back to article Weight, what? The perfect kilogram is nearly in Planck's grasp

One of the standards world's toughest nuts, how to redefine the kilogram in terms of universal constants, is close to being resolved – unless a Russian experiment in 2017 throws a spanner in the works. That's exciting for standards boffins, since it means anyone can have an accurate kilogram without having to trek to Paris for …

  1. Kaltern Silver badge

    Well it's been a long weight, but on balance the results should measure up perfectly.

    1. Primus Secundus Tertius Silver badge

      That guy sure torques the talk.

  2. Dwarf Silver badge

    Heavy science

    At least it will be a weight off everyone's mind when they have finished

    1. Tim Jenkins

      Re: Heavy science

      Bah; trivia. What we really need to know is, exactly how thick is a Planck?

      1. hammarbtyp Silver badge

        Re: Heavy science

        Also what colour should it be...

      2. Mage Silver badge
        Boffin

        Re: Heavy science

        We do know the length of a Planck.

        Could we thus call the Planck Interval, the thickness?

        They do claim: "there is no reason to believe that exactly one unit of Planck time has any special physical significance"

        and

        "There is currently no proven physical significance of the Planck length; it is, however, a topic of theoretical research. Since the Planck length is so many orders of magnitude smaller than any current instrument could possibly measure, there is no way of examining it directly."

        Possibly nothing smaller can be measured, no matter how good instruments get, unless someone invents an Heisenberg Compensator.

        1. Omgwtfbbqtime Silver badge

          Re: "...unless someone invents an Heisenberg Compensator."

          I'm uncertain whether that is possible.

          1. Anonymous Coward
            Anonymous Coward

            Re: "...unless someone invents an Heisenberg Compensator."

            "I'm uncertain whether that is possible."

            Certainly is! I've got one right here in this box...

          2. Electron Shepherd

            Re: "...unless someone invents an Heisenberg Compensator."

            I'm uncertain whether that is possible.

            Right not, I agree with you, or to put it another way:

            "At the moment, that's my position"

            1. Omgwtfbbqtime Silver badge

              Re: "...unless someone invents an Heisenberg Compensator."

              Are you certain you wouldn't like to put some spin on it?

        2. ian 22
          Pirate

          Re: Heavy science

          Arr, we'll all walk the Planck, and wish it were longer than it be!

        3. John Brown (no body) Silver badge
          Coat

          Re: Heavy science

          They do claim: "there is no reason to believe that exactly one unit of Planck time has any special physical significance"

          Correct. You need two short Plancks for significance.

      3. Scubaman66

        Re: Heavy science

        A standard plank is 6 x 2 x whatever length so depending on the orientation it could be 2 or 6 or an infinitely variable number.

      4. Scubaman66

        Re: Heavy science

        Or alternatively it is 0.25 X the thickness of a climate change expert.

    2. Anonymous Coward
      Anonymous Coward

      Re: Heavy science

      "At least it will be a weight off everyone's mind when they have finished"

      Lucky my old physics teacher is unlikely to be reading this ... as otherwise he'd be shouting "Unit! Unit! You nit!" at you while probably dispatching a well aimed piece of chalk in your direction. The kilogram measures mass and not weight!

      1. Cynical Observer

        Re: Heavy science

        So physics teachers all over the world would be suffering mass hysteria at such comments?

      2. Anonymous Coward
        Anonymous Coward

        Re: Heavy science

        "Lucky my old physics teacher is unlikely to be reading this ... as otherwise he'd be shouting "Unit! Unit! You nit!" at you while probably dispatching a well aimed piece of chalk in your direction. The kilogram measures mass and not weight!"

        ...yet is presently defined by a weight.

        I fancy your old master would thoroughly approve of OP and his chalk would be flying towards gay Paris.

        1. jonathanb Silver badge

          Re: Heavy science

          No the reference kilogramme will weigh a different number of Newtons depending on where you do the measurement, but it will always be 1kg of mass.

        2. Patrick Moody

          Re: Heavy science

          The kilogram(kg) is not a measure of weight. The Newton(N) is.

          "...yet is presently defined by a weight."

          The weight (object) you refer to has a mass of exactly one kilogram, since it is the reference for that. It will still have that same mass, wherever it happens to be.

          On Earth's surface, the weight (force of gravity) of a weight (object) with a mass of 1kg will be approximately 9.81N give-or-take depending where and when you measure it.

  3. mikecoppicegreen

    So - it's about balancing one's spheres on a length of 4 by 2??? Maybe.

  4. LDS Silver badge
    Joke

    Sorry, but Russia is going to define kilogram in reference to Putin mass

    Rumors says that the Russian Academy of Science will soon be asked to redefine all standards in terms of Putin dimensions. Thereby the meter will shrink to ensure Putin is 4.5 metres tall, while the kilogram will be larger to ensure he's light as a butterfly. Time will also be redefines so he's still in his twenties.

    1. 2+2=5 Silver badge
      Joke

      Re: Sorry, but Russia is going to define kilogram in reference to Putin mass

      > while the kilogram will be larger to ensure he's light as a butterfly

      Ridiculous! The kilogram will be made much smaller so he can bench press 700 kg.

  5. Mike Taylor

    So what if they disagree - a discussion is a good thing in science

    Just don't call it a mass debate.

  6. meanioni

    What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

    Does this mean these will be reduced to mathematical equations as well? :-O

    1. Chemist

      Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

      "What does this mean for the "Olympic Swimming Pool/"

      As the pool is filled with essentially water it could be defined in moles

      1. Stumpy

        Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

        "... it could be defined in moles"

        So, sort of like my garden then?

      2. PNGuinn Silver badge
        Coat

        Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

        "As the pool is filled with essentially water it could be defined in moles"

        As opposed to non essentially water??

        Why moles? are they aquatic?

        How about kippers??

        And BACON.

        Thanks - the one with a map of Friday in the pocket.

        NURSE!

        1. Anonymous Coward
          Anonymous Coward

          Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

          moles ARE aquatic, my wife has fished two out of the swimming pool! I was amazed, but they CAN swim.

          For those interested, there are several youtube videos of them swimming quite well.

          1. CrazyOldCatMan Silver badge

            Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

            > moles ARE aquatic, my wife has fished two out of the swimming pool! I was amazed,

            > but they CAN swim.

            The ones I generally see can't. Probably because they are missing major body parts (like the body) with delicate cat-gnasher marks on the remains..

            1. Eddy Ito Silver badge
              Joke

              Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

              with delicate cat-gnasher marks on the remains.

              Excellent! You've just proven we can now determine the mass of a cat by counting how many moles are in them.

              1. John Brown (no body) Silver badge

                Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

                "Excellent! You've just proven we can now determine the mass of a cat by counting how many moles are in them."

                Furrets Last Theorem depends on modular moles?

        2. DougS Silver badge

          Essentially water

          Well some of it is chlorine. And with use, urea is often added.

          1. Trigonoceps occipitalis

            Re: Essentially water

            "And with use, urea is often added."

            So not like a VW then.

    2. Anonymous Coward
      Anonymous Coward

      Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

      No relationship as one measurement is volumetric and the other is mass.

  7. This post has been deleted by its author

    1. harmjschoonhoven
      Angel

      Re: Pray all goes well.

      But should we make te sign of the cross in the traditional Russian Orthodox way with two fingers or with three fingers as introduced by Patriach Nikon in the 1650's?

      1. Rich 11 Silver badge

        Re: Pray all goes well.

        When it comes to matters of religion I generally favour a two-finger sign.

        1. Anonymous Coward
          Anonymous Coward

          @Rich 11

          Allow me to bless you my son

  8. rhydian

    But what effect will this have on the Jub?

    Will we have to reconvene the Standards Soviet?

    http://www.theregister.co.uk/2007/10/28/additional_reg_standards/

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

  9. Your alien overlord - fear me

    Should the Irish be involved if we want to measure 2 short Planck's?

    1. Sir Runcible Spoon Silver badge
      Meh

      The 70's called - they want their joke book back

      1. TeeCee Gold badge

        http://xkcd.com/1072/

        1. CrazyOldCatMan Silver badge

          > http://xkcd.com/1072/

          Some people know far too much about xkcd for their own sanity.. (I should know - my nephew is one of them!)

  10. Sir Runcible Spoon Silver badge
    Paris Hilton

    Sir

    It's all very well working out how to measure the mass of an object, but what about how much it weighs?

    Are they taking gravitational fluctuations into account when creating these spheres?

  11. Anonymous Coward
    Anonymous Coward

    At the end of the day, what's the point?

    1. Cynical Observer
      Coat

      I think you'll find that with spheres - there isn't one.

      1. Trigonoceps occipitalis

        I think you'll find that with spheres - there isn't one.

        Its OK, my dog Arrow has one.

        (One "attaboy" to anyone who knows the cultural reference.)

        1. Mike Moyle Silver badge

          Re: I think you'll find that with spheres - there isn't one.

          Hey... You don't have to have a point to have a point!

    2. Ugotta B. Kiddingme

      "At the end of the day, what's the point?"

      it's right there, on back of your head.

  12. Yugguy

    Weight a minute!

    Someone needs to tell the purveyor of the shonky unbranded 10kg weight plates I bought that were actually 9Kg.

    Ah well, they was cheep.

    1. PNGuinn Silver badge
      Headmaster

      Re: Weight a minute!

      They'll probably be ok when they grow up and go cockadoodledo.

    2. Anonymous Coward
      Anonymous Coward

      Re: Weight a minute!

      Ah well, they was cheep.

      so they were defined in Budgerigars?

    3. Bluto Nash

      Re: Weight a minute!

      Hence the "SALE - 10% OFF!" sign nearby at the shop.

  13. ratfox Silver badge

    Kelvin?

    I thought the Kelvin was pretty much well defined by the triple point of water?

    1. Sir Runcible Spoon Silver badge

      Re: Kelvin?

      yet the triple point of water is not a measurement (it's a reference point therefore not measured against anything else) and also involves pressure

      1. ratfox Silver badge

        Re: Kelvin?

        Precisely, it involves pressure, in that the pressure is precisely defined… And since 0K is pretty much defined to be absolute zero, you don't need anything else. What do I miss?

        1. Yet Another Anonymous coward Silver badge

          Re: Kelvin?

          It's rather tricky to reach absolute zero in order to calibrate your thermometer.

          The unit of a kelvin is based on a degree centigrade which is based on the melting point of a couple of metals (don't remember which) because ice/water/steam is a bit too variable.

          1. ratfox Silver badge
            Stop

            Re: Kelvin?

            The unit of a kelvin is based on a degree centigrade which is based on the melting point of a couple of metals (don't remember which) because ice/water/steam is a bit too variable.

            Sorry, that's incorrect. The Kelvin is defined as being 0 at absolute zero, and 273.16 at the triple point of water. That's the current official definition, which they are planning to change:

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

            1. Ken Hagan Gold badge

              Re: Kelvin?

              "That's the current official definition, which they are planning to change:"

              To judge from the link, they are at roughly the point that they were with kilograms a few decades ago. They've decided what they'd like the definition to be, but don't know how to reproduce it with the required accuracy. You'll excuse me if I don't hold my breath.

          2. Scubaman66

            Re: Kelvin?

            Wasn't Celsius originally based on 0C being the boiling point of water and 100C being the freezing point.

            1. ratfox Silver badge

              Re: Kelvin?

              Wasn't Celsius originally based on 0C being the boiling point of water and 100C being the freezing point.

              1) No, that's the reverse.

              2) The boiling temperature and to a lesser extent the freezing temperature of water depend on the pressure, so that was a little bit imprecise. Celsius are now defined by the triple point of water, which determines both a precise pressure and temperature. The definition is now roughly: "absolute zero is 273.15 °C = 0 K, and at the pressure of the triple point of water, the temperature of the triple point of water is 0.01 °C = 273.16 K". The 0.01 value was chosen because that was the approximate value under the previous definition, and they didn't want to change all existing thermometers.

  14. Loyal Commenter Silver badge
    Coat

    In Soviet Russia, Kilogram Defines You!

    Alright, alright, I've got my coat..

  15. PhilipN Silver badge

    Avogadro?

    Bloody hell! I thought I'd heard the last of that bastard at Chemistry O-Level donkeys years ago.

    1. Yugguy

      Re: Avogadro?

      No, I don't like the taste.

      1. Sir Runcible Spoon Silver badge

        Re: Avogadro?

        If you make smoothies with it instead of bananas it's much nicer

        edit: I didn't mean making bananas of course

  16. theOtherJT

    Wouldn't it be easier...

    To just go back to defining it in terms of water/temperature/volume - seeing as we already have nice clean definitions for temperature and volume? I mean, that's the nice thing about the metric system. The units relate to one another.

    1. A K Stiles
      Childcatcher

      Re: Wouldn't it be easier...

      Nice theory, and I did like the linky, but is the water in solid, liquid or gas phase? Which you can't tell unless you define the pressure on the water , which leads you to a density calculation, which leads back to mass units? (haven't done the full thinking so I'm sure someone will be along to correct me shortly. Icon 'cos at least he's doing some thinking)

      1. theOtherJT

        Re: Wouldn't it be easier...

        You're probably right - I just wanted an excuse to post that image again ;)

    2. jonathanb Silver badge

      Re: Wouldn't it be easier...

      It leads to a circular reference, because you need to specify the pressure of the water, in Pascals, and that unit is derived from the kg.

  17. GrumpenKraut Silver badge

    Correction

    > ...will slide into gentle retirement.

    Shouldn't that be "roll into retirement"?

    1. CrazyOldCatMan Silver badge

      Re: Correction

      > Shouldn't that be "roll into retirement"?

      Cognac, Armagnac, Burgundy and Beaune,

      This old man came rolling home.

      Some fine songs by those gentlemen. Much missed..

  18. John Savard Silver badge

    Too Bad About the Litre

    If it weren't for the fact that the litre used to be 1.000028 cubic decimetres - that has since been redefined to be exactly 1 - the gram could be defined as the mass of one cubic centimetre of water. Which was its original definition back when the metric system was first invented. Of course, the trouble with that is that water dissolves nearly everything, at least to a small extent, and so maintaining pure water is difficult.

  19. John H Woods Silver badge

    Another problrem with the standard ...

    ... is that, being from 19th C. technology, who knows what's in it? I heard it had shrunk by about 50µg since its manufacture (my guess would be loss of about 1ml of H2 but it could be loss of surface greases)

  20. Aristotles slow and dimwitted horse Silver badge

    1kg

    And there was me thinking that the SI measure for 1kg was the ubiquitous bag of Tate & Lyle.

    Who knew.

  21. Derek Jones

    6.022 140 82x10^23, plus or minus 180,000,000,000,000,000

    Some might say that an error of plus/minus one hundred and eighty million billion atoms is not that accurate.

    1. Chris Evans

      Re: 6.022 140 82x10^23, plus or minus 180,000,000,000,000,000

      Yes whilst 12 parts per billion is very accurate I'd have thought they needed even more than extremely accurate.

  22. David 132 Silver badge
    Happy

    Not overheard..

    Phrases you won't be hearing at NIST/the International Avogadro Coordination project/NPL/NRC:

    "Close enough"

    "Just a smidge more"

    "Eh, it'll do"

    "Give it to the work experience kid* to finish off"

    "Let's take the average and call it good"

    (* but I bet the work experience kid got sent off for "a long weight")

    My own take? Just define it as 2.2lb and the job's a good'un.

    1. Anonymous Coward
      Anonymous Coward

      Re: Not overheard..

      Almost there, just a gnat's more off the end

      1. Andrew Peake

        Re: Not overheard..

        "Close enough for Jazz"

  23. GrumpyWorld
    Headmaster

    Balls

    Why the piccy of a ball-bearing?

    The reference kilo is a cylinder....

    1. Anonymous Coward
      Anonymous Coward

      Re: Balls

      They wanted to test your reading comprehension and ability to connect pieces of information.

      In the article there's a paragraph "One technique is to count the atoms in a sphere of material (Australia's CSIRO has helped contribute to this with its own silicon sphere)."

      The picture's label is "CSIRO's silicon sphere".

      Since you failed to connect the paragraph to the image, I would call that an E-PIC FAIL.

  24. Stevie Silver badge

    Bah!

    But gosh, doesn't using a sphere introduce the need for Pi, and a consequent inaccuracy due to rounding errors?

    Why not use a diamond shape? That's how the atoms want to arrange the selves anyway.

    1. Ken Hagan Gold badge

      Re: Bah!

      As I understand it, they've chosen a sphere because they believe corners are susceptible to round-off errors during handling.

      1. Stevie Silver badge

        Re: Bah!

        A sharp observation, sir.

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