Just over 40 years ago, what began as a routine safety test at the Chernobyl nuclear power plant (or Chornobyl in Ukrainian) in Soviet Ukraine spiraled into one of the most recognizable disasters of the 20th century. The reactor exploded and burned, spewing chunks of nuclear debris into the sky. Among that toxic litter were countless tiny “hot particles,” fragments of nuclear fuel smaller than the width of a human hair (somewhere between 8 and 50 micrometers across). Those particles are called hot because they’re highly radioactive, and still are four decades later. Today, scientists entering the areas of the Chernobyl Exclusion Zone where the hot particles are located are required to wear a full protective suit.
But after decades of study, scientists still know surprisingly little about what their particles are made of at the molecular level. A team of researchers from Germany recently set out to change that by analyzing six particles collected from two sites in the Exclusion Zone using synchrotron X-ray diffraction. Surprisingly, they discovered the particles remained far more chemically stable than they had expected. Their crystal structures were largely intact, suggesting they changed little since forming during the disaster and its aftermath.
The hot particles thrown out of the Chernobyl plant fall into three general categories. The first is fuel that remains chemically and physically similar to the reactor’s original uranium dioxide. The second type consists of fuel that melted during the explosion and fused to its zirconium-alloy protective casing. The third type is fire-damaged fuel.
As the reactor’s graphite burned for 10 days after the explosion, the intense heat oxidized some of the fuel into other uranium compounds.
Particles, crystals…and dogs
For this particular study, the team sourced their six samples from two areas in the exclusion zone, and all three hot particle categories were represented. Two came from asphalt in Pripyat, roughly 2 miles from the reactor, while the other four came from farm soil samples in Kopachi, about 3 miles away.
With the samples selected, the researchers isolated individual particles pulled from the soil, mounted each type to a tiny tungsten electrode, and then sent them to the European Synchrotron Radiation Facility in Grenoble, France. There, a team analyzed the particles using intense X-rays produced by a synchrotron, a circular particle accelerator. The researchers rotated each particle in an X-ray beam, measuring it from roughly 2,000 different angles. Watching how the x-rays bounced off all that material revealed how its atoms were arranged, showing which compounds each particle was made of and, most importantly for this study, how intact its crystal structure remained.
Hot particle from the 1986 reactor accident: The nuclear fuel particle is partially fused with zirconium oxide. Image: Laura Stalmann.
They expected to see particles that had been broken down by years of exposure to the elements. Instead, the crystal structures were still largely intact. That surprising finding suggests the particles are far more chemically stable than previously assumed, holding their radioactive contents locked inside their crystal structures.
Though some of the particles showed more oxidation (of a loss of electrons when they interact with other chemicals) than others, two showed virtually none at all. Importantly, two of the particles pulled from the same soil near Kopachi included both a sample heavily oxidized and one that was largely untouched. The authors suggest that if weathering from the environment were the cause of the oxidation, then both particles sitting side by side should look similar. Instead, they say the oxidation likely happened during the disaster itself, when the reactor fire baked some of the fuel for days.
That timeline is potentially good news for the areas around the power plant. If the particles are indeed holding onto that radioactive material and not oxidizing, that could mean less harmful material is making its way into the soil and, in turn, the surrounding ecosystem. Still, the researchers quickly caveat any broad claims. These were just six samples, after all. Making any wider claim about the soil in the region generally would require more research.
Though it’s still too early to say with any certainty, that lack of leaching dangerous material into the environment could partly help explain why the exclusion zone has become home to an ever-growing neighborhood of furry mammals in recent years. In fact, the area’s lack of humans has made it a thriving ecosystem for foxes, bears, and bison. It’s a modern, albeit a little unorthodox, example of rewilding. Of course, even in this new frontier, the consequences of a nuclear disaster aren’t totally absent. A recent study of roaming dogs living in the Chernobyl Exclusion Zone, many believed to be descendants of dogs left by their owners during the 1986 evacuation, show distinct genetic differences from dogs in an area just 10 miles away.
The 2026 Nobel Prize for Physics has gone to Francis Halzen for his “decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin”.
In this episode of the Physics World Weekly podcast I am joined by the University of Oxford neutrino physicist Kirsty Duffy and Physics World’s Matin Durrani to talk about this year’s prize. This is the fifth time a Nobel prize has been awarded for work on neutrinos, and we explore why physicists are so enamoured with these elusive particles.
In this podcast we refer to my video conversation with Francis Halzen and his colleague James Roth and to Halzen’s book Quarks & Leptons. Kirsty Duffy presents the Even Bananas series of videos about neutrinos.
This podcast is supported by American Elements, the world’s leading manufacturer of engineered and advanced materials. The company’s ability to scale laboratory breakthroughs to industrial production has contributed to many of the most significant technological advancements since 1990 – including LED lighting, smartphones, and electric vehicles.
Physicists smashed gold nuclei together at nearly the speed of light and found an unexpected pattern in the particles these collisions sprayed out. If confirmed, that pattern could help reveal how the hot soup of quarks and gluons that filled the universe in the first few microseconds after the Big Bang cooled and condensed into the protons and neutrons that make up ordinary matter today.
In every collision, particles are flung out sideways; how hard they are flung, on average, varies slightly from one collision to the next. Physicists expected the size of these variations to change smoothly as they adjusted the collision energy. Instead, the variations dipped, shrinking and then growing again. This dip could be a sign of a long-sought "critical point," a special set of conditions at which nuclear matter changes the way it transforms from one form to another.
The signal, detected by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York, is strong enough that it is very unlikely to be a statistical accident. However, the researchers cautioned that the dip is a tantalizing hint, not proof of the long-sought transition. They published their findings Sept. 22 in the journal Physical Review Letters.
A rulebook for extreme matter
Protons and neutrons are made of smaller particles called quarks, which are held together by the "strong force" carried by particles called gluons. When heated or squeezed enough, protons and neutrons melt into a hot soup of free quarks and gluons known as a quark-gluon plasma. It's thought that this primordial soup of particles filled the universe in the first milliseconds after the Big Bang.
Physicists want to pin down how this soup-ification happened, by measuring the so-called equation of state of nuclear matter. "For water, it tells you how pressure, temperature and density are linked, and therefore when it freezes, boils or expands," study co-author Rutik Manikandhan, a postdoctoral physics scholar at The Ohio State University, told Live Science in an email. For nuclear matter, "it is the basic rulebook for matter under the most extreme conditions in nature, such as the cores of neutron stars," Manikandhan added.
The "critical point" is a key landmark in that rulebook "For water, it is the point where the boundary between liquid and steam disappears," Manikandhan said, and theorists have long suspected that nuclear matter has a similar point. At extremely high temperatures, matter melts smoothly and gradually into quark-gluon plasma, but at higher densities, the change may become abrupt.
The critical point would mark where one kind of transition turns into the other. Some recent calculations place this point within reach of RHIC's lower-energy collisions. "But all of this is still conjectured and there is nothing concrete yet, either from the experimentalists or theorists," Manikandhan said.
The work also matters for cosmology. "Because the matter we create in these collisions resembles the matter that filled the universe a few microseconds after the Big Bang, mapping how it behaves helps us understand how the universe evolved from a hot soup of quarks and gluons into the protons and neutrons that make up everything today," Manikandhan said.
The central part of the three-story STAR detector at the Relativistic Heavy Ion Collider (RHIC). Scientists recently used the detector to study the conditions of the early universe, just milliseconds after the Big Bang. (Image credit: Brookhaven National Laboratory)
A dip where a smooth trend was expected
To explore this territory, the researchers ran RHIC at a range of collision energies. The lower the energy, the more tightly the colliding matter was squeezed. For its lowest-energy runs, STAR used a "fixed-target" setup, in which a beam of gold nuclei strikes "a thin gold foil placed inside the detector," Manikandhan said, instead of a second, oncoming beam. This produces the densest matter RHIC can make.
Collision energies are measured in electron volts (the energy an electron gains when accelerated across 1 volt). That is a minuscule amount, so particle physicists usually work in billions of electron volts, or giga electron volts (GeV). One GeV is roughly the energy locked up in the mass of a single proton, according to Einstein's famous equation E = mc2. The team analyzed roughly 1 billion collisions at energies between 3 and 7.7 GeV per pair of colliding protons or neutrons. That is the bottom of RHIC's range, which reaches 200 GeV.
In each collision, the team measured how hard charged particles were flung sideways out of the fireball — a quantity known as transverse momentum. The researchers then looked for correlations between the particles. A correlation measures whether two things tend to change together. Here, the team checked whether pairs of particles from the same collision tended to both be flung harder than average, or both more gently. That reveals something about the fireball as a whole. If a fireball is slightly hotter, or expands more forcefully, all of its particles get an extra sideways kick together.
"Those correlations reflect how much the temperature and the flow of the fireball fluctuate," Manikandhan said.
Close to a critical point, the matter's heat capacity — the amount of energy needed to raise its temperature — is expected to shoot up. That makes the fireball's temperature harder to budge, so the correlations should weaken. "If the matter approaches a critical point or a phase change, we would expect to see those correlations change in an unusual, non-smooth way as we vary the collision energy," Manikandhan said.
That is what the team saw in the most head-on collisions. "Instead of changing smoothly with energy, the correlations show a dip," Manikandhan said. The researchers compared the data with a smooth trend anchored by earlier STAR measurements at higher energies. The dip departs from that trend with a statistical significance of 5 sigma, the standard physicists usually demand before treating a signal as real. It means that if the true trend were smooth, random scatter in the data would produce such a pronounced dip only about once in 3.5 million tries.
"A smooth trend is what you'd expect from ordinary nuclear matter, so a dip suggests something more interesting is happening at those conditions," Manikandhan said.
By contrast, a widely used computer simulation of the collisions, which contains no critical point, reproduced the overall trend but not the dip. Off-center collisions showed only a faint hint of the same feature, which is too weak to count as evidence on its own.
Not the final word yet
"The result is suggestive, not proof of a critical point," Manikandhan said. Effects unrelated to a critical point can also shape these fluctuations, and how much of the dip they could explain remains unclear, the researchers noted.
Still, the dip "does point to a set of conditions where the behavior of nuclear matter changes, and it gives theorists a new, precise measurement to test their calculations against," Manikandhan said.
Next, the team plans to use the correlations to "extract the specific heat of the hot matter," Manikandhan said. They will then compare it with supercomputer simulations that calculate the behavior of quarks and gluons from first principles.
The researchers also plan to test the dip against more theoretical models and combine it with other measurements, such as fluctuations in the number of protons produced in the collisions. "Only when different measurements agree can we say confidently whether a critical point exists," Manikandhan said.
Our basic understanding of core-collapse supernovae hasn't changed in decades. Large stars burn through all the fuel at their cores and start creating heavier elements in reactions that consume energy. The lack of energy from these reactions allows gravity to pull the interior of the star in on itself, collapsing it into a neutron star or black hole. The energy released by this process then blows the remainder of the star apart.
And, generally, that's right. But there's an entire busload of devils in the details. The statistics of supernovae that we've observed indicate that the model may be seriously incomplete. And on the theoretical side, there are still plenty of uncertainties, including over some of the basics, such as whether all core collapses actually result in a supernova.
A paper being released by Physical Review D provides what might be a potential explanation for the discrepancy: flavor-changing neutrinos. Neutrinos play a key role in our current models of supernovae, and right now, those models don't take into account one of neutrinos' most striking features: their ability to change identity.
Our basic understanding of core-collapse supernovae hasn't changed in decades. Large stars burn through all the fuel at their cores and start creating heavier elements in reactions that consume energy. The lack of energy from these reactions allows gravity to pull the interior of the star in on itself, collapsing it into a neutron star or black hole. The energy released by this process then blows the remainder of the star apart.
And, generally, that's right. But there's an entire busload of devils in the details. The statistics of supernovae that we've observed indicate that the model may be seriously incomplete. And on the theoretical side, there are still plenty of uncertainties, including over some of the basics, such as whether all core collapses actually result in a supernova.
A paper being released by Physical Review D provides what might be a potential explanation for the discrepancy: flavor-changing neutrinos. Neutrinos play a key role in our current models of supernovae, and right now, those models don't take into account one of neutrinos' most striking features: their ability to change identity.
Many of the world’s greatest scientific minds remain in startling disagreement with one another about the nature of reality itself. After conducting what is likely the largest survey of its kind, researchers reported that a vast majority of physicists suspect the big bang doesn’t necessarily mark the beginning of time. And as their additional responses indicate, scientists diverge even more when it comes to other hot-button cosmological topics.
In 2025, researchers put out an international open call for their Big Mysteries in Physics survey. Anyone could partake in the questionnaire, but responses from self-identifying physicists were later separated and reviewed to identify any particularly striking areas of agreement or disagreement. After reviewing answers from over 1,600 physicists, the questionnaire’s authors published their key takeaways earlier this year in Physics Magazine.
The results? Physicists are very divided on explanations for some of the universe’s fundamental operations.
The most dramatic relates to the big-bang theory (technically known as the Lambda Cold Dark Matter theory). About 68 percent of respondents said they don’t think the famous moment necessarily marks the beginning of time. Some of this has to do with how the big bang is presented in popular culture—contrary to many depictions, the theory specifically explains how the universe expanded from a single extremely hot, dense prior state of existence. This means it technically may have very little to do with the beginning of time.
The only other majority opinion pertains to the immediate moments following the big bang. Only 51 percent of physicists agreed that the immediate moments following the big bang involved an incomprehensibly fast period of expansion commonly known as inflation.
Subjects got far more contentious from there, although some of it was understandable. Given how much remains to still learn about dark matter, 17 percent of survey takers think the mysterious material is composed of an undiscovered particle or particles. Around 12 percent argued it could be explained by tweaking the theory of gravity. At best, barely 21 percent of physicists hypothesized it may be some combination of these and other answers.
Quantum physics continues the chaos. Nearly 19 percent of scientists think string theory is likely the best way to integrate gravity into quantum physics, while only 12 percent offered loop quantum gravity as an alternative. Meanwhile, 18 percent lean towards the suspicion that gravity can’t be integrated in any way.
If the survey presents one clear takeaway, it’s that these diverse theories are in no way an indictment of the present-day state of physics. These aren’t amateurs—they’re researchers who base their arguments on volumes’ worth of data, calculations, and scientific testing.
“Consensus, or its absence, tells us where the evidence feels settled and where researchers still see room for radically different ideas,” Niayesh Afshordi, a University of Waterloo physicist and study co-author, explained in a statement. “In this sense, lack of consensus can be a clue. It marks places where better data, sharper theory, or new connections between subfields may be needed”
Afshordi noted that unlike other polls, scientific reality isn’t settled by a majority vote. It’s supported by clear, demonstrable evidence.
“The interesting point is not that physicists are confused. It is that the frontier is genuinely alive,” he added.
The most impressive science fiction stories emphasize “science” over spectacle. The Star Trek franchise has featured plenty of examples since the original series premiered 60 years ago this month, but one of its most famous sci-fi moments may prove even more fascinating than fans realized. At Brazil’s Federal University of ABC, physicist Níckolas de Aguiar Alves determined that an early episode of Star Trek: The Next Generation demonstrates an aspect to the theory of relativity even better than its creators likely anticipated.
Season One’s ninth episode, “The Battle,” introduces a bit of backstory to Jean-Luc Picard’s illustrious career in the Federation. Years before he became captain of the USS Enterprise, Picard oversaw a ship called the Stargazer when it came under fire from an unknown assailant. Picard needed to navigate closer to the mystery attacker before responding, but the Enterprise’s shields were down.
The captain then quickly improvised what later became known as the “Picard Maneuver.” He ordered his crew to rush their foe at warp speed (faster than the speed of light) then quickly halt and begin firing. Relativistic physics dictated that if Stargazer traveled faster than visible light, it would technically generate two images of the ship from their attacker’s point of view—one Stargazer at the location just prior to warp speed, then a Stargazer where it halted. The operation was risky, but it gave Picard and his crew a 50/50 chance that the enemy would continue firing on an afterimage of Stargazer.
Traveling faster than lightspeed is widely considered impossible, but the underlying principles of Picard’s Maneuver don’t only hold up to expert scrutiny—its depiction in Star Trek is hypothetically less accurate than it should be. According to de Aguiar Alves, Picard’s odds technically would be even higher in such a scenario. But while a fan of the series, the physicist wasn’t intentionally trying to stress test the episode’s logic. Instead, de Aguiar Alves was working on an actual particle physics problem that involved a slower light speed. At one point, he began sketching out the scenario to double check his work.
“And after I drew one or two diagrams, I started noticing, ‘Hey, I think I’ve thought about something like this before,’” de Aguiar Alves said in a recent interview with Ars Technica.
In actuality, Picard’s Maneuver wouldn’t result in two Stargazer ships; it would make three of them. This is because Picard’s crew didn’t travel at a constant speed during the gambit–they first sped up, then stopped closer to their opponent. That means Stargazer technically accelerated not once, but twice. This makes all the difference.
The physicist doesn’t hold it against the episode’s writers. If anything, the overall conceit is an excellent scenario to ponder while studying theoretical physics.
“The main thing they got perfectly, and I think it is a great illustration,” he said.
By the time naval architecture firm George G. Sharp tasked Jack Heaney with the design of the world’s first nuclear-powered merchant ship, the Glasgow-born designer had already broken many styling norms. In the mid-1940s, Heaney transformed routine ocean transport into a festive occasion when he designed the interiors of the SS President Wilson and SS President Cleveland with Hawaiian murals, carved glass panels, and a smoking lounge dressed in playful, exotic wall art. His gift for making the mundane desirable wasn’t confined to ocean liners—New York’s Museum of Modern Art had already put one of his stackable aluminum chairs on display in 1947. But nothing in Heaney’s career had prepared him for the commission that reached his drawing board in 1957.
At the time, the shadow of 1945, when the world first witnessed the terrifying power of the atom, loomed large. Following World War II, the United States and Soviet Union were locked in a nuclear arms race, and the public associated splitting atoms with annihilation. Atoms meant war.
To shift that sentiment, President Eisenhower launched his Atoms for Peace initiative, aimed at demonstrating the civilian benefits of nuclear technology—and the NS Savannah, or Nuclear Ship Savannah, was to be its flagship. Heaney suddenly had a much more daunting task than usual; he would have to make the feared desirable.
More than half a century since theSavannah was decommissioned in 1971, there is no nuclear-powered merchant ship in active commercial service anywhere in the world. Four nations have tried. None succeeded, mostly because the economics were not compelling enough and no one trusted nuclear ships.
In the interim, nuclear reactors have only become smaller and safer. Now, as the true cost of burning oil at sea comes due—commercial shipping produces more than three percent of global greenhouse gas emissions—the economics of nuclear-powered merchant ships may finally be compelling. But the problem Heaney was hired to solve in 1957 still stands in the way, persuading people to trust what they fear.
The making of a maritime designer
John “Jack” Heaney was born in Glasgow in 1904. He grew up during a time when the River Clyde, which runs through the heart of Glasgow, served as the world’s premiere shipbuilding hub, with nearly 40 shipyards situated on its banks. Heaney studied naval architecture at the University of Glasgow, while taking classes at the Glasgow School of Art and apprenticing at the Fairfield Shipbuilding and Engineering Company.
When Heaney emigrated to New York in 1926, he worked a string of jobs, including a brief stint as a door-to-door refrigerator salesman, before joining the New York City-based naval architecture firm George G. Sharp, Inc. in 1937. At Sharp, Heaney quickly developed a reputation for having an engineer’s eye and artist’s hand, helping design the interiors of several prominent passenger-cargo ships—a specialized form of merchant ship that is part cruise liner, part cargo vessel—including the Robin Line, the Delta Line, and the American President Lines. In 1947, the same year MoMA put his chair on display, Heaney opened his own design firm on West 54th Street in Manhattan. A decade later, the Savannah project came across his bow.
Originally tasked with the ship’s exterior design, Heaney eventually assumed responsibility for the ship’s interior styling, too. From stem to stern, it was Heaney’s job to design a nuclear-powered ship that passengers would want to cruise on for pleasure, and that businesses would want to ship merchandise on for commerce.
The NS Savannah was the first nuclear-powered merchant ship. Image: Contributor / Getty Images / Mondadori Portfolio
Atoms for Peace
Eisenhower had announced the Atoms for Peace initiative four years earlier, in a December 1953 address to the United Nations. The atom, he argued, should be turned from a great destructive force “into a great boon, for the benefit of all mankind.” Under Eisenhower, the U.S. began sharing reactor technology and medical isotopes with allied nations. Atoms for Peace sought to prove that the technology that had obliterated two cities could also light homes, treat cancer, build harbors, and move ships.
The U.S. Navy, meanwhile, saw the advantages of a vessel that could continuously plow the ocean without refueling for months, or even years. The USS Nautilus was the first atomic-powered vessel, a sub, launching in 1955. By the time Sharp signed Heaney to the Savannah project, two more atomic-powered subs were patrolling the world’s oceans (USS Skate and USS Seawolf). But military vessels primarily keep to military ports, so the public rarely saw them.
Eisenhower needed a civilian showcase that would disassociate atom-splitting from mushroom clouds. That showcase would be Heaney’s NS Savannah. As a passenger-cargo ship, the Savannah would routinely sail into commercial harbors like Rotterdam, Le Havre, and New York, normalizing nuclear reactors and demonstrating their safety. At least, that was the goal.
How safe is our A-ship?
In 1959, the same year the Savannah launched, Popular Science ran a short feature designed to quell readers’ fears: “How Safe Is Our A-Ship Savannah?” The staff-written story read more like a safety brief than an objective review. While boasting about its efficiency—“on a single loading of A-fuel, the Savannah will have a range of 350,000 nautical miles”—the article focused mainly on the “worst possible accidents that might befall the first atomic merchant vessel.” Such caution seemed justified. That same year, Denmark canceled a scheduled visit by the USSSkate to Copenhagen, and England agreed to receive visiting nuclear submarines only at the remote Isle of Portland, population 12,000, rather than major ports.
Popular Science’s initial coverage was not anomalous. “Passengers will receive no more radiation on the Savannah than they receive from normal background radiation of the earth in their day-to-day lives,” The New York Times reassured its readers.
By 1961, however, as the Savannah prepared to begin its cargo and passenger service, which commenced in 1962, Popular Science’s editors were fully onboard, launching a four-part series that spanned four consecutive issues and more than a dozen pages. The do-it-yourself mini-manual provided detailed instructions for readers to build and sail their own four-foot model of the ship. Four different writers and editors took part in the project: hull casting one month, superstructure the next, then a working steam turbine, and finally radio controls. Even as Popular Science promoted its features, the real Savannah was being fitted with Heaney’s final touches.
The January 1961 issue of Popular Science shows a model of the NS Savannah assembled with screws and dowels. Image: Popular Science, January 1961 issue
Domesticating the atom
On a conventional ship, fuel is stored low in the hull, in tanks that any port can refill with diesel by hose. But Savannah’s single, massive fuel core had to sit in the hull’s center, beneath an opening in the deck, so it could be accessible by overhead crane for refueling. Heaney’s answer to this exterior design problem became the ship’s signature: a streamlined, teardrop-shaped superstructure. Popular Science’s writers praised Savannah’s sleek, futuristic lines as “graceful as a racing yacht’s,” and called its reactor housing “a well-placed superstructure [that] blends airfoil curves with sharply angled planes for a dazzling effect.”
Below decks, Heaney took the fear problem head on, weaving Atomic Age motifs into the ship’s interior. In the veranda, the cocktail bar’s backlit wine rack depicted the trilinear chart of the nuclides in blue, red, and yellow glass; the tables ringing the dance floor glowed, their tops lit by “panelescent,” or electrically charged luminescent panels. Even the floor tiles in the main stairwell carried the atomic theme. A separate lounge nearby offered passengers a closed-circuit television view into the reactor containment vessel. Overhead light beamed down through light fixtures adorned with stylized atoms.
In the dining room, sculptor Pierre Bourdelle installed a wall mural titled “Fission.” Nearby, suspended in glass, hung a small gold model of the NSSavannah’s namesake, the 1819 steamship SSSavannah, the first ship to cross the Atlantic under sail and steam. Heaney hoped such Old World symbolism would make people feel comfortable dining, dancing, and sleeping no more than a dozen yards from a nuclear reactor.
As a design achievement, Savannah was a triumph. Her passenger cabins were mostly full from 1962 to 1965, and more than 1.4 million people toured the ship across 46 ports in 13 countries.
Even the plates and silverware used on the NS Savannah had an atomic motif. Image: Baltimore Sun / Contributor / Getty Images / Kim Hairston
Sunk by economics—and fear
But novelty was never going to be enough to move public sentiment or make Savannah pay for itself. The combined ship-and-reactor construction cost ran to roughly $46 million, three to four times what a comparable conventional freighter cost at the time, and the ship’s specialized nuclear crew commanded specialized wages. No private insurer would touch a nuclear-powered merchant ship; the U.S. government had to indemnify it instead, extending $500 million in federal liability coverage just to get foreign ports to receive the ship. Every port call required a small diplomatic mission of its own, negotiated weeks in advance, with tugs standing by in case of an accident. Some countries, like Australia, New Zealand, and Japan, never accepted Savannah.
By the end of the 1960s, the U.S. Defense Department, one of merchant shipping’s largest customers, had concluded that conventional freighters remained the better bet. With no federal appetite left to continue funding a revenue-losing program, Savannah was withdrawn from service in late 1971 with no plans to build another.
The timing proved fateful. Two years after Savannah was decommissioned, the 1973 oil embargo sent fuel prices soaring; had it still been sailing, the ship’s independence from oil might have tipped the scales for commercial customers, even if the public remained fearful.
Fear kills future “A-ships”
In 1979, the partial meltdown at Three Mile Island—eight years after Savannah’s own retirement—hardened American public fear of nuclear power for more than a generation. The Soviet Union’s Chernobyl accident in 1986 and Japan’s Fukushima accident in 2011 reinforced that fear.
Three other nations tried what the U.S. attempted with Savannah, and each ran into the same wall. West Germany’s nuclear-powered merchant ship Otto Hahn logged 650,000 nautical miles over a decade before port restrictions and rising costs forced her conversion to diesel in 1979—the same year as Three Mile Island.
Japan’s nuclear-powered Mutsu fared worse. Local fishermen blockaded it in harbor for two years before the ship could even sail, and when its reactor went online in 1974, it leaked. The crew had to improvise radiation shielding using boiled rice and old socks.
The Soviet Union’s nuclear-powered Sevmorput, the last of the four and the only one to operate into the 21st century, has sat idle at a dock in Murmansk since 2024. As of today, not a single nuclear-powered merchant ship plows the seas anywhere on Earth.
And yet, military fleets have proven the technology works. The U.S. Navy alone has logged more than 6,200 accident-free reactor-years since 1955. What’s more, reactor designs have advanced significantly since Heaney’s day. Small modular reactors, or SMRs, have been engineered to be smaller, safer, and simpler to certify than anything available in 1959. SMRs are now in active development for maritime use, including a Norwegian consortium’s NuProShip program, and a molten-chloride test reactor that Core Power and TerraPower are building at the Idaho National Laboratory.
The pressure to act has intensified, too. Commercial shipping produces more than three percent of global greenhouse gas emissions—a share that could climb to 10 percent by 2050 if the industry does nothing while the rest of the world decarbonizes. In 2023, the International Maritime Organization, which governs commercial shipping, committed its member states to a net-zero target by 2050, a goal serious enough that the IMO is now weighing previously unthinkable measures like SMRs.
But none of it matters if nuclear-powered merchant ships remain taboo.
Sixty-five years after Jack Heaney tried to make the atom desirable, the real problem with nuclear reactors was less about the technology and more about public perception. Unfortunately, that perception has kept a viable climate solution off the table for more than half a century, at a cost now measurable in our planet’s atmosphere. As the shipping industry searches for a way to shed its considerable share of global carbon emissions, it is not physics but persuasion that remains unsolved.
In A Century in Motion, Popular Science revisits fascinating transportation stories from our archives, from hybrid cars to moving sidewalks, and explores how these inventions are re-emerging today in surprising ways.
Almost a hundred years ago, physicists theorized out what free fall should do to a quantum wave. If the solution they came up with is wrong, quantum mechanics and Einstein's theory of gravity flatly contradict each other. But testing it has been impossible because nobody has managed to build an interferometer that could perform the necessary measurement.
Now, a team led by Ron Folman, a physicist at Ben-Gurion University of the Negev, with collaborators in Germany, the UK, and the US, including Nobel laureate Roger Penrose, has done it. They built a new interferometer that gives a single atom two possible paths at once: one that involves a free fall, and another where it is held perfectly still. Both paths end at the same place at the same moment, allowing the team to measure what the fall does to a wave-like property of the atom.
Long time coming
Ever since Galileo, physicists have known how to describe a falling object—where it is, how fast it goes, or how quickly it accelerates. Quantum mechanics, though, insists that every object is also a wave. “Every particle, doesn't matter if it's a car or a spaceship or an atom, is a wave,” Folman says. “Everything that is a wave, like sea waves or sound waves, goes up and down. And if you're up or down, this is measured by something called a phase. A phase just tells you if you are at the top of the wave or at the bottom.”
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.
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.
A demonstration of the equivalence principle. (Image credit: Robert Lea (created with Canva))
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.
The 2D MOT apparatus which feeds the science chamber with cold atoms. At the center is a glass cell held under vacuum between coils producing magnetic fields. The atoms go into the science chamber through the tiny hole that may be seen in the center of the yellow (reflecting) surface. (Image credit: Or Dobkowski.)
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 journalScience 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.
The tiny magnet used by the Rice University research team (Image Credit: Christopher Tunnell/Rice University).
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.
The Rice research unit, led by associate professor Christopher Tunnel (left).
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 atmicah@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.”
All four major LHC experiments have found new evidence that collisions between oxygen and neon may produce the extreme state of matter that existed during the first microseconds after the Big Bang. Inside the Large Hadron Collider (LHC), collisions between relatively light oxygen and neon nuclei may be producing matter from the earliest moments of [...]
Beyond familiar particles such as electrons and protons, scientists have discovered a zoo of "quasiparticles" with exotic names, such as magnons, angulons, dropletons and polaritons. But what are quasiparticles, exactly? And given the "quasi" in their name, are they considered real particles?
One way to understand quasiparticles is to explore what a particle is. The standard mental picture of a particle "is of a discrete object, like a ball," Douglas Natelson, a condensed matter physicist at Rice University in Houston, told Live Science. However, this classic image of particles changed with the advent of quantum physics, which revealed that the universe becomes fuzzy at its smallest levels. For example, in 1924, French physicist Louis de Broglie showed that particles such as electrons could also behave as waves — a discovery that earned him a Nobel Prize.
Modern physics suggests that particles are excitations in fields that permeate the entire universe, a bit like a ripple in a pond, Ross McKenzie, a theoretical condensed matter physicist and professor emeritus at the University of Queensland in Australia, told Live Science. Each type of particle has its own corresponding field. For instance, photons of light are ripples of the electromagnetic field, McKenzie noted.
The quantum nature of particles means they can not only fly through an empty vacuum but also ripple through matter. For instance, photons can zip through transparent and translucent materials, and electrons can flow inside wires.
If you can picture a standard particle, such as an electron, as a ripple traveling within a material, you can also envision other kinds of excitations within matter. These other types of ripples are quasiparticles.
For example, think of "the wave" done at a sporting event. "You can watch it propagate around a football stadium; it has a location and a speed," Natelson said. "It only exists within the stadium, though, and it's made up of the collective response of all the interacting fans."
In much the same way, "quasiparticles can only exist within some medium or material, because they are built up from the response of that material's constituents or building blocks," Natelson said; in contrast, particles such as electrons and protons "can exist in free space."
Electrons have a negative charge and orbit around the nucleus of an atom. (Image credit: agung fatria viaGetty Images)
In other words, quasiparticles can't exist in a vacuum and they can't exist on their own. They're reliant on particles acting together and being in a material where they can emerge, just as a wave carried out in a stadium can only exist when there is a group of people there who can perform it.
A philosophical question concerning quasiparticles is whether they are real, McKenzie noted. After all, "quasi" in Latin means "almost."
"Fundamental particles can exist in isolation in a vacuum, and quasiparticles need many interacting particles to exist," McKenzie said. "Still, I would say quasiparticles are, for all intents and purposes, just as real as particles, in how you can detect them and manipulate them."
A zoo of quasiparticles
The concept of quasiparticles originated with theoretical physicist Lev Landau in the 1950s, McKenzie said, and the idea ultimately helped Landau win the Nobel Prize in physics in 1962. Scientists have now proposed the existence of dozens of quasiparticle types, including the following:
The phonon, which is a quasiparticle of sound — it is the smallest packet of vibrational energy that makes up sound in matter, McKenzie said.
The electron hole, often simply called a hole, is the positively charged vacancy left behind once an electron has left its original place, McKenzie noted.
The electron quasiparticle, which essentially consists of an electron and its interactions with its surrounding environment. This combined package means the electron quasiparticle requires more force to move, so it effectively has more mass than a regular electron, McKenzie explained.
The exciton, a quasiparticle made of an electron and a hole orbiting each other.
The anyon, a kind of quasiparticle so far only seen in two-dimensional systems, which may carry only a fraction of an electric charge.
"How many kinds of quasiparticles are there?" McKenzie said. "Just like there are an infinite number of possible states of matter, I would say that, in principle, there are an infinite number of types of quasiparticles."
Scientists describe activity in material as quasiparticles "because it simplifies everything dramatically," McKenzie said. In the same vein, Natelson said that "very often the math behind physical phenomena in solids is described well by quasiparticles."
Quasiparticles are not simply useful for bookkeeping. For instance, researchers typically describe the behavior of electricity in electronic devices in forms of quasiparticles such as holes and excitons, Natelson said.
All in all, the answer to the question of whether quasiparticles are real is a matter of interpretation. If the question is whether or not a quasiparticle is an elementary particle such as an electron, the answer is no — they cannot exist on their own, and they depend on the materials in which they manifest.
However, if the question is whether or not quasiparticles are real phenomena, the answer is yes — they are things that scientists can measure that can behave like particles and effectively have many of the same properties that other particles do.
A photon is a single particle of light, and under normal circumstances, it can't be divided. But a photon is also not a particle, in the sense that it does not have a specific location. Instead, it is an extended object.
So if a photon is only partway through the process of reflecting from a perfect mirror and you yank the mirror away, what happens? The answer, from a trio of Norwegian physicists, turns out (arxiv.org link) to be more complex than I expected.
A photon divided?
Let’s first talk briefly about dividing and combining photons. If this were a common experience in our lives, then shining a single color of light through a piece of glass or reflecting it from a surface might cause photons to divide or combine. This would lead to an amazing array of colors: Our universe would be the most fantastic and legal LSD trip you could imagine. But this doesn't generally happen, hence LSD.
After more than two decades of searching, scientists have finally observed a phenomenon in a hot and dense particle 'soup' similar to that which filled the cosmos moments after the Big Bang. The observation could help cosmologists better understand the incredibly hot and dense state of the universe in its earliest moments.
The world's most powerful particle accelerator, the Large Hadron Collider (LHC), regularly creates this so-called quark-gluon plasma by smashing together the atomic nuclei of heavy elements like lead and generating sprays of particles called jets, from which this hot and dense particle soup emerges. This is necessary because in the modern universe, quarks and gluons, referred to as "partons," are only ever found together comprising particles like protons and neutrons. Thus, it takes the kind of energy generated by smashing atoms together at near-light-speeds to free these partons and generate the hot 'soup' known as quark-gluon plasma.
As particles ripple through the quark-gluon plasma, they lose energy and momentum to this medium, which should create wakes in this primordial soup, much like that which is created when the hull of a boat pushes through the ocean. However, researchers had failed to see this so-called "diffusion wake" for two decades. That is, until now.
"Observing and quantifying the quark-gluon plasma diffusion wake opens the door to the new precision characterization of the properties and dynamics of the quark-gluon plasma, and promises new insights into the evolution of the early universe,” team leader Raghunath Pradhan of the University of Illinois Chicago (UIC) said in a statement.
A new approach in the hunt for particle wakes
Previously, the search for wave signals had involved generating events involving the production of a jet alongside a particle called a Z boson. However, while this had provided some evidence of particle wakes, signals from these wakes are subtle and easily drowned out by other jet-related effects, meaning these detections weren't statistically significant enough to be classed as a confirmed detection.
To search for the wave signal, this team took a different approach and used the LHC to smash together two lead nuclei to create jets of particles that were back-to-back, called a dijet event. The unique shape of these events meant that signals from wakes could be more easily disentangled from surrounding noise.
Display of a lead-lead collision, which produced two back-to-back jets, recorded by the CMS experiment. The jets are indicated by the orange cones. (Image credit: CERN)
The team's measurement showed a clear lack of particles behind the direction of the jets, which was particularly prominent at relatively low momentum. That is exactly what would be expected for a diffusion wake.The strongest wake signals were detected in more centralised lead-lead collisions, which create more quark-gluon plasma.
"This observation is a culmination of a decades-long quest to observe the wake phenomenon; it has been predicted by theory over 20 years ago, but remained elusive in the experimental data," team leader Olga Evdokimov of UIC said.
The team's research was accepted for publication on June 25 in the journal Physical Review Letters.
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