Press kit 26th General Conference on Weights and Measures (CGPM)

Towards a historic revision of the International System of Units (SI)

A historic milestone. World Metrology Day held on 20 May 2018 was the first step towards the historic revision of the International System of Units (SI); a change that is eagerly awaited by the entire international metrology community and which represents one of the most significant changes to the SI since its creation. This landmark decision is expected be taken on the final day of the 26th meeting of the General Conference on Weights and Measures (CGPM), which will be held at the Palais des Congrès in Versailles from 13 to 16 November 2018, when the BIPM Member States will be asked to vote for the adoption of a Resolution that will redefine four of the seven base units of the SI. The revision of the SI will also mark the end of the link between the SI and artefacts.

The International System of Units (SI), which has been under the responsibility of the International Bureau of Weights and Measures (BIPM) since its adoptions by the 11th CGPM in 1960, superseded over the Metric System, which was one of the most important legacies of the French Revolution. Today, the SI is the legal system of units in use in almost all countries around the world. This revision of the SI is the culmination of many years of intensive scientific cooperation between the National Metrology Institutes and the BIPM.

The BIPM, an international future-oriented organization. The BIPM, located in Sèvres near Paris, was created on 20 May 1875 by a treaty, the Metre convention, and is mostly known to the general public as the custodian of the international prototypes of both the metre and the kilogram,. It is one of the oldest international organizations. Funded to address the growing needs for reliable and uniform measurements in society, trade and industry, the BIPM was, in the late 19th century, at the heart of the first international cooperation in the field of metrology that has been successfully expanding ever since. Today, the BIPM has 60 Member States and 42 Associates of the CGPM. The BIPM activities are at the heart of the big challenges faced by today’s world, including climate change, health and energy sustainability. The BIPM carries out high-level scientific activities in the field of metrology and acts as a forum for its Member States.

In November 2018, it is expected that the definitions of four units (the kilogram, the ampere, the kelvin and the mole) will be revised. The definitions of all the units of the revised SI will be linked to physical constants, which will guarantee their stability and universality.

The kilogram, the last unit to be defined from an artefact (the famous international prototype of the kilogram, sanctioned by the first CGPM in 1889 and kept at the Pavillon de Breteuil), will henceforth be linked to the Planck constant.

The new definitions will use ‘the rules of nature to create the rules of measurement’ linking measurements at the atomic and quantum scales to those at the macroscopic level. As science and technology progress, the demands for measurements to underpin new products and services will increase. Metrology is a dynamic branch of science and the steps taken by the BIPM and the wider metrology community to advance the SI in 2018 will underpin these requirements and meet these needs for many years to come.

Martin Milton, Director of the BIPM

For your agendas!

Several events will be organized to mark the revision of the SI:

26th CGPM: Open session on 16 November 2018 (morning)

For the first time, an open session with the press/media will be organized during the 26th meeting of the CGPM. Online registration at https://form.jotform.com/BIPM/CGPM-MEDIA-open-session

• Competition “Français et sciences” 2018

To promote the revision of the SI to a wider public, the BIPM and the LNE (Laboratoire national de métrologie et d’essais) are partners in the competition “Français et Sciences” (French Language and Sciences) which this year focuses on the theme "Weights and Measures". The objective is to answer the question “In the infinitely small or the infinitely large, which measurement or unit is your preferred one?” by writing, in French, a personal and creative text of a maximum of two pages (double-side). The competition was launched on World Metrology Day (20 May 2018) and will end a few days before the 26th CGPM meeting (13-16 November 2018). The competition is open to French teachers in France and abroad, cultural centres, "Instituts français" or "Alliances françaises", libraries, museums or French language teaching centres.

https://www.bipm.org/utils/fr/pdf/concours-mesures-unites-2018.pdf

• Cycle of conferences on the SI measurement units

The LNE organizes a cycle of conferences “Les jeudis de la mesure” in Paris, from May to November 2018, to inform the general public about measurement. Each conference is dedicated to one of the seven base units of the SI and deals with the theme: “Evolution of the measurement units: a revolution?”.

https://www.lne.fr/fr/actualites/cycle-conferences-unites-mesure-si

• Exhibition “Sur mesure, les 7 unités du monde” This exhibition that will take place from 16 October 2018 to 5 May 2019 at the Musée des Arts et Métiers in Paris will explore the theme of measurement from every angle.

https://www.arts-et-metiers.net/musee/sur-mesure-les-7-unites-du-monde-lexposition-qui-donne-la-mesure-au-musee-des-arts-et-metiers

www.bipm.org

The BIPM Headquarters (Sèvres, France)

(on the left) The International prototype of the kilogram: sanctioned by the General Conference on Weights and Measures at its first meeting, it is kept by the BIPM since 1889. The kilogram is the last unit to be defined in terms of an artefact; the kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram. (on the right) Towards the new definition of the kilogram: the Kibble Balance of the BIPM

Photos © BIPM

Chronology

 

CHRONOLOGY: Key steps in the history of the International System of Units (SI) 

 

17 April 1795  The law of 18 Germinal Year III (Republican calendar) established the Metric System in France.  

22 June 1799  Two platinum standards representing  the metre and  the kilogram were deposited  in  the French National Archives. 

1832  Carl Friedrich Gauss introduced a system of “absolute” units based on the millimetre, the milligram and the second.  

1874  The British Association for the Advancement of Science introduced the CGS System.  

20 May 1875  The Metre Convention was signed in Paris by representatives of seventeen nations, which created the BIPM. 

1889  The first CGPM sanctioned the new international prototypes of the metre and the kilogram.  

1901  Giovanni Giorgi proposed  to  the Associazione Elettrotecnica  Italiana a new  system enabling  the combination of the fundamental units, the kilogram, the metre and the second, with a fourth unit of an electrical nature.  

1921  Revision of the Metre Convention extending the activities of the BIPM to new fields of metrology. 

1927  The  Consultative  Committee  for  Electricity  was  created  by  the  CIPM.  It  was  the  first  such committee.  

1935  IEC adopted the Giorgi System known as the MKS System.  

1939  The CCE recommended the adoption of the MKS System based on the metre, the kilogram and the second (following discussion within IEC and IUPAP).  

1946  As a first step that had already been planned in 1933, the CIPM approved the MKS System to replace the former system of electrical units called the “international System”. 

1948  The 9th CGPM requested the CIPM to launch an international survey, the outcome of which was  to be used to formulate recommendations for a single practical system of measurement units, suitable for adoption by all countries.  

1954  The CGPM approved the introduction of the ampere, the kelvin and the candela as base units for electric current, thermodynamic temperature and luminous intensity respectively.  

1960  The 11th CGPM adopted the name of the International System of Units (SI) for the system based on six base units: the metre, the kilogram, the second, the ampere, the kelvin and the candela. The 11th CGPM also adopted a new definition of the metre.  

1967  The second was redefined as an “atomic second”. The new definition depended henceforth on the properties of a caesium atom.  

1971  The 14th CGPM added a new unit to the SI: the mole as the unit for amount of substance.  

1979  The candela was redefined in terms of a monochromatic radiation.  

1983  For the first time a definition of a base unit of the SI was based on a fundamental constant: the speed of  light. The metre was henceforth  the  length of  the path  travelled by  light  in vacuum during a specific fraction of a second. 

1990  New practical conventions based on quantum phenomena were adopted for the ohm and the volt. 

2018  Four base units of the SI will be redefined: each definition will be linked to a constant of physics. The 1990 conventions will no longer be needed and will be abolished. 

20 May 2019  World Metrology Day on 20 May 2019 will mark the official entry in force of the revised SI. 

 

 

Information on the revision of the SI

Information for users about the proposed revision of the SI

The International System of Units1, the SI, which is based on the second, the metre, the kilogram, the ampere, the kelvin, the mole and the candela (the base units), is being revised to update the definitions of four of these units. In November 2018 revised definitions of the kilogram, ampere, kelvin and mole are expected to be approved by the General Conference on Weights and Measures (CGPM), the international body responsible for the global comparability of measurements. The revised definitions are expected to come into force on 20 May 2019.

The revised definitions will be based on seven physical constants (for example the speed of light, the Planck constant and the Avogadro constant) and are therefore inherently stable. The quantities have been chosen so that the revised definitions will not need to be modified to accommodate future improvements in the technologies used to realize them. The revision of the SI in this way was foreseen in Resolutions of the CGPM adopted in 2011 and 20142,3. Additional requirements contained in these Resolutions will ensure a smooth transition to the four revised definitions. Most users will not notice the change. A new edition of the SI Brochure1 will provide essential information for users and will be available after the revised definitions are adopted formally. Guidance on the practical realization of the units will be available4-8.

Some information about how these changes might affect the different areas of measurement is given below:

• The kilogram will be defined in terms of the Planck constant, guaranteeing long-term stability of the SI mass scale. The kilogram can then be realized by any suitable method, (for example the Kibble (watt) balance or the Avogadro (X-ray crystal density) method). Users will be able to obtain traceability to the SI from the same sources used at present (the BIPM, national metrology institutes and accredited laboratories). International comparisons will ensure their consistency. The value of the Planck constant will be chosen to ensure that there will be no change in the SI kilogram at the time of redefinition. The uncertainties offered by NMIs to their calibration customers will also be broadly unaffected.

• The ampere and other electrical units, as practically realized at the highest metrological level, will become fully consistent with the definitions of these units. The transition from the 1990 convention to the revised SI will result in small changes to all disseminated electrical units. For the vast majority of measurement users, no action need be taken as the volt will change by about 0.1 parts per million and the ohm will change by even less. Practitioners working at the highest level of accuracy may need to adjust the values of their standards and review their measurement uncertainty budgets.

• The kelvin will be redefined with no immediate effect on temperature measurement practice or on the traceability of temperature measurements, and for most users, it will pass unnoticed. The redefinition lays the foundation for future improvements. A definition free of material and technological constraints enables the development of new and more accurate techniques for making temperature measurements traceable to the SI, especially at extremes of temperature. After the redefinition, the guidance on the practical realization of the kelvin will support its world-wide dissemination by describing primary methods for measurement of thermodynamic temperature and equally through the defined scales ITS-90 and PLTS-2000.

• The mole will be redefined with respect to a specified number of entities (typically atoms or molecules) and will no longer depend on the unit of mass, the kilogram. Traceability to the mole can still be established via all previously employed approaches including, but not limited to, the use of mass measurements along with tables of atomic weights and the molar mass constant Mu. Atomic weights will be unaffected by this change in definition and Mu will still be 1 g/mol, although now with a measurement uncertainty. This uncertainty will be so small that the revised definition of the mole will not require any change to common practice.

The revised definitions of the kilogram, ampere, kelvin and mole will have no impact on the second, the metre and the candela.

• The second will continue to be defined in terms of the hyperfine transition frequency of the

caesium 133 atom. The traceability chain to the second will not be affected. Time and frequency metrology will not be impacted.

• The metre in the revised SI will continue to be defined in terms of the speed of light, one of the

fundamental constants of physics. Dimensional metrology practice will not need to be modified in any way and will benefit from the improved long-term stability of the system.

• The candela will continue to be defined in terms of Kcd, a technical constant for photometry and

will therefore continue to be linked to the watt. Traceability to the candela will still be established with the same measurement uncertainty via radiometric methods using absolutely-calibrated detectors.

The SI has been revised several times since its formal adoption by the CGPM in 1960. However, redefining four base units at one time is unprecedented, requiring simultaneous world-wide collaborations in diverse fields of metrology. As in the past, care has been taken to ensure that there will be no perceptible impact on daily life and that measurements made with previous definitions of the units remain valid within their measurement uncertainties. Few users outside national metrology laboratories will notice the changes. Reaching the experimental accuracies and fulfilling the conditions requested in the CGPM resolutions has been a remarkable accomplishment, which will ensure that the SI continues to meet the needs of even the most demanding users.

1. http://www.bipm.org/en/publications/si-brochure/ 2. http://www.bipm.org/en/CGPM/db/24/1/ 3. http://www.bipm.org/en/CGPM/db/25/1/ 4. http://www.bipm.org/en/publications/mises-en-pratique/ 5. http://www.bipm.org/cc/CCM/Allowed/15/02A_MeP_kg_141022_v-9.0_clean.pdf 6. http://www.bipm.org/cc/CCEM/Allowed/26/CCEM-09-05.pdf1. 7. http://www.bipm.org/cc/CCT/.../MeP-K-14_DRAFT_Dec_2015.pdf 8. http://www.bipm.org/cc/CCQM/Allowed/22/CCQM16-04_Mole_m_en_p_draft.pdf This note was prepared by the Consultative Committees of the CIPM in 2017 for the purpose of creating awareness of the revision of the International System of Units expected for 2018.

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Frequently Asked Questions about the proposed Revised SI (Updated October 2018)

Q1: What is going to change? A1: The kilogram, kg, ampere, A, kelvin, K, and mole, mol, will have new definitions, but

they will be so chosen that at the moment of change the magnitudes of the new units will be indistinguishable from those of the old units. The new definitions are expected to be approved by the 26th General Conference of Weights and Measures (CGPM) in November 2018 and to come into force on 20 May 2019.

Q2: So what is the point of changing to new definitions? A2: Defining the kilogram in terms of fundamental physical constants will ensure its long-term

stability, and hence its reliability, which is at present in doubt. The new definitions of the ampere and kelvin will significantly improve the accuracy with which electrical, and radiometric temperature measurements can be made. The impact on electrical measurements will be immediate: the most precise electrical measurements are already made using the Josephson and quantum Hall effects, and fixing the numerical values of the Planck constant h and the elementary electrical charge e in the new definitions of the units will lead to exact numerical values for the Josephson and von Klitzing constants. This will eliminate the current need to use conventional electrical units rather than SI units to express the results of electrical measurements (see A14). The conversion factor between measured radiance and thermodynamic temperature (the Stefan-Boltzmann constant) will be exact using the new definitions of the kelvin and kilogram, leading to improved temperature metrology as technology improves. The revised definition of the mole is simpler than the current definition, and it will help users of the SI to better understand the nature of the quantity “amount of substance” and its unit, the mole. All in all, the Revised SI will be a better fit to the technology of this century.

Q3: What about the definitions of the second, s, metre, m, and candela, cd? A3: The definitions of the second, s, metre, m, and candela, cd, will not change, but the

way the definitions are written will be revised to make them consistent in form with the new definitions for the kilogram, kg, ampere, A, kelvin, K, and mole, mol. These new wordings are expected to be approved by the 26th CGPM in November 2018 and to come into force on 20 May 2019.

Q4: What will happen to the International Prototype of the Kilogram (IPK) once the Revised SI takes effect? Will it go to a museum where the general public can at last see it?

A4: There are no plans to change the storage conditions for the IPK. It will remain at the BIPM and it will not be on display for the general public. The IPK will retain a bit of metrological interest and therefore it will be monitored very sporadically in the future to avoid as much as possible any surface damage. Measurements of the mass stability of the IPK in the future may help us extrapolate its mass stability in the recent past.

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Q5: Will I get my standard of mass calibrated under the Revised SI in the same way as I do now?

A5: After the redefinition of the kilogram, you can continue sending your mass standard to your National Metrology Institute (NMI) for calibration or to a secondary calibration laboratory just as you do now. However, the traceability path that your NMI will use to link it to the SI kilogram will change.

Indeed, after the redefinition of the kilogram, the BIPM will organize an ongoing comparison among primary realizations of the kilogram and a consensus value of the kilogram will be determined from it. National Metrology Institutes having a realization of the kilogram will be requested to avail themselves of the consensus value when disseminating the unit of mass according to the new definition, until the dispersion in values becomes compatible with the individual realization uncertainties, thus preserving the international equivalence of calibration certificates and in accordance with the principles and agreed protocols of the CIPM Mutual Recognition Arrangement.

Member States not having realizations of the new definition of the kilogram will have direct access to traceability to the same consensus value through the calibration services of the BIPM during the phase where the consensus value will be used.

Q6: Once laboratories can realize the kilogram themselves, how can we be sure that inter-laboratory results are compatible?

A6: In the case of the kilogram, when the consensus value will no longer be needed, all laboratories will need to demonstrate traceability to the definition of the kilogram, which will be based on physical constants. Since it is always possible to underestimate an experimental uncertainty or just to make a mistake, laboratories that claim the smallest uncertainties will compare results periodically to assess compatibility with their peers. A basic mechanism for this already exists and is widely used in metrology. It is based on the CIPM Mutual Recognition Arrangement established in 1999.

Q7: Will NMIs also be requested to avail themselves of a consensus value for the dissemination of the three other redefined units?

A7: No. The kilogram is a special case. Electrical units and the kelvin have been mentioned in A14 and A8. As for the mole, there will be no change to current practice.

Q8: Will I get my thermometer calibrated under the Revised SI in the same way as I do now?

A8: Yes. The new definition of the kelvin has no immediate impact on the status of the widely-used ITS-90 and PLTS-2000 temperature scales. The Consultative Committee for Thermometry (CCT) has published information concerning immediate and future advantages of the new definition.

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Q9: In the Revised SI the reference constant for the kilogram is the Planck constant h, with unit J s = kg m2 s−1. It would be much easier to comprehend if the reference constant had the unit of mass, the kg. Then we could say: “The kilogram is the mass of <something>”, such as perhaps the mass of a specified number of carbon or silicon atoms. Would that not be a better definition?

A9: This is to some extent a matter of subjective judgement. However note that the reference constant used to define a unit does not have to be dimensionally the same as the unit (even though it may be conceptually simpler when this is the case). We already use several reference constants in the current SI that have a different unit to that being defined. For example the metre is defined using as reference constant the speed of light c with unit m/s, not a specified length in m. This definition has not been found unsatisfactory. This practice first began in 1960, with the present definition of the ampere which is based on the fixed value of a constant whose unit is kg m s−2 A−2. (The new definition of the ampere will be simpler.)

Although it may seem intuitively preferable to define the kilogram using a mass as the reference constant, using the Planck constant has other advantages. For example, if both h and e are exactly known as proposed in the Revised SI, then both the Josephson and von Klitzing constants KJ and RK will be exactly known, with great advantages for electrical metrology. (Physics tells us that we cannot fix both h and the mass of <something>, for instance the mass of a carbon 12 atom m(12C), without consequently redefining the second in a very impractical way.)

Q10: Despite the answer to Q9 above, there are still people who question the wisdom of defining the kilogram by using h as a reference rather than by using m(12C). One of the arguments they use is that the Kibble1 balance (KB) experiment to determine h uses a complex apparatus that is difficult to use and expensive to build, in comparison with the XRCD (x-ray crystal density) experiment to measure the mass of a silicon 28 atom, and hence the mass of a carbon 12 atom. What are the principal reasons for choosing h rather than m(12C) as the reference constant for the kilogram?

A10: These are really two unrelated questions:

1. Why choose h rather than m(12C) as the reference constant for the kilogram?

2. Does the choice of h or m(12C) determine whether the kilogram will be realized inpractice by a KB experiment or by the XRCD experiment?

1. Once the numerical value of a constant is given a fixed value, the constant neednot, indeed cannot, be measured subsequently. For example, in 1983 when the SIwas modified by making the speed of light in vacuum, c, the reference constant forthe metre, the long history of measuring c abruptly ended. This was an enormousbenefit to science and technology, in part because c enters into so many domains ofscience and technology that every time there was a change to the recommended SIvalue of c, the values of numerous constants and conversion factors related to c

1 To recognize Bryan Kibble’s invention of the watt balance

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needed to be updated. The decision to define the numerical value of c as exact was obviously correct.

Similarly, h is the fundamental constant of quantum physics and consequently its SI value is used in many diverse fields of modern science and technology. Changes to the recommended value of h as experiments improve are at best annoying and at worst confusing. The rationale for defining the numerical value of h is similar to that for defining c, but has the specific advantages in electrical metrology given in A2.

Of course m(12C) is undeniably a constant and is undeniably important, especially for chemistry and the physics of atoms. This is because atomic weights (if you are a chemist), also known as relative atomic masses (if you are a physicist), are all based on m(12C). Nevertheless, atomic weights do not depend on the present definition of the kilogram and, of course, they will be unaffected by a new definition.

2. No. The choice of which reference constant is used to define the kilogram does notimply any particular method to realize the kilogram, and none is mentioned in DraftResolution A (CGPM 2018). We do know that any realization must be traceable toh since h will be the reference constant in the new definition of the kilogram.However, it is also known that h/m(12C) = Q, where Q represents a product of exactnumerical factors and experimentally-determined constants. The relative standarduncertainty of Q is only 4.5 × 10−10 based on the current recommended values ofthe constants involved. An apparatus, such as the KB, which measures a 1 kg massstandard directly in terms of h (through electrical measurements made withquantum devices) and auxiliary measurements of length and time can be used torealize the kilogram. However, an experiment that measures a 1 kg mass standardin terms of m(12C), as in the XRCD project, also has the potential to realize thekilogram. This is because m(12C)Q = h, and thus the price to pay for arriving at hby way of m(12C) is the added uncertainty of Q, which is negligible in the contextof realizing the new definition. It is premature to speculate whether one type ofrealization will prevail in the long run or whether different types will coexist. Atpresent, all such experiments are difficult and expensive.

Q11: Are the seven base quantities and base units in the current SI going to change in the Revised SI?

A11: No. The seven base quantities (time, length, mass, electric current, thermodynamic temperature, amount of substance, luminous intensity) and corresponding base units (second, metre, kilogram, ampere, kelvin, mole, candela) will remain unchanged.

Q12: Are the 22 coherent derived units with special names and symbols going to change?

A12: No, the 22 coherent derived units with special names and symbols will remain unchanged in the Revised SI.

Q13: Are the names and symbols of the multiple and sub-multiple prefixes (kilo for 103, milli for 10−3, etc.) going to change in the Revised SI?

A13: No, the names and symbols for the prefixes will remain unchanged.

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Q14: Will the magnitudes of any of the units change in the Revised SI? A14: No. So-called “continuity conditions” have been established to help ensure that there

will be no change in magnitude of any of the SI base units, and hence no change in any units derived from the base units.

(There is a small exception involving electrical units: since 1990, the electrical units used in practice have been based on conventional values for the Josephson constant and the von Klitzing constant rather than on their present SI definitions. Today, we know that there are small offsets between the conventional and the SI values. The revised SI will bring the practical electrical units back into the SI. This will lead to a one-time change of + 0.1 parts per million (ppm) for voltage values and of + 0.02 ppm for resistance values when expressed in the units of the Revised SI.)

Q15: How can you fix the value of a fundamental constant like h to define the kilogram, and e to define the ampere, and so on? How do you know what value to fix them to? What if it emerges that you have chosen the wrong value?

A15: We do not fix – or change – the value of any constant that we use to define a unit. The values of the fundamental constants are constants of nature and we only fix the numerical value of each constant when expressed in its SI unit. By fixing its numerical value we define the magnitude of the unit in which we measure that constant at present.

Example: If c is the value of the speed of light, {c} is its numerical value, and [c] is the unit, so that

c = {c} [c] = 299 792 458 m/s

then the value c is the product of the number {c} times the unit [c], and the value never changes. However the factors {c} and [c] may be chosen in different ways such that the product c remains unchanged.

In 1983 it was decided to fix the number {c} to be exactly 299 792 458, which then defined the unit of speed [c] = m/s. Since the second, s, was already defined, the effect was to define the metre, m. The number {c} in the new definition was chosen so that the magnitude of the unit m/s was unchanged, thereby ensuring continuity between the new and old definitions of the units.

Q16: OK, you actually only fix the numerical value of the constant expressed in its unit. For the kilogram, for example, you choose to fix the numerical value {h} of the Planck constant expressed in its unit [h] = kg m2 s−1. But the question remains: suppose a new experiment shortly after you change the definition suggests that you chose a wrong numerical value for {h}, what then?

A16: After making the change, the mass of the international prototype of the kilogram (the IPK), which has defined the kilogram since 1889, will have to be determined by experiment. If we have chosen a “wrong value” it simply means that the new experiment will tell us that the mass of the IPK is not exactly 1 kg in the Revised SI.

This situation would only affect macroscopic mass measurements; the masses of atoms and the values of other constants related to quantum physics would not be affected. Continuing with the definition of the kilogram agreed in 1889 would continue the practice of using a reference quantity (i.e. the mass of the IPK) that we cannot be sure

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is not changing with time compared to a true invariant such as the mass of an atom or the Planck constant.

There has been much debate over the years about how much the mass of the IPK might be changing with respect to the mass of a true physical constant. The advantage of the new definition will be that we will be certain that the reference constant used to define the kilogram is a true invariant.

Q17: Each of the fundamental constants used to define a unit has an uncertainty; its value is not known exactly. But it is proposed to fix its numerical value exactly. How can you do that? What has happened to the uncertainty?

A17: The present definition of the kilogram fixes the mass of the IPK to be one kilogram exactly with zero uncertainty, ur(mIPK) = 0. The Planck constant is at present experimentally determined, and has a relative standard uncertainty of 1.0 part in 108, ur(h) = 1.0 × 10−8. In the new definition the value of h will be known exactly in terms of its SI unit so that ur(h) = 0. But the mass of the IPK would have to be experimentally determined, and it would have a relative uncertainty of about ur(mIPK) = 1.0 × 10−8. Thus the uncertainty is not lost in the new definition, but it moves to become the uncertainty of the previous reference that is no longer used, as in the table below.

Constant used Current SI Revised SI to define the kilogram status uncertainty status uncertainty ___________________ _____________ _____________

mass of the IPK, m(K) exact 0 expt. 1.0 × 10−8

Planck constant, h expt. 1.0 × 10−8 exact 0

Q18: The unit of the Planck constant is the unit of action, J s = kg m2 s−1. How does fixing the numerical value of the Planck constant define the kilogram?

A18: Fixing the numerical value of h actually defines the unit of action, J s = kg m2 s−1. But

if we have already defined the second, s, to fix the numerical value of the caesium hyperfine transition frequency ∆νCs, and the metre, m, to fix the numerical value of the speed of light in vacuum, c, then fixing the magnitude of the unit kg m2 s−1 has the effect of defining the unit kg.

Q19: Are not the proposed definitions of the base units in the Revised SI circular definitions, and therefore unsatisfactory?

A19: No, they are not circular. A circular definition is one that makes use of the result of the definition in formulating the definition. The words for the individual definitions of the base units in the Revised SI specify the numerical value of each chosen reference constant to define the corresponding unit, but this does not make use of the result to formulate the definition.

7/7

Q20: Can we still check the consistency of physics if we fix the values of all the fundamental constants?

A20: We are not fixing the values of all the fundamental constants, only the numerical values of a small subset and combinations of the constants in this subset. This has the effect of changing the definitions of the units, but not the equations of physics, and it cannot prevent researchers from checking the consistency of the equations.

Q21: The physical constants c, h and e will all have fixed numerical values. But doesn’t this fix the value of the fine-structure constant, which must not be given a fixed value?

A21: No. The value of the fine-structure constant will continue to be determined by experiment. In the SI, the fine-structure constant has always depended on c, h, e and µ0. The fourth constant is the vacuum magnetic permeability, which presently defines the ampere but in the Revised SI will be determined experimentally from a measurement of the fine-structure constant.

Draft Resolution A – 26th meeting of the CGPM (13-16 November 2018)

Draft Resolution A

On the revision of the International System of Units (SI)

The General Conference on Weights and Measures (CGPM), at its 26th meeting,

considering

− the essential requirement for an International System of Units (SI) that is uniform and accessible world-wide for international trade, high-technology manufacturing, human health and safety, protection of the environment, global climate studies and the basic science that underpins all these,

− that the SI units must be stable in the long term, internally self-consistent and practically realizable being based on the present theoretical description of nature at the highest level,

− that a revision of the SI to meet these requirements was proposed in Resolution 1 adopted unanimously by the CGPM at its 24th meeting (2011) that laid out in detail a new way of defining the SI based on a set of seven defining constants, drawn from the fundamental constants of physics and other constants of nature, from which the definitions of the seven base units are deduced,

− that the conditions set by the CGPM at its 24th meeting (2011), confirmed at its 25th meeting (2014), before such a revised SI could be adopted have now been met,

decides that, effective from 20 May 2019, the International System of Units, the SI, is the system of units in which:

− the unperturbed ground state hyperfine transition frequency of the caesium 133 atom ∆νCs is 9 192 631 770 Hz,

− the speed of light in vacuum c is 299 792 458 m/s,

− the Planck constant h is 6.626 070 15 × 10−34 J s,

− the elementary charge e is 1.602 176 634 × 10−19 C,

− the Boltzmann constant k is 1.380 649 × 10−23 J/K,

− the Avogadro constant NA is 6.022 140 76 × 1023 mol−1,

− the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, is 683 lm/W,

where the hertz, joule, coulomb, lumen, and watt, with unit symbols Hz, J, C, lm, and W, respectively, are related to the units second, metre, kilogram, ampere, kelvin, mole, and candela, with unit symbols s, m, kg, A, K, mol, and cd, respectively, according to Hz = s–1, J = m2 kg s– 2, C = A s, lm = cd m2 m –2 = cd sr, and W = m2 kg s–3.

notes the consequences as set out in Resolution 1 adopted by the CGPM at its 24th meeting (2011) in respect of the base units of the SI and confirms these in the following Appendices to this Resolution, which have the same force as the Resolution itself,

Draft Resolution A – 26th meeting of the CGPM (13-16 November 2018)

invites the International Committee for Weights and Measures (CIPM) to produce a new edition of its Brochure entitled “The International System of Units” in which a full description of the revised SI will be given.

Appendix 1. Abrogation of former definitions of the base units

It follows from the new definition of the SI described above that, effective from 20 May 2019:

− the definition of the second in force since 1967/68 (13th meeting of the CGPM, Resolution 1) is abrogated,

− the definition of the metre in force since 1983 (17th meeting of the CGPM, Resolution 1) is abrogated,

− the definition of the kilogram in force since 1889 (1st meeting of the CGPM, 1889, 3rd meeting of the CGPM, 1901) based upon the mass of the international prototype of the kilogram is abrogated,

− the definition of the ampere in force since 1948 (9th meeting of the CGPM) based upon the definition proposed by the CIPM (1946, Resolution 2) is abrogated,

− the definition of the kelvin in force since 1967/68 (13th meeting of the CGPM, Resolution 4) is abrogated,

− the definition of the mole in force since 1971 (14th meeting of the CGPM, Resolution 3) is abrogated,

− the definition of the candela in force since 1979 (16th meeting of the CGPM, Resolution 3) is abrogated,

− the decision to adopt the conventional values of the Josephson constant KJ–90 and of the von Klitzing constant RK–90 taken by the CIPM (1988, Recommendations 1 and 2) at the request of the CGPM (18th meeting of the CGPM, 1987, Resolution 6) for the establishment of representations of the volt and the ohm using the Josephson and quantum Hall effects, respectively, is abrogated.

Appendix 2. Status of constants previously used in the former definitions

It follows from the new definition of the SI described above, and from the recommended values of the 2017 special adjustment of the Committee on Data for Science and Technology (CODATA) on which the values of the defining constants are based, that effective from 20 May 2019:

− the mass of the international prototype of the kilogram m(K) is equal to 1 kg within a relative standard uncertainty equal to that of the recommended value of h at the time this Resolution was adopted, namely 1.0 × 10–8 and that in the future its value will be determined experimentally,

− the vacuum magnetic permeability µ0 is equal to 4π × 10–7 H m–1 within a relative standard uncertainty equal to that of the recommended value of the fine-structure constant α at the time this Resolution was adopted, namely 2.3 × 10–10 and that in the future its value will be determined experimentally,

Draft Resolution A – 26th meeting of the CGPM (13-16 November 2018)

− the thermodynamic temperature of the triple point of water TTPW is equal to 273.16 K

within a relative standard uncertainty closely equal to that of the recommended value of k at the time this Resolution was adopted, namely 3.7 × 10–7, and that in the future its value will be determined experimentally,

− the molar mass of carbon 12, M(12C), is equal to 0.012 kg mol–1 within a relative standard uncertainty equal to that of the recommended value of NAh at the time this Resolution was adopted, namely 4.5 × 10–10, and that in the future its value will be determined experimentally.

Appendix 3. The base units of the SI

Starting from the new definition of the SI described above in terms of fixed numerical values of the defining constants, definitions of each of the seven base units are deduced by taking, as appropriate, one or more of these defining constants to give the following set of definitions, effective from 20 May 2019:

− The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency ∆νCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s–1.

− The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m/s, where the second is defined in terms of ∆νCs.

− The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10–34 when expressed in the unit J s, which is equal to kg m2 s–1, where the metre and the second are defined in terms of c and ∆νCs.

− The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 × 10–19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of ∆νCs.

− The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 × 10– 23 when expressed in the unit J K–1, which is equal to kg m2 s–2 K–1, where the kilogram, metre and second are defined in terms of h, c and ∆νCs.

− The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol–1 and is called the Avogadro number.

The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

− The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, to be 683 when expressed in the unit lm W–1, which is equal to cd sr W–1, or cd sr kg–1 m–2 s3, where the kilogram, metre and second are defined in terms of h, c and ∆νCs.

Open Session during the 26th CGPM

8:30 - Start of session

Opening of the sessionSébastien Candel (Président de l’Académie des sciences)/Barry Inglis (CIPM President)

Progress towards a redefinition of the SI and report from the CCUJoachim Ullrich (CIPM Vice-President)

Achievements in the measurement of k and report from the CCTYuning Duan (CIPM)

Achievements with the quantum electrical effects and report from the CCEMGert Rietveld (CIPM)

Achievements in the measurement of h and report from the CCMPhilippe Richard (CIPM)

Questions and discussion followed by coffee

General Conference on Weights and Measures (CGPM)Palais des Congres, VersaillesFriday 16th November 2018

10:50 - Start of webcast

Keynote lectures

"The quantum Hall effect and the revised SI"Klaus von Klitzing (Nobel laureate, Max Planck Institute, Stuttgart)

"The role of the Planck constant in physics"Jean-Philippe Uzan (Centre national de la recherche scientifique (CNRS), Paris)

"Optical atomic clocks – opening new perspectives on the quantum world"Jun Ye (JILA, Boulder)

"Measuring with fundamental constants; how the revised SI will work"Bill Phillips (Nobel laureate, NIST, Gaithersburg)

Introduction to the Resolution “On the revision of the International System of Units (SI)”Martin Milton (BIPM Director)

Voting on Draft Resolution A and closing remarksBarry Inglis

13:25 - End of session

Open session to consider the re-definition of the SI base units.

[The planned times may be subject to change]

In order to provide the opportunity for a wider audience to be part of this event, the session will be open to a limited number of ticket holders. Tickets will be available from the BIPM.

In addition, the lectures by the Keynote Speakers and the voting on the proposed resolution will be transmitted as a webcast. Further information will be available from the BIPM website.

World Metrology Day

World Metrology Daywww.worldmetrologyday.org

© 2

018

BIPM

-OIM

L

Constant evolution The International System of Units

20 May 2018

Constant Evolution of the International System of Units (SI)

Release:

May 20 is World Metrology Day, commemorating the anniversary of the signing of the Metre Convention in 1875. This treaty provides the basis for a coherent measurement system worldwide that underpins scientific discovery and innovation, industrial manufacturing and international trade, as well as the improvement of the quality of life and the protection of the global environment.

The theme for World Metrology Day 2018 is Constant Evolution of the International System of Units (SI). This theme was chosen because in November 2018, the General Conference on Weights and Measures is expected to agree one of the largest changes to the International System of Units (the SI) since its inception. The proposed changes are based on the results of research into new measurement methods that have used quantum phenomena as the basis for standards that are fundamental. The SI will be based on a set of definitions each linked to the laws of physics and have the advantage of being able to embrace further improvements in measurement science and technology to meet the needs of future users for many years to come.

Across the world, national metrology institutes continually advance measurement science by developing and validating new measurement techniques at whatever level of sophistication is needed. The national metrology institutes participate in comparisons coordinated by the Bureau International des Poids et Mesures (BIPM) to ensure the reliability of measurement results worldwide. The BIPM also provides a forum for its Member States to address new measurement challenges. The International Organization of Legal Metrology (OIML) develops International Recommendations, the aim of which is to align and harmonize requirements worldwide in many fields.

World Metrology Day recognizes and celebrates the contribution of all the people that work in intergovernmental and national organizations throughout the year on behalf of all.

Further information, including a message from the Directors, posters, and a list of events, is available at www.worldmetrologyday.org – Contact: wmd@worldmetrologyday.org

Notes for Editors:

World Metrology Day is an annual event during which more than 80 countries celebrate the impact of measurement on our daily lives.

This date was chosen in recognition of the signing of the Metre Convention on 20 May 1875, the beginning of formal international collaboration in metrology. Each year World Metrology Day is organized and celebrated jointly by the International Bureau of Weights and Measures (BIPM) and the International Organization of Legal Metrology (OIML) with the participation of the national organizations responsible for metrology.

The international metrology community which works to ensure that accurate measurements can be made across the world endeavors to raise awareness each World Metrology Day through a poster campaign and web site. Previous themes have included topics such as measurements for the global energy challenge, for safety, for innovation, and measurements in sport, the environment, medicine and trade.

About the BIPM

The signing of the Metre Convention in 1875 created the BIPM and for the first time formalized international cooperation in metrology. The Convention established the International Bureau of Weights and Measures and laid the foundations for worldwide uniformity of measurement in all aspects of our endeavors, historically focusing on and assisting industry and trade, but today just as vital as we tackle the grand challenges of the 21st Century such as climate change, health, and energy. The BIPM undertakes scientific work at the highest level on a selected set of physical and chemical quantities. The BIPM is the hub of a worldwide network of national metrology institutes (NMIs) which continue to realize and disseminate the chain of traceability to the SI into national accredited laboratories and industry.

About the OIML

In 1955 the International Organization of Legal Metrology (OIML) was established as an Intergovernmental Treaty Organization in order to promote the global harmonization of legal metrology procedures with the Bureau International de Métrologie Légale (BIML) as the Secretariat and Headquarters of the OIML. Since that time, the OIML has developed a worldwide technical structure whose primary aim is to harmonize the regulations and metrological controls applied by the national metrological services, or related organizations.

Press release WORLD METROLOGY DAY – 20 May 2018

Dr Martin Milton Director of the BIPM

Using the rules of nature to create the rules of measurement

The International System of Units (SI) is the accepted set of units for all applications of measurement worldwide. Since it was first given the name SI nearly 60 years ago, improvements have been agreed to it whenever it has been possible to exploit advances in measurement technologies to address new requirements.

In November 2018, the General Conference on Weights and Measures is expected to agree one of the most significant changes to the SI which will base it on a set of definitions each linked to the laws of physics. This historic change towards using the laws of nature in the definitions will eliminate the final link between the SI and definitions based on physical artefacts. Following the revisions, the kilogram will be linked to the exact value of the Planck constant rather than the International Prototype of the Kilogram, as sanctioned by the 1st CGPM in 1889.

For over 200 years, a collective ambition for the “metric system” has been to provide universality of access to the agreed basis for worldwide measurements. The definitions expected to be agreed in November will be a further step towards this goal. They are based on the results of research into new measurement methods that have used quantum phenomena as the basis for standards that are fundamental. Great attention has been paid to ensure that these new definitions will be compatible with the current ones at the time the change is implemented. The changes will be unnoticeable to all but the most demanding users.

Whilst providing the necessary level of continuity for existing users, the changes have the advantage of being able to embrace future improvements in measurement methods to meet the needs of future users because they are based firmly on the laws of physics. The new definitions will use ‘the rules of nature to create the rules of measurement’ linking measurements at the atomic and quantum scales to those at the macroscopic level.

As science and technology progress, the demands for measurements to underpin new products and services will increase. Metrology is a dynamic branch of science and the steps taken by the BIPM and the wider metrology community to advance the SI in 2018 will underpin these requirements and meet these needs for many years to come.

Message from the BIPM Director

WORLD METROLOGY DAY – 20 May 2018

Competition "Français et Science" 2018

« L’ARBRE EST-IL LE MEILLEUR AMI DE L’HOMME ? »

FRANÇAIS ETSCIENCES CONCOURS

1ER PRIX ENSEIGNANT

UN VOYAGE À PARIS

2018

Vous êtes enseignant de français, de sciences ou de sciences en français ou encore formateur, médiateur, dans une université, un établissement scolaire, un centre culturel, un Institut ou Alliance française, une bibliothèque, un musée ou un centre d’enseignement de la langue française.Nous vous proposons, du 20 mai 2018 au 31 octobre 2018, de participer au Concours Français et Sciences 2018 « Mesures et unités du monde », concours international francophone.

De quoi s’agit-il ? Il s’agit de répondre à la question : Dans l’infi niment grand ou l’infi niment petit, quelle est votre

mesure ou unité préférée ? En rédigeant, en français, une réponse personnelle et créative en deux pages recto-verso maximum (en police de 12) comportant obligatoirement 5 mots choisis par le ou la participant(e) symbolisant à son avis, le domaine des poids mesures et unités du monde ; ces 5 mots qui formeront le « petit lexique du participant(e) » seront indiqués sur le bulletin d’inscription au concours.

Ce texte de deux pages au maximum, doit avoir selon le règlement des qualités littéraires et scientifi ques à la fois. Il peut s’agir d’un article de journal, d’un récit d’expérience, d’une histoire vécue ou inventée, d’un conte, parodie ou fable ou poésie pour les élèves. Pour écrire ce texte, le ou la participant(e) pourra s’appuyer sur ses propres recherches documentaires. Pour motiver les participant(e)s, une aide est proposée ci-dessous, sous forme de bibliographie, et sitographie.

PARTICIPEZ AU CONCOURS FRANÇAIS ET SCIENCES !

Le thème : « Mesures et unités du monde » concerne chacun d’entre nous au quotidien. Organisé cette année avec le Bureau International des Poids et Mesures (BIPM) en raison de la révision

historique du Système international d’unités (SI) attendue en novembre 2018.

MESURES&UNITÉS MONDE

« DANS L’INFINIMENT GRAND OU L’INFINIMENT PETIT, QUELLE EST VOTRE MESURE OU UNITÉ PRÉFÉRÉE ? »

Balance de Kibble du BIPM vers la nouvelle défi nition du kilogramme

Grimm, Le voyage du Petit Poucet par Hermann Stockmann (1867-1938), 1925.

Grimm, Le voyage du Petit Poucet par Hermann Stockmann (1867-1938), 1925.

Grimm, Le voyage du Petit Poucet

Et pour ma classe et mes élèves, ou mon groupe de jeunes ?Ce concours 2018 s’adresse en premier aux « adultes » enseignants qui produisent leur propre écrit. Mais 50% des prix (des livres offerts) seront destinés aux élèves. L’enseignant(e) ou le formateur devra sous sa responsabilité, limiter le nombre d’envois individuels à 5 par classe ou groupe d’appre-nants (article 9 du règlement). A noter que le 1er prix (un voyage à Paris) ne peut concerner les élèves, du fait de leur âge. Ce 1er Prix est destiné au 1er lauréat, adulte et enseignant.

Les organisateurs et les critères du juryLe concours a comme objectif principal : d’associer langue française et science et ainsi promouvoir une double culture, littéraire et scientifi que. L’écrit de 2 pages proposé au jury des partenaires du concours, sera un texte en langue française de bon aloi (minimum requis pour les élèves niveau B1-CECR) qui allie ces doubles qualités pour être primé.Le Jury réunira, en novembre 2018, les partenaires du concours, experts de la culture, de la recherche, de la langue française, des sciences, de la santé, de la Francophonie, de l’international, de l’édition et le BIPM, l’organi-sation intergouvernementale spécialiste des mesures et unités.

Quels sont les prix du concours ? Qui seront les gagnants ?Le concours est doté de 50 prix. Le 1er Prix est un voyage à Paris. Les 49 prix suivants sont des livres offerts par les partenaires du concours. Seul (e) le ou la 1èr(e) lauréat(e) du concours est informé(e) de son 1er Prix. Les 49 autres prix sont adressés par voie postale à l’adresse indiquée dans le bulletin d’inscription obligatoire.

Comment participer ?

La participation se fait uniquement en langue française et par voie numérique entre le 20 mai et le 31 octobre 2018.

Votre proposition individuelle et créative (2 pages au maximum format Pdf, Word ou Open Offi ce, en police 12) doit être adressée avec le bulletin d’inscription dûment complété à l’adresse : mesures.concours-cst2018@sfr.fr

Vous devez lire le règlement et l’accepter en cochant la case du bulletin d’inscription sans oublier d’indiquer vos 5 mots clés. Le règlement est disponible sur simple demande à l’adresse : mesures.concours-cst2018@sfr.fr

Et l’aide de :

Et diffusé avec l’aide de la Fondation Alliance Française, de la mission laïque française (MLF),de l’Agence pour l’enseignement français à l’étranger (AEFE) et les associations d’enseignants AFEF, APBG, APHG et UDPPC.

Sous le Haut patronage de : Avec le soutien de la Délégation Générale à la langue française et aux langues de France

Et le soutien de :

FRANÇAIS ET SCIENCES 2018CONCOURS

Pour vous aider, méthode et documentationPour tout(e) participant(e), il s’agit d’abord de se documenter.

1. BibliographieLes grandes expériences scientifi ques à Paris par Frédéric Borel, éditions ParigrammeLe Bureau des poids et des mesures par Anne Gaëlle Balpe et Vincent Mahé, éditions MilanLe fos et la classe de langue FLE par M.Grandmangin et J.Tolas, éditions CLE International Poids et mesures roman de HM Van den Brink, édition Gallimard.

2. Sitographiewww.bipm.org site du Bureau International des poids et mesures, le site principal à consulter !www.metrologie-francaise.fr/fr/si/unites-mesure.asp : les défi nitions des unités de basewww.fondation-lamap.org propose un grand nombre de ressources pédagogiques https:/fr.wikipedia.org/wiki/unites_de_mesure

MESURES&UNITÉS MONDE

Logo du Système international d’unités (SI)

Je déclare avoir pris connaissance du règlement mis à ma disposition et accepter intégralement celui-ci

5

CINQ MOTS CHOISIS

43

21

Introductiongénérale

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Règlement du concours Mesures et unités du monde - 2018 / �1

LE REGLEMENT

EN 18 ARTICLES

CONCOURS MESURES & UNITÉS DU MONDEFrançais et Sciences 2018 Du 20 mai 2018 au 31 octobre 2018

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Règlement du concours Mesures et unités du monde - 2018 / �2

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Règlement du concours Mesures et unités du monde - 2018 / �3

Partenairesetorganisateursdu

«ConcoursMesuresetunitésdumonde,françaisetsciences2018»

Remerciements

PourleHaut-patronageaccordéparl’OrganisationInternationaledelaFrancophonie(OIF).

PourlaparticipationetlesoutienduBIPMetduLaboratoireNationaldeMétrologieetd’Essais.PourlesoutienapportéparleMinistèredelaCultureetdelaCommunication,laDélégationGénéraleàlalanguefrançaiseetauxlanguesdeFrance.Pourl’aideapportéeparlesInstitutionsetassociationsfrançaisessuivantes:

- l’AssociationCultureSciencesetTerritoires(CST),

- leCentrenationald’étudesspatiales(CNES),

-laFondationAllianceFrançaise,

- laFédérationInternationaledesProfesseursdeFrançais(FIPF),

- laMutuelleGénéraledel’EducationNationale(MGEN),

- laCASDEN,

- l’InstitutFrançais,

- Parigramme,l’éditeurParisien.

Pourl’aideapportéeàladiffusionduconcourspar:

- l’Agencepourl’enseignementfrançaisàl’étranger(AEFE),

- laMissionlaïquefrançaise(mlf),

- lesAssociationsfrançaisesdeprofesseurs:

APBG,associationdesprofesseursdebiologiegéologie,

APHG,associationdesprofesseursd’histoireetgéographie,UDPPC,UniondesphysiciensetdesProfesseursdeChimie,

AFEF,associationfrançaisedesenseignantsdefrançais.

Règlement du concours Mesures et unités du monde - 2018 / �4

Cycle of Conferences on units organised by LNE

Exhibit "Sur mesure, les sept unités du monde"at the museum Arts et Métiers (Paris)

Surmesureexposition Musée des Arts et Métiers

60 rue Réaumur, Paris 3e

www.arts-et-metiers.net

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Communiqué de presse5 juillet 2018

Un parcours dans la collection permanente complète l’exposition temporaire. Il met un coup de projecteur sur une sélection d’objets dont le rôle a souvent été décisif dans l’histoire de la mesure. On y retrouve le mètre et le kilogramme du Conservatoire, une horloge d’espacement des trains ou encore le télescope spatial Sigma.

Les 7 unités de base du Système international Le mètre • longueur Le kilogramme • masse L’ampère • intensité du courant électrique La seconde • temps Le kelvin • température La mole • quantité de matière La candela • intensité lumineuse

L’omniprésence de la mesure Destinée à un large public, l’exposition révèle aux visiteurs l’omniprésence de la mesure dans notre quotidien et son rôle d’aide à la décision : le temps qui passe, la vitesse de notre voiture, notre poids, le « la » en musique, les gigaoctets de nos ordinateurs… Sans la mesure, l’humain n’aurait pas de repère. Elle fait partie intégrante de notre société, tellement évidente et inévitable qu’elle se fait oublier. La mesure est néanmoins essentielle et indispensable à l’humanité pour échanger et innover en toute confiance.

Le parcours de l’expositionDéclinée en cinq thèmes, l’exposition est une expérience à vivre. En guise d’introduction, le visiteur est invité à réfléchir sur les objets de mesure qui l’entourent dans son quotidien (réveil, compteurs). Si le corps humain peut être mesuré à l’image du célèbre Homme de Vitruve de Léonard de Vinci, les activités humaines peuvent l’être aussi : pendule de pointage, dactymètre qui mesure la frappe des dactylos, « détecteur de mensonges ».

Musée des Arts et Métiers 60 rue Réaumur - Paris 3e

www.arts-et-metiers.net

Horaires d’ouvertureDu mardi au dimanche inclus,de 10h à 18h.Nocturne le jeudi jusqu’à 21h30

Contacts presse :Heymann Renoult AssociéesSarah HeymannAlexandra Corsi Chopin 01 44 61 76 76 a.corsichopin@heymann-renoult.com

Musée des Arts et MétiersAmélie Zanetti 01 53 01 82 77amelie.zanetti@lecnam.net

LNEAlexandre Papin 01 40 43 38 92alexandre.papin@lne.fr

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qui donne la mesure au musée des Arts et Métiers

Aujourd’hui, 7 unités universelles et fondamentales permettent de quantifier notre monde. L’exposition Sur mesure, les 7 unités du monde présentée au musée des Arts et Métiers, du 16 octobre 2018 au 5 mai 2019, explore le thème de la mesure sous toutes ses coutures. De tout temps, l’homme a cherché à mesurer ou à se mesurer. Horloge, balance, sablier, sextant, gyroscope, thermomètre… Les instruments anciens et contemporains, en passant par ceux du quotidien, en sont les témoins.

Construite en partenariat avec le Laboratoire national de métrologie et d’essais (LNE), cette exposition fait écho à un événement majeur qui aura lieu à l’automne 2018 : la redéfinition de quatre des sept unités de base, le kilogramme, l’ampère, le kelvin et la mole. Ces nouvelles définitions poursuivent l’ambition d’universalité et de dématérialisation au cœur de la création du Système international d’unités.

La profusion d’instruments présentés illustre la complexité de l’acte de mesurer : thermomètre, altimètre ou encore smartphone géant détaillant les capteurs qui le composent. La mesure fait aussi appel à notre imaginaire par la charge symbolique qu’elle a pu revêtir dans l’histoire : la pesée des âmes dans l’Égypte des pharaons, le nombre d’or à la Renaissance.

Au cœur de l’exposition, le visiteur découvre les 7 unités de base du Système international sur lesquelles reposent toutes les mesures de notre univers. Cet espace agrémenté de bornes sonores invite à « rencontrer » un ingénieur, un chercheur ou un professeur qui explique pourquoi et comment sont définies chacune de ces unités. Un cabinet de curiosité présente quelques unités disparues, certaines au nom évocateur tels les chevaux-vapeur.

Mesurer c’est aussi appréhender des notions de sensibilité, d’incertitude, de fidélité, d’exactitude, de précision, d’erreur… Pour cela, il faut toute une chaîne de contrôle pour garantir la validité des mesures et instruments utilisés.

La dernière partie aborde le rôle vital de la métrologie, la science de la mesure, dans les différents secteurs d’activité (industrie, recherche...). Des appareils relatifs à la santé et au bien-être permettent de donner quelques clés pour comprendre comment les valeurs sont mesurées et les informations traitées. Enfin, les visiteurs sont invités à aller au-delà des mesures physiques pour découvrir les multiples usages de la mesure, plus subjectifs, dans la vie en société : mesure d’opinion, de comportement, statistiques…

Commissaire de l’exposition : Bruno Jacomy, ingénieur, historien des techniques et conservateur enchef du patrimoine.

L’exposition temporaire et le parcours dans la collection permanente sont présentés en français et en anglais.

Autour de l’exposition

Exposition temporaire• des visites guidées quotidiennes à 15 h 30 ;• des ateliers pour les enfants de 7 à 12 ans et des ateliers en famille ;• un livret d’aide à la visite pour les 7-12 ans ;• un catalogue imprimé, français/anglais ;• des ateliers (CE2 au CM2) et visites (collèges, lycées et +) pour le public scolaire ;• des ateliers périscolaires (7 à 12 ans) ;• des visites à l’intention des professeurs ;• un dossier de l’enseignant (niveaux collège et lycée).

Collection permanente• un livret d’aide à visite ;• des visites sur le thème de la mesure ;• une enquête-jeu pour les enfants de 7 à 12 ans et leurs parents ;• des ateliers (à partir du CE2) et visites (à partir du CM2) pour le public scolaire.

Une programmation musicale • Jeudis 8 novembre 2018, 10 janvier, 14 mars et 16 mai 2019 à 20 h :saison de concerts donnée par l’ensemble Quadrivium ;• Mardi 30 avril 2019 à 20 h : Concert impromptudont le Poème symphonique pour 100 métronomes de György Ligeti.