Recent measurements of the gravitational constant as a function of time (1505.01774v2)

Abstract: A recent publication (J.D. Anderson et. al., EPL 110, 1002) presented a strong correlation between the measured values of the gravitational constant $G$ and the 5.9-year oscillation of the length of day. Here, we provide a compilation of all published measurements of $G$ taken over the last 35 years. A least squares regression to a sine with a period of 5.9 years still yields a better fit than a straight line. However, our additions and corrections to the G data reported by Anderson {\it et al.} significantly weaken the correlation.

Recent Measurements of the Gravitational Constant as a Function of Time

The paper by Schlamminger, Gundlach, and Newman presents an examination of the gravitational constant (G) based on measurements accumulated over the last 35 years. The paper is a critique and extension of a prior finding by Anderson et al., which proposed a correlation between G measurements and the periodic oscillation of the Earth's length of day at a period of 5.9 years. This work aims to provide a more comprehensive overview of G measurements and analyze any potential time-dependent variability, reinforcing the need for precision in experimental physics.

Overview of G Measurements

The gravitational constant G remains a pivotal parameter in physics, yet its value has historically been rife with uncertainties and inconsistencies across different measurements. The authors compile measurements from various distinguished experiments conducted since 1980, evaluating their precision and effective time periods. Their analysis encapsulates a wide range of methodologies, including torsion balance in both time-of-swing and electrostatic servo modes, pendulum experiments, and atom interferometry, underscoring the diversity in experimental approaches aimed at pinpointing G.

Re-evaluating Correlation Claims

The primary question this paper addresses is the purported correlation between G and the Earth's rotational dynamics suggested by Anderson et al. After reassessing the measurement data, the authors acknowledge that while a sinusoidal fit with a period of 5.9 years appears to yield a better correlation than a linear trend, the correlation's strength diminishes considerably when accounting for updated and corrected measurements.

Numerical Results

By undertaking a least squares regression analysis incorporating all available data, the authors report a mean G value ($\bar{G}$) of $$6.67388 \times 10^{-11} \, \text{m}^3\text{kg}^{-1}\text{s}^{-2}$$ with an amplitude of the sinusoid at $1.07 \times 10^{-14}$, which drastically lowers the proposed amplitude reported by Anderson et al. Further analyses introducing varying periods exhibit no period that stands out conclusively as influencing the measured G values, thereby weakening the oscillation hypothesis initially postulated.

Implications and Future Directions

The paper highlights the persistent challenge of reducing systematic errors in experimental measurements of G. Despite sophisticated techniques and diverse methodologies, discrepancies remain, hinting at the potential existence of unrecognized systematic uncertainties. This difficulty compels a collaborative effort within the scientific community to refine experimental techniques and share insights, aiming for enhanced precision and concordance in future G measurements.

The broader implication of this research reaches into theoretical and practical considerations in fields dependent on precise gravitational measurements—particularly, geophysics and fundamental physics theories. Achieving consensus on the value of G and understanding its stability holds the potential to clarify or redefine physical constants and laws.

Conclusion

In summary, the authors present a crucial consolidation of experimental data that questions previously reported periodic variability in G. This work advocates for the necessity of rigor and cross-examination in experimental physics, emphasizing that any observed correlation with Earth dynamics must be critically evaluated against potential systemic biases in the data. Moving forward, the importance of uniformity in gravitational constant measurements is underscored, calling for methodological advances and global cooperation among the scientific community to reconcile existing contradictions.