[Paper Review] A critical review of the CCU 2016 Draft of the Brochure for the New SI definition using (fundamental) constants

Franco Pavese|arXiv (Cornell University)|Dec 30, 2015

Scientific Measurement and Uncertainty Evaluation2 citations

TL;DR

This paper critically evaluates the CCU 2016 Draft of the BIPM's 9th SI Brochure, analyzing how the use of fundamental constants in defining the SI base units introduces conceptual and practical challenges. It highlights inconsistencies in the interpretation of constants, unresolved issues in fixing their numerical values, and difficulties in conveying the new SI structure clearly—even to informed users—emphasizing the urgency of resolving these foundational issues before final adoption.

ABSTRACT

This v.3, in addition to: (a) discussion of the role of constants (called fundamental until 2015) in the proposed New SI formulation of the definition of the International System of Units, namely in the present official documents and in some relevant literature. The meaning assigned to the use of constants is found substantially different even among the advocates of the proposal; (b) focusing on how the stipulation of their numerical values is obtained, according to the specific features of measurement units, arising some special problems, not all cleared yet, that the stipulation of a fundamental constant can place when it becomes part of the definition of the New SI and of a base unit of it. Some reasons are discussed why it is urgent that these basic issues are clarified; (c)in the Appendix, a specific critical review is now added of the text of Sections 1 and 2 of the CCU 2016 Draft, the last implementation of the New SI for the 9th Brochure on the SI, published on the BIPM website on January 4, 2016, and now under examination by the SI top stakeholders. Though this draft is advanced with respect to the CCU 2013 Draft, it is shown how the description of the complex structure of the new definition may still be difficult to be clearly caught even by informed readers, while most users might be lost about their tasks needed to implement the new definition.

Motivation & Objective

• To examine the role and interpretation of fundamental constants in the proposed New SI formulation, especially as presented in official documents and literature.
• To identify and analyze unresolved problems arising from fixing the numerical values of fundamental constants within the definition of base units.
• To assess the clarity and comprehensibility of the CCU 2016 Draft’s description of the New SI structure for both experts and general users.
• To emphasize the urgency of resolving conceptual and technical ambiguities in the New SI framework before final implementation.

Proposed method

• Conduct a comparative analysis of the CCU 2016 Draft with the earlier CCU 2013 Draft to identify improvements and persistent issues.
• Examine the role of constants in unit definitions, focusing on how their numerical values are stipulated and the implications for measurement science.
• Evaluate the coherence and clarity of the New SI structure as described in Sections 1 and 2 of the CCU 2016 Draft using a critical review approach.
• Analyze discrepancies in the interpretation of constants among proponents of the New SI, highlighting conceptual inconsistencies.
• Use the Appendix to provide a detailed textual critique of the draft’s language and structure, especially regarding the interdependence of constants and units.
• Highlight systemic problems in the transition from measured to defined constants, particularly regarding metrological traceability and operational implementation.

Experimental results

Research questions

• RQ1 How do different stakeholders interpret the role of fundamental constants in the New SI, and what inconsistencies emerge from these interpretations?
• RQ2 What technical and conceptual problems arise when fixing the numerical values of fundamental constants as part of unit definitions?
• RQ3 To what extent is the CCU 2016 Draft’s description of the New SI structure clear and implementable for users, including experts and practitioners?
• RQ4 Why are unresolved issues in the definition of constants still problematic despite progress from the 2013 to 2016 draft?
• RQ5 What are the implications of unclear or ambiguous definitions for the traceability and reliability of measurements in the New SI?

Key findings

• The interpretation of fundamental constants in the New SI varies significantly even among supporters, indicating a lack of consensus on their conceptual role.
• Fixing the numerical values of constants introduces unresolved metrological challenges, particularly regarding the distinction between measured and defined values.
• Despite improvements over the 2013 draft, the CCU 2016 Draft still fails to clearly convey the complex interdependence of constants and units, especially to non-specialist users.
• The draft’s description of the New SI structure remains difficult to grasp even for informed readers, suggesting a need for clearer formulation.
• The current formulation risks confusion in implementation due to ambiguous language and insufficient transparency in how constants are integrated into unit definitions.
• The paper concludes that urgent clarification is needed on foundational issues to ensure the stability and coherence of the New SI framework.