There was a secret inside the envelope in the hands of Stephan Schlamminger, one of the world’s leading experts in experimental tests of gravity. He appeared to be on the verge of opening the envelope during a presentation at the April 2022 meeting of the American Physical Society, to read a number that would reveal whether his latest efforts in a lifelong passion had been a success.
Schlamminger, of the National Institute of Standards and Technology in Gaithersburg, Md., sought to measure Newton’s gravitational constant. The secret number in the envelope was a kind of code — an intentional and specific error inserted into his NIST experiment to obscure the measurement as it progressed. Only one person knew the number. And that person was not Schlamminger.
Without access to it, he couldn’t know what the experiment had found. Schlamminger had imposed the secrecy on himself to protect against bias in the experiment, including the unconscious bias that can beset even the best experimentalists. It was extra precaution to ensure the integrity of an experiment that could help untangle mysterious discrepancies in measurements of the constant, known as G, that have crept up over the last few decades.
G, often called “big G” (to distinguish it from “g,” which depends on G and is the special case of the acceleration of gravity near the surface of the Earth), reflects the strength of gravity between any things with mass. It determines the orbits of planets and galaxies, and describes the force that pulls you to the ground. Nobody knows how to predict from theory what the actual value of G should be, says Clive Speake, a physicist at the University of Birmingham in England who developed the instrument that Schlamminger is using at NIST.
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