Newton’s gravitational constant, G, is crucial for fundamental physics: it governs how much spacetime curves for a given mass, is essential for metrology, and might give clues to a deeper understanding of quantum gravity. However, G continues to present unexpected issues in need of resolution. Determinations over the last thirty years have yielded inconsistencies between experiments significantly greater than their reported individual uncertainties, oddly with possible periodic behavior. To push forward, the National Science Foundation (NSF) has recently called for new “high-risk/high-impact” proposals to produce a step-change improvement in measurements (NSF 16-520).
In response, we propose taking advantage of the classic gravity train mechanism by sending a solid sphere with a cylindrical bore hole along its diameter into deep space and measuring the period of oscillation of a test mass moving within the hole using laser ranging techniques from a far removed host spacecraft. As is well known, the oscillator’s period is directly dependent upon G (mass and dimensions of the sphere are known to a certain accuracy before launch), and thus provides a means for determining its value. To ensure stability, the bored sphere must be composed of a dense inner core surrounded by a less dense outer envelope.
Preliminary estimates of the relative uncertainty (63 ppb) yield a near one thousand times improvement versus previous measurements on Earth. As with any new proposal, there are questions that need to be addressed more thoroughly, e.g. precise modeling of stray small force gradients within the hole, charge accumulation due to galactic cosmic ray bombardment, release mechanism from the host, but our goal is to add to the discussion for ways to produce the aforementioned step-change improvement in determining G.
Read the full article for free* in Classical and Quantum Gravity:
Deep space experiment to measure G
M R Feldman, J D Anderson, G Schubert, V Trimble, S M Kopeikin and C Lämmerzahl 2016 Class. Quantum Grav. 33 125013
*until 25 June 2016
Sign up to follow CQG+ by entering your email address in the ‘follow’ box at the foot of this page for instant notification of new entries.
CQG papers are selected for promotion based on the content of the referee reports. The papers you read about on CQG+ have been rated ‘high quality’ by your peers.
The author(s) licence this work to IOP Publishing Limited under Creative Commons Attribution 3.0 Unported (CC BY 3.0) licence.
By submitting the work to IOP Publishing Limited, the author(s) confirm that the work does not infringe on any third party rights, it contains nothing libelous or unlawful, all factual statements are, to the best of the authors’ knowledge, true or based on valid research conducted according to accepted norms and all required permissions have been obtained in writing.
You must be logged in to post a comment.