Scientists have spotted the first hints that Albert Einstein's formulation of gravity operates in the quantum realm.

The hints have to do with observations of a falling quantum object, and though this may not seem like a huge deal (literally, we are talking about atoms here), it could be an important step on the road to a theory of ... everything.

To start, we have to go back to the early years of the 20th century. Consider Einstein's iconic theory of gravity, general relativity, and the elusive realm of quantum mechanics. While the former describes the universe on scales of planets, stars and black holes, even demonstrating how galaxies and galaxy clusters formed, the latter describes the counterintuitive physics found on scales smaller than atoms. But there is a problem: these two important theories don't play well together.

There is no quantum theory of gravity. However, scientists think we're getting closer to one.

A team of researchers has performed an experiment to find the point where quantum mechanics and general relativity meet. Namely, how the quantum properties of atoms change as those atoms fall under the influence of gravity.

"This is a unique paper, in the sense that it combines a hard experiment with a far-reaching theoretical interpretation, about one of the most fundamental questions in physics: How can gravity, described by Einstein's theory of relativity, and quantum theory, be unified into one understanding of the universe?" team leader Ron Folman of the Ben-Gurion University of the Negev said in a statement. "These two pillars of modern physics have so far eluded all attempts at a unified theoretical framework, but this complex experiment gives more hints as to how such a unification may be achieved."

Elevators and equivalence

At the cornerstone of the team's experiment is an important element of general relativity called the equivalence principle.

The equivalence principle states that, for an observer in free fall, gravity should disappear. If that sounds confusing, consider this popular analogy: You are inside a closed elevator with no view of your surroundings. You feel heavy. You might drop a ball, and it would fall to the floor of the elevator. Why would these things happen? Well, there are two options.

You might be sitting stationary on the ground floor, or the elevator could be moving upwards at an acceleration equal to the gravitational field strength of Earth, 9.8 meters per second squared. You can't tell the difference between gravity and acceleration. That's the equivalence principle.

Now, let's shake that up. Suddenly, you can't feel weight anymore. You drop the ball, and it floats. Gravity has disappeared, or the upward acceleration has ended. Inside the elevator, two things may have happened, and you can't distinguish between these two either. The elevator cable may have snapped, and you may now be in free fall, or the upward acceleration may have carried you to space and then ceased.

The big question now is: How do you test this on a quantum scale, especially for particles that behave as waves as they travel?

Wave hello to quantum gravity?

To measure the equivalence principle at a quantum scale, the researchers turned to a piece of equipment called the Quantum Galileo Interferometer. This allowed them to split the quantum wave associated with a traveling atom into two paths. One was held in place while the other was allowed to fall freely.

The team then reunited the wave to observe the changes gravity had introduced to the falling wave.

For the experimental subjects, the team chose a cloud of rubidium atoms, which they cooled to just above absolute zero. These were placed close to the surface of a specially designed atom chip. Using microwave pulses, the scientists placed the atoms in what is known as a quantum superposition.

A superposition is one of those really weird things unique to quantum physics, effectively allowing a quantum system to simultaneously exist in two or more contradictory states. In this case, the superposition allowed each atom to travel along two different paths at the same time.

Magnetic fields generated by the atomic chip applied an upward push along one path, counteracting the downward pull of gravity and holding it stationary. The other path was subjected to magnetic pulses pushing the atoms upwards. The pulses were then shut off, allowing the atoms to fall freely under gravity like a ball thrown into the air.

When the waves were reunited, the team used an effect called interference, which occurs when the peaks and troughs of two misaligned waves meet, to measure changes in the free-falling wave.

This represented the first time that the effects of gravity and free fall on the phase of a quantum wave had been measured.

However, while this is an effective demonstration of Einstein's equivalence principle in the quantum realm, it isn't a demonstration of quantum gravity. Yet it remains a step along a frustratingly long road physicists have been traveling down for over a century with no end in sight.

"We have no consistent theory telling us why quantum physics should fail," team member Vlatko Vedral said in the statement. "This experiment pushes quantum mechanics into one of its most intriguing frontiers, gravity, and shows that, once again, its predictions hold."

The team's research was published on Wednesday (Sept. 2) in the journal Science Advances.

In a promising advancement in the search for dark matter, scientists have transformed a tiny magnet into a detector that can sense some of nature’s faintest forces—with a little help from levitation.

The research could help researchers detect some of the heaviest particles that are believed to have ever inhabited the universe, according to physicists.

Led by Rice University physicist Christopher Tunnell, the achievement was made using a tiny permanent magnet—one around the size of a grain of sand—which they levitated over a superconductor that was chilled to freezing cold temperatures just above absolute zero.

Since the magnet floats without encountering any surfaces, this dramatically reduces friction, allowing the Rice team to carefully monitor its movements, some of which are as small as around one-hundredth of a single atom. Such subtleties of its motion offer a novel possibility: that the magnet’s faint movements could serve as an effective signal if a massive dark matter particle passed through the detector.

Unusual Candidates for Dark Matter Particles

“Dark matter could be hiding at masses that our traditional experiments were never built to reach,” Tunnell said in a recent statement, noting that by leveraging the team’s novel detector, “we can begin searching a part of the dark matter landscape that has largely been out of experimental reach despite being the focus of extensive theoretical study by my Rice cosmology colleague Andrew Long.”

Among the most mysterious phenomena in the universe, dark matter is believed to comprise most of the matter that populates the cosmos and exerts gravitational effects that influence the formation and behavior of galaxies. Despite this, scientists have remained unsuccessful in detecting it or even determining what it is comprised of.

There are several experiments that hunt for hypothetical dark matter particles, which scientists believe have masses that are similar to those of atoms or subatomic particles. Still, there are some theoretical models which suggest much heavier particles could also qualify—some approaching sizes as large as a human cell.

A Novel Means of Detecting Dark Matter

Detecting something so large would require a very different kind of dark matter detector. To search for the kinds of interactions that smaller particles would be expected to generate, the Rice researchers instead looked for an impulse—one more likely to result from such an “ultraheavy” dark matter particle as it interacted with the detector.

“Instead of looking for a steady signal, we are waiting for very small knocks,” explained Rice postdoctoral researcher Juehang Qin.

Over the course of one month, the team collected observations that focused mainly on quiet overnight periods when vibrations and other environmental disturbances were minimized. Unfortunately, no promising detections were made during this time.

Still, important results can also be derived from a lack of any definitive discoveries, especially when it comes to a field like particle physics. In this case, that’s because the absence of a signal allowed the researchers to place a few constraints on the combinations of dark matter masses and interaction strengths that should have been expected to produce detectable effects.

Altogether, the team’s experiment looked at nine orders of magnitude in its search for possible dark matter particle passes, which included searches for particles as much as 10 million times heavier than those investigated in past similar experiments.

Next Steps

Going forward, the next step would be to increase the experiment’s sensitivity by cooling the magnet even further, observing for longer periods, and eventually successfully levitating several magnets simultaneously. Multiple detectors could also help scientists determine whether real interactions involving dark matter are occurring, as opposed to false positives that might arise from vibrations or other kinds of interference.

Although the Rice team’s work is only a first step, their experiments with a tiny levitating magnet mark a promising pathway toward future potential detections, which may finally unlock new clues to the universe’s mysterious dark matter landscape.

The team’s research was detailed at the 2026 International Conference on Particle Physics and Cosmology, and additional details can be found here.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.

String theory has been famously untestable for decades. This week the Economist reported that has changed, and the reason involves an extra dimension of space that might be just big enough to notice in a tabletop experiment. There is a rather different way to read the situation. Let's take a look.

The dark matter search LUX-ZEPLIN has announced that they have made a detection that could be the first ever evidence for a dark matter particle. Just what have they measured, what could it be, and what does it mean? I have a brief summary.

Shadowy dark matter has eluded scientists for decades. The LZ experiment may have spotted one particle, called a WIMP, but more data is needed to check.

By analysing the signals from extragalactic fast radio bursts, astronomers at the Massachusetts Institute of Technology (MIT) say that the “missing matter” in the universe is distributed further away from galaxies than most theoretical simulations predict. Their finding – which is counterintuitive since the gravity from galaxies tends to pull everything closer to them – could help us better understand how highly energetic galactic activities, such as jets from supermassive black holes and explosions from old dying stars, impact the formation of cosmological structures.

“Ordinary” matter, which is built from atoms and their protons and neutrons (collectively known as baryons), makes up stars and galaxies and everything we see around us. However, the best models of the universe we have today suggest that close to 90% of this baryonic matter is “missing”.

The radio signals of FRBs are stretched

As their name implies, fast radio bursts (FRBs) are brief, intense bursts of radio waves spanning multiple wavelengths. They were first detected in 2007 and since then, astronomers have spotted thousands of others, including some within our own galaxy. They are thought to originate from cataclysmic processes involving compact celestial objects such as neutron stars and typically last a few milliseconds or even less. And these FRBs can be used to probe the missing baryonic matter.

As they pass through the missing matter, the radio signals of FRBs are stretched (or “dispersed”) over time – that is, their overall duration becomes longer. The more missing matter they pass through, the more the signals are dispersed. The missing matter has an extremely low density – of just a single proton per cubic metre – so it is extremely difficult to identify, but researchers recently found that they could use the dispersion effect to detect it. In that previous study, they confirmed that intergalactic space, which contains most of the universe’s baryons, is home to tenuous clouds or filaments of diffuse plasma that make up the missing matter.

Data from CHIME and DESI

In the new work, a team led by astrophysicists Haochen Wang and Kiyoshi Masui has now gone a step further and mapped the extent to which this plasma extends. They did this by cross correlating the locations of millions of galaxies with the dispersion of nearly 3000 background FRBs on length scales of 0.1 to 50 Mpc.

The researchers used data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) catalogue and the Dark Energy Spectroscopic Instrument (DESI) survey. CHIME, a large radio telescope located in British Columbia, scans the entire northern sky for incoming radio waves and it can detect ultrashort, ultrabright radio signals. Indeed, it has detected about 4000 FRBs since it became operational. DESI, for its part, is an instrument mounted on the Mayall Telescope at Kitt Peak National Observatory, near Tucson, Arizona. It makes detailed measurements of the light coming from over 30 million galaxies – originally to provide estimates of dark energy, the mysterious force that is driving our universe’s expansion.

In all, the researchers detected 2870 FRB signals with CHIME and correlated these with the locations of around six million galaxies with DESI.

Missing baryonic matter scattered across a large radius

Their analyses revealed that on scales smaller than about 1 Mpc, the missing baryonic matter was indeed found around galaxies and galaxy clusters, but rather than being close to galaxies in a dense ball as expected, it was scattered across a large radius. “A galaxy is maybe a few 100,000 light years across, and we found missing matter out to about four million light years,” Masui says. “That’s further than the simulations predict.”

The new result backs up the idea that missing matter is projected out from a galaxy through highly energetic events, such as jets from supermassive black holes and explosions from old dying stars. These processes could be much more energetic than we think, note Wang and Masui, and they are stronger and much more violent.

The work, which is detailed in Physical Review Letters, proves that FRBs are a good way to study large-scale structures in the universe – in a similar way to how cosmologists have been using galaxies and the cosmic microwave background for decades, says Wang. “It has helped to establish FRBs as a new cosmological probe, especially for detecting the missing matter.”

FRBs will only become a more popular tool in this context, he adds, especially given that several new radio telescopes, with upcoming surveys such as CHORD, DSA-2000 and the SKA, are being constructed around the world to offer much better FRB data in the coming years. “Indeed, we have already received more FRB data from our telescopes and are working on expanding our study,” Wang tells Physics World.

And that is not all: the researchers say they are also busy improving their analysis technique. “Until now, we have mostly examined the dispersion of FRBs but we are now working on extracting information from FRBs’ spatial positions relative to galaxies. This will reveal more details on how the missing matter is distributed in the universe.”

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