Precision measurement, scientific personalities and error budgets: the sine quibus non for big G determinations

Abstract

Determinations of the Newtonian constant of gravitation (big G ) fit into the oftentimes-unappreciated area of physics called precision measurement—an area which includes precision measurements, null experiments and determinations of the fundamental constants. The determination of big G —a measurement which on the surface appears deceptively simple—continues to be one of Nature's greatest challenges to the skills and cunning of experimental physicists. In spite of the fact that, on the scale of the Universe, big G 's effects are so large as to single-handedly hold everything together, on the scale of an individual research laboratory, big G 's effects are so small that they go unnoticed…hidden in a background of much larger forces and noise sources. It is this ‘smallness’ that makes determining the precise value of this (seemingly unrelated to the rest of physics) fundamental constant so difficult.

Not Normal: the uncertainties of scientific measurements

“…As Beveridge famously noted [91], often everyone else believes an experiment more than the experimenters themselves. Researchers always fear that there are unknown problems with their work, and traditional error analysis cannot "include what was not thought of" [47].…”

“…As Beveridge famously noted [91], often everyone else believes an experiment more than the experimenters themselves. Researchers always fear that there are unknown problems with their work, and traditional error analysis cannot 'include what was not thought of' [47]. It is not easy to make accurate a priori identifications of those measurements that are so well done that they avoid having almost-Cauchy tails.…”

“…Measurements of Newton's gravitation constant are notoriously variable [14,47], so a data-set without G N results was examined. The heavy tail is reduced, albeit with large uncertainty.…”

Robert Dicke and the naissance of experimental gravity physics, 1957–1967

“…The pendulums usually seen in teaching laboratories for measurements of the acceleration, g, of gravity look very different from the ones illustrated in Figure 8 and used in the Hoffmann (1962) and Curott (1965) experiments to probe possible evolution of g. They look very different again from the sketch in Figure 12 of Faller's (1963) falling corner reflector experiment to measure the absolute value of g. These Princeton experiments, and the two versions of the Eötvös experiment (Liebes 1963;Roll, Krotkov, and Dicke 1964), were designed, or we may say purpose-built, to be optimum for a specific measurement. The Pound and Rebka (1959) laboratory measurement of the gravitational redshift was a purpose-built experiment too, but it was inspired by the appearance of a new tool, the Mössbauer effect, which made the experiment possible.…”

“…That is to be compared to the present CODATA standard, G = 6.6741 × 10 −8 cm 3 g −1 s −2 , with fractional uncertainty reduced from Heyl by about a factor of two. Faller (2014a) reviewed this situation.…”