CODATA Recommended Values of the Fundamental Physical Constants: 2018

Area of Science:

• Physics and Chemistry
• Metrology
• Fundamental Constants

Background:

• Accurate physical and chemical constants are crucial for scientific advancement and technological development.
• The Committee on Data of the International Science Council periodically updates recommended values based on new experimental and theoretical data.
• The transition to the revised International System of Units (SI) has significant implications for the definition and values of fundamental constants.

Purpose of the Study:

• To report the 2018 self-consistent recommended values for physical and chemical constants and conversion factors.
• To discuss major improvements and remaining inconsistencies in the data.
• To highlight the impact of the revised SI on the values and uncertainties of fundamental constants.

Main Methods:

• A least-squares adjustment of all available theoretical and experimental data up to December 31, 2018.
• Incorporation of the revised International System of Units (SI) with exact values for the Planck constant, elementary charge, Boltzmann constant, and Avogadro constant.
• Analysis of uncertainties and identification of inconsistencies in the adjusted values.

Main Results:

• Reduced uncertainty in the dimensionless fine-structure constant.
• Significant improvement (nearly two orders of magnitude) in the accuracy of particle masses in kilograms.
• Many constants are now exact or have substantially reduced uncertainties due to the revised SI.
• Persistent inconsistencies noted for the gravitational constant and the muon magnetic-moment anomaly.
• Partial resolution of the proton charge radius puzzle through improved hydrogen energy level measurements.

Conclusions:

• The 2018 adjustment provides a highly accurate and self-consistent set of physical and chemical constants.
• The revised SI has fundamentally improved the metrological framework, leading to more precise constant values.
• Ongoing research is necessary to address remaining inconsistencies and further refine fundamental constant values.