Git for Metrology: A Versioned Approach to Fundamental Physical Constants

 # Git for Metrology: A Versioned Approach to Fundamental Physical Constants

**Author:**  J. Rogers

**Date:**  11 Apr 2025 1837  

**License:** CC BY-SA 4.0

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## Abstract

We propose a radical shift in how fundamental physical constants (e.g., the fine-structure constant α, elementary charge e, Planck constant h) are defined and distributed. Instead of enforcing a single, centralized value (e.g., CODATA’s periodic updates), we advocate for a versioned, Git-like repository of constants, where:

- Every measured value is preserved (including historical data).

- Users select which "branch" or "tag" to use (e.g., 2023/g-2 vs. 2018/CODATA).

- Derived constants auto-update when switching versions.

This system enables reproducible science, transparent uncertainty tracking, and user-defined precision standards.

---

## 1. The Problem with Current Metrology

### 1.1 Static Constants Are Obsolete

- CODATA updates constants every ~4 years, discarding older measurements.

- Forces global redefinition (e.g., 2019 SI overhaul).

- No way to compare competing experimental methods.

### 1.2 One-Size-Fits-All Doesn’t Work

- A quantum physicist may need 12-digit α from g-2 experiments.

- An engineer may prefer 6-digit α for circuit design.

- A historian may want Bohr’s 1913 value for replication.

### 1.3 Lost Knowledge

- Pre-2019 SI defined μ₀ ≡ 4π×10⁻⁷ (exact), but this hid α’s true precision.

- Older values (e.g., 1947 α) are not easily accessible.

---

## 2. The Versioned Constants System

### 2.1 Core Principles

**Git-Like Repository**

Every constant has:

- Branches (experimental methods: g-2, lattice-QCD, hydrogen-spectra).

- Tags (releases: CODATA-2018, SI-2019, BIPM-2023).

- Commits (individual measurements).

**Dynamic Derivation**

- Changing α updates all dependent constants (e, μ₀, etc.).

**User Choice**

Select constants by:

```python

from metrology import constants

constants.use("2023/g-2")       # Latest Penning trap α

constants.use("legacy/SI-1983") # Pre-quantum values

```

---

### 2.2 Example Repository Structure

```

/fundamental_constants  

├── /alpha  

│   ├── g-2/  

│   │   ├── 2023.json  (α = 0.0072973525693 ± 1.1e-11)  

│   │   └── 2021.json  (α = 0.0072973525691 ± 2.3e-11)  

│   └── hydrogen/  

│       ├── 2022.json  (α = 0.0072973525698 ± 9e-12)  

│       └── 1980.json  (α = 0.007297352568 ± 1.2e-9)  

└── /e  

    ├── derived/       # Auto-computed from α  

    └── measured/      # Direct experiments (Millikan, etc.)

```

---

### 2.3 Benefits

- **Reproducibility**: Pin constants like software dependencies.

- **Transparency**: Full history of how α changed over time.

- **Flexibility**: Choose precision levels per application.

---

## 3. Implementation

### 3.1 The Reference Database

A public Git repo (e.g., GitHub) storing:

- Raw experimental data

- Uncertainty calculations

- Derivation graphs (e.g., how e depends on α)

---

### 3.2 The API

```python

import metrology

# Switch to 2023’s best α (g-2 measurement)  

metrology.use("alpha/2023/g-2")  

# Get derived elementary charge  

e = metrology.get("e")  # Computed from latest α  

# Compare with 2018 CODATA  

metrology.use("alpha/2018/CODATA")  

e_old = metrology.get("e")  

print(f"Δe = {e - e_old:.3e}")  # Difference due to α-update

```

---

### 3.3 Integration with Tools

- **Symbolic math**: SymPy plugins for versioned constants.

- **Lab equipment**: Firmware that pulls constants by tag.

- **Education**: Interactive Jupyter notebooks showing α’s evolution.

---

## 4. Challenges

### 4.1 Resistance from Standards Bodies

- CODATA/BIPM may oppose decentralizing "their" constants.

- **Solution**: Fork their data and prove utility via adoption.

### 4.2 Theoretical Consistency

- Does QED allow α to vary across versions?

- **Answer**: No—but measurements do. This system tracks empirical uncertainty, not theory.

### 4.3 Legacy Code

- Old software assumes fixed constants.

- **Solution**: A compatibility layer with "default" values.

---

## 5. Call to Action

We call for:

- A community-run constants repository (Git + CI/CD for validation).

- Adoption by major physics engines (SciPy, ROOT, Wolfram).

- New publication standards requiring constant-version citations.

---

## Conclusion

The era of static constants is over. Let’s build a system that:

- Preserves history  

- Empowers users  

- Makes metrology agile  

---

**Repository:**  

`git clone https://github.com/fundamental-constants/alpha.git`  

**Try it:**  

`pip install metrology-versioned`

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## Appendices

### A1: Comparison to Software Versioning

- Git: Version control for constants.

- SemVer-style tags: e.g., alpha@2023.1.0

### A2: Example Use Cases

- **Quantum**: Tracking precision shifts in α across g-2 updates.

- **Cosmology**: Compare constants over redshift-calibrated epochs.

- **Engineering**: Select stable values with safe error bounds.

### A3: Governance Model

- Open-source maintainers.

- CI/CD verification of derived constants.

- Public peer review for new commits.

---

## References

- CODATA 2018  

- NIST SI Redefinition 2019  

- Git: https://git-scm.com  

- g-2 Collaboration (2023), Phys. Rev. Lett.

---

**Footnote**  

This paper is itself versioned. Pull requests welcome at:  

[Git for Metrology: A Versioned Approach to Fundamental Physical Constants](https://github.com/BuckRogers1965/Physics-Unit-Coordinate-System/blob/main/docs/Git_for_Metrology.md)