Gravity’s oldest secret. That is Big G. The gravitational constant turned 340 this year. Newton tucked it into the center of his universal law way back in 1686. He published Principia Mathematica soon after, offering an estimate but refusing to pin down an exact number. He didn’t measure it. He left it hanging.
Centuries passed. Science advanced. Computers got faster. Precision instruments shrank.
Yet Big G remains the most stubborn fundamental constant we know.
We still don’t agree on what it actually is. The values scientists derive keep drifting. We have a range. Not a number. A fuzzy zone of uncertainty that makes physicists uneasy. Especially metrologists. Like Stephan Schlamminger at the National Institute of Standards and technology (NIST).
He spent ten years trying to fix this mess.
The drama was real. The process involved opening an envelope. Not a birthday card. An envelope holding a hidden bias. The kind of reveal you’d see at the Oscars, except the winner is just a slightly different number for gravity.
Big G is everywhere in our equations. If its value wobbles, everything else shakes too. That discomfort is justified.
“G is gravity’s best-kept secret,” Schlamminger told Space.com. “It sits in this peculiar position: it is the oldest fundamental constant… and yet it remains the least precisely-known of all of them.”
He calls it one of the great embarrassments of physics.
Maybe it deserves to be.
Rethinking Big G
Newton introduced Big G as the anchor of his law of universal gravitation. The equation describes attraction between every particle in the universe. It scales down with distance. Squared. Inverse. Simple enough. But Big G is fixed. While mass and distance change from place to place, Big G should not.
Unless it does.
Einstein changed the game in 1915. His theory of general relativity replaced Newton’s pulling force with geometry. Space-time bends around mass. Curvature is gravity.
But Big G survived the coup.
It shifted roles, nothing more. It now measures the stiffness of space-time. A smaller G means space resists warping. A larger G lets stars and planets crumple reality easier. Schlamminger describes it as baked into the fabric of existence, immutable across space and time.
In Newtonian physics, it gave strength to the pull. In Einstein’s universe, it gives elasticity to the void.
We first measured it properly in 1798. Henry Cavendish hung lead spheres from a beam. He watched them tug at each other. Weakly, obviously, he calculated Earth’s density and derived a value for G.
It has been 227 years since Cavendish’s torsion balance experiment. We have satellites now. Lasers. Supercomputers.
We are no better at pinning down the number.
“Gravity is by far the weakest force.”
Isolating it is a nightmare. You can shield yourself from magnetic fields. Put metal between you and a magnet and the problem vanishes. Try that with gravity.
Everything pulls. Always. Every atom in your body, the building, the planet. There are no off-switches.
Schlamminger’s team can’t crank up the signal. They take what gravity gives them. Usually, it is nothing.
There are 17 accepted measurements of G out there. They should align. They scatter instead. Like wet paint hitting a floor. Nobody knows why. Metrologists hate this. Converging data is the whole point of measurement.
When numbers refuse to meet in the middle, you suspect an error in the method. Or something in the method is lying to you.
The Envelope Trick
To get a fresh result, Schlamminger’s team in Gaithersberg, Maryland, recreated a BIPM experiment from Sèvres, France. Replication is risky. Humans are pattern-matching machines. If you know what a good result looks like, your brain starts steering toward it. Unconsciously. Subtly.
We call it “intellectual phase-locking.” You stop the experiment too early. Or you ignore outlier data points. It is not malicious. It is biological. We want confirmation, not correction.
Schlamminger refused to risk it.
He hired a colleague to add a fake offset. A “bias.” They changed the weights slightly, just enough to throw off the calculation, then hid the correction factor in a sealed envelope. The experimentalists ran the test. They weighed their samples. They collected the raw data.
None of them knew their real Big G value.
Not until the end.
The plan called for opening that envelope in 2022. It waited four years longer. July 2011? No, wait—Schlamminger missed something. A tiny error in how air pressure affects the mass readings.
Physics requires patience. Even for people who know how air behaves.
Finally, in July 2024.
They opened the flap.
The resulting value of Big G was lower than the standard accepted figure set by the Committee on Data (CODATA). Specifically, 0.0000064 less.
Let that sink in. That is infinitesimally small.
But gravity multiplies things. Over large masses and vast distances, small changes explode into big consequences. Schlamminger offered an analogy involving time. If a watch drifts by 0.006 seconds a day, after a full year that watch loses about 34 minutes.
Tiny slips accumulate.
If this new Big G measurement holds water, the implications are physically heavy. Our Earth is heavier than we thought. Much heavier. About 320 quintillion kilograms more than the current accepted mass. Or roughly 360 billion trillion pounds of rock we somehow forgot to count.
It changes nothing for breakfast. You don’t need extra food for lunch. The planet isn’t crushing you. But cosmologists care. Planetary models depend on precise gravity constants.
Was the mystery solved?
No.
One team with a fresh setup is not the same as consensus. The other 16 measurements still argue against Schlamminger’s number. The scatter remains. The data still fights back.
“The underlying disagreement… will still be there,” Schlamminger said, admitting the headache persists.
For him, the work is done. Ten years chasing a number is a lifetime in research.
“As for me, am I turning my attention to electrical quantities…”
He’s walking away. Resisting resistors. Testing capacitors. Precision electronics instead of cosmic pull.
He hopes to cause the same trouble there.
We should probably expect it. If gravity won’t settle, why should electricity?
Schlamminger is done.
The universe isn’t.
