Very Tiny Gravitational Constant Measured

A rubidium fountain, though this is a clock, not an experiment.

Wait a minute, says everyone who's taken a physics class.  Don't we already know what the
gravitational constant is?  Isn't it part of Newton's equations? Yes, the gravitational constant has been measured many times, although not actually by Newton himself.  It was first calculated in 1798, and has been adjusted quite a bit over the years to considerable accuracy.  Or so we thought.  As it turns out, all those values for the gravitational constant in the equation
F_g = G * m₁m₂ / r² were wrong.  The problem is that the gravitational force is so tiny that virtually anything could cause errors.  So the value of the gravitational constant is not nearly as well known as other constants such as the speed of light.


In an experiment involving a rubidium atomic fountain and several hundred kilograms of tungsten, scientists have found an error-free value for the gravitational constant.  The value they got is 6.67191 × 10^-11 m³ kg^-1 s^-2, while the previously accepted value was 6.67384 × 10^-11 m³ kg^-1 s^-2.  That doesn't sound like very much, I know I only used 6.67 in my physics classes, and I'm sure that's all anybody would use just using that equation casually.  But for physicists, that is a big difference.  This new value isn't as precise as old values, but it is more accurate, and it raises hopes that a both precise and accurate value for the gravitational constant will soon be agreed upon.

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