This week in stories we’re covering from The Debrief, a new twist on gravity measurement, hidden in a mysterious envelope, may point to a subtle flaw in our understanding of the universe. Elsewhere, researchers are breaking the tiny bounds of Quantum mechanics by creating a massive Schrödinger cat particle under ultracold conditions. And finally, NASA officials just confirmed a rare event captured in satellite images that caused loud booms heard throughout New England.
Meanwhile, here’s a look at other stories we’re covering right now in our reporting at The Debrief:
A twist on gravity measurement, hidden in a mysterious envelope, may point to a subtle flaw in our understanding of the universe, raising new questions about its underlying forces.
That envelope held the key to an experiment led by National Institute of Standards and Technology (NIST) physicist Stephan Schlamminger, which attempted to confirm a measurement of the universal gravitational constant made by a French team in 2007.
Working based on the previous team’s processes, Schlamminger made an important discovery that deepens our understanding of the fundamental force of gravity, as revealed in a recent paper published in Metrologia.
Of the four forces that govern the universe, gravity, electromagnetism, the weak nuclear force, and the strong nuclear force, gravity has remained the most elusive to clearly understand. The problem is that it is incredibly weak compared to the other three, making precise measurements difficult.
An easy example of this disparity is that even a small magnet, small enough to fit in the hand, can overcome the gravitational pull of the entire mass of the Earth, despite the extreme disparity in size. Despite its weakness, gravity is the force that binds our universe together, forming galaxies and holding moons in their orbits around planets, and those planets in orbit around their host stars.
A challenge scientists have pursued for over two centuries is measuring the universal gravitational constant, also known as big G, the fundamental strength of gravity throughout the universe. Schlamminger dedicated a decade to his pursuit of the universal gravity constant problem.
While we can obviously notice the effect of gravity at the scale of our planet’s effect on our bodies, when considering objects small enough to be manipulated and measured inside a laboratory, the strength of gravity is so faint as to be almost imperceptible.
Scientists have devised various methods using extremely precise equipment to measure the universal gravitational constant, but their results have failed to align. The most intriguing part is that the differences extend beyond the expected room for error in the precision instruments employed, suggesting that physicists’ basic understanding of gravity may be in error.
To investigate these errors, Schlamminger spent a decade leading an effort to recreate a 2007 experiment conducted by the International Bureau of Weights and Measures (BIPM) in France. If Schlamminger could confirm that finding, it would suggest that physicists may finally have a handle on gravity; otherwise, it could indicate some serious fundamental issue in their understanding.
The primary concern for Schlamminger was maintaining the work’s integrity, even in the face of any subconscious bias he may hold. To do so, he had a colleague subtract a number from the data and record it in an envelope to be opened later. Only at the end of the project, with all of the work completed, would the figures be adjusted by the mystery number, ensuring that the data would not be forced to fit the previous outcome.
In 2022, Schlamminger came very close to opening the envelope before suddenly identifying one factor that had gone unaccounted for in his experiment, and adding another two years to the work. Finally, in 2024, he spent the envelope and was pleasantly surprised to see a large negative number, something in the ballpark of what would put his work in agreement with the 2007 findings after the adjustments were made.
However, after the adjustments were made, the mystery number was slightly too large, resulting in a 0.0235% difference from the French measurement.
“At face value, we learned that the new measurement at NIST and the previous measurement at BIPM do not agree with each other,” Schlamminger told The Debrief. “That gives us some idea on the reproducibility of the experiment(s). Since this was the very first time that a big G experiment was repeated, that is significant and new information.”
“While at NIST, we found a brand-new effect that was never described in the literature before. It is a spurious torque that is mediated by a tiny temperature gradient and the residual gas in the vacuum chamber. It is unclear how much that effect may have biased the BIPM result, because we know little about the temperature gradients in that lab or their vacuum pressure,” Schlaminger continued. “Based on some estimates that I made, it seems unlikely that it accounts for the complete difference. But this effect is definitely something that was not accounted for in their uncertainty budget.”
In conversation with The Debrief, Schlamminger noted the bittersweet nature of repeating an existing experiment and ruminated on how he would advise the next generation to pursue the problem. While pointing out that repeating an experiment can be a learning experience, it remains beholden to ideas that may be outdated.
He specifically called attention to the cumbersome coordinate measurement machine used in the work, saying that a pendulum design created by University of Washington researchers in the early 2000s would have been much more practical. His primary advice to future scientists is to scour the literature for anything that may be useful, but also to think outside the box to push the envelope even further.
“Lincoln famously said: Give me six hours to chop down a tree, and I will spend the first four sharpening the axe,” Schlaminger concludes. “So analogous: Give me six years to measure G, and I will spend the first four thinking about the best way.”
The paper, “Redetermination of the Gravitational Constant with the BIPM Torsion Balance at NIST,” appeared in Metrologia on April 16, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
The Tiangong experiment tests a basic question: can human development begin in space?A single atom is one of the last places one would expect to find a gravitational wave. These ripples in spacetime are caused by movements of massive objects such as black holes, and they are typically detected using instruments that measure tiny changes in the distance between mirrors separated by kilometres. Their home territory is on large scales, not the microscopic scale of an atom.
Despite this, physicists have questioned for decades whether gravitational waves might affect how often atoms spontaneously emit photons. Previous theoretical studies suggested that the answer was no: the total spontaneous emission rate of a single atom remains unchanged, so the atom appears unaffected by the wave.
This null result is not surprising. Gravitational waves stretch space in one direction while squeezing it in a perpendicular direction. Detectors such as LIGO measure this effect by sending light between mirrors in perpendicular “arms” and comparing how long the light takes to travel along each arm. For a single atom, there is no comparable separation to measure, so scientists did not expect that passing gravitational waves could be detected this way.
In a new study, published in Physical Review Letters, Navdeep Arya and collaborators at Stockholm University in Sweden and Eberhard Karls Universität Tübingen in Germany identified a loophole in this argument. Although gravitational waves do not leave an imprint in the number of photons emitted, Arya and colleagues calculated that they do affect how those photons are distributed in angle and frequency.
This distinction is crucial. Because a gravitational wave does not make the atom emit more or fewer photons overall, its effects will cancel out if one only measures the total number of photons. However, if the photons are sorted by their direction and frequency, a characteristic pattern emerges that reflects the wave’s stretch-and-squeeze geometry. Depending on the wave’s frequency, this pattern can manifest either as a small shift in the emitted photon frequencies or as additional sidebands in the spectrum.
The reason this is possible, Arya explains, is that the atom isn’t the only thing the gravitational wave interacts with. “It’s actually the atom and the [quantum] field,” he says. Because the field is a global object, he adds, it can carry information about the gravitational wave even when the atom itself does not.
The existence of these effects opens a new way of thinking about gravitational-wave detection. Instead of watching how spacetime changes the distance between mirrors, a next-generation detector might look for how a passing wave changes the light emitted by atoms. This approach would make it possible to detect lower-frequency gravitational waves, which are difficult to reach with ground-based detectors such as LIGO.
A system that could detect these effects experimentally would look very different from a traditional gravitational-wave detector. Instead of measuring how a passing wave changes the distance between mirrors, one would need to excite a large cloud of atoms, collect the photons they emit through spontaneous emission, and resolve the angles and frequencies of those photons.
Though this is not a standard experiment, parts of the required technology already exist. Cold-atom experiments, for example, routinely trap and control millions of atoms. The challenge is to combine these capabilities with sufficiently precise measurements of the directions and frequencies of the emitted photons, while also controlling technical noise.
The researchers say their next step is to understand whether the signal will survive under realistic experimental conditions. According to Jerzy Paczos, the Stockholm PhD student who led the study, the most important task will be to consider the full range of technical noise that would appear in a real experiment, determine which noise sources matter most, and conclude from that whether their proposal is truly feasible. The researchers are also interested in whether cavities or collective effects in atomic arrays could amplify the signal.
For now, the work suggests that gravitational waves may leave traces in a place that physicists have not fully looked before: not in how fast an atom emits light, but in the detailed pattern of the light it gives off. In doing so, it points to a new way of using quantum systems to probe spacetime itself.
The post Gravitational waves could leave traces in light from cold atoms appeared first on Physics World.
Login
