid of anything that would interact with light passing through any given point. As long as nothing interacts with it, it's full speed around (because space is curved). ;)

    2. Voyna i Mor Silver badge

      "Is there such a thing as a complete physical vacuum even in observable space?"

      Yup, just go somewhere where the density is around 1 hydrogen atom per cc, and select a region of about half a cc. Fifty percent of the time you'll have a complete vacuum.

      1. ridley

        No, no no.

        If you went down that path you would eventually be able to say where that Hydrogen atom actually is and that just isnt allowed...

        1. Baldrickk Silver badge

          uncertainty

          If you went down that path you would eventually be able to say where that Hydrogen atom actually is and that just isnt allowed...

          Of course it is.

          Only problem being that you would have no idea where it was going.

        2. Voyna i Mor Silver badge

          "If you went down that path you would eventually be able to say where that Hydrogen atom actually is and that just isnt allowed"

          I carefully avoided precisely that issue by saying that 50% of the time you would have a pure vacuum in one half cc. I did not say you could identify which that one was. Several people seem to have failed to notice that I was referencing Erwin's feline.

      2. Anonymous Coward
        Anonymous Coward

        Yeah, but when you get the dilution that low the vacuum *remembers* that it once had hydrogen in it...

    3. ridley

      No, Heisenberg tells people off if they tell you where something is or isnt.

      1. asdf Silver badge

        Yep quantum tunneling makes sure there is no such thing as a truly closed system (sorry if not using official technical term right as layman).

      2. John Brown (no body) Silver badge

        "No, Heisenberg tells people off if they tell you where something is or isnt."

        A meeting between Heisenberg and Yoda might be fun.

    4. asdf Silver badge

      Oh yeah forgot virtual particles as well even if there is no real particles in your vacuum. Quantum stuff makes a mess of classical world at smallest scales.

      1. Alan Brown Silver badge

        "virtual particles as well even if there is no real particles in your vacuum"

        Which gets even messier when you start apparently extracting energy from those virtual particles. Evidence of extra dimensions that we simply can't perceive?

    5. Schultz

      As with most scientific concepts, you extrapolate.

      Nuff said.

  4. #define INFINITY -1 Bronze badge

    "c"

    "you can derive the distance wherever you are without relying on a single artificial reference object."

    Is there an app for that?

    (There's also the question not answered here, as to how the Ampere will be accurately measured--whether the process of measuring a single "e" is stable yet)

  5. Anonymous Coward
    Anonymous Coward

    Sad case of science ignoring the evidence

    What seems to being ignored here is that somehow the various copies of the kilogram made over the years, with the best equipment of the time, ended up being different to each other.

    At one time this would have been enough to warrent an investigation but now it seems easier for science to just ignore the anomaly and redefine the kilogram as something else.

    1. TRT Silver badge

      Re: Sad case of science ignoring the evidence

      Blame the weight loss on weapons of mass destruction. And when it gains, weapons of mass creation.

      So it's either the bomb or God. Take your pick.

    2. #define INFINITY -1 Bronze badge

      Re: Sad case of science ignoring the evidence

      It seems more that the journalism has been tailored for those less inquisitive and more willing to believe 'new tech'. I'm sure there is an explanation--I would guess when it was removed from the vacuum in order to compare to the other standards.

      Are there any physicists around who can argue that gold would not have been a better choice?

      1. A.P. Veening

        Gold no better choice

        The weight loss (small but measurable) is a result from the cleaning, necessary because stuff from the air will cling to it. As gold is much softer than the used alloy of platinum and iridium, more weight would have been lost.

        1. ridley

          Re: Gold no better choice

          or from oxidation etc making it heavier. Hence the need to clean it.

        2. Charles 9 Silver badge

          Re: Gold no better choice

          "The weight loss (small but measurable) is a result from the cleaning, necessary because stuff from the air will cling to it."

          Wasn't that taken into consideration by placing the prototypes under double bell jars?

          1. tfb Silver badge

            Re: Gold no better choice

            I think you have to take them out of the bell jars to use them.

      2. Lars Silver badge
        Happy

        Re: Sad case of science ignoring the evidence

        "Are there any physicists around who can argue that gold would not have been a better choice?".

        I don't know, but I would guess that the economists and others would had been against it much because 40 prototypes were produced to start with.

        1. #define INFINITY -1 Bronze badge

          @Lars Re: Sad case of science ignoring the evidence

          Except I have a suspicion that a Kibble balance costs more than 40kg of gold....

          Is the relative cost comparable to the relative difference in accuracy?

        2. A.P. Veening

          Re: Economists

          I suggest you look up some economy books, platinum is normally more expensive than gold. It is just a matter of a couple of physical properties.

          1. #define INFINITY -1 Bronze badge

            @A.P. Veening Re: Economists

            In 1889?

            1. Voyna i Mor Silver badge

              Re: @A.P. Veening Economists - In 1889?

              It's interesting. In 1889 the gold price per troy ounce was about $20. Platinum was cheap - about $4. I don't have a price for iridium, but in 1911 it was $62, at which time platinum was $43 and gold was still about $20 (because of course the dollar was linked to it).

              The standard kilogram is only about 10% iridium so the alloy looks to have been much cheaper than gold, but by WW1 the standard kilogram material was much more expensive than gold.

              If I was a billionaire, I think I'd have a boat with the heat exchangers made out of platinum iridium alloy, because I could. No corrosion worries.

              1. Lars Silver badge
                Happy

                Re: @A.P. Veening Economists - In 1889?

                Why not the keel too, it's heavier than led. There was one well known and quite successful French yachtsman who had a keel of uranium in his offshore racing yacht for that reason.

                1. agurney

                  Re: @A.P. Veening Economists - In 1889?

                  Why not the keel too, it's heavier than led. There was one well known and quite successful French yachtsman who had a keel of uranium in his offshore racing yacht for that reason.

                  I trust you mean denser. A kilo of lead is far heavier than a gram of uranium.

                2. Voyna i Mor Silver badge

                  Re: @A.P. Veening Economists - In 1889?

                  " There was one well known and quite successful French yachtsman who had a keel of uranium in his offshore racing yacht for that reason."

                  Wait long enough, of course, and it would turn to lead.

                  But the ideal keel material would be osmium. You'd need 10 years of world supply to make a decent keel, but you'd be able to work up quite a clip around your volcanic island lair with the wind blowing the right way.

                  1. Charles 9 Silver badge

                    Re: @A.P. Veening Economists - In 1889?

                    "But the ideal keel material would be osmium."

                    In terms of density, yes, but last I checked osmium's also very brittle, meaning a hard knock can break it: NOT a good thing when it comes to a keel.

                    1. TRT Silver badge

                      Re: Ship's keel.

                      Unobtanium?

                      1. Michael Habel Silver badge
                        Mushroom

                        Re: Ship's keel.

                        I propose we build the Ships Keel out of Sodium.

                        1. defiler Silver badge

                          Re: Ship's keel.

                          I propose we build the Ships Keel out of Sodium.

                          Seconded.

                          1. DropBear Silver badge
                            Trollface

                            Re: Ship's keel.

                            Oh, a lunacy competition...? Woohoo, I'm in! How about... sawdust and ice?!?

                  2. cray74

                    Re: @A.P. Veening Economists - In 1889?

                    But the ideal keel material would be osmium.

                    Osmium oxidizes too easily and its common tetroxide is poisonous. It also only offers a slight density gain over platinum, which is more common and better behaved chemically, and only a modest gain over tungsten and uranium.

                    Another approach to enhance sailboat performance is switch to a multi-hull so you're not burdened with a heavy keel.

                3. Loyal Commenter Silver badge
                  Coat

                  Re: @A.P. Veening Economists - In 1889?

                  it's heavier than led

                  That's because LEDs are light...

              2. cray74

                Re: @A.P. Veening Economists - In 1889?

                If I was a billionaire, I think I'd have a boat with the heat exchangers made out of platinum iridium alloy, because I could. No corrosion worries.

                If the rest of the boat is made of non-platinum group metals then you'd need to be careful of galvanic (dissimilar metal) corrosion. Platinum's at the far end of the galvanic series so it's a threat to most other metals. It's relatively easy to address if you can separate the metals with non-conductive barriers (e.g., paint), but I wouldn't say "no worries."

        3. Loyal Commenter Silver badge

          Re: Sad case of science ignoring the evidence

          I don't know, but I would guess that the economists and others would had been against it much because 40 prototypes were produced to start with.

          Except both platinum and iridium are more expensive than gold.

          1. cray74

            Re: Sad case of science ignoring the evidence

            Except both platinum and iridium are more expensive than gold.

            Now, yes. However, platinum used to be considerably cheaper than gold.

    3. ibmalone Silver badge

      Re: Sad case of science ignoring the evidence

      The solution is to move to better ways of measuring mass, which is what they've done.

      1. doublelayer Silver badge

        Re: Sad case of science ignoring the evidence

        They redefined the kilogram because we already know what the kilogram is. We know this with things that can actually be calculated easily in a science lab, like a specific quantity of a substance with a known density, measured under a known pressure. That isn't infinitely measurable, so it can't be used by the SI people, but they didn't need to investigate why the kilogram chunks had different masses because they knew why and they didn't need to find the one true kilogram because they knew what a kilogram is. They just needed a math problem to give the mass of a kilogram so everyone else in labs can keep measuring mass exactly the same way.

    4. jmch Silver badge

      Re: Sad case of science ignoring the evidence

      "somehow the various copies of the kilogram made over the years, with the best equipment of the time, ended up being different to each other"

      I'm somewhat confused by the graph showing "Le Grand K" mass changing over time, together with the mass change of all the copy Ks. After all, 1kg was BY DEFINITION the mass of "Le Grand K", so if the other copy masses changed relative to it, I would have to say that teh other cylinders were gaining or losing mass.

      Of course I understand that it's possible that a physical object can have very slight mass gains or losses... but if I measure K at 1kg, then 10 years later I find it weighs 9.9999kg or 10.00001kg, how can I make the claim that "Le Grand K" has lost or gained mass rather than that my balance is no longer well calibrated / my copy cylinder has gained/lost mass?

    5. Alan Brown Silver badge

      Re: Sad case of science ignoring the evidence

      "At one time this would have been enough to warrent an investigation"

      It did. Several. And then several more. Some variances were explainable (fingerprint contamination, etc) and others just seem to be random noise of the universe

      The things may have been under jars, but it's not an inert space and they were periodically cleaned. The opportunity to pick up or lose a few molecules of contamination arose, but even when the greatest of care was taken to ensure no contamination took place, successive measurements on the same balances would give different results on different days.

      Even le grand K has varied a few nanograms between measurements - sometimes when measurements were taken within weeks of each other. This variance and the continued variances between the lesser Ks is what drove the search for a better reference (which started about 40 years ago)

      1. Ken Moorhouse Silver badge

        Re: the search for a better reference (which started about 40 years ago)

        Now that's what I call a long weight.

  6. John Smith 19 Gold badge
    Thumb Up

    Handy if you want to send a description of some technology to another civilisation.

    The thing is once you need maximum precision (maybe because you want to build something very big, or very small) it turns out that a lot of physical "constants" (like the length of an Earth day for example) actually aren't.

    Very impressive.

    1. #define INFINITY -1 Bronze badge

      Re: Handy if you want to send a description of some technology to another civilisation.

      Wouldn't the other civilization be inclined to assign the correlation to coincidence?

  7. Charles 9 Silver badge

    I have a thought, though. How can one define the mole by Avogadro's Constant when the constant is defined in terms of moles? Sounds circular if you ask me.

    1. Justin Case

      There's only one way to get rid of a mole

      Blow his bloody head off!

    2. bombastic bob Silver badge
      Boffin

      not sure why it says '1023' either - I thought it was 6.02nnn x 10^23

    3. Aleph0

      A mole of X

      As I understand it, the definition of "mole" as a measuring unit is simply a fancy way of saying "In a mole of X there are 6.02#### * 10^23 units of X".

      As always there's a relevant XKCD.

      1. ratfox Silver badge

        Re: A mole of X

        I didn't get that part. I thought that the Avogadro number was already the definition of a mole. What was it before?

        1. Yet Another Anonymous coward Silver badge

          Re: A mole of X

          It's the number of atoms of C12 in 0.012kg of C12, change kg and you change the number.

          Personally I'm a bit sad that the way cooler, count the number of Si atoms in a kg sphere of Si, method didn't win

          1. TRT Silver badge

            Re: Avagadro's number...

            Is the ratio of mass of stone to flesh divided by the price of two slices of gluten free bread.

            Or was that Avocado's paradox?

  8. TeeCee Gold badge

    Kibble balance?

    So, the new standard is actually based on American pet food?

    1. DJV Silver badge

      Re: Kibble balance?

      "Unfortunately Kibble balances are a) insanely expensive, b) the size of a small room, and hence c) only exist in around five special laboratories around the world"

      They forgot: d) have to be replaced often due to cats eating them.

  9. Pascal Monett Silver badge

    So we've gone from six to five

    We have set aside 6 imperfect measurement units and now rely on 5 very expensive locations for a perfectly precise result.

    We may have gained in precision, but we've lost in numbers. I don't know how expensive one of those balances are, but I'm pretty sure we're not going to be building a whole lot more in any case. What else can a Kibble balance be good for ?

    1. Glen 1 Bronze badge

      Re: So we've gone from six to five

      Rather than 6 imperfect measurements, we have 5 places where *many* perfect replicas can be made.

      They can be periodically compared against the 5 kibble balances, and be shown to have a certain accuracy. If it drifts too much we can bin it and make another.

    2. bombastic bob Silver badge
      Devil

      Re: So we've gone from six to five

      apparently, a kibble balance can be used to measure Planck's constant.

      https://en.wikipedia.org/wiki/Kibble_balance

      Also I'd think it would require a VERY accurate definition of 'Ampere'.

      And if any two SI standards are recursively/mutually dependent (because of measurement techniques, etc.), could a converging solution be used to make them as accurate as possible?

      (I'd really hate for our measurement standards to end up as one big Catch 22 or chicken/egg paradox)

      1. Alan Brown Silver badge

        Re: So we've gone from six to five

        "I'd really hate for our measurement standards to end up as one big Catch 22 or chicken/egg paradox"

        What, you mean like being dependent on something as parochial as the rotation period of a particular planet in a binary planet/satellite pair(*), in a particularly short window of a period of their 7-8 billion year lifespan?

        Or the circumference of that particular planet?

        (*) Earth/moon are frequently described as a binary due to the size of the satellite having an easily observable effect on the barycenter of the pair (it's about 75% of the way towards the surface from the earth's core). It's not a classic binary inasmuch as the barycenter is still below the surface of the earth but it does mean there's a hell of a wobble in there and it would have been a true binary originally)

    3. Ken Hagan Gold badge

      Re: So we've gone from six to five

      "I don't know how expensive one of those balances are, but I'm pretty sure we're not going to be building a whole lot more in any case."

      On the contrary, I'd expect that in just a few years we'll have quite a number more. It's only technology.

      1. Voyna i Mor Silver badge

        Re: So we've gone from six to five

        "On the contrary, I'd expect that in just a few years we'll have quite a number more. It's only technology."

        The way things are going, if civilisation lasts that long, they'll be in mobile phones.

        I still can't quite get over the fact that my phone contains a magnetic compass, a barometer and a set of radios all of which would fit into the cathode of one of the valves on my first radio set.

        1. Will Godfrey Silver badge
          Angel

          Re: So we've gone from six to five

          But is' quite possible your first radio set would still work today (if there's still something being transmitted on those wavelengths).

          Your phone, however...

          Nuff sed?

          1. Voyna i Mor Silver badge

            Re: So we've gone from six to five

            "But is' quite possible your first radio set would still work today (if there's still something being transmitted on those wavelengths)"

            If you think I would be happy powering up something with 55 year old big electrolytics...

            Valves not a problem - I did test one of my old EF86s the other day and it seemed to work, no blue glow - but electrolytics are prone to degradation. I once worked with someone who had had a colleague die when a 68000 microfarad experimental capacitor exploded, after which they put in pressure relief valves.

  10. Anonymous Coward
    Anonymous Coward

    How easy it is to get an international deal

    ...when its not about power politics, but about making life easier in ways politicians don't even notice.

    1. Anonymous Coward
      Anonymous Coward

      Re: How easy it is to get an international deal

      ... interesting side-light on this was in the BBC documentaries on the fundemental scientific units a few years ago which, in the program about the history of weights and the kg, mentioned that when Germany occupied France in WWII they specifically did not make a claim over the bulding holding "Le Grand kg" as they maintained the convention that it was considered to be "International territory" and not part of France.

      1. arctic_haze Silver badge
        Holmes

        Re: How easy it is to get an international deal

        They treated it as an embassy. The only problem is embassy of what exactly?

    2. flokie

      Re: How easy it is to get an international deal

      French news were reporting on this last weekend, and surveyed random people on the streets for their thoughts.

      "Obviously, everybody uses kilos. Well, except the English, but then they're not normal".

      1. Credas Silver badge

        Re: How easy it is to get an international deal

        French news were reporting on this last weekend, and surveyed random people on the streets for their thoughts.

        Well they obviously didn't survey anyone who's actually been to England in a while, or they'd know that in practice you'd be hard pressed to find those old Imperial units anywhere (aside from the yard/mile on our roads for some strange reason, or a pint in a pub).

        1. Ken Moorhouse Silver badge

          Re: you'd be hard pressed to find those old Imperial units anywhere

          Shop space is still measured in square feet (very topical at the moment).

        2. Paul Crawford Silver badge

          Re: yard/mile on our roads for some strange reason

          Because of the extraordinary cost of changing all signs and then having to deal with most cars in the UK having mph as the only (or dominant) scale for a decade or two afterwards.

          1. Alan Brown Silver badge

            Re: yard/mile on our roads for some strange reason

            Having lived through such a change (Imperial to metric) in two countries in 1973 and 1974, the roadsign and car odometer change isn't that difficult to deal with, people just deal with it.

            For starters, all UK roadsigns are already positioned so they can be changed to 400m, 800m, 1/2km, 1km or 2km and have been for a very long time, despite being written in miles (1/4 mile and 400m are interchangable)

            Fahrenheit to Celcuis is far more annoying. Using a scale which choose frozen brine as zero and Ox blood as one hundred didn't make a heck of a lot of sense at the time and it really still doesn't. At least Celcuis stuck with the same substance at both ends of the scale.

            1. Charles 9 Silver badge

              Re: yard/mile on our roads for some strange reason

              I think one big stumbling block for changing temperature will be dealing with cookbooks. OLD cookbooks, especially large collections handed down through generations. I doubt there will be a service on hand to convert all the measurements and not that many people have a head for converting temperatures (especially over-boiling temperatures) on the fly.

          2. Anonymous Coward
            Anonymous Coward

            Re: yard/mile on our roads for some strange reason

            Because of the extraordinary cost of changing all signs and then having to deal with most cars in the UK having mph as the only (or dominant) scale for a decade or two afterwards.

            ===================================================================

            There are ways of changing the speedometer, and it's easier now, given that most vehicles are moving to digital displays and have been for years.

            As for the signs, once you change the default speed limits, there aren't all that many of them on a per capita basis, and you get new signs that don't have to be replaced for a long time. Maybe even better signs.

            It's past time to see off the last of the obsolete and often ambiguous measurement systems that are the measurement 'barnacles' of the past.

            If we can get the Yanks dragged into the 19th century as well, maybe we'll lose fewer space probes as a bonus.

            And with no more non-metric cookbooks, you can stop trying to guess which kind of pint the receipe expects you to use.

        3. disgustedoftunbridgewells Silver badge

          Re: How easy it is to get an international deal

          Or the weight/height of people and their pets, or distances in general.

          Fortunately my Spanish vet can convert from French units into English so I don't have to.

    3. Throatwarbler Mangrove Silver badge
      Trollface

      Re: How easy it is to get an international deal

      . . . until Brexit happens, and the UK decides to redefine the kilogram as the mass of a swallow carrying two coconuts.

      1. Yet Another Anonymous coward Silver badge

        Re: How easy it is to get an international deal

        Le kilogram Anglais ?

      2. Jellied Eel Silver badge

        Re: How easy it is to get an international deal

        . . . until Brexit happens, and the UK decides to redefine the kilogram as the mass of a swallow carrying two coconuts.

        Nah, we can go back to using pounds and ounces!

        1. tfb Silver badge

          Re: How easy it is to get an international deal

          The sad thing is that I have spoken to people who, apparently seriously, said this was an argument for brexit. It may be they were joking but I had to kill them anyway.

          1. disgustedoftunbridgewells Silver badge

            Re: How easy it is to get an international deal

            The argument isn't that we should use Imperial but that we should be allowed to choose for ourselves whether we mandate French, Imperial or neither.

            1. Anonymous Coward
              Anonymous Coward

              Re: How easy it is to get an international deal

              "we should be allowed to choose for ourselves whether we mandate French, Imperial or neither."

              I'd certainly go for neither. Degrees Réaumur is just annoying.

              Celsius and Kelvin all the way! Standard international units is the only reasonable choice.

  11. Anonymous Coward
    Anonymous Coward

    I am surprised...

    they didn't redefine the kg to make the Mars bar in your pocket half the size, but the same 'weight'

    1. #define INFINITY -1 Bronze badge
      Coat

      I despair

      ... that switching away from ounces made it easier to shave of 'grams'.

      Would you accept a change from a 4 once chocolate to 3? From 100g to 90g?

      Say, shall we take a survey of which of the two has actually happened?

      1. This post has been deleted by its author

      2. Charles 9 Silver badge

        Re: I despair

        "Would you accept a change from a 4 once chocolate to 3? From 100g to 90g?"

        Wouldn't matter. They'll do whatever they damn well please. A half-gallon of ice cream in America isn't really a half-gallon (as in 64 fluid ounces) anymore, anyway (for years it's been as little as 48 and no more than 56).

    2. Notas Badoff

      Re: I am concerned...

      In all these comments the weightier, larger question has been ingored: Will this make me fat?

      1. This post has been deleted by its author

  12. Fruit and Nutcase Silver badge
    1. #define INFINITY -1 Bronze badge

      Re: Reg Standards

      Good idea. Reg standards go relative and us commentards are found killing off Great White Sharks or Adult Badgers when the average ratio goes out of whack.

    2. Fruit and Nutcase Silver badge

      Re: Reg Standards

      Looking through that list...

      https://www.theregister.co.uk/Design/page/reg-standards-converter.html

      Amongst others, it lists the following two for Volume

      "Bulgarian airbag (C-cup Posh Spice)"

      "Bulgarian funbag (DD-cup Jordan)"

      I was thinking that a "Bulgarian goody-bag" would be a handy addition. Could the Reg Standards Bureau form a working party to look into the proposal please.

      1. John Brown (no body) Silver badge
        Coat

        Re: Reg Standards

        "I was thinking that a "Bulgarian goody-bag" would be a handy addition. Could the Reg Standards Bureau form a working party to look into the proposal please."

        Does that mean someone will have to be sent out with a tape measure and a Kibble balance to visit Miss Chesty Morgan?

  13. Totally not a Cylon
    Black Helicopters

    All very well until some bright spark discovers a tiny flaw in one of these constants and EVERYTHING changes!

    1. A.P. Veening

      That bright spark will actually be a dim wit in the period between publishing and burning at the stake.

  14. CiaranA

    My calculator is out of date

    The number wedged in my head for Avogadro's constant is 6.022045E23 - because it was a constant in my calculator at school, and you see that number quite a lot during physics lessons.

    Now I find it's changed over time! Proves the old adage that variables won't and constants aren't, I suppose.

    1. #define INFINITY -1 Bronze badge

      Re: My calculator is out of date

      Well... there's a thought. The redefinition will make 'physical ratios' as constant as Pi. How many decimal places will Planck's be? It's a matter of choice right now.

      1. DropBear Silver badge

        Re: My calculator is out of date

        You aren't really paying attention, are you. There's no choice involved (or rather, it's already decided that there won't be any, really soon):

        "On 16 November 2018, the International Bureau of Weights and Measures (BIPM) voted to redefine the kilogram by fixing the value of the Planck constant, thereby defining the kilogram in terms of the second and the speed of light. Starting 20 May 2019, the new value is exactly h = 6.62607015 × 10^-34 J ⋅ s"

        1. Charles 9 Silver badge

          Re: My calculator is out of date

          But will h STAY exactly 6.62607015 × 10^-34 J ⋅ s? Or will the increased use of Kibble balances reveal more significant digits that can result in a redefinition of h, which will in turn alter everything dependent on h?

    2. AIBailey

      Re: My calculator is out of date

      The only constant on my calculator was 58008

      1. John Brown (no body) Silver badge

        Re: My calculator is out of date

        Mine must have been the next model up from yours. Mine also included 5318008.

        1. Alan Brown Silver badge

          Re: My calculator is out of date

          Mine said 5318008618 (until the teacher saw and asked to have the joke explained. She pretended not to be amused)

          1. disgustedoftunbridgewells Silver badge
            Holmes

            Re: My calculator is out of date

            8Ɩ9 8008ƖƐϛ

            (For anybody else who couldn't be bothered working out what that was supposed to say )

  15. A 15
    Boffin

    A few comments

    It seems a little peculiar that they were quite happy to use the charge on an electron to define the Coulomb, but didn't wan't to use the mass on the electron to define the kg (it is known to an appropriate precision).

    In regards to the comment about someone else coming along and finding a flaw... well that isn't very likely; the definitions were not created on the grounds that science now knows these units perfectly so we'll just set them in stone. They were defined so that all the units that can be derived from the base units can be updated (slightly), when our measuring improves. The new way leaves a field with fewer moving goals.

    There is still a bit of awkwardness with certain units, like the definition of the second is based upon being measured at sea level (as general relativity plays a role).

    Also I will kind of miss Avagadro's constant being the number of atoms in 12 grams of carbon 12. Still, at least I have a set of numbers that I can learn and won't change now :p

    1. Charles 9 Silver badge

      Re: A few comments

      "It seems a little peculiar that they were quite happy to use the charge on an electron to define the Coulomb, but didn't wan't to use the mass on the electron to define the kg (it is known to an appropriate precision)."

      Except the rest mass of an electron is calculated from the Planck constant (and the Rydberg constant): any uncertainty in its measurement comes from the Planck constant, so you could say this is closer to the source.

      "There is still a bit of awkwardness with certain units, like the definition of the second is based upon being measured at sea level (as general relativity plays a role)."

      Took a bit of reading to figure out what's involved (time dilation caused by the differing scalar speeds at differing altitudes). I guess in the end you have to pick something because there are no real absolute points of reference in the universe.

      "Also I will kind of miss Avagadro's constant being the number of atoms in 12 grams of carbon 12."

      Probably because that would have to depend on the definition of the gram (or in this case, the kilogram). That puzzles me. Why does SI use the kilogram instead of the base gram? Might this change in future now that the standard-bearer has changed as well?

      1. A.P. Veening

        Re: A few comments

        "Why does SI use the kilogram instead of the base gram?"

        Because it was more convenient for a number of calculations.

        1. Yet Another Anonymous coward Silver badge

          Re: A few comments

          Of course it should have redefined the gram as the kilogram, or we should speak about milli-kilograms

        2. disgustedoftunbridgewells Silver badge

          Re: A few comments

          If they were going for convenience they'd have gone for a kg weighing 0.453kg

      2. Carpet Deal 'em
        Boffin

        Re: A few comments

        "Why does SI use the kilogram instead of the base gram?"

        The kilogram was originally called the "grave", but the name was dropped for various reasons and, in the process, some genius decided to base the default on the centimeter. Unsurprisingly, the original grave was the more convenient measure, but by then "gram" had stuck, so they popped the kilogram in its place.

    2. ibmalone Silver badge

      Re: A few comments

      It seems a little peculiar that they were quite happy to use the charge on an electron to define the Coulomb, but didn't wan't to use the mass on the electron to define the kg (it is known to an appropriate precision).

      One reason is related to a rather intractable debate I ended up with a computer scientist in. They didn't really see a difference in measuring things in relative units and SI units, they're both ratios right? But the reference ratio is only one part of the system, you need a reproducible way to calibrate other measurements, which is why these SI standards have two parts, one is the thing you're using as the basis of your definition and the other is the measurement process.

    3. John Brown (no body) Silver badge

      Re: A few comments

      "There is still a bit of awkwardness with certain units, like the definition of the second is based upon being measured at sea level (as general relativity plays a role)."

      And for that matter, what is "sea level"? Tides, gravitational variation at different points across the surface of not perfectly spherical Earth due to the non-even distribution of mass inside the wonky shaped Earth.

      1. Charles 9 Silver badge

        Re: A few comments

        They took that into consideration. The actual point of reference is MEAN sea level, which averages out variations and puts all the atomic clock calculations at the same height (it also specifies a target temperature so as to be more consistent).

  16. Charles 9 Silver badge

    Here's a little food for thought. It seems one big reason they wanted to redefine the kilogram was because the different prototype kilograms were diverging from each other, and they were a little puzzled as to why: was one losing mass or the other gaining mass, and so on. That and the research into using the Kibble balance meant they could move away from prototypes.

    Same for the temperature redefinition, as using the triple point basis wasn't consistent at extreme temperatures, and the Boltzmann constant was a better fit.

    1. #define INFINITY -1 Bronze badge

      I certainly hope not; that would be a total fail on the part of scientists.

      If they are diverging and they DO know why, then the redefinition has merit. Otherwise they're just bloody lazy and lack inquisitiveness.

      1. ibmalone Silver badge

        "Here's a little food for thought. It seems one big reason they wanted to redefine the kilogram was because the different prototype kilograms were diverging from each other, and they were a little puzzled as to why: was one losing mass or the other gaining mass, and so on. That and the research into using the Kibble balance meant they could move away from prototypes."

        I certainly hope not; that would be a total fail on the part of scientists.

        If they are diverging and they DO know why, then the redefinition has merit. Otherwise they're just bloody lazy and lack inquisitiveness.

        No, as alluded to in the comment you're replying to, how do you investigate this? You need a mass reference to do it. Enter the Kibble balance. Now you have a way to measure mass that doesn't depend on a chunk of gold alloy. If it turns out to be something mundane like tiny amounts of wear or adsorption then you can watch it happening, but if the only way to measure mass is by comparing to another chunk of alloy which is also changing in some way then you're rather stuck.

        Similar answer to the question of what happens if these universal constants aren't actually, you find some related processes that should be the same under your assumptions and start comparing them.

    2. swm

      The meter bars were slowly warping which is why the meter is now defined in terms of physical experiments and not physical artifacts.

      1. Ken Moorhouse Silver badge

        Re: The meter bars were slowly warping

        I'd say your monitor needs degaussing.

  17. DrBobK
    Headmaster

    The candela is odd.

    The candela is a measure of human perceived brightness. As people's perception of the brightness of a light source depends on the wavelength of the light (we are most sensitive to wavelengths corresponding to green (around 550nm) and less efficient to shorter and longer wavelength) the definition of the candela has to include a multiplier representing the relative luminous efficiency as a function of wavelength - this function is known as V-lambda. The definition of V-lambda is based on people subjectively matching the brightness of lights with different wavelengths. The standard V-lambda defined by the CIE (Commission Internationale de l'Éclairage) is, in fact, based on measurements from a very small number of observers. There are different versions of V-lambda for daylight adapted (photoptic) vision, dark adapted (scotopic) vision, and the intermediate state - mesopic vision. The candela is defined in terms of the physical power of a light over an illuminated area at a single standard wavelength (and so is entirely physical at that wavelength), but to use the candela as a measurement of luminous intensity at any other wavelength one has to use a subjectively defined multiplier from the appropriate V-lambda. All pretty weirdly subjective for an SI base-unit!

    (I study human vision for a living.)

    1. #define INFINITY -1 Bronze badge

      Re: The candela is odd.

      X-Windows has a few functions based on TekTroniks's research into HSV spaces--can't find much else on their theories relative to 'modern' ones that Adobe use. I understand the 30-59-11 of RGB is the values which make colour-to-gray TV's 'work'.

    2. Yet Another Anonymous coward Silver badge

      Re: The candela is odd.

      Everything about colour vision is a pain in the .....

      Typical of God/evolution, do a cheap rush job of the hardware and then try and fix it all in software later

    3. Glen 1 Bronze badge
      Joke

      Re: The candela is odd.

      I see. :3

  18. Def Silver badge
    Paris Hilton

    SI

    Standard measurements are good, obviously, but the ones we have are still arbitrary bullshit when you get down to it.

    One second is defined as 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.

    Why caesium? Why not hydrogen? Why not 10 billion periods? Or one billion?

    Why is one metre the distance light travels in 299,792,458th of a second? Another arbitrary number which exists today due to truly random historical definitions.

    You try and explain any of these to an alien civilisation and their reaction will be no different to someone in America trying to explain why a yard is three feet, or 36 inches to a child from [insert country here]. I wouldn't be surprised if eventually you ended up describing the width of a horse's arse, which would bring a whole different kettle of fish, and possible the police, into the conversation.

    When we finally start ruining other planets, will we take these arbitrary measurements with us? Or will we finally work out something more universal? (Which America will still ignore.)

    Paris because... well, why the fuck not? Where's the pub? :)

    1. Voyna i Mor Silver badge

      Re: SI

      "Standard measurements are good, obviously, but the ones we have are still arbitrary bullshit when you get down to it."

      Any system of units will be arbitrary since the convenient fundamentals of the universe, in human terms, are either very large (c) or very small (e.g. rest mass of electron). They are going to require big multipliers or dividers to get practical units. Why use exact powers of 10? Why not use binary numbers? The power of 2 used will still be arbitrary.

      In fact the metre, kilogram and second are pretty convenient human-scale units. You can argue for the foot and the pound if you like, but in powers of 10 terms there's no real difference and once gravity is involved, at a rather convenient roughly 10ms-2, or air pressure at an equally convenient approx, 10Ncm-2, SI has real practical advantages for rough calculations. The fact that the size of the mm more or less eliminates decimal points from building plans is an added convenience, unless you really like working with yards, feet, inches and 1/32inches. The cgs system, on the other hand, did give rather silly numbers.

      So, arbitrary but far from bullshit.

      1. Def Silver badge

        Re: SI

        You're kinda missing my point. (If I even had a point, which is doubtful, but there you go.)

        Let's start with the second. It's a convenient(ish) measurement for splitting up time on Earth. But what happens when we go to Mars, where there are 24 hours, 37 minutes, and 22 seconds in a day? That would just piss me right off. Or how about the moon, where one day lasts 29 days, 12 hours, and 44 minutes?

        Instead of 9,192,631,770 periods of the...blah blah blah...of caesium-133 atom, why not make it 10 billion. (I'm not going to bother finding out the difference between caesium and hydrogen.) A second would then be eight percent longer. I doubt many people would even notice. World record holders might be a bit miffed, admittedly, but simply convert the records and nothing would really change. We could even switch to a decimal time system, and then no specific world would be "special" with regards to time. (We're going to have to switch at some point in the future. Or at the very least every world will probably end up devising its own timescale to measure its sidereal rotation period - it'll be like the train network all over again. Will we stick to Earth times when in deep space? I don't ever recall hearing "Captain's Log, 13th of June..." after all. ;)

        Now let's look at the metre. If it were the distance light travelled in 300,000,000ths of a second instead of 299,792,458ths (which is still a bit arbitrary for me), it would be around 88 millimetres longer than it is today (with the new second). Personally I'd rather opt for 100,000,000ths of a second, which, ironically, would put it closer to the foot (actually just over 14 inches) than the metre. Still usable for human scales, but slightly less arbitrary.

        My point (yes, there really was one) was this: Why not redefine SI measurements to be less arbitrary instead of forcing what we currently have (which we only have for historical reasons) to fit some observed natural/physical phenomenon.

        And before you claim such changes would be impossible... every country on the planet has changed some or all of their measurements at some point in the past.

        1. Charles 9 Silver badge

          Re: SI

          "I don't ever recall hearing "Captain's Log, 13th of June..." after all. ;)"

          Actually, the reboot of Star Trek starting with the 2009 movie DOES do that. The rebooted Stardate is simply <Gregorian Year>.<Day of Year starting from 1>.

          As for why mks, it seems there IS some natural coherence between the units, particularly when you mesh electrical phenomena to physical ones. In fact, this is why the kilogram was used versus the gram: the relationships didn't fit with the g but did with the kg. In fact, modern science notes a lot of interrelation between mass, energy, and time. That's one reason for the redefinitions. With the second defined as it will be, one can redefine the kilogram in terms of the Planck constant (which uses time), redefine the ampere in terms of the elementary charge (which uses time), and redefine the Kelvin in terms of the Boltzmann constant (which uses time, mass, and distance which is unchanged).

          As for why cesium, it's easier to measure and more consistent than hydrogen.

          1. Def Silver badge

            Re: SI

            As for why cesium, it's easier to measure and more consistent than hydrogen.

            Ok, that's fair enough - I guess. I did wonder whether it was because of something like that.

          2. Def Silver badge

            Re: SI

            (Urgh, time ran out when editing the above. You really should stop the clock when someone clicks the edit button, El Reg.)

            As for why mks, it seems there IS some natural coherence between the units, particularly when you mesh electrical phenomena to physical ones. In fact, this is why the kilogram was used versus the gram: the relationships didn't fit with the g but did with the kg. In fact, modern science notes a lot of interrelation between mass, energy, and time. That's one reason for the redefinitions. With the second defined as it will be, one can redefine the kilogram in terms of the Planck constant (which uses time), redefine the ampere in terms of the elementary charge (which uses time), and redefine the Kelvin in terms of the Boltzmann constant (which uses time, mass, and distance which is unchanged).

            That sounds a bit suspect to me. In fact, reading into it a little bit, it seems a bit dodgy to me that a lot of science is based around arbitrary base-60 measurements of time. I can accept that the concept of the Planck constant (and what it represents) can be universal, but its value certainly can't be constant if it depends on the length of a second.

            Oooh, is that a can of worms? How nice... ;)

            1. doublelayer Silver badge

              Re: SI

              So what if we're on a different planet. The second does not need to change lengths. Whatever you change it to, the planets' days will still not line up, because you can't find a useful (or maybe at all) GCF of the rotations of every rock you decide to put something on. So your best option is to keep using the second, minute, and hour, because then at least you can speak of durations in the same way as people on the other planets.

              Maybe for convenience, you could define a rotation unit for the planet you're on to speak of time of day when discussing with people on your planet. When dealing with anything not on your planet, you will need a standard calendar where absolute dates and times could be used. I don't see a date like "2345-06-07 08:09:10 Gregorian, local time 12.0000" as in any way problematic. It tells me the absolute date, allowing me to compare in nearly zero time whether this happened before or after some other event. Meanwhile, I know this occurred at midday, assuming they decide to stick with the concept of 24 sections of a day. If they don't want to do that, how about percentages for local time? That way, a planet with a long day will work perfectly well. 0% = midnight, 50% = noon.

              And the second is perfectly defined using a seemingly random number of periods, because it is equal to the second we've been working with for a long time. Why redefine the second when almost nobody is actually using cesium to measure it? The people running atomic clocks can divide, while we can continue using all the standard second-based things we've used for a long time. Meanwhile, we've already limited this to running at sea level, so we can't avoid being arbitrary. For now, convenience. For later, simple utility. One arbitrary thing that prevents inefficiency is superior to two arbitrary things that require us to switch them. That's why we should stop changing our clocks twice a year.

              1. Charles 9 Silver badge

                Re: SI

                "That's why we should stop changing our clocks twice a year."

                That's another argument altogether owing to the need to synchronize everything in a locality (so just changing times as needed raises scheduling conflicts) combined with the problem of short days in the winter the closer to the pole you get (and limited daylight is more practical later in the day--and England gets it worse than in the US because it's farther north; the winter solstice really stinks up there).

                1. Def Silver badge

                  Re: SI

                  England gets it worse than in the US because it's farther north; the winter solstice really stinks up there

                  You think England is bad, you should come to Norway. ;)

                  1. defiler Silver badge

                    Re: SI

                    You think England is bad, you should come to Norway.

                    Was going to say Scotland, but you win!

                    1. disgustedoftunbridgewells Silver badge

                      Re: SI

                      You Scottish can't moan - it's your farmer's fault that we're still on GMT/BST rather than CET.

                  2. Charles 9 Silver badge

                    Re: SI

                    Which IINM crosses the Arctic Circle and puts it in Alaska territory: where it's SO extreme there are periods of summer with virtually no night ("Land of the Midnight Sun") and periods of winter with virtually no daylight to shift.

                  3. Pedigree-Pete
                    Thumb Up

                    Re: Winter GMT....

                    @ Def Norway, also try Northern Scotland.

                2. jmch Silver badge

                  Re: SI

                  "we should stop changing our clocks twice a year."

                  Yep, and we should stick to summer time rather than 'natural' time. Most of human activity is skewed towards the evening so it makes more sense to permanently have the middle of the day at 1pm rather than at noon, with 2 more hours in the afternoon/evening than the morning.

                  1. Anonymous Coward
                    Anonymous Coward

                    Re: SI

                    Yep, and we should stick to summer time rather than 'natural' time. Most of human activity is skewed towards the evening so it makes more sense to permanently have the middle of the day at 1pm rather than at noon, with 2 more hours in the afternoon/evening than the morning.

                    ------------------------------------------------------------------------------------------------------------------------

                    No, it doesn't.

                    That just means you have to wait longer for the sun to go down and for things to start cooling off, and for the UV to go away.

                    That means less sleep due to getting up at some horrible hour to go to work, which means tired drivers and workers and more traffic and industrial accidents.

                    1. Charles 9 Silver badge

                      Re: SI

                      Well, pick your poison. No one can just pick arbitrary times because they'll have to coordinate with everyone else: many of which are "locked in". When you get "oop north" in the winter, there just isn't enough daylight to go around, so you have to make a decision: favor it earlier so kids don't go to school in the dark (safety risks and concerned parents) or favor it later so people are more in a position to enjoy it (psychological issues).

                3. Daniel 18

                  Re: SI

                  Just go on UTC for the planet and have done.

                  No more time zones, no more changes, just set your working hours when it makes sense in your location for your business.

                  Light and dark will happen the same regardless. and there is no real advantage to changing time to accommodate that, particularly in a connected world with ample electric lighting.

                  If the local light patterns make something reasonable, then do it - just don't mess with the clocks, change your times for events.

            2. Tim99 Silver badge

              Re: SI

              @Def

              "Arbitrary base-60 measurements" go back to at least the Babylonians. Most of us cary an easy way of counting to 60 around with us - Using the thumb of one hand start counting by touching the top joint of the same hand's little finger, then the second joint, then the third; now move on to the ring finger and count the three joints, then the middle finger, and then the index finger giving a total of 12 - Now count off the thumb of the other hand for the first 12, then repeat and count off the index finger for 24, middle for 36, ring for 48, and little finger giving a total of 60. The number 60 is divisible by 2,3,4,5,6,10,12,15,20 and 30 - So for people who traded (and needed to count) a much better system than stopping at 10 (only divisible by 2 and 5), when you run out of fingers (and toes at 20 [sandal wearers?] divisible by 2,4,5 and 10).

              1. Def Silver badge

                Re: SI

                Yeah, I know where base 60 comes from. Our reasons for continuing to use it are still only out of tradition. :)

              2. Alan Brown Silver badge

                Re: SI

                "when you run out of fingers (and toes at 20 [sandal wearers?] "

                There's a Thai system for counting to 99 on your fingers, but multiplication isn't easy.

                (left hand fingers +1-4 thumb +5, right hand thumb +50, fingers +10-40. You use your fingers twice in each decade)

                1. Charles 9 Silver badge

                  Re: SI

                  You can count 0-9 one one hand by simply staring with fist for zero, then raise the fingers in one direction for 1-5, then close them in the SAME direction to get 6-9 back to the fist. Because the raised fingers are on opposite ends of the hand, it's easy to distinguish a 2 from an 8. Meaning you can count from 0 to 99 using both hands. And I'm not being all that efficient. With a mastery of binary, one can go from 0 to 1023 using both hands.

        2. ibmalone Silver badge

          Re: SI

          Instead of 9,192,631,770 periods of the...blah blah blah...of caesium-133 atom, why not make it 10 billion.

          This desire for base ten measurements is completely anthropocentric.

          At least it's not an irrational number. Greg Bear's Anvil of Stars features aliens with no concept of discrete numbers. (Whether such a species could develop advanced technology is another matter.)

        3. Anonymous Coward
          Anonymous Coward

          Re: SI

          Why not redefine SI measurements to be less arbitrary

          ---------------------------------------------------------------------------------------------------------------

          Because:

          Any choice of unit is arbitrary, if only through picking a definition.

          Mass? Rest mass of an electron, a proton, an neutron, a pi-meson?, a hydrogen atom? Any of these is arbiitrary.

          Other units have similar quandrys.

          For that matter, choosing which units are fundamental and which are derived is arbitrary as well.

      2. Alan Brown Silver badge

        Re: SI

        "Why use exact powers of 10? Why not use binary numbers? The power of 2 used will still be arbitrary."

        The Babylonians used 12 and 60 (can you guess where we still use those?)

        The Romans used 12 a lot. 10 was mostly only used for military work.

        In both cases it's because the number of divisors make them easier to work with than 10s.

    2. Alan Brown Silver badge

      Re: SI

      "if eventually you ended up describing the width of a horse's arse"

      Two of those has an intrinsic tie-in to the width of a standard gauge rail line. Can you guess why?

      .

      .

      .

      .

      Railways use 4'8 because that's what was already in use most places (+- a couple of inches)

      Railways originally used the same track width width as horse drawn tramways

      Horse drawn tramways used wagon chassis, with standard widths

      Wagons were a standard width due to ruts in the road. Noone built to other widths as doing so was to invite broken wheels.

      Roads had ruts in them due to centuries of wear, many dating back to the roman empire (when they were better maintained)

      Ruts in roman roads were caused by chariots, wagons and other horse drawn traffic.

      Roman roads were as wide as they were to allow two way traffic

      Wagons tended to be the same width as chariots because chariots defined the width of the roads

      Chariots defined the width of the roads as they were military traffic and the roads were military roads.

      Roman chariots were built to a standard width to allow interchangability of most parts (and to ensure they would pass freely across the empire.)

      That width was defined by rear ends of the two horses operating side by side in front of the chariot.

  19. georgezilla

    Soooo ....

    Would that be the American "pound". or the English one?

    If it's the American, is it a pound of feathers, or a pound of lead?

    Personally, I'd prefer the English version. That way I can buy me a cup of tea.

    1. Charles 9 Silver badge

      Re: Soooo ....

      "If it's the American, is it a pound of feathers, or a pound of lead?"

      So you're telling if you put a pound of feathers on one end of a balance and a pound of lead on the other, it wouldn't balance given they're both supposed to be a pound?

      1. doublelayer Silver badge

        Re: Soooo ....

        Of course not. The pound of feathers will form an untidy heap on the scale, and feathers will start to waft away almost immediately, worse if your scale is outdoors, indoors near an air sensor, or indoors near any moving thing including humans. So a pound of lead is heavier than a pound of feathers unless you place an item of sufficient weight (about one pound) to force the feathers to stay on the scale.

        1. Charles 9 Silver badge

          Re: Soooo ....

          Or you just put both of them in identical sacks...

        2. Yet Another Anonymous coward Silver badge

          Re: Soooo ....

          But the pound of lead would be covered in 2 pounds of warning labels and disclaimers about how dangerous it is and how that isn't their fault (unless it's lead for bullets in which case it is as wholesome as apple pie)

  20. Gene Cash Silver badge
    Coat

    A modest proposal

    We should rename the kilogram to kibble, and then we can rename grams to bits!

    Kibbles'n'bits! They're yummy!

    1. Tromos
      Joke

      Re: A modest proposal

      Let me introduce the kibblegram. A unit of weight equal to 1024 grams. Primary purpose: to allow us to whinge about being given short measure in anything purchased by weight.

      1. Ken Moorhouse Silver badge

        Re: Let me introduce the kibblegram... to allow us to whinge

        You can take that one stage further and call it the Quibblegram.

      2. Dr_N Silver badge

        Re: A modest proposal

        I thought the kibblegram was the SI measure for weight of useless accumulated dross that people acquire/hoard. (Or that just randomly appears in your house/garage/shed.)

  21. Richard Boyce

    Scale

    "The Planck constant, named after the physicist Max Planck, is incredibly small (it's 6.62607015 x 10-34 Js)"

    I think we need to be careful about describing units as large or small, when the magnitude of the numerical parts of their value is a function of the units we've chosen to use.

    For example, would it be reasonable to describe the speed of light as incredibly small because it's 9.71561e-9 parsecs per second?

    1. swm

      Re: Scale

      The speed of light is about one foot per nanosecond.

    2. DropBear Silver badge

      Re: Scale

      "I think we need to be careful about describing units as large or small"

      I don't think so. Until you can produce a complete set of Planck constants compared to which we may rigorously classify ours as absolutely small medium or large, everything we measure will necessarily be numerically compared to whatever arbitrary units we ended up using owing to practical scales of our existence.

      And the example you provide is a particularly unfair one given that the speed of light seems to be the largest of all possible speeds we need to concern ourselves with - most other things we measure don't really seem to have limits like this. Nonetheless, rest assured that if we ever discover some clever way to get from A to B faster than light (probably without actually needing to exceed the speed of light), "c" will indeed be considered laughably small whenever discussed in the context of interstellar travel...

      1. Charles 9 Silver badge

        Re: Scale

        I believe some science fiction already refer to two c-related units: PSL (percent speed of light) for subluminal and TSL (times speed of light) for supraluminal. 100PSL=c=1TSL.

    3. ibmalone Silver badge

      Re: Scale

      "The Planck constant, named after the physicist Max Planck, is incredibly small (it's 6.62607015 x 10-34 Js)"

      I think we need to be careful about describing units as large or small, when the magnitude of the numerical parts of their value is a function of the units we've chosen to use.

      For example, would it be reasonable to describe the speed of light as incredibly small because it's 9.71561e-9 parsecs per second?

      The Planck constant is small compared to everyday experience though. E=hbar ω. For any frequency we can experience as human beings, the energy implied by this is much smaller than any we could notice. (Similar to the speed of light, it's much faster than our senses could measure.) That's even if you include visible light as a frequency we can experience, since the energy of an individual photon isn't something we can relate to normal experience.

      1. disgustedoftunbridgewells Silver badge

        Re: Scale

        That Sir Stanley Matthews was so quick he was able to turn off his light and get in bed before the room got dark teaches us two things:

        1: The speed of light is perceptible

        2: 1950's jokes are terrible

  22. JeffyPoooh Silver badge
    Pint

    "Kibble balances....only exist in around five special laboratories around the world."

    Where the local gravity will be measured and monitored to exquisite precision.

  23. ReadyKilowatt

    That Kibble balance looks a lot like old gyroscopes from the early 20th century. I wonder how long until someone figures out how to build one on a chip and every smartphone has one?

  24. saxicola

    Re: I Propose that it's Renamed the Kibblegram

    And now see it's already proposed because I didn't read ALL the comments. (Leaves, feeling slightly silly).

  25. the Jim bloke Bronze badge
    Headmaster

    Slight correction to article title

    Holy moley! The amp, kelvin and kilogram will never always be the same again from now on

    FTFY

  26. Anonymous Coward
    Anonymous Coward

    Science, yes, but

    will my weekly bag of grass bought in the pub car park weigh more or less now?

    1. Geekpride

      Re: Science, yes, but

      It will weigh the same, provided it's spherical grass in a vacuum.

  27. Anonymous Coward
    Anonymous Coward

    Filthy SI Units

    Post Brexit these accursed European bureaucratic affectations will be assigned to the dustbin of history. Because it's what we voted for! Pounds, pints and inches: Good enough for our forebears, they are good enough for us!

    Gibber.

    1. plrndl

      Re: Filthy SI Units

      Presumably, post Brexit, we will revert to the avoirdupois "system" which as any fule kno, is based on peas, pounds and ounces (1 pea ~ 0.23gm). Who needs froggy measurements?

  28. jimbob8719

    More than 5 Kibble balances in the world

    They're really not that hard to build if you only want 3 or 4 significant figures. If you're OK with 2 significant figures (already better than your kitchen scale!), you can even build your own out of Legos and some electronic bits:

    https://www.nist.gov/si-redefinition/nist-do-it-yourself-kibble-balance-made-lego-bricks

    The big 5 balances are the ones that aim to reproduce at least all 9 significant figures from the definition of h. But the fact that anyone can build a balance and realize the kilogram themselves (rather than needing to sign an international agreement to get access to Le Grand K!) is why this is such a big deal. Yes, to get better than maybe 4 digits you need a vacuum chamber and some thermo-mechanical design, but because the read-out of the Kibble balance is fundamentally electronic, I expect that there will be commercially available 6- or 7-digit balances within the next 5 years, since a 6.5 digit DMM is only $1200 USD and.a 7.5 digit is only $3k.

  29. disgustedoftunbridgewells Silver badge

    Far easier to just define it as everybody important* knows it - 6'3.

    * Ie: Englishmen

  30. sisk Silver badge
    Headmaster

    Given that Le Grande K has slowly deteriorated over time, it might be more accurate to say that the kilogram will always be the same from now on.

  31. This post has been deleted by its author

  32. DustyP

    Remember the Zanzibar Fallacy

    Redefining two standards at the same time (I'm certain that they haven't)

    The Zanzibar Fallacy

    There was once an explorer who came to the tropical island of Zanzibar. Now, it happens that the island of Zanzibar is much longer than it is wide, so that the opposite ends of the island are separated by many miles of hilly jungle country.

    This traveller was a naval man by profession, and he had not been long on the island before he was told of a retired naval officer, a countryman of his, who lived at the extreme western end of the island, in a wooden house built high up on the cliffs overlooking the ocean.

    The explorer thought that he would like to visit his fellow expatriate, so he journeyed to the man's house, taking but one porter with him, for he preferred to travel light and, anyway, was not an excessively wealthy man. The journey took two days, or maybe it was three, but apart from the expected privations of crossing jungle terrain there was nothing remarkable about his trip. Nothing, that is, except that at noon each day he heard the sound of a naval gun, booming out from beyond the hills to the west and scattering the brightly-coloured tropical birds about his head.

    When he reached the ex-officer's house he was made very welcome. All morning they sat together on the veranda overlooking the sea, drank chukka pegs, and talked of home and their lives in the navy. As the time approached midday, the owner asked to be excused. He walked to the far end of the veranda, where there was a quarter-pound cannon, and, consulting his watch, fired a single shot at precisely twelve o'clock. 'I do that every day,' he said to the traveller, who understood perfectly his host's desire to observe naval tradition. 'Tell me,' he asked him. 'How do you ensure that you always fire your gun at exactly midday? Do you take sightings?'

    'No need,' he other replied. I kept the ship's chronometer from the old Arethusa and I set my own watch to it every morning.'

    'Ah,' said the first. 'But how do you know that the chronometer is correct?'

    'That is simple. At the other end of the island there is a clockmaker of great renown who keeps all his timepieces in perfect order. Twice a year I send my chronometer to him and he regulates it for me.'

    The traveller spent several enjoyable days at the naval officer's house and they became great friends. 'Give my regards to Mister Jones the clockmaker, won't you?' the old seaman said as they parted. 'I will,' the explorer replied, and they shook hands warmly.

    Two weeks later, the traveller reached the far eastern end of Zanzibar and there, in a small town nestling under a ridge of green trees and grey rocks, he found Mr Jones' shop. It was a shop such as you may find anywhere there are clocks and watches to be made or mended – dim and cool, filled with the soft sounds of ticking and chiming. Our explorer introduced himself to the clockmaker and, noticing how well all the watches and clocks in his shop were synchronised, asked him how he made sure that they were all keeping the right time.

    'That is simple,' the clockmaker responded. 'At the other end of the island there is a retired naval officer who, every day at twelve o'clock precisely, fires a gun. I set all my clocks by him.'

    1. DustyP

      Re: Remember the Zanzibar Fallacy

      Redefining two standards at the same time (I'm certain that they haven't)

      The Zanzibar Fallacy

      There was once an explorer who came to the tropical island of Zanzibar. Now, it happens that the island of Zanzibar is much longer than it is wide, so that the opposite ends of the island are separated by many miles of hilly jungle country.

      This traveller was a naval man by profession, and he had not been long on the island before he was told of a retired naval officer, a countryman of his, who lived at the extreme western end of the island, in a wooden house built high up on the cliffs overlooking the ocean.

      The explorer thought that he would like to visit his fellow expatriate, so he journeyed to the man's house, taking but one porter with him, for he preferred to travel light and, anyway, was not an excessively wealthy man. The journey took two days, or maybe it was three, but apart from the expected privations of crossing jungle terrain there was nothing remarkable about his trip. Nothing, that is, except that at noon each day he heard the sound of a naval gun, booming out from beyond the hills to the west and scattering the brightly-coloured tropical birds about his head.

      When he reached the ex-officer's house he was made very welcome. All morning they sat together on the veranda overlooking the sea, drank chukka pegs, and talked of home and their lives in the navy. As the time approached midday, the owner asked to be excused. He walked to the far end of the veranda, where there was a quarter-pound cannon, and, consulting his watch, fired a single shot at precisely twelve o'clock. 'I do that every day,' he said to the traveller, who understood perfectly his host's desire to observe naval tradition. 'Tell me,' he asked him. 'How do you ensure that you always fire your gun at exactly midday? Do you take sightings?'

      'No need,' he other replied. I kept the ship's chronometer from the old Arethusa and I set my own watch to it every morning.'

      'Ah,' said the first. 'But how do you know that the chronometer is correct?'

      'That is simple. At the other end of the island there is a clockmaker of great renown who keeps all his timepieces in perfect order. Twice a year I send my chronometer to him and he regulates it for me.'

      The traveller spent several enjoyable days at the naval officer's house and they became great friends. 'Give my regards to Mister Jones the clockmaker, won't you?' the old seaman said as they parted. 'I will,' the explorer replied, and they shook hands warmly.

      Two weeks later, the traveller reached the far eastern end of Zanzibar and there, in a small town nestling under a ridge of green trees and grey rocks, he found Mr Jones' shop. It was a shop such as you may find anywhere there are clocks and watches to be made or mended – dim and cool, filled with the soft sounds of ticking and chiming. Our explorer introduced himself to the clockmaker and, noticing how well all the watches and clocks in his shop were synchronised, asked him how he made sure that they were all keeping the right time.

      'That is simple,' the clockmaker responded. 'At the other end of the island there is a retired naval officer who, every day at twelve o'clock precisely, fires a gun. I set all my clocks by him.'

  33. plrndl
    Pint

    Avoirdupois

    I am disappointed to see that no-one has translated this article into proper el reg units.

    Standards are falling.

    I'm off to the pub.

  34. rpark

    Holy Moley Batman !

    ...more accurate article title would be ...amp, kelvin and kilogram will always be the same again.

  35. Ken Moorhouse Silver badge

    The Daylight Saving Time controversy

    To me the most rational solution is to not decide on either GMT or BST, but to compromise by changing the clocks by half an hour and then sticking to that new time zone, moving forward. The "elephant in the room" is the sub-optimal definition of GMT, which everyone historically wanted to use as a basis, rather than shifting to a more optimal base.

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