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Fundamental Physical Constants

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Mission and objectives 

The purpose of the CODATA Task Group on Fundamental Physical Constants (TGFC) is to periodically provide the scientific and technological communities with a self-consistent set of internationally recommended values of the basic constants and conversion factors of physics and chemistry based on all relevant data available at a given point in time.

Significance

The TGFC’s commitment to producing a new least squares adjustment (LSA) of the fundamental constants on a four-year cycle incorporates all relevant data from diverse scientific interests and fields of research.   This function primarily provides the scientific and metrological communities the most consistent set of the values of the fundamental constants and conversion factors used in physics and chemistry.  Moreover, performing an analysis over a broad spectrum of experimental and theoretical information relevant to the constants has important value.  In general, such an analysis may uncover errors in theoretical calculations or experiments; it reevaluates uncertainties so that all are expressed in a consistent manner (i.e. standard uncertainties); it identifies inconsistencies among results and weaknesses in certain areas of research; it stimulates new experimental and theoretical work due to inconsistencies; and it summarizes a large amount of rather diverse information in one place. These values contribute to the high profile of the TGFC’s LSA and the TGFC’s continued reputation as the authoritative source for the best determination of the fundamental constants.  The review articles of each LSA are very highly cited and contribute significantly to CODATA’s international reputation.

Task Group websites

Impact

The next regular CODATA-TGFC four-year cycle adjustment of the fundamental constants will be the 2026 adjustment with a closing date of 31 December, 2026. Relevant data will be collected and reviewed for possible impact on the determination of the values of the fundamental constants. The results of the 2026 CODATA-TGFC adjustment will be made available early 2027 with the accepted input data and analysis to be published in a review article.
The last regular CODATA-TGFC four-year cycle adjustment of the fundamental constants was the 2022 adjustment.

Planned (and later on actual) activities and outputs for 2025-2027

  • The 2025 CODATA-TGFC meeting was held 4-5 September 2025 as a hybrid meeting at the the University of Warsaw, Poland with virtual attendance as an option. In-dept discussions and presentations were given on the status of the theory and experiments of molecular hydrogen ions and an update on efforts to measure the gravitational constant, including a new result.
  • The 2026 CODATA-TGFC meeting will be held at the BIPM September 2026. The meeting will focus on preparing for the upcoming 2026 adjustment of the fundamental constants with a closing date of 31 December 2026. Special scientific sessions will be held with invited experts in the fields of hydrogen and deuterium energy levels, muonium energy levels and hyperfine structure, charge radii of light nuclei, electron and nuclear magnetic moments from spectroscopy of hydrogenic ions, electron and muon magnetic moment anomalies, HD+ spectroscopic measurements, atomic masses of light nuclei, and measurements on the gravitational constant G.
  • The first preliminary results of 2026 CODATA adjustment of the fundamental constants will be discussed at the 2027 CODATA-TGFC meeting, including relevance of data, tension and inconsistencies among the data and the possible need to expand uncertainties.

Past Achievements 

The 2023 TGFC meeting was hosted by the BIPM in a hybrid form 12 – 13 September 2023. Preliminary results of the 2022 CODATA-TGFC adjustment of the fundamental constants were discussed at length, focusing on the publication, possible help from TGFC members of specific sections, and the posting of the results. The 2022 TGFC meeting minutes were accepted and are posted on the BIPM website: https://www.bipm.org/en/hosting/codata-tgfc

The results of the 2022 CODATA-TGFC adjustment of the fundamental constants were made available in 2024 at https://pml.nist.gov/cuu/Constants/ with the accepted input data and analysis published: https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958143

The 2024 CODATA-TGFC meeting was held 10-11 September 2024 as a hybrid meeting at the BIPM, Paris with virtual attendance as an option. Discussions focused on newly available results with scientific presentations on the review of the 2022 adjustment, an update on molecular spectroscopy, precision Rydberg spectroscopy on simple atoms, and nuclear radii of simple atoms.

Contacts

  • Chair: Prof. Krzysztof Pachucki , Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, POLAND
  • Co-Chair: Dr Eite Tiesinga, NIST, Bldg. 220, Rm. B342, 100 Bureau Drive, Stop 8423, Gaithersburg, MD 20899, USA

TGFC Membership

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