Stephan Schlamminger stood on a conference stage in July 2024, holding a sealed envelope he’d been forbidden from opening for two years past its original deadline. Inside was the one number that would tell him whether a decade of his working life had actually meant anything. He later admitted he wasn’t entirely sure he wanted to know.
The Constant Nobody Can Quite Pin Down
Gravity is the force keeping your feet on the ground, holding planets in orbit, and gluing entire galaxies together, and yet the number describing its exact strength, the universal gravitational constant known as “big G,” has resisted precise measurement for over 225 years. Henry Cavendish first measured it in 1798. Since then, physicists have tried again and again, and the results simply refuse to agree with each other, differing by amounts far too large to blame on ordinary random error.
Schlamminger, a physicist at the National Institute of Standards and Technology, decided in 2016 to attempt something more ambitious than just adding another data point to an already messy pile. He set out to independently replicate a highly precise, if contested, 2007 measurement made by the International Bureau of Weights and Measures in France, using a torsion balance, a device sensitive enough to detect the twist of a metal fiber caused by nothing more than the gravitational pull between two nearby masses.
Ten Years of Not Knowing
To keep his own expectations from unconsciously creeping into the results, a genuine risk in precision measurement, Schlamminger asked a colleague not involved in the experiment to secretly scramble the true masses of his equipment with an unknown offset, then seal the real numbers inside an envelope. Schlamminger would run the entire experiment blind, unable to check his own progress against any expected answer, all the way through.
The toll of a decade spent effectively guessing in the dark was real. “It was really kind of walking through a dark valley,” Schlamminger later said, describing the experience elsewhere as life-sucking. “It felt to me like it was like a random number generator. I felt like I was going to a casino every day to work.” The envelope’s opening, originally scheduled for 2022, ended up delayed two additional years after Schlamminger caught a subtle error in how his team had been accounting for air pressure, forcing a fresh round of corrections before he’d trust the result at all.
An Answer That Deepened the Mystery Instead of Solving It
When the envelope finally opened on that conference stage in 2024, the number inside let Schlamminger unscramble his data for the first time. The result: 6.67387 × 10⁻¹¹ cubic meters per kilogram per second squared, measurably different, by about 0.0235 percent, from the very 2007 measurement he’d set out to confirm. In the strange world of fundamental constants, where most values are pinned down to a few parts per million, that’s a genuinely uncomfortable gap. If you’re curious about how this same fundamental force behaves in far more extreme conditions, our Black Hole Time Dilation Calculator lets you explore what gravity does once you’re close enough to a black hole for it to warp time itself.
Passing the Torch
Schlamminger’s team went further too, running the experiment twice, once with copper masses and once with sapphire, specifically checking whether the material itself might secretly be skewing the result. It wasn’t, the two versions matched almost exactly, ruling out one more possible explanation and leaving the core mystery fully intact. After ten years, Schlamminger has decided he’s done chasing it. “I’ll leave it to younger generations of scientists to work on the problem,” he said. Whatever finally resolves the mystery of big G, it likely won’t be him, and after a decade spent unable to even watch his own results take shape, it’s hard to blame him for handing off the search.
For more on the experiment, check out the full announcement from NIST and the detailed account from CNN.