Physicists have been trying to measure basic gravityal so for more than two hundred years. In the meantime a large acceptable amount Gas known, it is 6.67430 × 10-11 cubic meters kilogram per square second. It also has an uncertainty of ±0.00015 × 10-11 m3/(kg s2). As for the constants of the universe, that is very uncertain.
Stephan Schlamminger
Schlamminger is a physicist at the US National Institute of Standards and Technology.
Stephan Schlamminger recently completed a 10-year effort at the US National Institute of Standards and Technology to replicate the previous large measure. G from the International Bureau of Weights and Measures, or BIPM (located near Paris) which is higher than most measurements. He spoke to him IEEE Spectrum about why it took so long to find the number—6.67387 x 10-11 m3/(kg s2)—and why it is significantly lower than the BIPM result, reaching 0.0235 percent.
Why is it so difficult to measure big G?
Stephan Schlamminger: Gravity is very weak. When you were a kid, you probably played with fridge magnets, and it was a force you could feel. But if you have two cups of coffee, you can try all you want—you can’t feel the power between them. It is there, but it is very, very weak.
How did you try to measure the size G?
NIST used a torsion balance with a quadruple geometry. This animation shows an exaggerated version of how the blue mass outside attracts the blue mass inside.S. Kelley/NIST
Schlaminger: We used what is called a torsion balance. An important idea in the torsion balance is that it separates the vertical gravity from the Earth from the horizontal gravity, and that makes it sensitive to the masses around the torsion balance but not the Earth below.
Ours had a fourfold geometry. It has a very small torsion bar, and then four cylinders in a “combination symbol” configuration. All of this is within a vacuum. Outside, we have four large cylinders that pull down four small masses on them. If I move the outer mass just a little bit, the coordinate symbol will rotate, and we measure that angle of movement. That angle is equal to the torque of gravity.
Why are you trying to multiply the value of BIPM?
Schlaminger: We can move the field forward. The measurements were plagued with inconsistencies, so by re-testing, we hope to shed some light on the inconsistencies.
We haven’t found a smoking gun, so there’s no single reason why we’re different—our price versus their price. It’s still a big question.
What was it like to spend 10 years on this?
Schlaminger: It’s like herding cats. I’ve measured some basic solids, like Planck’s constant, and in most experiments, they have some sort of self-balancing built in. But with gravity equations, you have to keep track of all the moving mass—where it is, how big it is, and what it measures.
How does your result compare to others?
Schlaminger: Our result is slightly below the average number of accepted literature. I’m disappointed because it doesn’t match the value of BIPM, or the value of the books. If there is something wrong with the BIPM test, the number of books—including that score—should probably go down a bit. But that is not for me to say. I think someone else, independently, should figure out what the new value should be.
From Your Site Locations
Related Topics on the Web
