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Science

Exactly One Kilogram Of Silicon 95

Posted by timothy from the objective-or-arbitrary dept.
Ed Pegg Jr writes "You may know of the importance of 299792458 for length, and 9192631770 for time. However, the official standard for weight is still a block of platinum/iridium made a hundred years ago. A group of scientists from the Avogadro Project are hoping to change that, though, by producing a perfect sphere of ultrapure silicon."
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Exactly One Kilogram Of Silicon More

Exactly One Kilogram Of Silicon

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  • A perfect sphere? (Score:5, Funny)

    by ptaff ( 165113 ) on Thursday March 20, 2003 @07:45PM (#5561050) Homepage
    A perfect sphere would imply fractional quarks and fractional parts of quarks, and ... an infinite precision!

    Pi is still irrational, isn't it?

    Don't tell me the all my math teachers lied to me!

    • Re:A perfect sphere? (Score:5, Funny)

      by sporty ( 27564 ) on Thursday March 20, 2003 @07:52PM (#5561119) Homepage
      A perfect sphere would imply fractional quarks and fractional parts of quarks, and ... an infinite precision!


      Pi is still irrational, isn't it?


      And worrying on the quark level might make you a little irrational too ;) There's always room for error...er.. jello.
    • No, I think it's have to be a Bose-Einstein Condensate. The waveform would be spherical, with none of those pesky particle-like properties. I expect it'd be expensive to make, maintain and, well, somewhat difficult to weigh.

    • My girlfriend already has a couple of perfectly round 2.2lbs of silicone; and don't ask for photographic proof.
    • I'm no physicist, but ok imagine a liquid sphere in space where all forces (gravity, etc) are equal around the sphere. The sphere would have to maintain perfect symmetry in respect to it molecular/atomic structure, otherwise there would be movement, which would mean non-perfection, because the blob moves. Isn't that how the big bang theory works in regards to the formation of galaxies -where imperfections --> globs of matter --> galaxies? So then can you stack a series of balls such that you end up wi

  • Honest Question (Score:5, Insightful)

    by Anonymous Coward on Thursday March 20, 2003 @07:46PM (#5561059)
    What exactly is the benefit of having an object with a mass of exactly one kilogram if we already know, mathematically, how much one kilogram is?

    • Re:Honest Question (Score:5, Informative)

      by qengho ( 54305 ) on Thursday March 20, 2003 @08:13PM (#5561291)

      What exactly is the benefit of having an object with a mass of exactly one kilogram

      To calibrate scales.

    • Do we know, mathematically, how much a kilogram is? What is the mathematical definition of a kilogram that does not depend upon fundamental constants whose value, in turn, depends upon the kilogram?

      The current definition of the kilogram is "the mass of that lump of metal near Paris". We the define other constants, such as Avogadros's number, in term of that kilogram
      • Fortunately, we have a reference point for the kilogram that is *not* dependent upon units already derived from the kilogram - 2.20462 pounds!

        • Re:Honest Question (Score:3, Interesting)

          by norton_I ( 64015 )
          Actually, the pound is derived from the kilogram, as all English measument units are defined (by NIST) in terms of metric quantities, and have been for some time, now. So, the official defenition of an inch is 2.54 cm, and so forth.

      • Do we know, mathematically, how much a kilogram is?

        Yes. Exactly 1/12th mol of Carbon-12. However, that may take some time to count.

    • Mathematics != Real World (Score:5, Informative)

      by aricusmaximus ( 300760 ) on Saturday March 22, 2003 @09:22AM (#5573625)
      A good question. The reason is that a kilogram is not a mathematical object (which is pure idea). It is a scientific object (which can and should have a real world representation).

      Pi does not exist in the real world. If you don't agree, show me an object in the real world that has exactly pi length, weight, or volume.

      By contrast, the kilogram is an idea (an agreement really), that leads to a real world object (bar of platinum, sphere of silicon) that people can test their measuring devices against.

      Ask yourself this: if you and your friend had two scales, how would you know which one is more accurate?

      Answer: you would test them against a scale you agreed was more accurate.

      But, in order to test for accuracy, you need a very "accurate" object. You need something that everyone agrees weighs a certain amount (say a kilogram?) And your "most accurate" scale had better exactly weigh that object as exactly one kilogram.

      That's basically what calibration is: you take an object you declare to be 1 kg (or 1 g) and then you set your scale to indicate it as such. Obviously, there is more to it than that, but that's the very basics.

      Science relies tremendously on these types of standards. One of the biggest (and unsung) "wins" of the 20th century was the tremendous increase in the objective standards of accuracy. Imagine trying to build a microprocessor if everything was designed in terms of hand lengths or feet lengths of the various contractors. Without increasingly tight, objective standards of measurement, modern science and technology would not exist.

      Ironically enough, I'm a mathematician. I would encourage you to talk to a professional scientist or engineer and ask them about it.
      • Given a specific amplitude at a specific frequency (such that the length along the wave divided by the frequency is equal to pi), you'd have a pi length (over half a wavelength -- determined by measuring for (eg) 5 seconds of a 10 second frequency -- of a standing wave (which may be experimentally ideal)). All you'd need to do is determine the equation that would relate power input to frequency. You could then (using a fixed amount of power, or a fixed frequency) determine pi (assuming you could measure a
      • I wonder though if how they compensate for variations in gravitational force between both scales... Sorry, I can't respect the current method unless they do that... Maybe there's some novel way waiting to be discovered for mass comparisons that will be unaffected by gravity (effectively)..
    • Well, funny posts aside, as scales get more and more accurate, we find that the old ways of measuring how much something is (such as the mass of one kilogram) aren't accurate enough (possibly a small amount of variance that the old instruments couldn't measure, but the newer, more precise scales can).

      So, we need new, more precise methods of defining things like how much mass one kilogram has.

      Or something like that ;)
    • They want to change the definition of the kilogram from "the platinum-iridium" standard to "a specified number of atoms of a specified isotope".

      They want to do it without changing the actual value of the kilogram by more
      than 1 part in 10^8 (the accuracy to which the current standard is consistent).

      To do that, they need to determine the mass of an object and the number of atoms in it to a combined accuracy of better than 1 in 10^8. In principle, once they have done this, they can throw away the object.

      One

  • Next they need to work on NULL pointer checks (Score:4, Funny)

    by devphil ( 51341 ) on Thursday March 20, 2003 @07:51PM (#5561103) Homepage


    I'm tired of reassuring the coding standards people that, yes, such-and-such a pointer has been tested against the platinum/iridium void* kept in a vault in Paris.

  • Old news (Score:5, Funny)

    by L. VeGas ( 580015 ) on Thursday March 20, 2003 @07:53PM (#5561127) Homepage Journal
    producing a perfect sphere of ultrapure silicon

    Pam Anderson has already cornered this market.
    Ohhhh, silicon...

  • Stick it to the French (Score:5, Funny)

    by An. (Coward) ( 258552 ) on Thursday March 20, 2003 @09:16PM (#5561710)
    We'll come up with our own standard of mass, and we'll call it the Freedom Sphere. So put that in your pipe and smoke it, Jacques Chirac! With your burned lips!

  • why kilogram? (Score:4, Interesting)

    by Anonymous Coward on Thursday March 20, 2003 @09:26PM (#5561793)
    the SI unit for length is the metre - not the kilometre

    why is the unit for mass the kilogram when it should more logically be the gram?

    using the gram might be easier to accurately measure too.

    • Re:why kilogram? (Score:4, Informative)

      by RobKow ( 1787 ) on Thursday March 20, 2003 @10:23PM (#5562140)
      Consistency of units we already have.

      We've got cgs (centimeter-gram-second) and MKS (meter-kilogram-second) systems, and at least one more.

      If you're not satisfied, make your own. And watch the rush to adopt it!

      I'm partial to MKS myself; less silly multiplication by powers of ten to correct units.

      • Re:why kilogram? (Score:5, Informative)

        by Anonymous Coward on Thursday March 20, 2003 @10:56PM (#5562304)
        Neither system is consistent in the sense I suspect the original poster meant. Both systems mix purportedly "basic" units with a different sort of unit that requires a prefix, despite the fact that it's supposed to be basic:

        centimeter - gram - second
        meter - kilogram - second

        It's just a matter of names. Logically, either system should be all "basic" units, with no prefixes. If a meter happened to be defined as 1/100th the current length, then you'd have the "meter gram second" system for the first case, and it would make more sense.

        Of course, you still have the problem that a kilo of water is a cubic decimeter, not a cubic meter. So in the MKS system, you'd have to have a "gram" weighing rather inconveniently 1000 times as much, and a meter 1/10th the size, to make this "meter gram second" system more consistent.

        The real answer, of course, lies in that word "convenient". The metric system, despite the claims of some proponents, is not really particularly inherently logical. Sure, it uses powers of ten. But the units themselves were chosen completely arbitrarily. And they were chosen simply to be relatively close to units already in use at the time - yards, bushels, pounds, quarts, and so on, because those were convenient sizes people were used to, not because there was some overriding scientific reason for choosing those sizes. (1/10^7 of the distance from Paris to the North Pole, indeed. Talk about chauvinisitic... as if there were a fundamental scientific principle rooted in the location of Paris!)

        A truly "scientific" system would have units sized on fundamental constants - speed of light, Planck's constant, permitivity/permissivity of free space, all those sorts of numbers. You'd know you had such a system because they would be nice round numbers rather than arbitary long strings of digits as they are in the current metric (or English) system.

        And when it comes to prefixes, you could always argue that the English system is far more logical in the age of computers. The metric system goes by powers of ten, which happens to be convenient for manual calculation. But the English system goes by powers of two; e.g, 16 cups = 8 pints = 4 quarts = 2 half gallon = 1 gallon. Much nicer for computers; no roundoff error there in the floating point processor, and you can change units by a simple shift operation rather than the hugely more time-consuming multiplication by ten. Same logic, different base.

        • meter nit (Score:5, Informative)

          by yerricde ( 125198 ) on Thursday March 20, 2003 @11:24PM (#5562471) Homepage Journal

          1/10^7 of the distance from Paris to the North Pole,

          Actually, the meter was defined as roughly 1e-7 of the distance from the equator to the North Pole along Paris's meridian, making the earth roughly 4e7 m (40,000 km) around.

        • Re:why kilogram? (Score:5, Funny)

          by david duncan scott ( 206421 ) on Thursday March 20, 2003 @11:39PM (#5562540)
          There is a system based on fundamental constants, the Planck Units [planck.com].

          Still, just try getting a .75 centipace wrench. You can't even order them, and without that, just how the hell are you supposed to repair the flux capacitor?

        • Re:why kilogram? (Score:4, Interesting)

          by Idarubicin ( 579475 ) on Friday March 21, 2003 @11:01AM (#5564685) Journal
          But the English system goes by powers of two; e.g, 16 cups = 8 pints = 4 quarts = 2 half gallon = 1 gallon. Much nicer for computers; no roundoff error there in the floating point processor, and you can change units by a simple shift operation rather than the hugely more time-consuming multiplication by ten. Same logic, different base.

          Yes, 3 feet to the yard (for surveyors, 66 feet to the chain), 1760 yards to the mile...

          Please, tell me how to use a shift operation to divide by 1760. :P The other nice thing about metric is the consistent prefixes. There is one MKS symbol for length (m), not many (in, ft, yd, mi...) and it can be associated with a set of prefixes (micro, milli, kilo, mega, etc.) that have consistent meaning across all metric units. For us humans, it is easy to find a unit that lets you express values in "comfortable" form--living cells are on the order of 10 micrometers across, not 0.00001 meters; it's 100 kilometers to Grandma's house, not 100000 meters. And since it's in easy powers of ten, I can tell you immediately that you can line up 10^10 cells along the road to Grandma's, if you want to know.

          • The other nice thing about metric is the consistent prefixes. There is one MKS symbol for length (m), not many (in, ft, yd, mi...) and it can be associated with a set of prefixes (micro, milli, kilo, mega, etc.) that have consistent meaning across all metric units.

            So does that mean that I should say that I have 1 gram of wheat or 1 millikilogram when I use the MKS system?

            • Re:why kilogram? (Score:3, Informative)

              by Idarubicin ( 579475 )
              So does that mean that I should say that I have 1 gram of wheat or 1 millikilogram when I use the MKS system?

              I know you're just joking, but SI (the metric system) does deal explicitly with this. You can use one prefix, at most.

              Engineers are in the habit of occasionally abusing this convention--instead of using u (mu, for micro-, 10^-6) as a prefix for some units (uH, microhenries of inductance) they will use mm (millimilli, presumably, as in mmH).

              As far as I know, nobody ever combines prefixes associ

        • But the English system goes by powers of two; e.g, 16 cups = 8 pints = 4 quarts = 2 half gallon = 1 gallon.

          = 128 ounces = 256 tablespoons = 768 teaspoons = ... 768? Aw, crap!

      • Re:why kilogram? (Score:4, Interesting)

        by dublin ( 31215 ) on Sunday March 23, 2003 @12:13AM (#5576967) Homepage
        There are good reasons to hate the metric system, other than because it's French.

        Case in point - I was working with pressure instrumentation this week, and have a new appreciation of what absolutely *insane* units have to be used by the poor folks that prefer metric.

        I'm talking, of course about that riduculous unit the Pascal, that defames the name of one of history's great scientists and thinkers.

        The idiot who decided that a pressure as ridiculously low as one Newton per square meter was a useful unit of pressure should have been stood up against the wall and summarily shot. That such a thing exists as an ISO standard seems to fit the inherent silliness of every ISO-developed standard I've ever encountered.

        I'm only half joking. This is such a ridiculously low pressure that any sort of real-world engineering use requires kilo-, or more likely megaPascals in order to express it. To put this silliness in perspective, realize that the very low pressure of 1 Atmosphere is equivalent to 101,325 Pascals. No wonder the civilized world calls it 14.7 psi instead... :-)
    • why is the unit for mass the kilogram when it should more logically be the gram

      because they would then need a standard unit for the value of "one thousand". Duhhhh!

    • Re:why kilogram? (Score:2, Funny)

      by C21 ( 643569 )
      because then it wouldnt be big and cool looking. This way the scientists can toss it around and make geeky jokes at the expense of their silicon ball.

  • BILLY! (Score:5, Funny)

    by teamhasnoi ( 554944 ) <teamhasnoi AT yahoo DOT com> on Thursday March 20, 2003 @09:42PM (#5561916) Journal
    How many times have I told you NOT to play with your perfect sphere of ultrapure silicon outside the house! It's the official standard of weight and here YOU are rolling it through a SANDBOX! No telling how many nanograms of mass you've abraded off of it!

    Get in here this INSTANT, and bring it with you! When your father [nist.gov] gets home you are going to be grounded, young man! Two weeks to the PICOSECOND by the atomic clock in the kitchen. Now go stand in the corner, and NO LEANING! You'll probably throw the wall out of plumb, or expand the angle to 90.7632+1E degrees or something, you troublemaker!

  • To Mr. Pegg (Score:5, Informative)

    by Captain Nitpick ( 16515 ) on Thursday March 20, 2003 @10:59PM (#5562319)
    However, the official standard for weight is still a block of platinum/iridium made a hundred years ago.

    ITYM mass. SI has no unit for weight. There's the newton for force, but it is not defined in terms of gravity. It is also not a SI base unit.

    • Re:To Mr. Pegg (Score:4, Funny)

      by big_groo ( 237634 ) <groovisNO@SPAMgmail.com> on Friday March 21, 2003 @12:18PM (#5565399) Homepage
      Directly from the PDF:

      2.1.1.2 Unit of Mass (kilogram)

      The international prototype of the kilogram, made of platinum-iridium, is kept at the BIPM under conditions specified by the 1st CGPM in 1889 (CR, 34-38) when it sanctioned the prototype and declared:

      'This prototype shall henceforth be considered to be the unit of mass.'

      The 3rd CGPM (1901: CR, 70), in a declaration intended to end the ambiguity in popular usage concerning the word 'weight' confirmed that:

      The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

    • SI has no unit for weight.

      What do you think a newton is? The force exerted by one gram begin accelerated at one G (or its weight at one G).

      • Re:To Mr. Pegg (Score:3, Interesting)

        by Captain Nitpick ( 16515 )
        What do you think a newton is? The force exerted by one gram begin accelerated at one G (or its weight at one G).

        A newton is defined as 1 kg-m/s^2. As the AC already stated, you're off by roughly a factor of 100, and even that isn't exact.

  • New Austin Powers movie plot. (Score:5, Funny)

    by Anonymous Coward on Thursday March 20, 2003 @11:11PM (#5562387)
    I've always have this strange idea of a Austin Powers movie where DR EVIL has stolen the "Kilogram" and held the entire world hostage for one trillion pesos.

    What an idea.

  • Did anyone else think of... (Score:5, Funny)

    by AEton ( 654737 ) on Thursday March 20, 2003 @11:48PM (#5562577)
    It's the new, improved, Happy Fun Silicon Ball!
    Warning: Pregnant women, the elderly and children under 10 should avoid prolonged exposure to Happy Fun Silicon Ball.
    Discontinue use of Happy Fun Silicon Ball if any of the following occurs:
    • Chipping
    • Scratching
    • Spontaneous degeneration
    • Conversion from matter to energy (E = mc^2 = c^2 energy!)
    • Sudden change in mass of everything around you
    Happy Fun Silicon Ball has been shipped to our troops in Kuwait and is also being dropped by our warplanes on Iraq. Our Westernization process of SI imperialism will defeat them!
    When not in use, Happy Fun Silicon Ball should be returned to its special container and kept under refrigeration...
    Do not taunt Happy Fun Silicon Ball.

    Happy Fun Silicon Ball
    Accept no substitutes!

  • Diamond (Score:3, Insightful)

    by tsa ( 15680 ) on Friday March 21, 2003 @05:27AM (#5563387) Homepage
    Pity they can't make a perfect sphere of 1 kg of diamond. Diamond has, I think, a less complicated chemistry to take into account. At least I never heard of diamond surfaces oxidizing.
    • Diamond would be much worse. The reason it's so hard to grow is that the surface lattice structure is different than the internal lattice structure at atmospheric pressures. Furthermore, diamond is unstable, so it would (albeit slowly) turn into graphite over time. As for it oxidizing, have you ever heard of carbon dioxide? It would definitely oxidize on its surface.
    • Diamond is like aluminum, an exposed surface oxidises almost immediately, but the oxidized coating stays tightly bound to the pure substance underneath.

    • Re:Diamond (Score:5, Informative)

      by SEE ( 7681 ) on Saturday March 22, 2003 @05:18AM (#5573265) Homepage
      Not only do diamonds' surfaces oxidize, they're pretty easy to burn, and only metastable in any case.

      Diamonds are *not* forever.

  • Why does it have to be a SPHERE? (Score:4, Interesting)

    by DancingSword ( 412552 ) on Friday March 21, 2003 @05:29AM (#5563397) Homepage Journal

    Is there some inherent problem with other geometries?

    Like, say, the cylinder ( as the original kilogram were )

    Isn't machining a sphere, perfectly, more .. error-prone?

    • Re:Why does it have to be a SPHERE? (Score:4, Informative)

      by sarabob ( 544622 ) on Friday March 21, 2003 @08:50AM (#5563965)
      as TFA says, it's to avoid having edges which can be chipped etc.
    • Their reasons are right there in the article. [npl.co.uk]

      • Sorry, I'd been thinking-of a rounded-edge-cylindar, not a sharp-edged-one... ( or a rounded-tablet, or something )...

        ..but simply putting the thing down onto a cradle will change its mass, whereas with a flat-bottom'd object, it could be placed on a fluorinated diamond surface ( on a gimbal-table, like they used to have in ships, 'cause it'd be slippery ), and gain/lose rather close to nothing, and thereby remove that source-of-error...

        • Tbe point here is not to replace the definition of the kilogram as "the mass if this block of metal" with "the mass of this sphere of silicon" but to change the definition to "the mass of N atoms of Silicon". That constitues a mathematica definition, so anybody with the appropriate tools could construct a "reference kilogram" and you don't have to worry about it changing over time or being destroyed. Right now we have an essentially irreplacable block of platinum-irridum sitting in Paris.

          If they do this,

          • in other words, I DID read the thing, and they're using nitrogen-doped-silicon to suppress, what was it ? spiral .. swirl defects, so the sphere isn't pure crystalline silicon, to begin with, AND...

            they're measuring it by diameter, which isn't, I'd a' thought, the perfect way to discover how many atoms are in the object, and

            they're using IT as a reference, so therefore they are using the object as a reference, so changes in mass ( due to some infinitesimally teensy amount being acquired-from or lost-to

  • Please Correct me (Score:3, Interesting)

    by smurf975 ( 632127 ) on Friday March 21, 2003 @08:18AM (#5563855) Homepage Journal
    I always thought one kilogram is one liter of pure water?

    If I'm correct what is the point? They should worry about what makes a liter and what is pure water.
    • You are correct as I recall. We had quite an interesting argument with our calculus teacher over this specific topic. Due to America using non-metric standards he says the density of water is 62.4 lb/ft^3 where as all of our learning to this point in highschool has made it out to be one kg/m^3 (I think my units are correct, if not I am sure I will be corrected). But, what I am saying is that how can us students interrelate each system. It would be much easier to learn one system for schooling as a whole, ra

      • Due to America using non-metric standards he says the density of water is 62.4 lb/ft^3 where as all of our learning to this point in highschool has made it out to be one kg/m^3 (I think my units are correct, if not I am sure I will be corrected).

        You are correct in thinking that you will be corrected :)

        Water is roughly 1000 kg/m^3; it's also roughly 1 g/cm^3 which is how I originally learned the ratio (there are 10^6 cm^3 in a m^3).

        I went to public US junior and senior high schools, all the science I lear

        • Why is it then that I am still learning this. As I am only a senior in highschool. I would have hoped by now someone would have changed the laws (or whatever governs these sort of things) so that I don't have to learn two systems. I mean wouldn't it just make more sense?

    • Okay, you asked for it (Score:5, Informative)

      by Noren ( 605012 ) on Friday March 21, 2003 @01:46PM (#5566305)
      A kilogram is a unit of mass and a liter is a unit of volume. (You probably knew that...)

      Water expands and contracts as the temperature and pressure around it change, even in the range where it is still liquid.

      It turns out that liquid water at 1 atmosphere pressure is most dense at about 4 degrees Centigrade, where its density is 0.9999750 g/cm^3. at closer to room temperature- at 22 degrees C- its density is only .9977735 g/cm^3. It never actually gets up to 1 g/cm^3 the unit system was originally designed to use, I think because of the limits of accuracy of measurements when the current definitions of individual units were set. In defining a unit, all those significant figures are relevant, so for these purposes the above are unacceptably big differences.

      Measuring mass by what the volume of water is would be more complicated and less accurate than the current system. Besides, a liter is trickier to define than a kilogram, so it'd likely be the other way around if defined in terms of each other.

      • Re:Okay, you asked for it (Score:4, Interesting)

        by dublin ( 31215 ) on Sunday March 23, 2003 @12:30AM (#5577009) Homepage
        It turns out that liquid water at 1 atmosphere pressure is most dense at about 4 degrees Centigrade, where its density is 0.9999750 g/cm^3. at closer to room temperature- at 22 degrees C- its density is only .9977735 g/cm^3. It never actually gets up to 1 g/cm^3 the unit system was originally designed to use, I think because of the limits of accuracy of measurements when the current definitions of individual units were set.

        This extremely unusual quirk of water (along with its inverse density as a solid) is one of the chief reasons that stable oceans are pretty much impossible with other substances, despite waht science fiction authors like to imagine: Because water is densest at 4 C, the entire volume of a body of water has to first reach that temperature (since it sinks to the bottom at that temp) before freezing at the top. Any other scenario results in bad things happening, like, say, all bodies of water freezing solid, making the continuation of life through winter rather difficult for aqautic species... One more reason to question whether naturalistic notions of origins really hold up under close scrutiny. (Don't even get me started on eclipses...)
        • Because water is densest at 4 C, the entire volume of a body of water has to first reach that temperature (since it sinks to the bottom at that temp) before freezing at the top. Any other scenario results in bad things happening...

          Ice-9 anybody?
      • um, isn't 1 litre = 1 cubic decimeter?

        and we have defined a meter as a fraction of the distance that light travels in 1 second, so I fail to see the problem in defining a litre.

  • that won't help much (Score:5, Interesting)

    by u19925 ( 613350 ) on Friday March 21, 2003 @02:08PM (#5566685)
    the problem of mass standard is not that it was made 100 years ago. the problem is that there is no way to describe it so that it can be reproduced independently. as one of the famous scientist said, "we can communicate our definition of length and time to aliens 1000 light years away (if they are listening us), but we can't tell them what we mean by 1 kilo".

    Secondly, it doesn't matter either what exactly is 1 kilogram. what matters is some reference atomic mass and then pick up Avogadro number (based on existing 1 kilo mass) and then get rid of the existing standard. this would allow independent reproduction (e.g. 1 kg is equivalent of 6.02...... x 10^23 atoms of Oxygen 16 in certain energy state. this scheme too has problem. there is no practical way of verifying that you have met the standard definition. so, two scientists can argue that each is possesing exact 1 kg and this cannot be arbitrated.

    • "we can communicate our definition of length and time to aliens 1000 light years away (if they are listening us), but we can't tell them what we mean by 1 kilo"

      And then:

      what matters is some reference atomic mass and then pick up Avogadro number (based on existing 1 kilo mass) and then get rid of the existing standard.

      Doesn't the use of an Avagadro number of atoms, of specified number of protons and neutrons, exactly solve the weight description problem? You've got a point about ensuring that the ensem
    • I think that is actually what they are doing--saying 1 kg is N atoms of silicon. They are picking silicon since it is the closest material we can come to creating an object with precicely 10^23 atoms.

      That difficulty is the only reason the kg hasn't been redefined already--a standard definition isn't very useful if you can't actually implement it.
  • This is sort of on and off topic at the same time.

    Anyone know of any good books about the history of measurement?

    Like what came when and how things like horsepower or slugs and pounds came into use and how they originated?

    I know about how stuff works type webpages, but I'm looking for a book with indepth info about English-Metric and whatever systems there used to be.

    Thanks!
  • The Avogadro Project's web page calls the CSIRO the "Council for Scientific and Industrial Research". This is incorrect. The CSIRO's correct name is the "Commonwealth Scientific and Industrial Research Organisation".

  • Is this more than a handful or less?
  • Soon after it's finished, a big rock-eating lasagna-with-plenty-of-sauce comes wiggling out of a tunnel, headed straight for the first guy it sees wearing a red shirt. Then it burns the message "No Kill I" on the ground, but after noting the quizzical looks on everyone's faces, and no Spock doing a mind meld on it and screaming, "Pain!" it stops, says, "Er, sorry. Wrong universe," and heads back in the other direction.

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