![]() ![]() Yet despite hundreds of elegant experiments since British physicist Henry Cavendish first measured it 225 years ago, G remains among the least precisely known of the fundamental constants.Īnd in a way, our understanding of G has only worsened in recent decades as new, incompatible measurements have come in. It’s one of the oldest recorded constants - only the speed of light was measured earlier. Along with the masses of elementary particles, the charge on an electron and the speed of light, G is one of dozens of constants crucial to science today ( SN: 11/12/16, p. While the masses and distances differ depending on whether you’re considering the forces between you and the Earth, for example, or a planet orbiting the sun, G is always the same. The force of gravity depends on three factors: the masses involved, the distances between the masses and G. Still, back here on Earth, it’s Newton’s theory of gravity that concerns Schlamminger and others wanting to measure G. It took Einstein’s theory to explain the intense gravity of black holes and the warping of space and time. We now know that Newton’s theory is only an approximation of Einstein’s more encompassing version of gravity, the general theory of relativity. The constant, named for Newton two centuries later, was instead wrapped into the masses involved. ![]() Apples falling, planets in orbit and the surprisingly squashed shape of the Earth are just a few of the countless phenomena that Newton’s theory explained, all without explicitly mentioning G. He was primarily interested in how the force moved objects. ![]() Though Isaac Newton developed his theory of gravity in the 17th century, he didn’t think in terms of G. Newton’s gravitational constant is a misnomer. The envelope would remain sealed for at least another year as Schlamminger went back to the lab to take another shot at one of the most challenging measurements in physics. Puzzling discrepancies in the measurements meant the numbers could not be trusted. The time had come to tear open the envelope. Presumably other physicists and science reporters around the world were, like me, hunched over screens waiting to see what the secret number would tell us about G. Like so many science presentations in the time of COVID-19, Schlamminger’s reveal was set to be virtual. “If the measurements are right, then it could be the greatest discovery since Newton.” “There’s this haunting elephant in the room which suggests that maybe there’s something going on that we don’t understand,” Speake says. The scattered values could be a sign of trouble with the measurement techniques among various groups, or there might be a more intriguing aspect. A handful of labs around the world have turned up values that disagree ( SN Online: 4/30/15). After two centuries of improved precision, recent measurements of G are troubling. 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. It determines the orbits of planets and galaxies, and describes the force that pulls you to the ground. 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 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. 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. Without access to it, he couldn’t know what the experiment had found. Schlamminger wants to settle discrepancies in recent measurements from labs around the globe. Stephan Schlamminger of the National Institute of Standards and Technology in Maryland is leading an effort to measure Newton’s gravitational constant, or G, using an experiment that previously tested the value in Sèvres, France. ![]()
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