Newton's gravitational constant tells how much gravitational force there is between two masses -- the Earth and sun, for instance -- separated by a known distance.
The gravitational constant along with the speed of light and Planck's constant (a key value in quantum mechanics) are considered the three most fundamental and universal constants in nature.
"That is a huge embarrassment for modern physics, where we think we know everything so well and other constants are defined to many, many digits," Gundlach said.
If accepted, the measurement by Gundlach and Merkowitz would reduce the uncertainty by nearly a factor of 100 from the currently accepted figure, making it far more precise than even the 1987 figure. Gundlach notes his numbers could change as additional data are analysed in preparation for submitting the work for peer review.
To make their measurements, the researchers are using a device called a torsion balance that records nearly imperceptible accelerations from the gravitational effects of four 8.14-kilogram stainless steel balls on a 3- by 1.5-inch gold-coated Pyrex plate just 1.5 millimeters thick.
The device, operating inside an old cyclotron hall in the UW nuclear physics laboratory, is similar in nature to one used 200 years ago to make the first Big G measurement. But it is computer controlled and contains numerous mechanical refinements that make the more precise measurement possible.
Gundlach acknowledged that the more precise calculation probably wouldn't mean much to the average person.
"Just because we know the value of G won't make better cell phones," he said. "But it's something mankind should know because it's such a fundamental constant."