AMOTopic

Measuring Newton's gravitational constant G

G sets how strongly masses attract, and it is the least precisely known fundamental constant. Careful experiments disagree with each other by far more than their stated errors.

Why it matters

The scatter in G is a long-running failure of precision measurement that limits geophysics and astrophysics and may hide an unknown experimental effect.

Review

C. Rothleitner, S. Schlamminger, Invited Review Article: Measurements of the Newtonian constant of gravitation, G, Review of Scientific Instruments, 2017. https://doi.org/10.1063/1.4994619 reference checked

Proof

Signed record: e5522d18821c…
Public log: Entry 18, in checkpoint 2,123
Bitcoin date: Block 969,698, 2026-10-03

Download proof How this works

3 problems

Atom interferometry determination of G at 10 ppm
Open

Atoms in free fall make test masses that cannot twist, stretch or be magnetized like a pendulum fiber, so they could give G free of the usual suspects. Their best result so far is about ten times less precise than needed.
Why laboratory values of G scatter beyond their stated uncertainties
Open

About a dozen top experiments, each claiming an error of a few parts in 100000, give values of G that spread by about 5 parts in 10000. Something in how G is measured is not understood.
Same apparatus design, different G: the NIST versus BIPM discrepancy
Open

NIST rebuilt the instrument used by the international measurement bureau (BIPM) and got a value about 2 parts in 10000 lower. Since the design is the same, the difference should be traceable to a specific cause.

Measuring Newton's gravitational constant G

Why it matters

Review

Proof

3 problems

Atom interferometry determination of G at 10 ppm

Why laboratory values of G scatter beyond their stated uncertainties

Same apparatus design, different G: the NIST versus BIPM discrepancy