Celebrating its 340th birthday this year, the gravitational constant is the oldest fundamental constant in physics. "Big G" as it is affectionately known, was first placed at the heart of Newton's law of universal gravitation during its formulation in 1686 and formally published a year later as an estimate yet-to-be-measured in Newton's book Philosophiæ Naturalis Principia Mathematica. But after all these centuries, Big G is ironically still the fundamental constant with the least well-constrained value.
Scientists currently estimate a range of values arrived at for Big G, which means we can't be totally certain if we have a good understanding of gravity or if there is something missing from our formulation. That is a situation that Stephan Schlamminger of the National Institute of Standards and Technology (NIST) has spent the last ten years trying to resolve, an endeavor that ended with the opening of an envelope containing an unknown answer, a situation more usually associated with the Oscars or some other glitzy awards ceremony than a physics experiment.
In this case, however, the drama is warranted; Big G is so ubiquitous in the equations we use to describe the universe that the uncertainty in its value is somewhat uncomfortable for scientists, especially for metrologists (nothing to do with the weather, but scientists who study measurement) like Schlamminger.
