For more than two centuries, scientists have been trying to determine one of the most important numbers in physics: the universal gravitational constant, known as the “big.” GThis defines the strength of gravity throughout the universe, affecting everything from falling objects on Earth to the motion of galaxies. However, despite its importance, researchers still cannot agree on its exact value.
That uncertainty weighed heavily on National Institute of Standards and Technology physicist Stephen Schlamminger as he prepared to open a sealed envelope containing an important secret number. For nearly a decade, Schlamminger has devoted much of his career to large measurements. G With amazing precision. The numbers hidden inside the envelope will eventually allow you to decipher the team’s results.
Why measuring gravity is so difficult
Gravity may shape the universe, but it is surprisingly weak compared to nature’s other fundamental forces. For example, electromagnetism is much more powerful. Even a small magnet can lift a paperclip against the entire Earth’s gravity.
This weakness poses a major challenge in the laboratory. Scientists need to measure the force of gravity between relatively small objects, but the force is incredibly weak. The masses used in the experiment are about 500 billion times smaller than Earth, making it extremely difficult to accurately detect the gravitational force between them.
Researchers have spent more than 225 years trying to improve the measurements of big game. G Since Isaac Newton first explained gravity mathematically. Despite increasingly advanced equipment, modern experiments still yield slightly different answers. The difference is small, about 1 in 10,000, but it is larger than the expected experimental uncertainty.
That raised uncomfortable questions. Are scientists overlooking subtle flaws in their experiments, or is there something flawed in our understanding of gravity itself?
Reproducing groundbreaking gravity experiments
To investigate this discrepancy, Schlamminger and his colleagues decided to replicate a highly acclaimed experiment conducted in 2007 by the International Bureau of Weights and Measures (BIPM) in Sèvres, France. The goal was simple in principle: to see if an independent team at NIST in Gaithersburg, Maryland, could achieve the same results.
Schlamminger also wanted to avoid the possibility of bias. He was worried that knowing the expected value would unconsciously influence the analysis. To prevent that, he asked his colleague Patrick Abbott to scramble some of the data.
Abbott subtracted secret values from measurements that included part of the experimental population. Only Abbott knew the number. Until he opened the envelope, Schlamminger had no way of knowing the true value of his experiment.
moment of truth
The envelope had almost been opened once before. Schlamminger was ready to publish the results in 2022, but stopped at the last minute after realizing that subtle atmospheric pressure effects could affect the measurements. He postponed his presentation and continued refining his analysis.
Finally, that moment arrived on July 11, 2024, at the Annual Conference on Precision Electromagnetic Measurements in Aurora, Colorado.
Schlamminger missed the conference’s morning session, distracted by concerns about temperature fluctuations, changes in barometric pressure and other small effects that could skew the results. “I dotted all the i’s and crossed all the t’s in the experiment,” he said.
During an afternoon presentation, he opened the envelope and read Abbott’s hidden number. At first he seemed relieved. For the experiment to work as expected, the secret value must be large and negative.
it was.
But as the days passed, that sense of relief faded. This number was too large for NIST’s results to match earlier French experiments.
New contradictions in Big G
After two more years of detailed analysis, Schlamminger and his collaborators published their results in the following paper: Metrology. Their measurements are G 6.67387×10-11 m3/kilogram/s2, 0.0235% lower than the French measurement.
It may sound trivial, but physicists take such differences seriously. Most other fundamental constants are found to be in much better agreement with six or more significant figures.
The difference is not large enough to affect daily life. It won’t change the weight on the scale or change the way manufacturers measure ingredients like peanut butter in a 16-ounce jar. However, throughout the history of science, small contradictions can signal major discoveries or reveal hidden gaps in existing theory.
How do scientists measure gravity?
Both the BIPM and NIST experiments relied on a device called a torsion balance, which detects very small forces by measuring the amount of twist in thin fibers.
The technique dates back to British physicist Henry Cavendish, who performed pioneering gravity experiments in 1798. Cavendish suspended two lead balls from a wire and placed a larger mass nearby. The gravitational attraction between them causes the suspended beam to rotate slightly and twist the wire. By measuring its movement, Cavendish estimated the strength of gravity.
The latest versions used by BIPM and NIST were much more advanced. The setup included eight cylindrical metal blocks. Four large cylinders were placed on a rotating merry-go-round, with four smaller blobs suspended inside by hair-thick ribbons of copper beryllium.
As the outer mass attracted the inner mass, the torsion balance rotated and twisted the ribbon. By measuring that small movement, one estimate of the large movement was obtained. G.
The team also used a second technique using electricity. The researchers applied a voltage to electrodes near the inner mass, creating an electrostatic force that counteracts gravity. By carefully adjusting the voltage until the balance stopped spinning, they obtained another independent measurement. G.
Testing of copper and sapphire ingots
Schlamminger’s team added an additional step to their experiment. To determine whether the material itself affected the measurements, they repeated the study using chunks of both copper and sapphire.
The results are nearly identical, suggesting that the composition of the public is not the cause of the discrepancy.
Although this experiment did not solve any major mysteries, Gadded another important data point to the growing body of evidence.
“Every measurement matters because the truth matters,” Schlamminger said. “For me, making accurate measurements is a way to bring order to the universe, whether the numbers match expectations or not,” he added.
Schlamminger says he has been pursuing this problem for 10 years and is ready to take the next step.
“We will leave it to the younger generation of scientists to tackle this problem,” he added.
“We have to move forward.”
Big G vs Little G
Newton’s law of gravity states that “a large G” and “small g”, but they represent different things.
A small g refers to the acceleration caused by gravity near a large object, such as the Earth. At the Earth’s surface, a small g is about 9.8 m/s2. On the Moon, gravity is weak due to the Moon’s small mass, with a small g of only about 1.62 m/s2.
big GOn the other hand, is considered universal. Scientists believe that it has the same value everywhere in the universe. Determine the force of gravity between two objects, such as planets, people, or laboratory weights.
Newton’s equation calculates gravity by multiplying two masses, dividing by the square of the distance between them, and multiplying by a large G. Written mathematically, the law is expressed as: Gm1m2/r2.
