In CUriosity, experts across the �鶹��Ѱ�����Boulder campus answer pressing questions about humans, our planet and the universe beyond.

Previously, astrophysicist Jeremy Darling tackled: “What is the biggest thing in the universe?” This week, Ethan Neil, associate professor in the Department of Physics, answers: “What is the smallest thing in the universe?”

As with everything in physics, the answer may melt your brain—just a little. It also hinges on how you define “small,” said Ethan Neil, a theoretical physicist who studies incredibly small things.

Does smallest mean, for example, the object with the least mass? Or is it more about size, how much space an object takes up?

  Previously in CUriosity

What is the biggest thing in the universe?

Or read more CUriosity stories here

As Neil put it: “The question is more complicated than it seems on the surface, partly just due to the weirdness of quantum physics. The world is unintuitive when we get to very short distance scales.”

Let’s start with mass. Neil explained that the universe, at least as we know it, is made up of elementary particles like electrons and quarks, small things that can’t be broken down into even smaller stuff. Think of them as the basic ingredients for making everything in the cosmos.

Physicists capture the family tree of these particles in a theory that dates back to the 1960s known as the Standard Model. Within that tree, the electron is superbly petite. Writing out its mass in kilograms, you’d get 0.000000000000000000000000000000911 (that’s 30 zeros). Another elementary particle, the electron neutrino, has an even smaller mass—although no one knows exactly how small. The sun ejects neutrinos constantly and, at this moment, trillions are moving through your body.

The question of size, however, is where things really get weird.

“In the Standard Model, things like the electron don’t have any size,” Neil said.

In other words, you could zoom in and in on them and never see anything. But how sure are scientists that electrons are truly infinitely small?

Using facilities like the at CERN in Switzerland, scientists have probed the universe down to really small scales. So far, they’ve been able to observe the universe down to about 20 zeptometers.

Or, as Neil put it: “If a single atom was the size of a human being, 20 zeptometers would be the size of an atom.”

If an electron has size, it has to be smaller than that. But theoretical physicists like Neil have also thought about what could exist at even smaller scales. That includes at the Planck length, a distance that, in meters, would take a decimal point followed by 34 zeros to write out.

At that scale, Neil explained, the inherent randomness and uncertainty of the universe dominates so much that concepts like size and distance become more or less meaningless. In fact, physicist John Baez predicted that if you tried to measure something that small, you’d concentrate enough energy to form a black hole.

That doesn’t, however, mean that there’s nothing there. One popular theory suggests that the elementary particles themselves are made up of vibrating strings that are about the size of the Planck length—meaning that everything you know could be the product of a concerto played by an orchestra of impossibly tiny violins. 

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A team of physicists and engineers at the �鶹��Ѱ�����Boulder has discovered a new way to measure the orientation of magnetic fields using what may be the tiniest compasses around—atoms. 

The group’s findings could one day lead to a host of new quantum sensors, from devices that map out the activity of the human brain to others that could help airplanes navigate the globe. The new study, , stems from a collaboration between physicist Cindy Regal and quantum engineer Svenja Knappe.

It reveals the versatility of atoms trapped as vapors, said Regal, professor of physics and fellow at between �鶹��Ѱ�����Boulder and the National Institute of Standards and Technology (NIST).

“Atoms can tell you a lot,” she said. “We’re data mining them to glean simultaneously whether magnetic fields are changing by extremely small amounts and what direction those fields point.” 

These fields are all around us, even if you never see them. Earth’s iron-rich core, for example, generates a powerful magnetic field that surrounds the planet. Your own brain also emits tiny pulses of magnetic energy every time a neuron fires.

But measuring what direction those fields are pointing, for precise atomic sensors in particular, can get tricky. In the current study, Regal and her colleagues set out to do just that—with the aid of a small chamber containing about a hundred billion rubidium atoms in vapor form. The researchers hit the chamber with a magnetic field, causing the atoms inside to experience shifts in energy. They then used a laser to precisely measure those shifts.

“You can think of each atom as a compass needle,” said Dawson Hewatt, a graduate student in Regal’s lab at JILA. “And we have a billion compass needles, which could make for really precise measurement devices.”

Magnetic world

The research emerges, in part, from Knappe’s long-running goal to explore the magnetic environment surrounding us.

“What magnetic imaging allows us to do is measure sources that are buried in dense and optically opaque structures,” said Knappe, research professor in the Paul M. Rady Department of Mechanical Engineering. “They’re underwater. They’re buried under concrete. They’re inside your head, behind your skull.”

In 2017, for example, Knappe co-founded the company that manufactures atomic vapor magnetic sensors, also called optically pumped magnetometers (OPMs). The company builds integrated sensors the size of a sugar cube and fits them into helmets that can map out the activity of human brains.

These OPMs also have a major limitation: They only perform well enough to measure minute changes in magnetic fields in environments shielded from outside magnetic forces. A different set of OPMs can be used outside these rooms, but they are only adept at measuring how strong magnetic fields are. They can’t, on their own, record what direction those fields are pointing. That’s important information for understanding changes brains may undergo due to various neurological conditions.

To extract that kind of information, engineers typically calibrate their sensors using reference magnetic fields, which have a known direction, as guides of a sort. They compare data from sensors with and without the reference magnetic fields applied to gauge how those sensors are responding. In most cases, those references are small metal coils, which, Knappe said, can warp or degrade over time.

Regal and her team had a different idea: They would use a microwave antenna as a reference, which would allow them to rely on the behavior of atoms themselves to correct for any changes of the reference over time.

Study co-authors included Christopher Kiehl, a former graduate student at JILA; Tobias Thiele, a former postdoctoral researcher at JILA; and Thanmay Menon, a graduate student at JILA.

Atoms guide the way

Regal explained that atoms behave a bit like tiny magnets. If you zap one of the team’s atoms with a microwave signal, its internal structure will wiggle—a sort of atomic dance that can tell physicists a lot.

“Ultimately, we can read out those wiggles, which tell us about the strength of the energy transitions the atoms are undergoing, which then tells us about the direction of the magnetic field,” Regal said. 

In the current study, the team was able to use that atomic dancing to pinpoint the orientation of a magnetic field to an accuracy of nearly one-hundredth of a degree. Some other kinds of sensors can also reach this level with careful calibration, but the researchers see atoms as having significant potential with further development.  

Unlike mechanical devices with internal parts that can morph, “atoms are always the same,” Regal said.

The team still has to improve the precision of its tiny compasses before bringing them out into the real world. But the researchers hope that, one day, airplane pilots could use atoms to fly around the globe, following local changes in Earth’s magnetic field, much like migratory birds using their own biological magnetic sensors.

“It’s now a question of: ‘How far can we push these atomic systems?’” Knappe said.

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When it comes to putting science into action, last year was one for the record books. From July 2023 to June 2024, �鶹��Ѱ�����Boulder helped to launch 35 new companies based on research at the university—a big tick up from the previous record of 20 companies in fiscal year 2021.

The new businesses are embracing technologies from the worlds of healthcare, agriculture, clean energy and more—including sensors that could one day help farmers improve their crop yields and breathalyzers that can detect signs of infection in the air you breathe out.

Here’s a look at how scientists, with the help of the university’s commercialization arm Venture Partners at �鶹��Ѱ�����Boulder, seek to use discoveries from the lab to make a difference in peoples’ lives.

Mana Battery: Cheaper, longer lasting batteries for clean energy

This company is set to spark a renewable energy revolution. Founded by Chunmei Ban, associate professor in the Paul M. Rady Department of Mechanical Engineering, along with �鶹��Ѱ�����alumni Nick Singstock and Tyler Evans, Mana Battery is developing a cheaper, safer and longer lasting alternative to the traditional lithium-ion battery.

Lithium-ion batteries are the most common type of rechargeable battery on the planet, powering everything from TV remotes to cell phones and even electric vehicles. But the materials used in these batteries, such as lithium and cobalt, are rare and expensive. In contrast, Mana’s batteries run on sodium, an abundant mineral, offering a more affordable and sustainable alternative.

Currently, sodium-ion batteries come with a host of technological challenges. For example, they typically store less energy than lithium-ion batteries of the same size. 

Ban and her team are working on improving sodium-ion battery designs to increase the amount of energy they can store. Their goal is to develop sodium-ion batteries with the same energy density as lithium-ion batteries at just 35% to 75% of the cost. 

The renewable energy industry could reap the benefits. Sodium-ion batteries could store excess clean energy generated by solar panels or wind turbines, providing power even during cloudy or windless days.  

“The use of batteries has significantly supported, and will continue to promote, the widespread use of electric vehicles and low-cost energy storage solutions for the power grid,” Ban said. 

Flari Tech: Laser-based nose to sniff out disease

Imagine a day when, instead of giving blood, saliva or other bodily fluids, you simply exhaled to get a read on what was happening with your health.

That’s the idea behind a new laser-based technology designed to harness human breath for faster, cheaper and less invasive medical diagnostics.

“There is a real, foreseeable future in which you could go to the doctor and have your breath measured along with your height and weight. … Or you could blow into a mouthpiece integrated into your phone and get information about your health in real time,” said Jun Ye, a JILA fellow and adjoint professor of physics who helped develop the technology along with physics doctoral candidate Qizhong Liang.

Humans exhale more than 1,000 distinct molecules with each breath, producing a unique chemical fingerprint or “breath print” filled with clues about what’s happening deep inside them. Scientists have long sought to harness that information, turning to dogs and other animals to sniff out cancer, diabetes and more.

Liang and Ye’s “frequency comb breathalyzer” could someday do the sniffing instead.

It uses frequency comb lasers, which feature narrow optical lines spread across a vast spectral window, to distinguish between different kinds of breath molecules, which are known to vary in concentration when people are sick. Paired with sophisticated algorithms for machine learning and data analysis, their laser-based nose has been shown to be able to detect whether someone has COVID-19 in a matter of seconds.

Research is underway, in close collaboration with medical doctors from the �鶹��Ѱ�����Anschutz Medical Campus, to see if breath can also be used to detect chronic obstructive pulmonary disease (COPD), pediatric respiratory issues and even lung cancer. The team also plans to miniaturize their technology.

In 2023, Flari Tech Inc.—named after the word ‘flari’ (“to smell”) in the Esperanto language—was formed to help move the technology from the lab to the bedside. Much more research is necessary, but ultimately the researchers believe their work could lead to earlier diagnoses for patients—and save lives.

Space Dust Research & Technologies: Tools for cleaning up dust on the moon

When future astronauts travel to the moon, they’ll face a little-known problem: The moon’s dust, or regolith, is made up of particles as sharp as glass that stick to everything.

“As we learned from the Apollo missions, lunar dust readily sticks to all surfaces of exploration systems, causing damage to spacesuits, degrading thermal radiators and solar panels and posing risks to crew health when inhaled,” said Xu Wang, a research associate at the Laboratory for Atmospheric and Space Physics (LASP) at �鶹��Ѱ�����Boulder.

Wang and Mihály Horányi, professor of physics and a researcher at LASP, launched a company to help. will pioneer technology known as Electron-beam Lunar Dust Mitigation (ELDM). ELDM devices generate a beam of electrons that add electric charges to those sticky particles of dust—causing them to, literally, jump off of surfaces.

This technology is versatile enough that it could work in handheld devices or in larger “car washes” that could clean entire spacesuits or rovers.

Space Dust Research & Technologies will also develop a separate type of technology that can sort through dust on the moon and arrange grains by size—an important step in mining regolith to turn it into building materials and more. The company’s work emerged out of years of research in LASP’s NASA-funded Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) lab.

Biosensor Solutions: Biodegradable sensors for tracking soil microbes

Scientists have long known that healthy soils and crops depend on vibrant communities of bacteria and other microbes living in the dirt. There’s just one problem: These microbial communities can be difficult to keep track of.

Until now. Engineer Gregory Whiting and his team at �鶹��Ѱ�����Boulder recently invented a way to measure soil microbial communities using low-cost, printed sensors. The trick: tasty electronics. The sensors include biodegradable resistors that soil microbes eat and degrade over time.

“It’s like a bait for microbes,” said Whiting, associate professor in the Paul M. Rady Department of Mechanical Engineering. “As they eat the device, the signal changes.”

That, in turn, could allow farmers to get a sense of how many microbes are in their soil.

The Boulder-based company , led by co-founders David Beitz and Carl Kalin, licensed this technology in 2024. The group is currently piloting the sensors with an initial group of local companies, precision agriculture providers and growers. According to company officials, “Data and insights from these new sensors will help growers increase yields and save resources on water, fertilizer, pesticides and herbicides.”

Mesa Quantum: Navigation devices based on the behavior of atoms

One new startup could make it easier to navigate the globe, even when GPS satellites go out, such as during bad storms.

For decades, scientists at the National Institute of Standards and Technology (NIST) have pioneered the technology of atomic clocks. These devices keep track of time and can help to track your location by measuring the behavior of electrons whizzing around atoms.

Svenja Knappe, associate research professor in the Paul M. Rady Department of Mechanical Engineering at �鶹��Ѱ�����Boulder, recently helped to improve on those inventions. She discovered a way to make atomic clocks more reliable while also shrinking them down to the size of a computer chip.

Sristy Agrawal and Wale Lawal, who founded Mesa Quantum in 2024, have high hopes for these chips. They say the company's atomic clocks could one day become part of a suite of technologies that enable GPS-free navigation—allowing anyone, from farmers to airplane pilots, to pinpoint their locations on Earth more reliably and precisely than ever before.

“The agricultural sector in Colorado relies heavily on GPS for the operation of tractors, irrigation systems and other modern equipment,” said Agrawal, who earned her doctorate in physics from �鶹��Ѱ�����Boulder in 2024. “As the industry moves toward greater automation, these systems will become even more dependent on precise and reliable positioning data.”

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Editor's note: On Monday, Jan. 20, President Donald Trump signed an executive order delaying the TikTok ban in the United States for 75 days.

The graveyard of social media platforms past: MySpace, Vine, Friendster and now, maybe, TikTok, at least in the United States.

This morning, the U.S. Supreme Court issued a decision allowing a ban of TikTok, the popular app for sharing short-form videos, to go into effect across the country. Lawmakers passed the bill in 2024 after raising concerns about TikTok’s parent company, ByteDance, which is based in China.

Casey Fiesler was among the content creators anxiously awaiting the decision. She studies technology ethics and policy as an associate professor in Department of Information Science at �鶹��Ѱ�����Boulder. She’s also @professorcasey on TikTok where she shares videos on AI and social media with her more than 100,000 followers.

Fiesler noted that apps like TikTok come with a lot of risks. But she said that millions of people around the world have also turned to TikTok to find community—and maybe even learn something.

“Someone could be scrolling through cat videos or dance videos, and then, suddenly, there’s me explaining how algorithms work,” Fiesler said. “To me, that’s magical.”

As the possible ban looms, Fiesler weighs in on what will happen to TikTok’s online communities—and whether they can rebuild those connections on another app.

What is happening with TikTok?

There is a possibility that TikTok will be banned in the United States in just a few days, which is pretty wild. In this country, completely banning a social media platform is not something that has happened before.

But it's also unclear exactly what happens should TikTok become officially banned in the United States. It means that app stores would not be permitted to carry it, so, eventually, we wouldn't be able to get updates on the app, which might make it unusable. It also could mean that third party service providers wouldn’t be allowed to service TikTok—things like PayPal. But it’s unclear exactly what this would look like.

What makes TikTok different from other video-sharing apps?

One thing that feels very special about TikTok is that the recommendation algorithm that determines what you see next in your scroll tends to show people what they want to see. Now, this can be good and bad because you don't always know what kinds of signals you're giving the system. Have you been doomscrolling? More of the same, please.

This algorithm is also creating communities. It can help you find a community that you didn't even necessarily know you needed.

What kinds of communities?

What I found first on TikTok were a lot of other academics and professors who were interested in public education and science communication, and that's been a fun community for me. But I’ve also been lurking on BookTok—I love seeing all of the book content. I also find myself in the middle of a social justice activist community on TikTok.

People are worried about losing these communities. You can try to reconstitute a community on a different platform, but it's not going to be exactly the same.

Do you think people will try to do that—rebuild on another app?

It’s very easy to say, ‘Instagram Reels is just like TikTok. Why don't you just go there?’ But it's not just about the functionality of the app. It's also the fact that you can't bring your community and your audience with you. You have to rebuild from scratch. For some people, particularly those who have built large platforms, this represents a huge amount of work over many, many years.

Recently, a lot of TikTok users have been flocking to the app RedNote, which is also owned by a Chinese company. Is that a viable alternative?

It seems unlikely to me that this can be a lasting thing, in part because of the regulatory issues in both China and the United States. I also think that part of what’s happening is that people are trying to make a point.

Some commentators have pointed out that many U.S. lawmakers don’t seem to know what they’re banning—that technology literacy is fairly low in Congress. Do you agree?

It’s clear that policymakers might not have an understanding of how TikTok is similar to, or sometimes different than, other social media platforms. Many of the critiques that have been very justifiably hurled at TikTok apply equally to X, Instagram or basically any social media platform.

One of the frustrating things about watching this law move forward is that some of the things that are at the basis of this law—data privacy, for example—are incredibly important. It's frustrating, therefore, to see the ban of an entire platform rather than see lawmakers enact data privacy laws.

What can we learn from this saga?

One of the things that's frustrating to me when policymakers talk about the risks and harms of TikTok is that they don't seem to be weighing those risks and harms against the benefits of the platform and against the risks and harms of the platform going away. TikTok is really important to a lot of people—for community, social support, income. It’s incredibly important for small businesses, and these are concrete, tangible harms that will happen if the app goes away.

All social media is good for us and bad for us at the same time. What we have to do is think about how to get more of the good and less of the bad without throwing the baby out with the bath water.

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The trick to creating a better quantum sensor? Just give it a little squeeze.

For the first time ever, scientists have used a technique called “quantum squeezing” to improve the gas sensing performance of devices known as optical frequency comb lasers. These ultra-precise sensors are like fingerprint scanners for molecules of gas. Scientists have used them to spot methane leaks in the air above oil and gas operations and signs of COVID-19 infections in breath samples from humans.

Now, in a series of lab experiments, researchers have laid out a path for making those kinds of measurements even more sensitive and faster—doubling the speed of frequency comb detectors. The work is a collaboration between Scott Diddams at �鶹��Ѱ�����Boulder Boulder and Jérôme Genest at Université Laval in Canada.

“Say you were in a situation where you needed to detect minute quantities of a dangerous gas leak in a factory setting,” said Diddams, professor in the Department of Electrical, Computer and Energy Engineering. “Requiring only 10 minutes versus 20 minutes can make a big difference in keeping people safe.”  

He and his colleagues in the journal Science. Daniel Herman, a postdoctoral researcher in ECEE, led the study.

While normal lasers emit light in just one color, frequency comb lasers send out pulses of thousands to millions of colors—all at the same time. In the new study, the researchers used common optical fibers to precisely manipulate the pulses coming from those lasers. They were able to “squeeze” that light, making some of its properties more precise and others a little more random.

The research, in other words, represents a victory over some of the natural randomness and fluctuations that exist in the universe at very small scales.

“Beating quantum uncertainty is hard, and it doesn’t come for free,” he said. “But this is a really important step for a powerful new type of quantum sensors.”

Photon wrangling

The results represent the latest step in the evolution of frequency combs, a technology born at between �鶹��Ѱ�����Boulder and the National Institute of Standards and Technology (NIST). Diddams was part of a team led by JILA’s Jan Hall that first pioneered frequency comb lasers in the late 1990s. Hall would go on to win a in 2005.

As these laser pulses travel through the atmosphere, for example, molecules in the way will absorb certain colors of light, but not others. Scientists can then identify what’s in the air based on what colors go missing from their laser light. Picture it a bit like a hair comb that’s lost a few of its teeth—hence, the name.

But those measurements also come with intrinsic uncertainties, Diddams said.

Light, he noted, is made up of tiny packets called photons. While lasers may look orderly from the outside, their individual photons are anything but.

“If you’re detecting these photons, they don't arrive at a perfectly uniform rate like one per nanosecond,” Diddams said. “Instead, they arrive at random times.”

Which, in turn, creates what he calls “fuzziness” in the data coming back from a frequency comb sensor.

Enter quantum squeezing.

Giving the squeeze

In quantum physics, many properties are coupled so that measuring one precisely will make your measurements of the other less precise. A classic example is the speed and location of a small particle like an electron—you can know where an electron is or how fast it’s moving, but never both at the same time. Squeezing is a technique that maximizes one type of measurement at the expense of the other.

In a series of lab experiments, Diddams and his colleagues achieved that feat in a surprisingly simple way: They sent their pulses of frequency comb light through a normal optical fiber, not so different from what delivers internet to your home.

The structure of the fiber altered the light in just the right way so that photons from the lasers now arrived at a more regular interval. But that increase in orderliness came at a price. It became a little harder to measure the frequency of the light, or how the photons oscillated to produce specific colors.

That trade-off, however, allowed the researchers to detect molecules of gas with a lot fewer errors than before.

They tested the approach out in the lab using samples of hydrogen sulfide, a molecule that is common in volcanic eruptions and smells like rotten eggs. The team reported that it could detect those molecules around twice as fast with its squeezed frequency comb than with a traditional device. The researchers were also able to achieve this effect over a range of infrared light around 1,000 times greater than what scientists had previously accomplished.

The group still has work to do before it can bring its new sensor out into the field.

“But our findings show that we are closer than ever to applying quantum frequency combs in real-world scenarios,” Herman said.

Diddams agreed: “Scientists call this a ‘quantum speedup,’” he said. “We’ve been able to manipulate the fundamental uncertainty relationships in quantum mechanics to measure something faster and better.”

Other �鶹��Ѱ�����Boulder co-authors of the new study included Professor Joshua Combes; graduate students Molly Kate Kreider, Noah Lordi, Eugene Tsao and Matthew Heyrich; and postdoctoral researcher Alexander Lind. Mathieu Walsh, a graduate student at Université Laval, was also a co-author.

The work at �鶹��Ѱ�����Boulder was supported by the U.S. National Science Foundation through the Quantum Systems through Entangled Science and Engineering (Q-SEnSE) Quantum Leap Challenge Institute and by the Office of Naval Research.

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