Support us | Visit us | Contact us
Sr+ ion optical clock chamber, courtesy of NPL.
Organised by Dr Terry Quinn CBE FRS, Professor Ian Mills FRS and Professor Patrick Gill
From the origins of the metric system, when the metre was a fraction of the arc of the Paris meridian and the kilogram the weight of a cubic decimetre of water, the ultimate goal has been a system of measurement based on invariant quantities of nature. After more than 200 years we are now within reach of achieving this. While the kilogram is still defined as the mass of a Pt-Ir cylinder kept in a vault in Sèvres, serious plans now exist to redefine the kilogram by fixing the numerical value of the Planck constant h; and the ampere, kelvin and mole by fixed numerical values for e, k and NA. With the metre already being defined by the speed of light and the second by an atomic microwave transition, but likely soon to be redefined by an optical transition of much higher frequency, we shall have at last achieved what the savants of the 18th century had sought. The Discussion Meeting will review the relation of the International System of Units to the fundamental constants of physics and progress towards the redefinitions.
The biographies and audio files are available below.
The proceedings of this meeting are scheduled to be published in a future issue of Philosophical Transactions A.
Dr Terry Quinn CBE FRS Adapting the International System of Units to the 21st century (with Professor Ian Mills FRS)
Terry Quinn is Emeritus Director of the International Bureau of Weights and Measures (BIPM) at Sèvres in France where he was Director from 1988 until 2003. He received a B.Sc. in physics at the University of Southampton in 1959 and D.Phil. from the University of Oxford in 1963. He was at the National Physical Laboratory until 1977 working in temperature and absolute radiometry, developing the cryogenic radiometer with his colleague J. E. Martin. At the BIPM he took up experimental work in mass metrology, studying flexure and torsion strips for balances and gravitational measurements. On becoming Director he was much involved in international metrology, notably the organization of a Mutual Recognition Arrangement for national standards signed in 1999. Since retiring from BIPM he has continued his interest in metrology but also in history of science as editor from 2004 until 2007 of the Society’s journal for the history of science Notes and Records of the Royal Society.
Professor Ian Mills FRSAdapting the International System of Units to the 21st century (with Dr Terry Quinn CBE FRS)
Ian Mills is an emeritus professor of Molecular Spectroscopy in the School of Chemistry at the University of Reading. After graduating with a D.Phil. in high resolution infrared spectroscopy from St. John’s College, Oxford, in 1954, followed by research fellowship positions at the University of Minnesota and in Theoretical Chemistry at the University of Cambridge, he was appointed to a Lectureship in Chemistry at the University of Reading in 1957. He was promoted to a Readership in 1964, and to a Personal Professorship in 1966, from which he retired in 1995. He has about 180 publications in various aspects of high resolution spectroscopy and the application of quantum mechanics to the analysis of molecular spectra, and he was elected to Fellowship of the Royal Society in 1996. He has held a variety of positions in the Faraday Division of the Royal Society of Chemistry, and in IUPAC, and at the BIPM, related to his interests and publications in the language of science. Since 1995 he has been President of the Consultative Committee on Units at the BIPM.
Professor Patrick Gill When should we change the definition of the second?
Patrick Gill is a Senior NPL Fellow at the National Physical Laboratory in Teddington, Middlesex. He received his D.Phil in 1976 from the University of Oxford for gas laser research at the Clarendon Laboratory, and then joined the National Physical Laboratory, developing iodine-stabilised lasers for length metrology. He started research into laser-cooled single trapped ion optical frequency standards during the 1980s. He was appointed an NPL Individual Merit scientist in 1992, and subsequently a Senior NPL Fellow in 1997. Currently, he leads the optical frequency standards research activities at NPL, with interests in optical clocks for redefinition of the second, applications to fundamental physics and clock technology for future aerospace applications. He has published over 100 papers in peer-reviewed journals. He is a visiting professor in physics at the University of Oxford and Imperial College London.
Stephen Cox CVO, Executive Director, Royal SocietyWelcome
David Willetts MP, Minister for Universities and ScienceIntroduction
Dr Peter Becker The Avogadro constant: counting atoms in a single-crystal 28Si sphere
P. Becker, born in 1945, studied Physics from 1966 – 1971 at the University of Münster with focus on solid state physics, mathematics, and geophysics. He received his Ph.D. degree from University of Dortmund in 1974 (Professor Dr. U. Bonse), and was assistant lecturer at in Dortmund from 1971 to 1974. He joined the Physikalisch-Technische Bundesanstalt (PTB) in 1974 and was head of the section for x-ray metrology from 1978 until 2004. Since 1995 he is Chair of the CCM Working Group on the Avogadro Constant (WGAC) and since 2003 also coordinator of the international Avogadro project within the CCM dealing with the re-determination of the Avogadro constant with the aim to re-define the unit of mass, the kilogram. In 2004 he became head of the department „Quantum metrology and length unit“ at PTB. His research interests are: x-ray optics, silicon micro-machining, and determination of fundamental physical constants.
Dr Michael Stock The watt balance: determination of the Planck constant and redefinition of the kilogram
Michael Stock is a physicist at the International Bureau of Weights and Measures (BIPM) in Sèvres, close to Paris, where he leads the Electricity Department and the watt balance project. He received the diploma in physics from the University of Osnabrück (Germany) in 1989 and the Ph.D. degree from the Technical University of Berlin in 1995. His professional career started in 1990 at the Physikalisch-Technische Bundesanstalt (PTB), Berlin, where he carried out a comparison of three radiometric primary standards. In 1996, he joined the BIPM, working on research and development related to the realization of radiometric and photometric quantities. From 2001 to 2003 he was Head of the Radiometry Section and since 2004 he is responsible for the calculable capacitor and the watt balance projects. In July 2007 he became Head of the Electricity Section. He also serves as the Executive Secretary of the Consultative Committees for Radiometry and Photometry (CCPR) and for Electricity and Magnetism (CCEM), which bring together the world's experts in their specified fields as advisers on scientific and technical matters.
Professor Klaus von Klitzing ForMemRSQuantum Hall Effect and Metrology
Since 1985 Klaus von Klitzing is director at the Max Planck Institute for Solid State Research and honorary Professor at the University of Stuttgart, Germany. He received his PhD from the University of Würzburg in 1972 and became a Professor at the Technical University Munich in 1980. Klaus von Klitzing was awarded the Nobel Prize in Physics in 1985 for the discovery of the Quantum Hall Effect which plays a major role in metrology, not only as a resistance standard but also in connection with the discussion of a new SI system based on fundamental constants. His present research activities concentrate on quantum transport in low dimensional electronic systems with a focus on correlation phenomena in nano-devices.
Dr Richard Davis The role of the international prototype of the kilogram after the redefinition of the SI units
Richard Davis is Director of the Mass Department at the International Bureau of Weights and Measures (BIPM), a position he will hold until November 2010. Located in Sèvres, France, the BIPM conserves and makes use of the Pt-Ir cylinder whose mass has defined the kilogram for well over a century. Richard Davis began his career in physics as a Post-Doc at the National Institute of Standards and Technology (NIST, USA). He eventually stayed on at NIST for 18 years, until moving to the BIPM in 1990. His research interests are largely related to mass metrology and the intersections between mass measurements and the constants of physics. He has contributed to accurate experimental determinations of the Faraday and Boltzmann constants. He is a Fellow of the American Physical Society.
Professor Christian Bordé Quantum theory of microscopic and macroscopic mass
Christian J. Bordé, born in 1943, is a French physicist, Director of research emeritus at CNRS. He founded the Laboratoire de Physique des Lasers (LPL) at the University Paris-Nord in 1972. He has invented new methods for ultra-high resolution laser spectroscopy, especially saturation spectroscopy, and applied them extensively to probe the internal dynamics and fundamental symmetries in molecules. In collaboration with J. Hall at JILA, he gave the first quantitative demonstration of the momentum exchange between laser light and molecules. He exploited this atomic recoil to conceive atom interferometers, widely used as optical clocks, gravito-inertial sensors and for the determination of atomic masses. His present research is on a new optical determination of the Boltzmann constant at LPL and on the theory of atom interferometers at SYRTE (Paris Observatory). He is member of the French Academy of Sciences, of the French Academy of Technologies and of the European Academy of Sciences. He is also chairman, with Jean Kovalevsky, of the Committee “Science and Metrology” of the Academy of Sciences and chairman of the CGPM since 1999. For further details please see www.christian.j.borde.free.fr
Dr Martin MiltonA new definition for the mole based on the Avogadro constant: a journey from physics to
Dr Martin Milton is a Fellow of the National Physical Laboratory. He has a degree in physics from Oxford University and a PhD in laser physics from Southampton University. His research concerns the development of accurate standards and measurement methods for gases and their standardisation internationally. He has published research on high-accuracy mass spectrometry, spectroscopic methods for the detection of single molecules and infrared sources for atmospheric spectroscopy. He is Chair of the CCQM Working Group on Gas Analysis, which oversees the comparability of gas measurements between National Measurement Institutes worldwide. He is also Chair of the CCQM Working Group on the “Re-definition of the Mole” and has published proposals for the re-definition of the mole with Professor Ian Mills.
Dr Adrian Bristow SI and non-SI units for biological quantities
After completing PhD studies in molecular enzymology at Newcastle University, and Post-doctoral research studies on molecular Endocrinology of the hypothalamo-pituitary-adrenal axis at the University of Sussex, Adrian Bristow joined the National Institute for Biological Standards and Control in 1979. Since that time he has worked in the Division of Endocrinology as a senior scientist until 1994, as the Head of Division until 2004, and most recently as the Head of the Technology Development and Infrastructure group. His research interests focus principally on characterization of the biological and physico-chemical properties of biological and biotechnological medicinal substances, and on principles of Biological Standardisation.
In addition to his work at NIBSC, Dr Bristow has been a member of the biologicals expert groups of both the European and British Pharmacopoeias for over 20 years, and is also a member of the steering committee of the EDQM Biological Standardisation Programme. He also attends regularly the WHO Expert Committee on Biological Standardisation, and has a central scientific role in developing and coordinating the NIBSC/WHO Biological Reference Material Program.
Dr Laurent Pitre The Boltzmann constant from the speed of sound in a not quite spherical cavity
Laurent Pitre is a Researcher at the French Metrology Organization LNE-CNAM since 2000. He holds a Phd in Low Temperature Thermometry - below 1 Kelvin (1999), and has started his career with the European project “Ultra Low Temperature”. He has worked for 2 years at the National Institute of Standards and Technology (NIST), Washington D.C. as a Guest Researcher, where he has started to conceive and develop a quasi spherical resonator applied for low temperature thermometry (2003-2005). Since his return to France, he has continued the development and the fine-tuning of the quasi spherical resonator. Today he leads a team, which uses this resonator for the re-determination of the Boltzmann constant and the thermometry in the range of 4K to 300K.
Dr Nigel Fox Accurate radiometry from space: an essential tool for climate studies
Nigel Fox is head of Earth Observation and a Fellow of NPL, which he joined in 1981 after obtaining a BSc in Astronomy and Physics from University College London. Since that time he has been engaged in the establishment and dissemination of primary optical radiation measurement scales spanning the optical range from UV to IR. The instrumentation and methodologies resulting from his developments (parts resulting in the award of a Phd) and technical leadership have led to nearly two orders of magnitude reduction in uncertainty in many of these scales and have been adopted worldwide throughout the metrological community. The latter half of his career has sought to extend and adapt these advances to address the specific needs of the Earth Observation and associated climate change community. He serves on various international committees including the chairmanship of the Infrared, Visible and Optical Sensors ((IVOS) sub-group of the Committee on Earth Observations Satellites (CEOS) and is leading international efforts to improve/establish SI traceability to this sector, both space and ground, often to meet uncertainty requirements comparable to primary realisations of the quantities in the lab. To meet this challenge he is currently leading an international team in a proposal to establish a “standards laboratory in space”.
Dr François Nez Spectroscopy of muonic hydrogen: determining the proton charge radius
François Nez received the PhD degree in Physics from the Pierre and Marie Curie University, Paris 6, Paris, France, in 1993. During his PhD he has realized the first pure frequency measurement of optical transition in atomic hydrogen. After a post doc, at LNE-Syrte in Paris observatory, he gets an associate researcher position at CNRS in the group of François Biraben, in laboratoire Kastler Brossel. His current research activities are in high resolution spectroscopy, cold atoms and fundamental constants measurements. Since 1998, François Nez is also a member of the Codata task group on fundamental constants.
Dr William D. Phillips Ultracold atoms and precise time standards (with Dr Gretchen Campbell)
William D. Phillips is a Fellow of the Joint Quantum Institute, a cooperative research organization of the National Institute of Standards and Technology and the University of Maryland that is devoted to the study of quantum coherent phenomena. At NIST he leads the Laser Cooling and Trapping Group in the Atomic Physics Division. At the JQI he is the co-director of an NSF-funded Physics Frontier Center focusing on quantum phenomena that span different subfields of physics. The Laser Cooling and Trapping Group at NIST has developed some of the main techniques now used for laser-cooled atomic frequency standards and for laser-cooling and cold-atom experiments generally. In 1997, Dr. Phillips shared the Nobel Prize in Physics "for development of methods to cool and trap atoms with laser light."
Dr Gretchen CampbellUltracold atoms and precise time standards (with Dr Bill Phillips )
In 2006 I received my Ph.D from MIT, where I worked with Wolfgang Ketterle and Dave Pritchard and used rubidium Bose-Einstein condensates in optical lattices to study atom interferometry, nonlinear atom optics and the superfluid – Mott Insulator phase transition. These experiments included the first direct observation of the atomic recoil momentum in dispersive media. More recently, I worked with Jun Ye on precision measurements and frequency metrology with an 87 strontium optical lattice clock. In the fall of 2009, I joined the Joint Quantum Institute and the Laser cooling and trapping group at NIST.
Dr John Hall Learning from: length, time and the redefined SI metre
At JILA and NIST in Boulder, Dr John L. Hall has pioneered the use of stabilized lasers to accomplish measurements of unprecedented accuracy and intrinsic physical interest. He introduced the HeNe/methane-stabilized laser and, with his NBS team, used it to measure accurately the speed of light, leading to a re-definition of the SI Meter. His group has stabilized various tunable lasers (including cost-effective diode lasers) to Hz, even sub-Hz linewidths. He showed how noise of even multi-km lengths of fiber could be actively suppressed to deliver phase-stable light at a remote site. His group pioneered the “Optical Comb” techniques which allow simple and direct measurement of optical frequencies. He has received more than 20 professional Awards, has more than 235 refereed publications, and holds 11 US patents. In 2004 he entered the Légion d'Honneur of France. In 2005 he was awarded the Nobel Prize in Physics, jointly with Prof. Hänsch of Munich and Prof. Glauber of Harvard.
Dr Bernard Guinot Metrology of time in the context of general relativity
B. Guinot, now retired, was Astronomer of the Observatoire de Paris. He devoted mainly his career to the definition and realization of reference systems in space and time for astronomy and geodesy, and to the parameters that link these systems, which include the Universal Time UT1. In the domain of time, as Director of the Bureau International de l’Heure (BIH) (1964-1988), he created the International Atomic Time TAI, official basis of all realized time scales. He participated to the creation and evolution of the version of TAI called Coordinated Universal Time (UTC). He is presently trying to simplify the concepts in these domains, which inherited many difficulties from history and tradition. He is Correspondant of the French Academy of Sciences and Member of the Bureau des Longitudes. Among several international past functions, one can mention the membership to the International Committee on Weights and Mesures.
Final Discussion and OverviewDr Terry Quinn CBE FRS
Public lecture 5 Dec
Conference 11 Dec
Enter your email address to receive updates about scientific meetings at the Royal Society
Full listing of our events and exhibitions.
Watch videos of past events.
Most of our talks are free and open to the public.
We host major conferences for leading scientists.
Explore our annual science exhibition
Contact the events team.