Category: 7. Science

Two centuries ago, the double-slit experiment revealed the strange nature of light – somewhat wave and somewhat particle. This quietly launched modern quantum theory.

Now, a team at the Massachusetts Institute of Technology (MIT) has stripped that classroom favorite to its bare bones and proved, once again, that you can never observe light behaving as both a particle and a wave at the same time.

Wolfgang Ketterle of MIT’s Research Laboratory of Electronics (RLE) led the work with graduate student Vitaly Fedoseev and colleagues. They made use of ultracold atoms spaced just a few ten-thousandths of an inch apart in a vacuum lattice.

Their results reset the century-old argument between Albert Einstein and Niels Bohr – this time, in favor of Bohr’s quantum view.

Updating a quantum certainty classic

The original demonstration, performed by Thomas Young in 1801, let sunlight pass through two narrow slits and produced an interference pattern, proving that light can travel as a wave.

More than a century later, Einstein proposed adding a delicate balance to each slit so that a passing photon would nudge it.

This setup, he argued, would let observers detect which path the particle took while still preserving the interference stripes.

Bohr responded that the Heisenberg uncertainty principle would make any such measurement blur the pattern beyond recognition, preserving the mystery.

Physicists have since tried countless versions of the experiment, using electrons, neutrons, and even full-sized molecules – each time confirming Bohr’s stance.

A recent study even formalized a conservation rule: the more information one gains about a particle’s path, the less visible its wave behavior becomes.

“Einstein and Bohr would have never thought that this is possible – to perform such an experiment with single atoms and single photons,” said Ketterle. His group went further by removing every classical component except the light and the scatterers.

Atoms stand in for slits

The researchers cooled more than 10,000 rubidium atoms to about 1 microkelvin – just above absolute zero – so that the atoms barely moved.

Laser beams arranged them into a crystal-like grid, with each site roughly 0.00004 inches apart. This spacing allowed any two neighboring atoms to act as the tiniest conceivable double slit.

A faint laser sent photons in, one by one; each photon scattered off the two adjacent atoms before reaching a camera that recorded interference fringes.

Because every atom was identical, the team could repeat the trial millions of times and build up crisp statistics without the noise that plagued earlier setups that used moving slits.

The heart of the design was controllable “fuzziness.” By loosening the trapping laser for a selected pair of atoms, the physicists enlarged each atom’s quantum position spread.

This increased the chance that an incoming photon would leave a telltale recoil – or which-way information.

When the atoms were sharply localized, the camera recorded bright, evenly spaced stripes – hallmarks of wave interference. Making the atoms fuzzier dissolved those stripes into a speckled blob, revealing particle-like hits instead.

Chasing the limits of certainty

Half-wave, half-particle operation came when the lattice depth was tuned so that only about fifty percent of the photons left detectable recoil.

That mix matched the trade-off predicted by complementarity, linking interference visibility to path knowledge.

To be sure the lattice itself was not acting like Einstein’s spring, the team briefly shut off the trapping light after each shot. This left the atoms freely floating for a millionth of a second before they fell under gravity.

Even without the “spring,” probing the path still erased the stripes, proving that it is the entanglement between photon and atom, not any macroscopic support, that decides the outcome.

“In many descriptions, the springs play a major role,” said Fedoseev, the study’s first author. “But we show, no, the springs do not matter here; what matters is only the fuzziness of the atoms.”

The finding dovetails with a recent analysis that simulated a tunable recoiling-slit scenario and reached an identical verdict. The measuring device can be virtual as long as it steals enough momentum information.

Einstein’s spring meets modern lasers

Einstein imagined a real mechanical balance that would move by about one ten-millionth of an inch, a heroic engineering task for 1927.

Today’s optical lattices create forces a thousand times smaller yet still track them, thanks to single-photon detectors cooled to near 0 °F.

Because the MIT arrangement uses atoms that are “Heisenberg-uncertainty limited,” every recoil event instantly entangles the photon with the atomic state.

As a result, the scattered light carries a fringe pattern only when the atom remains unperturbed. This mirrors Richard Feynman’s famous remark that the double-slit “contains the only mystery” of quantum mechanics.

The team’s control also let them test intermediate fuzziness values and verify that interference visibility falls off in strict proportion to path knowledge.

That linear relation is a long-sought benchmark for quantum resource theories that treat information as a conserved quantity.

The experiment closes a conceptual gap left by molecular and neutron versions, which always relied on extended slits or diffraction gratings. Here, the “slit” is a single particle, so nothing classical can be blamed for the trade-off.

Fuzziness still matters

Light-based computers, precision sensors, and secure communication channels all hinge on balancing wave-like coherence against particle-like detection signals.

Engineers use precise knowledge of how entanglement reduces interference to decide how much information they can extract before a quantum state decoheres.

The MIT results arrive in the United Nations-declared International Year of Quantum Science and Technology (IYQ), a timely reminder that foundational questions still guide applied research. 

Future work will try the same protocol with molecules and superconducting qubits to test whether the visibility-information law is truly universal.

If it holds, textbooks may soon replace drawings of slits in screens with sketches of floating atoms. This would give students a more faithful picture of how nature hides her clues.

The study is published in Physical Review Letters.

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This week in R&D: the first quantum computer in space is now orbiting the Earth; a potential new treatment for Alzheimer’s, thanks to cancer drugs; a startup is breaking ground on their first fusion power plant, they say they are on track to deliver fusion energy by 2030; Google DeepMind announced their AI Earth mapping model; physicists at Rutgers discovered a new state of matter with strange electrical properties; finally, a record-breaking lightning bolt stretched 515-miles.

Aerospace and defense technology

An international team sent the first quantum computer into space

The story: An international team of scientists sent the first quantum computer into space on June 23 and is now operational. 

The numbers:

• The quantum computer is orbiting Earth at approximately 550 km (342 miles)
• It fills a volume of 3 liters and uses about 10 watts of power

Why it matters: The quantum computer has an onboard camera that could be used for Earth observation. This mission will provide scientists with insight into the potential of quantum computers for space missions and what is required to make them small and resilient enough for space travel. 

Watch for: Project leader Philip Walther from the University of Vienna says demonstrations of the quantum computer’s ability will be released soon.

Health and medicine

Researchers discovered two cancer drugs that might reverse the effects of Alzheimer’s

The story: Researchers have discovered two cancer drugs that might reverse the effects of Alzheimer’s disease on the brain. With publicly available data, the scientists were able to produce gene expression signatures for Alzheimer’s disease in the brain that they compared to a database of the effects of thousands of drugs on human gene expression. 

The numbers:

• Out of 1,300 drugs, 111 reversed the gene signature of Alzheimer’s in one or multiple cell types. 
• Out of these, only 10 were approved by the FDA. 
• The researchers chose 2 cancer drugs from the top 5 candidates to test: letrozole and irinotecan. 
• In the database, compiled of cancer patients taking either drug who also had AD, as well as a control group of cancer patients not taking either drug who had AD, the prevalence of AD was 2.4%
• The prevalence of AD in patients taking letrozole was 2.18%, and 1.83% for irinotecan
• The researchers also conducted a study in mice to further investigate, finding that only the combination of letrozole and irinotecan resulted in significant rescue of memory impairment

Why it matters: AD affects 7 million people in the U.S., but it has a lack of effective treatments. Only two FDA-approved drugs are available, neither of which significantly slows the advancement of the disease. This study presents a promising potential treatment that could be more effective. 

Watch for: Further studies of irinotecan and letrozole for AD using brain cells at human-relevant dosages.

Energy

Helion Energy breaks ground on its first fusion power plant

The story: Helion Energy has started construction of its first power production reactor, the startup announced Wednesday. 

The numbers:

• The company says they are on track to deliver electricity within three years to Microsoft under a 2023 agreement 
• The startup has amassed $1 billion in investments, one of three developers to do so
• The plant is expected to produce at least 50 megawatts of power

Why it matters: Fusion energy is an attractive potential alternative to fossil fuels. It aims to harness the heat energy from the fusion of two light atoms, a process which occurs in stars. 

Watch for: Although there is uncertainty about when fusion power might be commercially possible, Helion has promised to deliver by 2030. Other companies have made similar goals: TAE Technologies aims for the early 2030s, and General Fusion says they are on track for the early to mid-2030s.

Artificial Intelligence and big data

Google DeepMind unveiled an AI ‘satellite’ that can map the Earth in “unprecedented detail”

The story: Google DeepMind has a new AI mapping system which can show the Earth in “unprecedented detail”, according to the press release published on Wednesday. The model is called AlphaEarth Foundations and is designed to provide scientists with a more complete picture of the planet. 

The numbers:

• According to the team’s paper, the new model has a 24% lower error rate than other models
• The model is powered by the Satellite Embedding dataset, which has over 1.4 trillion embedding footprints each year
• Each 10 meter pixel in the dataset is a 64-dimensional representation of surface conditions

Why it matters: This could help scientists and policy makers make informed decisions about issues including food security, deforestation, urban expansion and water resources. 

Watch for: The Satellite Embedding dataset is available in Google Earth Engine, and organizations are already embarking on projects utilizing it. To understand the real impact of this release, look for results from the UN’s Food and Agriculture Organization, Harvard Forest, MapBiomas, Global Ecosystems Atlas and more.

Physics

Rutgers physicist discovered a new state of matter

The story: Physicists at Rutgers University discovered a new state of matter: quantum liquid crystal. 

The details:

• The new state was discovered by combining Weyl semimetals and spin ice. 
• When combined, the electronic properties of the Weyl semimetal are influenced by the magnetic properties of spin ice. 
• This interaction leads to electronic anisotropy, where the material conducts electricity differently in different directions. 
• When the magnetic field is increased, the electrons flow in two different directions. 

Why it matters: This study reveals new methods for controlling the properties of materials. The findings could be applied to design ultra-sensitive quantum sensors of magnetic fields that would work in extreme conditions, such as in space. 

Watch for: Further studies exploring new quantum materials when they are combined into a heterostructure.

Meteorology

Record-breaking 515-mile lightning strike stretched from Texas to Kansas

The story: A record-breaking 515-mile lightning bolt was recorded stretching from eastern Texas to Kansas City. 

The numbers:

• The “megaflash” broke the previous record of 477 miles (from April 2020) by 38 miles. 
• The results come from a re-examination of satellite footage from a storm in Oct. 2017
• The National Oceanic and Atmospheric Agency’s GOES-16 satellite detects around one million lightning flashes per day, one of four NOAA satellites with geostationary lightning mappers
• Most lightning strikes are ten miles long or less; a bolt longer than 60 miles is considered a megaflash
• Less than 1% of thunderstorms produce megaflashes

Why it matters: The findings are helping scientists understand thunderstorms, improving public safety. Lightning regularly strikes 10-15 miles from the storm center, something most don’t realize. 

Other extreme lightning occurrences: 

• Longest duration of a flash: 17.102 seconds, June 18, 2020, during a storm over Uruguay and northern Argentina
• Deadliest direct strike: 21 people killed by a single flash in Zimbabwe in 1975
• Deadliest indirect strike: 469 people killed in Egypt when lightning struck a set of oil tanks in 1994

The key to our future climate might be lying on the bottom of the seafloor. In a study published in the journal Marine Geology, scientists recently mapped vast Antarctic canyon networks, and used the results to better understand climate change.

In the study, researchers from the Faculty of Earth Sciences at the University of Barcelona, Spain, and the marine geosciences research group at University College Cork, Ireland used data from the International Bathymetric Chart of the Southern Ocean to create a detailed map of 332 canyon networks – nearly five times the number of canyons identified in previous studies. In doing so, they found that the vast underwater depressions may have a greater influence on ice-sheets than previously thought.

Underwater canyons have been increasingly recognized as playing a crucial role in climate change. They are conduits for water exchange in the world’s oceans, funneling heat, sediment and nutrients along with it. There are canyons all over the seafloor, but as research team member David Amblàs told The Guardian, the ones in Antarctica “tend to be larger and deeper because of the prolonged action of polar ice and the immense volumes of sediment transported by glaciers to the continental shelf.”

“That’s why we must continue to gather high-resolution bathymetric data in unmapped areas that will surely reveal new canyons, collect observational data … and keep improving our climate models to better represent these processes and increase the reliability of projections on climate change impacts.”

August 1, 2025

As it soared past Mars in March, NASA’s Europa Clipper conducted a critical radar test that had been impossible to accomplish on Earth. Now that mission scientists have studied the full stream of data, they can declare success: The radar performed just as expected, bouncing and receiving signals off the region around Mars’ equator without a hitch.

Called REASON (Radar for Europa Assessment and Sounding: Ocean to Near-surface), the radar instrument will “see” into Europa’s icy shell, which may have pockets of water inside. The radar may even be able to detect the ocean beneath the shell of Jupiter’s fourth-largest moon.

“We got everything out of the flyby that we dreamed,” said Don Blankenship, the principal investigator of the radar instrument and a professor at the Jackson School of Geosciences. “The goal was to determine the radar’s readiness for the Europa mission, and it worked. Every part of the instrument proved itself to do exactly what we intended.”

The radar, which was developed by Blankenship and his team a the school’s Institute for Geophysics, will help scientists understand how the ice may capture materials from the ocean and transfer them to the surface of the moon. Above ground, the instrument will help to study elements of Europa’s topography, such as ridges, so scientists can examine how they relate to features that REASON images beneath the surface.

Limits of Earth

Europa Clipper has an unusual radar setup for an interplanetary spacecraft: REASON uses two pairs of slender antennas that jut out from the solar arrays, spanning a distance of about 58 feet (17.6 meters). Those arrays themselves are huge — from tip to tip, the size of a basketball court — so they can catch as much light as possible at Europa, which gets about 1/25th the sunlight as Earth.

The instrument team conducted all the testing that was possible prior to the spacecraft’s launch from NASA’s Kennedy Space Center in Florida on Oct. 14, 2024. During development, engineers at the agency’s Jet Propulsion Laboratory in Southern California even took the work outdoors, using open-air towers on a plateau above JPL to stretch out and test engineering models of the instrument’s spindly high-frequency and more compact very-high-frequency antennas.

But once the actual flight hardware was built, it needed to be kept sterile and could be tested only in an enclosed area. Engineers used the giant High Bay 1 clean room at JPL, where the spacecraft was assembled, to test the instrument piece by piece. To test the “echo,” or the bounceback of REASON’s signals, however, they’d have needed a chamber about 250 feet (76 meters) long — nearly three-quarters the length of a football field.

Enter Mars

The mission’s primary goal in flying by Mars on March 1, less than five months after launch, was to use the planet’s gravitational pull to reshape the spacecraft’s trajectory. But it also presented opportunities to calibrate the spacecraft’s infrared camera and perform a dry run of the radar instrument over terrain NASA scientists have been studying for decades.

As Europa Clipper zipped by the volcanic plains of the Red Planet — starting at 3,100 miles (5,000 kilometers) down to 550 miles (884 kilometers) above the surface — REASON sent and received radio waves for about 40 minutes. In comparison, at Europa the instrument will operate as close as 16 miles (25 kilometers) from the moon’s surface.

All told, engineers were able to collect 60 gigabytes of rich data from the instrument. Almost immediately, they could tell REASON was working well. The flight team scheduled the full dataset to download, starting in mid-May. Scientists relished the opportunity over the next couple of months to examine the information in detail and compare notes.

“The engineers were excited that their test worked so perfectly,” said JPL’s Trina Ray, Europa Clipper deputy science manager. “All of us who had worked so hard to make this test happen — and the scientists seeing the data for the first time — were ecstatic, saying, ‘Oh, look at this! Oh, look at that!’ Now, the science team is getting a head start on learning how to process the data and understand the instrument’s behavior compared to models. They are exercising those muscles just like they will out at Europa.”

Europa Clipper’s total journey to reach the icy moon will be about 1.8 billion miles (2.9 billion kilometers) and includes one more gravity assist — using Earth — in 2026. The spacecraft is currently about 280 million miles (450 million kilometers) from Earth.

More About Europa Clipper

Europa Clipper’s three main science objectives are to determine the thickness of the moon’s icy shell and its interactions with the ocean below, to investigate its composition, and to characterize its geology. The mission’s detailed exploration of Europa will help scientists better understand the astrobiological potential for habitable worlds beyond our planet.

Managed by Caltech in Pasadena, California, NASA’s Jet Propulsion Laboratory in Southern California leads the development of the Europa Clipper mission in partnership with the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, for NASA’s Science Mission Directorate in Washington. APL designed the main spacecraft body in collaboration with JPL and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, NASA’s Marshall Space Flight Center in Huntsville, Alabama, and Langley Research Center in Hampton, Virginia. The Planetary Missions Program Office at NASA Marshall executes program management of the Europa Clipper mission. NASA’s Launch Services Program, based at NASA Kennedy, managed the launch service for the Europa Clipper spacecraft. The REASON radar investigation is led by the University of Texas at Austin.

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More information about Europa Clipper: https://science.nasa.gov/mission/europa-clipper/

More information about the REASON radar: https://www.jsg.utexas.edu/news/reason/

This news release was adapted from a version originally published by NASA’s Jet Propulsion Laboratory: https://www.nasa.gov/missions/europa-clipper/nasas-europa-clipper-radar-instrument-proves-itself-at-mars/

For more information, contact: Anton Caputo, Jackson School of Geosciences, 210-602-2085; Monica Kortsha, Jackson School of Geosciences, 512-471-2241; Julia Sames, Department of Earth and Planetary Sciences, 210-415-9556.

Astronomers using the NASA/ESA/CSA James Webb Space Telescope have observed the Hubble Ultra Deep Field (HUDF), an area of deep space with nearly 10,000 galaxies in the constellation Fornax.

The original HUDF images were pioneering deep-field observations with Hubble published in 2004.

They probed more deeply than ever before and revealed a menagerie of galaxies dating back to less than a billion years after the Big Bang.

The area was subsequently observed many times by Hubble and other telescopes.

“The field shown here, known as the MIRI Deep Imaging Survey (MIDIS) region, was observed with the shortest-wavelength filter of Webb’s Mid-Infrared Instrument (MIRI) for nearly 100 hours,” the Webb astronomers said in a statement.

“This is Webb’s longest observation of an extragalactic field in one filter so far, producing one of the deepest views ever obtained of the Universe.”

“Combined with data from Webb’s Near-Infrared Camera (NIRCam), this image allows astronomers to explore how galaxies formed and evolved over billions of years.”

“These deep observations have revealed more than 2,500 sources in this tiny patch of sky.”

“Among them are hundreds of extremely red galaxies — some of which are likely massive, dust-obscured systems or evolved galaxies with mature stars that formed early in the Universe’s history.”

“Thanks to Webb’s sharp resolution, even at mid-infrared wavelengths, researchers can resolve the structures of many of these galaxies and study how their light is distributed, shedding light on their growth and evolution.”

In the new Webb image of HUDF, the colors that have been assigned to different kinds of infrared light highlight the fine distinctions astronomers can make with these deep data.

“Orange and red represent the longest mid-infrared wavelengths,” the astronomers said.

“The galaxies in these colors have extra features — such as high concentrations of dust, copious star formation, or an active galactic nucleus (AGN) at their center — which emit more of this farther infrared light.”

“Small, greenish-white galaxies are particularly distant, with high redshift.”

“This shifts their light spectrum into the peak mid-infrared wavelengths of the data, which are depicted in white and green.”

“Most of the galaxies in this image lack any such mid-infrared boosting features, leaving them most bright at shorter near-infrared wavelengths, which are depicted with blue and cyan colors.”

“Hearst Magazines and Yahoo may earn commission or revenue on some items through these links.”

Here’s what you’ll learn when you read this story:

• Our biological clock, or circadian rhythm, is immensely important to our health, and scientists are now unpacking the process’s secrets at the cellular level.

• Researchers successfully created synthetic, cell-like structures, or vesicles, to test how varying concentrations of so-called “clock proteins” affect the vesicles’ natural timekeeping.

• The team—amongst other discoveries—found that clock accuracy was proportional to both the amount of clock proteins and vesicle size.

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One of the many biological wonders of life on Earth is the near-perfect ways our bodies can sense the passage of time. Known as our biological clock or circadian rhythm, this natural process regulates our wake-sleep cycle and is highly attuned to Earth’s 24-hour rotation.

To better understand this mechanism, scientists from University of California Merced attempted to reconstruct this clockwork system in cyanobacteria. The team created cell-like structures known as vesicles (each only 2 to 10 micrometers in diameter) and loaded them with “clock proteins”—groups of proteins that play an important role in regulating the circadian rhythm. The results were published this week in the journal Nature Communications.

In this study, the authors used cyanobacterial clock proteins KaiA, KaiB, and KaiC. As Earth.com describes, KaiC acted as the system’s hub while the other proteins shifted the process forward and backward. The team then inserted the vesicle lipid with a fluorescent tag whose steady glow showed the circadian rhythm in action, and found that both vesicle size and the amount of “clock proteins” were proportional to how well the vesicles could keep time.

“This study shows that we can dissect and understand the core principles of biological timekeeping using simplified, synthetic systems,” Anand Bala Subramaniam from UC Merced, one of the lead authors on the study, said in a press statement.

When the proteins were reduced, however, the vesicles were no longer accurate timekeepers. The authors were able to reliably reproduce this gradual loss of timekeeping, and by building computational models of the vesicle population, the scientists also discerned that the circadian rhythm’s additional role of turning genes on and off—in order to control physiological and behavioral processes—did not interfere with this timekeeping ability on the individual level, but proved essential for synching clocks across the population.

“This new study introduces a method to observe reconstituted clock reactions within size-adjustable vesicles that mimic cellular dimensions,” Mingxu Fang, a microbiologist from Ohio State University who wasn’t involved with the study, said in a press statement. “This powerful tool enables direct testing of how and why organisms with different cell sizes may adopt distinct timing strategies, thereby deepening our understanding of biological timekeeping mechanisms across life forms.”

Understanding the ins and outs of circadian rhythm is immensely important, as the biological process—or the disruption of it—can lead to a variety of illnesses, including cardiovascular disorders and cancer. It can also impact the treatments for these diseases, and scientists have even explored a concept known as “chronochemotherapy” to increase the efficacy of the drugs while limiting toxicity by carefully timing doses.

The 24-hour clocks within our cells are the smallest on Earth, but they also might be the most important.

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CAPE CANAVERAL, Florida – A team of astronauts from Japan, Russia and the United States headed to the International Space Station aboard a SpaceX craft from Florida on Friday, marking the second space flight for Japanese astronaut Kimiya Yui.

The Crew-11 mission, also involving two Americans and one Russian, will stay at the ISS for about six months, partly to conduct experiments in hopes of helping future lunar exploration. It is expected to reach the ISS in the early hours of Saturday.

“My fellow Japanese out there, I have come back to space for the first time in 10 years,” Yui said in Japanese from inside the Crew Dragon capsule after it separated from the booster rocket. “I’m resolved to perform my duties well, shine like a star of the first magnitude and let people all over the world know great things about Japan.”

Yui, a 55-year-old Nagano Prefecture native and former Air Self-Defense Force pilot, previously stayed at the ISS between July and December 2015, and was responsible for the docking of an unmanned supply craft developed by Japan.

Japan’s Takuya Onishi, in command of the International Space Station since April, is due to return to Earth following a handover period of several days. The 49-year-old former airline pilot is the third Japanese astronaut to have served as ISS commander.

The Crew-11 mission comprises Yui of the Japan Aerospace Exploration Agency, Zena Cardman and Mike Fincke of the National Aeronautics and Space Administration, as well as Roscosmos cosmonaut Oleg Platonov.

Among other things, Yui will participate in a test of carbon dioxide removal technology necessary for Gateway, a space station that will orbit the Moon under the U.S.-led Artemis lunar exploration program.

Two recent studies by Professor Stefano Profumo at the University of California, Santa Cruz, propose theories that attempt to answer one of the most fundamental open questions in modern physics: What is the particle nature of dark matter?

Science has produced overwhelming evidence that the mysterious substance that accounts for 80% of all matter in the universe exists. Dark matter’s presence explains what binds galaxies together and makes them rotate. Findings such as the large-scale structure of the universe and measurements of the cosmic microwave background also prove that something as-yet undetermined permeates all that darkness.

What remains unknown are the origins of dark matter, and hence, what are its particle properties. Those weighty questions primarily fall to theoretical physicists like Profumo. And in two recent papers, he approaches those questions from different directions, but both centered on the idea that dark matter might have emerged naturally from conditions in the very early universe—rather than dark matter being an exotic new particle that interacts with ordinary matter in some detectable way.

Shadowy origins

The most recent study, published on July 8, explores whether dark matter could have formed in a hidden sector—a kind of “mirror world” with its own versions of particles and forces. While completely invisible to humans, this shadow sector would obey many of the same physical laws as the known universe.

The idea draws inspiration from quantum chromodynamics (QCD), the theory that describes how quarks are bound together inside protons and neutrons by the strong nuclear force. UC Santa Cruz has deep roots in this area: Emeritus physics professor Michael Dine helped pioneer theoretical models involving the QCD axion, a leading dark matter candidate, while research professor Abe Seiden contributed to major experimental efforts probing the structure of hadrons—particles made of quarks—in high-energy physics experiments.

In Profumo’s new work, the strong force is replicated in the dark sector as a confining “dark QCD” theory, with its own particles—dark quarks and dark gluons—binding together to form heavy composite particles known as dark baryons. Under certain conditions in the early universe, these dark baryons could become dense and massive enough to collapse under their own gravity into extremely small, stable black holes—or objects that behave much like black holes.

These black hole–like remnants would be just a few times heavier than the Planck mass—the fundamental mass scale of quantum gravity—but if produced in the right quantity, they could account for all the dark matter observed today. Because they would interact only through gravity, they would be completely invisible to particle detectors—yet their presence would shape the universe on the largest scales.

This scenario offers a new, testable framework grounded in well-established physics, while extending UC Santa Cruz’s long-standing exploration of how deep theoretical principles might help explain one of the biggest open questions in cosmology.

On the horizon

Profumo’s other recent study, published in May, explores whether dark matter might be produced by the universe’s expanding “cosmic horizon”—essentially, the cosmological equivalent of a black hole’s event horizon.

This paper asks, if the universe underwent a brief period of accelerated expansion after inflation—something less extreme than inflation, but still expanding faster than radiation or matter would allow—could that phase itself have “radiated” particles into existence?

“Both mechanisms are highly speculative, but they offer self-contained and calculable scenarios that don’t rely on conventional particle dark matter models, which are increasingly under pressure from null experimental results,” said Profumo, deputy director for theory at the Santa Cruz Institute for Particle Physics.

One could say Profumo wrote the book on the quest to understand the nature of dark matter. His 2017 textbook An Introduction to Particle Dark Matter presents lessons that he personally learned and used in his research work from state-of-the-art techniques that scientists have developed over the years to build and test particle models for dark matter.

The book describes the “paradigm of dark matter” as “one of the key developments at the interface of cosmology and elementary particle physics,” and is intended for anyone interested in the microscopic nature of dark matter as it manifests itself in particle physics experiments, cosmological observations, and high-energy astrophysical phenomena.

Connection to UC Santa Cruz

Researchers here have played a key role in cosmology for decades, contributing to the development of the standard Lambda-Cold Dark Matter model — still the best fit to all cosmological data — and to the theoretical and observational study of how structure forms in the universe. In addition, UC Santa Cruz has long supported a close interplay between theory and observation, with strengths in particle physics, astrophysics, and early universe cosmology. 

Profumo said these recent publications continue in that tradition, exploring ideas that connect the deepest questions in particle physics with the large-scale behavior of the cosmos. “And they do so in a way that remains rooted in known physics — whether quantum field theory in curved spacetime, or the well-studied properties of SU(N) gauge theories — while extending them to new frontiers,” he said.

Both studies appeared in Physical Review D, the American Physical Society’s premier venue for theoretical particle physics.