Wenzhao Wei and Dan Rederth are the first to earn physics PhDs within the state of South Dakota.
Completing a PhD in physics is hard. It’s even harder when you’re one of the first to do it not just at your university, but at any university in your entire state.
That’s exactly the situation Wenzhao Wei and Dan Rederth found themselves in earlier this year, when completing their doctorates at the University of South Dakota and the South Dakota School of Mines and Technology, respectively. Wei and Rederth are graduates of a joint program between the two institutions.
Wei found out just a few weeks before going in front of a committee at USD to defend her thesis. A couple of students ahead of her had dropped out of the PhD program, leaving her suddenly at the head of the pack.
“When I found out, I was very nervous,” Wei says. “When you’re the first, you don’t have any examples to follow, you don’t know how to prepare your defense, and you can’t get experience from other people who have already done it.”
She recalls running between as many professors and committee members as she could for advice. “I did a lot of checking with them and asking questions. I had no idea what they would be expecting from the first PhD student.”
Despite her wariness, and with some significant publications in the field as the first author, Dr. Wei’s defense was successful, and she is now working as a postdoc at the University of South Dakota.
Rederth knew he was the first at SDSMT but wasn’t aware it was a first in South Dakota until after he had handed in his dissertation and completed his defense. “The president of the school told me I was the first in South Dakota after I finished,” he says. “But I wasn’t aware that Wenzhao had also completed her PhD at the same time.
“Being the first, I was not prepared for the level of questioning I received during my defense – it went much deeper into physics than just my research. Together with Wenzhao, being the first in South Dakota really is a feather in the cap to something which took years of hard work to achieve.”Dan Rederth Different paths to physics
Rederth started on his path to physics research at a young age. “The most satisfying aspect of my PhD research dates back to my childhood,” he says. “I was always intrigued by magnetism and the mystery of how it works, so it was fascinating to do my research.”
His work involved studying strange magnetic quantum effects that arise when certain particles are confined in special materials. A computer program he developed to model the effects could help bring new technologies into electronics.
For Wei’s success, you might expect she had also always made a beeline to research, but physics was actually a late calling for her. At Central China Normal University, she had studied computer science and only switched to physics at master’s level.
“In high school, I remember liking physics, but I ended up choosing computer science,” Wei says. “Then at college, I had some friends who did physics who were part of the same clubs as me, and they kept talking about really interesting things. I found I was becoming less interested in computer science and more interested in physics, so I switched.”
Wei’s thesis, entitled “Advanced germanium detectors for rare event physics searches,” and her current research involve developing technologies for new kinds of particle physics detectors—ones that use germanium, a metal-like element similar to tin and silicon. Such detectors could be used for future neutrino and dark matter experiments.
South Dakota is already home to a growing suite of physics experiments located a mile beneath the surface in the Sanford Underground Research Facility. It was in part a result of these experiments being located in the same state that Wei’s pioneering PhD program came about. USD has been involved with several experiments at SURF, among them the Deep Underground Neutrino Experiment, which will study neutrinos in a beam sent from Fermilab 1300 kilometers away.
“DUNE and SURF have been a vehicle to move the physics PhD program at USD forward,” says Dongming Mei, Wei’s doctoral advisor at USD. “With the progress of DUNE, future PhD students from USD will be exposed to thousands of world-class scientists and engineers.”
Post-doctorate, Wei is now continuing the research she began during her thesis. But with a twist.
“For my PhD, I did lots of computer simulations of dark matter interactions, so I spent a lot of time stuck at a computer,” Wei says. “Now I’m actually able to get hands-on with the germanium crystals we grow here at USD and test them for things like their electrical properties.”
So where next for South Dakota’s first locally certified doctors of physics?
“I want to stay in physics for the long-term,” Wei says. “I taught some physics to undergraduates during my PhD and really loved it, so I’m hoping to be a researcher and lecturer one day.”
Rederth, too, wants to help inspire the next generation. “I want to stay in the Black Hills area to help raise science and math proficiency in the local schools. I’ve been a judge for the local science fair and would like to become more involved,” he says.
Perhaps some of their future students will go on to join the list of South Dakota’s physics doctorates, started by their trailblazing teachers.
Have a question for Fermilab? Tune in to a Fermilab frequency over the next two weeks.
Calling all amateur radio operators: Fermilab employees are taking to the air waves.
From December 2-17, the Fermilab Amateur Radio Club, whose membership includes laboratory employees, former employees and guests, is commemorating the lab’s 50th birthday with two weeks of ham radio activity. Tune in at the right frequency at the right time, and you could communicate directly with a member of the Fermilab community to ask your burning questions. How does an accelerator bring particles to near light speed? When did the universe begin? How did Fermilab begin?
You just might hear a friendly voice—or receive a Morse code message—at the other end.
The club has established a call sign for this special two-week event: W9F. They will operate daily on all frequencies and modes—voice, Morse code and others. The anticipated frequencies of operation are 14.260, 14.340, 7.250 and 7.275 MHz. There may also be operations on 7.040, 10.130 and 14.040.
“Amateur radio is the original electronic social media,” says Fermilab engineering physicist Kermit Carlson. “It’s practiced as an avocation without pay or pecuniary interest by people worldwide.”
According to ARRL, the national association for amateur radio, there are more than 800,000 amateur radio operators in the United States and roughly 2 million worldwide—in virtually every country.
“Amateur radio is the original electronic social media.”
“Ham radio is a hobby practiced by everyone from school kids to doctors,” Carlson says. “It’s a wide cross section of society.”
The Fermilab club has no radio station, so the approximately 10 on-air hosts will use their personal home stations to establish radio contacts. Harry Przekop, a retired medical physicist who conducted his graduate studies at Fermilab, came up with the idea for the event, and he will be one of the on-air hosts.
It’s a fitting way to celebrate a laboratory known for its forefront science. The world’s amateur radio operators tend to be technologically astute folks, club members say. And the wonder of channeling nature is often what draws people to using amateur radio.
“I remember when I was a little kid sitting in the dark in my grandparents’ living room listening to the BBC,” says Fermilab engineer David Peterson. “How could these signals come from thousands of miles away and get picked up on a little piece of wire in the tree outside my grandparents’ living room and come out the speaker of my radio?”
The technical side of operating amateur radio dovetailed with Peterson’s career fairly well.
“Electromagnetic fields — it’s all kind of the same technology,” Peterson says.
Once the two-week, on-air celebration is over, the hosts will make available a commemorative QSL card, requests for which can be sent to ARRL via email.
So tune in, say hi, and be a part of Fermilab’s 50th-anniversary on-air celebration. Talk to an on-air expert to learn what Fermilab does and the discoveries it’s made. Do it from the comfort of your ham radio setup. And maybe collect a QSL card for your collection.
The Fundamental Physics Prize recognizes WMAP’s contributions to precision cosmology.
The sixth annual Breakthrough Prize in Fundamental Physics has been awarded to an experiment that revolutionized cosmology and mapped the history of our universe. The $3 million prize was given to the science team and five leaders who worked on the Wilkinson Microwave Anisotropy Probe, which investigated matter, the Big Bang and the early conditions of our universe.
“WMAP surveyed the patterns of the oldest light, and we used the laws of physics to deduce from these patterns answers to our questions,” said Chuck Bennett, the principal investigator of WMAP. He received the award along with Gary Hinshaw, Norman Jarosik, Lyman Page and David Spergel. “Science has let us extend our knowledge of the universe to far beyond our physical reach.”
The Breakthrough Prizes, which are also awarded in life sciences and mathematics, celebrate both the science itself and the work done by scientists. The award was founded by Sergey Brin, Anne Wojcicki, Jack Ma, Cathy Zhang, Yuri and Julia Milner, Mark Zuckerberg and Priscilla Chan with the goal of inspiring more people to pursue scientific endeavors.
WMAP, a joint NASA and Princeton University project that ran from 2001 to 2010, has many claims to fame. Scientists have used the spacecraft’s data to determine the age of the universe (13.77 billion years old) and pinpoint when stars first began to shine (about 400 million years after the Big Bang). WMAP results also revealed the density of matter and the surprising makeup of our universe: roughly 71 percent dark energy, 25 percent dark matter and 4 percent visible matter.
From its home one million miles from Earth, WMAP precisely measured a form of light left over from the Big Bang: the cosmic microwave background (CMB). Researchers assembled this data into a “baby picture” of our universe when it was a mere 375,000 years old. WMAP observations support the theory of inflation—that a rapid period of expansion just after the Big Bang led to fluctuations in the distribution of matter, eventually leading to the formation of galaxies.
Scientists still hope to unlock more secrets of the universe using the CMB, and various experiments, such as BICEP3 and the South Pole Telescope, are already running to address these cosmological questions. One thing scientists would love to find? A twist on a hot topic: primordial gravitational waves left over from the Big Bang.
“There is still much we do not understand, such as the first moments of the universe,” Bennett said. “So there will be new breakthroughs in the future.”NASA/WMAP Science Team
In the Large Hadron Collider, protons become new particles, which become energy and light, which become data.
Scientists have never actually seen the Higgs boson. They’ve never seen the inside of a proton, either, and they’ll almost certainly never see dark matter. Many of the fundamental patterns woven into the fabric of nature are completely imperceptible to our clunky human senses.
But scientists don’t need to see particles to learn about their properties and interactions. Physicists can study the subatomic world with particle detectors, which gather information from events that occur much faster and are much smaller than the eye can see.
But what is this information, and how exactly do detectors gather it? At experiments at the Large Hadron Collider, the world's largest and most powerful particle accelerator, it all begins with a near-light-speed race.Starting with a bang
The LHC is built in a ring 17 miles in circumference. Scientists load bunches of protons into this ring and send them hurtling around in opposite directions, gaining more and more energy with each pass.
By the time the LHC has boosted the proton beams to their maximum energy, they will have traveled a distance equivalent to a round-trip journey between Earth and the sun. They will be moving so fast that they no longer convert energy into speed but in effect swell with mass instead.
Once the protons are ramped up to their final energy, the LHC’s magnets nudge the two beams into a collision course at four intersections around the ring.
“When two protons traveling at near light speeds collide head-on, the impact releases a surge of energy unimaginably quickly in an unimaginably small volume of space,” says Dhiman Chakraborty, a professor of Physics at Northern Illinois University working on the ATLAS experiment. “In that miniscule volume, conditions are similar to those that prevailed when the universe was a mere tenth of a nanosecond old.”
This energy is often converted directly into mass according to Einstein’s famous equation, E=mc2, resulting in birth of exotic particles not to be found anywhere else on Earth. These particles, which can include Higgs bosons, are extremely short-lived.
“They decay instantaneously and spontaneously into less massive, more stable ‘daughter’ particles,” Chakraborty says. “The large mass of the exotic parent particle, being converted back into energy, sends its much lighter daughters flying off at near light speeds.”
Even though these rare particles are short-lived, they give scientists a peek at the texture of spacetime and the ubiquitous fields woven into it.
“So much so that the existence of the entire universe we see today—ourselves as observers included—is owed to [the particles and fields we cannot see],” he says.
This CMS experiment event display identifies an electron and a muon passing through the detector.Courtesy of CMS Collaboration Enter the detector
All of this happens in less than a millionth of a trillionth of a second. Even though the LHC’s detectors encompass the beampipe and are only a few centimeters away from the collison, it is impossible for them to see the new heavy particles, which often disintegrate before they can move a distance equal to the diameter of an atomic nucleus.
But the detectors can “see” the byproducts of their decay. The Higgs bosons can transform into pairs of photons, for example. When those photons hit the atoms and molecules that make up the detector material, they radiate sparkles of light and jolts of energy like meteorites blazing through the atmosphere. Sensors inhale these dim twinkles and transform them into electrical signals, recording where and when they arrived.
“Each pulse is a snapshot of space and time,” Chakraborty says. “They tell us exactly where, when and how fast those daughter particles traversed our detector.”
A single proton-proton collision can generate several high-energy daughter particles, some of which produce showers of hundreds more. These streams of particles release detectable energy as they hit the detectors and generate electrical pulses. The time, location, length, shape, height and total energy of each electrical pulse are directly translated into data bits by an electronic readout card.
Much the way biologists chart animal tracks to study the speed, direction and size of a herd, physicists study the shape of these electrical pulses to characterize the passing particles. A long, broad electrical pulse indicates that a large stream of particles grazed across the detector, but a pulse with a sharp peak suggests that a small pack cut straight through.
These electrical pulses create a multifaceted connect-the-dots. Algorithms quickly identify patterns in the cascade of hits and rapidly reconstruct particle energies and tracks.
“We only have a few microseconds to reconstruct what happened before the next batch of collisions arrives,” says Tulika Bose, an associate professor at Boston University working on the CMS experiment. “We can’t keep all the data, so we use automated systems to crudely reconstruct particles like muons and electrons.
“If the event looks interesting enough based on this limited amount of information, we keep all the data from that snapshot in time and save them for further analysis.”
These interesting events are packaged and dispatched upstairs to a second series of automated gatekeepers that further evaluate the quality and characteristics of these collision snapshots. Preprogrammed algorithms identify more particles in the snapshot. This entire process takes less than a millisecond, faster than the blink of a human eye.
Even then, humans won’t lay eyes on the data until after it undergoes a strenuous suite of processing and preparation for analysis.
Humans can’t see the Higgs boson, but by tracing its byproducts back to a single Higgs-like origin, they were able to gather enough evidence to discover it.
“In the five years since that discovery, we’ve produced hundreds of thousands more Higgs bosons and reconstructed a good number of them,” Chakraborty says. “They’re being studied intensely with the goal of gaining insight into deeper mysteries of nature.”
For the first time, scientists have measured the rate at which high-energy neutrinos are absorbed by our planet, a development that could lead to discoveries about physics and the Earth.
When describing neutrinos to the public, scientists often share an astounding fact: About 100 trillion of them pass through your body every second. Neutrinos are extremely abundant in the universe, and they only rarely interact with other matter. That’s why they’re constantly streaming through you—and our entire planet.
But every once and a while, a neutrino hits something.
A new result from the IceCube experiment, published today in Nature, provides a unique measurement of how often that happens. Future improvements on the result could lead to discoveries about neutrinos, particle physics or even the Earth’s inaccessible core.
Colliding with matter can cause a neutrino to shed some or all of its energy. When a neutrino loses all of its energy, it is destroyed, converted into a shower of other particles. It’s a small but “very nasty explosion of stuff,” says scientist Sandra Miarecki, who led the recently published study as a student at UC Berkeley and who now works as a professor at the US Air Force Academy in Colorado.
The more energy a neutrino has, and the denser the matter through which it is traveling, the more likely this is to happen. When neutrinos reach energies of millions of billions of electronvolts, they should find it almost impossible to make it all the way through our planet.
That had been the prediction, at least. But until the IceCube experiment, no one had ever actually measured it.
IceCube is an array of 5160 basketball-sized light sensors sunk into a cubic kilometer of Antarctic ice. When a neutrino smacks into a nucleus in the Earth, it converts its energy into another particle, a muon, which creates a flash of blue light as it passes through the ice. IceCube’s sensors record the trail of that light, letting scientists know how much energy the neutrino had and what direction it came from. Measuring the direction tells scientists how much of the Earth the neutrino has traveled through to get there.
For her thesis, Miarecki used data from IceCube’s 2010-2011 year of operation (the year prior to the completion of the detector) to measure what’s called the neutrino cross-section, the likelihood that a neutrino would interact with a nucleus, depending on the neutrino's energy.
“The thing that’s really interesting about this measurement is that we’re using neutrinos with energies tens to hundreds of times higher than what’s available at accelerators like the Large Hadron Collider,” says Spencer Klein of Lawrence Berkeley National Laboratory and UC Berkeley, Miarecki’s thesis advisor. “IceCube is the first experiment that’s big enough to do anything like this.”
This first measurement of the neutrino cross-section at high energies matched scientists’ predictions based on the Standard Model of particle physics. In this dataset, no million-billion-electronvolt neutrinos made it through from the opposite side of the Earth.
The concept of seemingly unstoppable neutrinos finally meeting their match “actually shook me a little,” when he first joined the experiment, says IceCube Spokesperson Darren Grant of the University of Alberta. “I’d been working on neutrinos for, oh goodness, 10 years, but they’d always been at low energies.”
But with more data—and IceCube has collected almost seven more years’ worth since this study began—that measurement will grow more precise. There is still a chance it will reveal a discrepancy, which could point to a new discovery in physics. “It’s just going to take someone to do the work,” Miarecki says.
Knowing the neutrino cross-section with great accuracy could also help out another field: geology.
“It’s one of the few ways I am aware of where you could actually refine the deep interior picture of the Earth to some higher precision than we know it today,” Grant says.
Scientists’ current best measurements of the interior of the Earth come from sensors measuring how vibrations move through the planet during earthquakes. These measurements are highly accurate, and over the last couple of decades, no one has found a way to improve them.
But if scientists can combine their knowledge of neutrinos with their knowledge of the center of the Earth, they should be able to make very accurate predictions about how many neutrinos they will see coming through different sections of the ground. If their measurements disagree with those predictions, it could be a sign that there’s something going on inside the Earth that they don’t yet understand.
Sandra Miarecki went from Air Force pilot to neutrino physicist.
In a previous career, Sandra Miarecki flew high above the Earth’s surface. During a 20-year career in the US Air Force that included time as a test pilot, she flew aircraft including the B-52, F-16, MiG-15, helicopters and even the Goodyear Blimp.
She retired from the Air Force in 2007 to pursue a new calling in physics that would set her sights on the depths of the Earth. Now an assistant professor of physics, Miarecki served as the principal researcher in a just-released study that relied on data from a detector encapsulated in ice near the South Pole to determine how high-energy subatomic particles are absorbed as they travel inside the planet.
It was a chance seat assignment on a passenger jet in 2007 that put her next to Robert Stokstad, a Lawrence Berkeley National Laboratory physicist who was then serving as the project director for the lab’s IceCube Neutrino Observatory team. Miarecki was on a scouting trip to find housing in the San Francisco Bay Area in preparation for her pursuit of a PhD at UC Berkeley.
“He was playing with a camera, and I was involved with photography,” she recalls of the meeting on that Southwest Airlines flight, and they struck up a conversation. The subject of science came up, and his description of the IceCube project, then under construction, piqued her interest.
She would later attend a Berkeley Lab IceCube group meeting at Stokstad’s invitation. “I thought I was going to be a cosmology theorist when I first got to Berkeley,” she says, but hands-on experiments were also alluring.
So she worked on a summer project with the collaboration, and enjoyed the experience.
Spencer Klein, a longtime physicist at Berkeley Lab who now leads the lab’s IceCube team, suggested that Miarecki’s dissertation focus on the Earth’s absorption of high-energy neutrinos. Before joining the Air Force, Miarecki had earned a bachelor’s degree in astronomy, and also completed courses in physics and mathematics, at the University of Illinois at Urbana-Champaign.
“I had also toyed with the idea of being a geologist, and when you are using the Earth as an absorption material (for neutrinos), you have to understand the composition and density of the Earth. It was a really nice blend of all my previous experience,” she says. “I was so happy when we came up with this idea.”
Miarecki worked full-time on this research at Berkeley Lab from 2010 to 2015 before taking a job in January 2016 as a physics instructor at the Air Force Academy in Colorado Springs, Colorado. She continued working on her dissertation at the academy, completing that work in December 2016.
When Klein suggested that she submit her dissertation work for publication in Nature, Miarecki balked at first. “I said, ‘Really?’ Then I thought, ‘OK, let’s give it a try,’” she says. “It’s not expected that your graduate dissertation actually gets into Nature.” The study was published today.
She was promoted to assistant professor at the academy in January 2017 and now teaches physics coursework in classical mechanics and electromagnetism as well as the physics of combat aviation.
“When I was going through the military retirement transition course, the attendees had to answer the question, ‘What do you want to be when you grow up,’ which was tongue-in-cheek, of course, because all of us were over 40,” Miarecki recalls. “I realized that I wanted to teach, and I had always been told that I was a great teacher. The military also had selected me to be an instructor pilot at several times during my career.
“I debated whether my 42-year-old brain would be spongy enough to tackle a PhD program, but I decided that I had to try, or I could never live with myself wondering, ‘What could have been?’ Switching from the military to academia was not a big shock because I had spent so much of my military career in a teaching capacity.”
The assistant professor position at the Air Force Academy has brought her career full circle, she notes: “It represents a perfect blend of my previous Air Force career with my love of teaching physics.”
Editor’s note: A version of this article was published by Berkeley Lab.
Successful physics collaborations rely on cooperation between people from many different disciplines.
So, you want to start a physics experiment. Maybe you want to follow hints of an as yet unseen particle. Or maybe you want to learn something new about a mysterious process in the universe. Either way, your next step is to find people who can help you.
In large science collaborations, such as the ATLAS and CMS experiments at the Large Hadron Collider; the Deep Underground Neutrino Experiment (DUNE); and Fermilab’s NOvA, hundreds to thousands of people spread out across many institutions and countries keep things operating smoothly. Whether they’re senior scientists, engineers, technicians or administrators, each of them has an important role to play.
Think of it like a jigsaw puzzle: This list will give you an idea about how their work fits together to create the big picture.Dreaming up the experiment
Many particle physics experiments begin with a fundamental question. Why do objects have mass? Or, why is the universe made of matter?
When scientists encounter these big, seemingly inscrutable questions, part of their job is to identify possible ways to answer them. A large part of this is breaking down the big questions into a program of smaller, answerable questions.
In the case of the LHC, scientists who wondered about things such as undiscovered particles and the origin of mass designed a 27-kilometer particle collider and four giant detectors to learn more.
Each scientist in a collaboration brings their own unique perspective and skill set to the table, whether it’s providing an understanding of the physics or offering expertise in operations or detector design.Perfecting the design
Once scientists have an idea about the experiment they want to do and the approach they want to take, it’s the job of the engineers to turn the concepts into pieces of hardware that can be built, function and meet the experiment's requirements.
For example, engineers might have to figure out how the experiment should be supported mechanically or how to connect all the electrical systems and make signals available in a detector.
In the case of NOvA, which investigates neutrino oscillations, scientists needed a detector that was huge and free of dense materials, which made conventional construction techniques unworkable. They had to work with engineers who could understand plastic as a building material so they could be confident about using it to build a gigantic, free-standing structure that fit the requirements.Keeping things running
Technicians come in when the experimental apparatus and instrumentation are being built and often have complementary knowledge about what they’re working on. They build the hardware and coordinate the integration of components. It’s their work that, in the end, pulls everything together so the experiment functions.
Once the experiment is built, technicians are responsible for keeping everything humming along at top performance. When physicists notice things going wrong with the detectors, the technicians usually have first eyes on it. It’s a vital task, since every second counts when it comes to collecting data.Doing the heavy lifting
When designing and constructing the experiment, the scientists also recruit postdocs and grad students, who do the bulk of the data analysis.
Grad students, who are still working on their PhDs, have to balance their own coursework with the real-world experiment, learning their way around running simulations, analyzing data and developing algorithms. They also make sure that every part of the detector is working up to par. In addition, they may work in instrumentation, developing new instruments and electronics.
Postdocs, on the other hand, have already worked on experiments and obtained their PhDs, so they typically assume more of a leadership role in these collaborations. Part of their role is to guide the grad students in a sort of apprenticeship.
Postdocs are often in charge of certain types of analysis or detector operations. Because they’ve worked on previous experiments, they have a tool kit and experience to draw on to solve problems when they crop up.
Postdocs and grad students often work with technicians and engineers to ensure everything is properly built.Making the data accessible
The LHC produces about 25 petabytes of data every year, or 25 billion megabytes. If the average size of an MP3 is about one megabyte per minute, then it would take almost 50,000 years to play 25 petabytes of songs. In physics collaborations, computer scientists and engineers have to organize the computing networks to ensure against bottlenecks or traffic jams when this massive amount of data is shared.
They also maintain the software framework, which takes care of data handling and archiving. Say a scientist wants to know what happened on Feb. 27, 2015, at 3 a.m. Computing experts have to be able to go into the data catalogue and find, among the petabytes of data, where that event is stored.Sorting out the logistics
One often overlooked group is the administrators.
It’s up to the administrators to sequence all the different projects so they get the funds they need to make progress. They sort the logistics to make sure the right people are in the right places working on the right things.
Administrators manage a group of people who are constantly coming and going. Is someone traveling to a site from a different institution? The administrators make sure that people get connected, work out itineraries and schedule where visiting scientists will live and work.
Administrators also organize collaboration meetings, transfer money, and procure and ship equipment.Translating discoveries to the public
While every single person involved in an experiment has a responsibility to effectively communicate with others, it can be challenging to communicate about research in a way that’s relatable to people from different backgrounds. That’s where the professional communicators come in.
Communicators can translate a paper full of jargon and complicated science into a fascinating story that the rest of the world can get excited about.
In addition to doing outreach for the public and writing press releases and pitching stories for the media, communicators offer coaching to people in a scientific collaboration on how to relay the science to a general audience, which is important for generating public interest.Fitting the pieces
Now that you know many of the pieces that must fall into place for a large physics collaboration to be successful, also know that none of these roles is performed in a vacuum. For an experiment to work, there must be a synergy of tasks: Each relies on the success of the others. Now go start that experiment!
Barish explains how LIGO became the high-achieving experiment it is today.Illustration by Ana Kova
These days the LIGO experiment seems almost unstoppable. In September 2015, LIGO detected gravitational waves directly for the first time in history. Afterward, they spotted them three times more, definitively blowing open the doors on the new field of gravitational-wave astronomy.
On October 3, the Nobel Committee awarded their 2017 prize in physics to some of the main engines behind the experiment. Just two weeks after that, LIGO scientists revealed that they'd seen, for the first time, gravitational waves from the collision of neutron stars, an event confirmed by optical telescopes—yet another first.
These recent achievements weren’t inevitable. It took LIGO scientists decades to get to this point.
LIGO leader Barry Barish, one of the three recipients of the 2017 Nobel, recently sat down with Symmetry writer Leah Hesla to give a behind-the-scenes look at his 22 years on the experiment.What has been your role at LIGO? BB:
I started in 1994 and came on board at a time when we didn’t have the money. I had to get the money and have a strategy that [the National Science Foundation] would buy into, and I had to have a plan that they would keep supporting for 22 years. My main mission was to build this instrument—which we didn’t know how to make—well enough to do what it did.
So we had to build enough trust and success without discovering gravitational waves so that NSF would keep supporting us. And we had to have the flexibility to evolve LIGO’s design, without costing an arm and a leg, to make the improvements that would eventually make it sensitive enough to succeed.
We started running in about 2000 and took data and improved the experiment over 10 years. But we just weren’t sensitive enough. We managed to get a major improvement program to what’s called Advanced LIGO from the National Science Foundation. After a year and a half or so of making it work, we turned on the device in September of 2015 and, within days, we’d made the detection.What steps did LIGO take to be as sensitive as possible? BB:
We were limited very much by the shaking of the Earth—at the low frequencies, the Earth just shakes too much. We also couldn’t get rid of the background noise at high frequencies—we can’t sample fast enough.
In the initial LIGO, we reduced the shaking by something like 100 million. We had the fanciest set of shock absorbers possible. The shock absorbers in your car take a bump that you go over, which is high-frequency, and transfer it softly to low-frequency. You get just a little up and down; you don’t feel very much when you go over a bump. You can’t get rid of the bump—that’s energy—but you can transfer it out of the frequencies where it bothers you.
So we do the same thing. We have a set of springs that are fancier but are basically like shock absorbers in your car. That gave us a factor of 100 million reduction in the shaking of the Earth.
But that wasn’t good enough [for initial LIGO].What did you do to increase sensitivity for Advanced LIGO? BB:
After 15 years of not being able to detect gravitational waves, we implemented what we call active seismic isolation, in addition to passive springs. It’s very much equivalent to what happens when you get on an airplane and you put those [noise cancellation] earphones on. All of a sudden the airplane is less noisy. That works by detecting the ambient noise—not the noise by the attendant dropping a glass or something. That’s a sharp noise, and you’d still hear that, or somebody talking to you, which is a loud independent noise. But the ambient noise of the motors and the shaking of the airplane itself are more or less the same now as they were a second ago, so if you measure the frequency of the ambient noise, you can cancel it.
In Advanced LIGO, we do the same thing. We measure the shaking of the Earth, and then we cancel it with active sensors. The only difference is that our problem is much harder. We have to do this directionally. The Earth shakes in a particular direction—it might be up and down, it might be sideways or at an angle. It took us years to develop this active seismic isolation.
The idea was there 15 years ago, but we had to do a lot of work to develop very, very sensitive active seismic isolation. The technology didn’t exist—we developed all that technology. It reduced the shaking of the Earth by another factor of 100 [over LIGO’s initial 100 million], so we reduced it by a factor of 10 billion.
So we could see a factor of 100 further out in the universe than we could have otherwise. And each factor of 10 gets cubed because we’re looking at stars and galaxies [in three dimensions]. So when we improved [initial LIGO’s sensitivity] by a factor of 100 beyond this already phenomenal number of 100 million, it improved our sensitivity immediately, and our rate of seeing these kinds of events, by a factor of a hundred cubed—by a million.
That’s why, after a few days of running, we saw something. We couldn’t have seen this in all the years that we ran at lower sensitivity.What key steps did you take when you came on board in 1994? BB:
First we had to build a kind of technical group that had the experience and abilities to take on a $100 million project. So I hired a lot of people. It was a good time to do that because it was soon after the closure of the Superconducting Super Collider in Texas. I knew some of the most talented people who were involved in that, so I brought them into LIGO, including the person who would be the project manager.
Second, I made sure the infrastructure was scaled to a stage where we were doing it not the cheapest we could, but rather the most flexible.
The third thing was to convince NSF that doing this construction project wasn’t the end of what we had to do in terms of development. So we put together a vigorous R&D program, which NSF supported, to develop the technology that would follow similar ones that we used.
And then there were some technical changes—to become as forward-looking as possible in terms of what we might need later.What were the technical changes? BB:
The first was to change from what was the most popularly used laser in the 1990s, which was a gas laser, to a solid-state laser, which was new at that time. The solid-state laser had the difficulty that the light was no longer in the visible range. It was in the infrared, and people weren’t used to interferometers like that. They like to have light bouncing around that they can see, but you can’t see the solid-state laser light with your naked eye. That’s like particle physics. You can’t see the particles in the accelerator either. We use sensors to do that. So we made that kind of change, going from analog controls to digital controls, which are computer-based.
We also inherited the kind of control programs that had been developed for accelerators and used at the Superconducting Super Collider, and we brought the SSC controls people into LIGO. These changes didn’t pay off immediately, but paved the road toward making a device that could be modern and not outdated as we moved through the 20 years. It wasn’t so much fixing things as making LIGO much more forward-looking—to make it more and more sensitive, which is the key thing for us.Did you draw on past experience? BB:
I think my history in particle physics was crucial in many ways, for example, in technical ways—things like digital controls, how we monitored beam. We don’t use the same technology, but the idea that you don’t have to see it physically to monitor it—those kinds of things carried over.
The organization, how we have scientific collaborations, was again something that I created here at LIGO, which was modeled after high-energy physics collaborations. Some of it has to be modified for this different kind of project—this is not an accelerator—but it has a lot of similarities because of the way you approach a large scientific project.Were you concerned the experiment wouldn’t happen? If not, what did concern you? BB:
As long as we kept making technical progress, I didn’t have that concern. My only real concern was nature. Would we be fortunate enough to see gravitational waves at the sensitivities we could get to? It wasn’t predicted totally. There were optimistic predictions—that we could have detected things earlier — but there are also predictions we haven't gotten to. So my main concern was nature.When did you hear about the first detection of gravitational waves? BB:
If you see gravitational waves from some spectacular thing, you’d also like to be able to see something in telescopes and electromagnetic astronomy that’s correlated. So because of that, LIGO has an early alarm system that alerts you that there might be a gravitational wave event. We more or less have the ability to see spectacular things early. But if you want people to turn their telescopes or other devices to point at something in the sky, you have to tell them something in time scales of minutes or hours, not weeks or months.
The day we saw this, which we saw early in its running, it happened at 4:50 in the morning in Louisiana, 2:50 in the morning in California, so I found out about it at breakfast time for me, which was about four hours later. When we alert the astronomers, we alert key people from LIGO as well. We get things like that all the time, but this looked a little more serious than others. After a few more hours that day, it became clear that this was nothing like anything we’d seen before, and in fact looked a lot like what we were looking for, and so I would say some people became convinced within hours.
I wasn’t, but that’s my own conservatism: What’s either fooling us or how are we fooling ourselves? There were two main issues. One is the possibility that maybe somebody was inserting a rogue event in our data, some malicious way to try to fool us. We had to make sure we could trace the history of the events from the apparatus itself and make sure there was no possibility that somebody could do this. That took about a month of work. The second was that LIGO was a brand new, upgraded version, so I wasn’t sure that there weren’t new ways to generate things that would fool us. Although we had a lot of experience over a lot of years, it wasn’t really with this version of LIGO. This version was only a few days old. So it took us another month or so to convince us that it was real. It was obvious that there was going to be a classic discovery if it held up.What does it feel like to win the Nobel Prize? BB:
It happened at 3 in the morning here [in California]. [The night before], I had a nice dinner with my wife, and we went to bed early. I set the alarm for 2:40. They were supposed to announce the result at 2:45. I don’t know why I set it for 2:40, but I did. I moved the house phone into our bedroom.
The alarm did go off at 2:40. There was no call, obviously—I hadn’t been awakened, so I assumed, kind of in my groggy state, that we must have been passed over. I started going to my laptop to see who was going to get it. Then my cell phone started ringing. My wife heard it. My cell phone number is not given out, generally. There are tens of people who have it, but how [the Nobel Foundation] got it, I’m not sure. Some colleague, I suppose. It was a surprise to me that it came on the cell phone.
The president of the Nobel Foundation told me who he was, said he had good news and told me I won. And then we chatted for a few minutes, and he asked me how I felt. And I spontaneously said that I felt “thrilled and humbled at the same time.” There’s no word for that, exactly, but that mixture of feeling is what I had and still have.Do you have advice for others organizing big science projects? BB:
We have an opportunity. As I grew into this and as science grew big, we always had to push and push and push on technology, and we’ve certainly done that on LIGO. We do that in particle physics, we do that in accelerators.
I think the table has turned somewhat and that the technology has grown so fast in the recent decades that there’s incredible opportunities to do new science. The development of new technologies gives us so much ability to ask difficult scientific questions. We’re in an era that I think is going to propagate fantastically into the future.
Just in the new millennium, maybe the three most important discoveries in physics have all been done with, I would say, high-tech, modern, large-scale devices: the neutrino experiments at SNO and Kamiokande doing the neutrino oscillations, which won a Nobel Prize in 2013; the Higgs boson—no device is more complicated or bigger or more technically advanced than the CERN LHC experiments; and then ours, which is not quite the scale of the LHC, but it’s the same scale as these experiments—the billion dollar scale—and it’s very high-tech.
Einstein thought that gravitational waves could never be detected, but he didn’t know about lasers, digital controls and active seismic isolation and all things that we developed, all the high-tech things that are coming from industry and our pushing them a little bit harder.
The fact is, technology is changing so fast. Most of us can’t live without GPS, and 10 or 15 years ago, we didn’t have GPS. GPS exists because of general relativity, which is what I do. The inner silicon microstrip detectors in the CERN experiment were developed originally for particle physics. They developed rapidly. But now, they’re way behind what’s being done in industry in the same area. Our challenge is to learn how to grab what is being developed, because technology is becoming great.
I think we need to become really aware and understand the developments of technology and how to apply those to the most basic physics questions that we have and do it in a forward-looking way.What are your hopes for the future of LIGO? BB:
It’s fantastic. For LIGO itself, we’re not limited by anything in nature. We’re limited by ourselves in terms of improving it over the next 15 years, just like we improved in going from initial LIGO to Advanced LIGO. We’re not at the limit.
So we can look forward to certainly a factor of 2 to 3 improvement, which we’ve already been funded for and are ready for, and that will happen over the next few years. And that factor of 2 or 3 gets cubed in our case.
This represents a completely new way to look at the universe. Everything we look at was with electromagnetic radiation, and a little bit with neutrinos, until we came along. We know that only a few percent of what’s out there is luminous, and so we are opening a new age of astronomy, really. At the same time, we’re able to test Einstein’s theories of general relativity in its most important way, which is by looking where the fields are the strongest, around black holes.
That’s the opportunity that exists over a long time scale with gravitational waves. The fact that they’re a totally different way of looking at the sky means that in the long term it will develop into an important part of how we understand our universe and where we came from. Gravitational waves are the best way possible, in theory—we can’t do it now—of going back to the very beginning, the Big Bang, because they weren’t absorbed. What we know now comes from photons, but they can go back to only 300,000 years from the Big Bang because they’re absorbed.
We can go back to the beginning. We don’t know how to do it yet, but that is the potential.
Fantastical designs elevate physics in works by Fermilab’s first artist.
Planning to start up a particle physics lab? Better hire an artist.
That was Robert R. Wilson’s thought in the 1960s, when he began forming what would become the Department of Energy’s Fermi National Accelerator Laboratory. He wanted a space to do physics that would inspire all who set foot on the lab. He knew, even then, the importance of mingling art and science. The 11th person hired was artist Angela Lahs Gonzales, and in her three decades at the lab, she influenced the character and aesthetic of nearly every part of the site.
Gonzales, the daughter of two artists who fled with her from Nazi Germany, had worked with Wilson previously at Cornell University. At Fermilab, she found herself responsible for a multitude of artistic choices. Working closely with Wilson, she created the lab’s logo, a union of dipole and quadrupole magnets used in accelerators to guide and focus the particle beam. She chose a bold color scheme, with vibrant blues, oranges and reds that would coat Fermilab buildings. She designed covers for scientific publications and posters for lab events and lectures.
“There was no project too small or large for Angela,” says Georgia Schwender, the curator of Fermilab’s art gallery. “She seemed to put just as much care and thought into sketches for the Annual Report as she did for a community Easter egg hunt. The whole lab was her canvas and her muse.”
A mix of themes and styles, from history to mythology and op-art to realism, are wrapped around images of accelerators, experiments and the Fermilab site. The images are often bizarre and fantastical, nearly always impressive. In one drawing, Fermilab’s bison dine at an elegant table; in another, winged creatures stare into a bubbling cauldron that contains the Fermilab accelerator complex and main building, Wilson Hall.
Gonzales typically worked in pen, sketching intricate details across paper, but she also branched out into different media, crafting jewelry, flags, vases, tables and even the elevator ceiling tiles. Her reach extended to typography, designs around doorways and drawings of things you might not expect: mundane things like emergency preparedness kits and literal nuts and bolts.
Her word on artistic choices was final. Employees were known to get a talking to if they painted something without consulting Angela. Some colors became tied to the science at hand. One time, an accelerator magnet was painted the wrong shade of blue and thus installed incorrectly, causing some confusion in the control room.
“Gonzales was at the lab from 1967 to 1998, and in that time she was incredibly influential on the style of the lab,” says Valerie Higgins, Fermilab’s archivist. “But you can see how these tendrils of art spiral out to influence the science and the shape of the lab as well.”
More than 100 pieces by Gonzales were featured in a Fermilab art gallery exhibit earlier this year, as the lab celebrated its 50th anniversary. “A Lasting Mark” ran from June to September before briefly traveling and then being retired. An online catalog of the exhibit is available on the Fermilab site.
Angela Gonzales incorporated many Fermilab elements into the unofficial Fermilab seal, including Wilson Hall, the logo, particle symbols, and buildings and sculptures from around the site.Fermilab
Documents and books fill a Wilson Hall-shaped bookshelf on the cover of Publications from Fermilab Experiments (1987).Fermilab
Wilson Hall sits among other famous buildings (such as the Leaning Tower of Pisa and the Great Pyramid of Giza) on the cover of the Fermilab Annual Report (1990).Fermilab
Bold lines unite Wilson Hall and tigers on the cover of the Tiger Teams at Fermilab (1992).Fermilab
Wilson Hall sits among droplets representing the water cycle.Fermilab
Gonzales designed posters for many events, including colloquia, symposia and workshops.Fermilab
Wilson Hall becomes an ornament on the poster for Fermilab’s Christmas Dinner Dance in 1988.Fermilab
A whimsical rabbit urges families to attend the 1989 Easter egg hunt on the Fermilab site.Fermilab
Elegant bison dine at a table in this surreal Gonzales artwork.Fermilab
Many of Gonzales’s creations draw on mythology and creatures, as in this cover of the High Energy Particle Interactions in Large Targets. Volume 1: Hadronic Cascades, Shielding, Energy Deposition (1975).Fermilab
Feynman diagrams rain down on the Chicago skyline in the cover of Proceedings of the XVI International Conference on High Energy Physics (1972).Fermilab
The cover for the Fermilab Annual Report (1989) uses a nautical theme.Fermilab
Gonzales created art for complicated physics processes, such as cascading particle showers caused by cosmic rays interacting in the atmosphere.Fermilab
Gonzales’s artwork also touched the physical spaces at the lab. This image shows her design for the elevator ceiling tiles.Fermilab
The Fermilab logo was created in a collaboration between Wilson and Gonzales; the final version has rigorous specifications.Fermilab Previous Next
SLAC engineer Knut Skarpaas designs some of physics’ most challenging machines, finding inspiration in unexpected places.
At a recent meeting of the Mountain View Handweavers club, five women chatted in their rocking chairs with an unusual newcomer: Engineer Knut Skarpaas of SLAC National Accelerator Laboratory. He was an affable, inquisitive man about the age of their sons and grandsons.
He explained he was looking for advice on how to build a loom to help particle physicists catch dark matter.
This wasn’t the first time Skarpaas had consulted with experts well outside high-energy physics for a project. Not by a long shot. He has found inspiration for machine designs and fabrication methods in ancient Egyptian jewelry, silversmithing, origami, spider webs and honeycombs. He is currently seeking permission to build a machine primarily from sapphire.
“The mechanical world is his playground,” says colleague Michelle Dolinski of Drexel University.An insatiable curiosity
Back at his office, Skarpaas’s desk drawers rattle with the gears and tools he played with as a kid when his father, also a SLAC engineer, worked at the same desk.
“He has many of his father’s gifts, but they are not identical,” says Gordon Bowden, a fellow engineer at SLAC who has worked with father and son. “Curiosity has driven Knut to accumulate much diverse, direct, hands-on experience—a trait becoming more and more rare in engineering.”
In his briefcase, Knut carries a magnifying glass and a miniature microscope to examine objects he finds. He has picked apart and reassembled thousands of machines since childhood, from his father’s watch to sunken cameras salvaged on scuba expeditions and his grandmother’s Opel Kadett automobile.Artwork by Corinne Mucha
The details, he says, make the difference between something that works and something that doesn’t. But studying things that don’t work can be half the fun. “If the things are actually going to get thrown away anyway, you can take them apart more violently because you’re not going to put them back together,” Skarpaas says.
That might mean hitting them with a sledgehammer, or taking them back to his shop at home where he keeps his 20-ton press. “I can destroy pretty much—well, a lot of things will yield with 20 tons on them,” he says.
Skarpaas says taking things apart and looking at how they break—looking at failures—is important. It shows him the weak points, and then he can make sure those weak points don’t exist in his designs.
An especially interesting mechanism might earn a place in his filing cabinets among a collection of other components that prove useful when he discusses design problems with his colleagues.
“I’ll just pull one out and say, ‘You mean like this?’ And frequently one of those things can end up being a solution,” Skarpaas says.Working within extreme constraints
“Knut can see solutions that no one else would see,” says Dolinski.
She worked with Skarpaas on the construction of a neutrino experiment, the Enriched Xenon Observatory. EXO-200, a 200-kilogram container of liquid xenon, looks for an elusive type of radioactive decay that could help physicists discover fundamental truths about the neutrino, including the nature and origin of its mass.
Engineering for high-energy physics requires a healthy dose of imagination because it often requires working within extreme constraints, Dolinski says. The EXO-200 team, for instance, could not use anything that could be contaminated even slightly with radioactive material, such as most normal materials like steel and ceramics. When measuring to parts-per-quadrillion, almost all things are radioimpure.
So the team made the difficult choice to construct 1000 electrical connections with no solder, no gold plating and no wire bonds. In fact, no wire. Nothing could be bought from a commercial catalog. Every screw, connection, spring and contact was made in-house from a block of raw material. And the connections couldn’t fail. Ever. “Because once you seal this thing up, it’s inaccessible for, you know, a decade,” Skarpaas says.
Skarpaas recalls a refrain he used to hear from his department head: “Presume you have to make this out of gossamer.”
“And he means, basically, make this out of nothing,” Skarpaas says. Use the fewest materials and the lightest structure—effectively weightless—to have a minimum effect on the physics.
Year after year, Dolinski says, Skarpaas has always found elegant ways to do this. For the LZ dark matter detector, that means using four 1.47-meter-diameter high-voltage grids of hair-thin wires—carefully woven on a Skarpaas-designed loom, informed by the women of the Handweavers’ club.
Around the world, scientists and non-scientists alike celebrated the first international Dark Matter Day.
This year, October 31 was more than just Halloween. It was also the first global celebration of Dark Matter Day. In 25 countries, 11 US states and online, people interacted with scientists, watched demonstrations, viewed films, took in art exhibits and toured laboratories to learn about the ongoing search for dark matter.
Symmetry has collected a series of photos from participants around the world. Check out how people celebrated Dark Matter Day and download a commemorative dark matter poster (to be printed using visible matter).
Peter Sorensen of Berkeley Lab during a talk at the California Academy of Sciences in San Francisco on Oct. 31.Berkeley Lab
Employees at SLAC National Accelerator Laboratory celebrate Dark Matter DaySLAC National Accelerator Laboratory
Bart Bernhardt, co-founder of Nerd Nite SF, dons a Dark Matter Day T-shirt during an Oct. 18 event in San FranciscoNerd Nite SF
Obi-Wan Kenobi spotted in the Berkeley Lab Strategic Communications office in a Dark Matter Day t-shirt.Berkeley Lab
School children making their own dark matter particles during a workshop at STFC’s Rutherford Appleton Laboratory.STFC
Packed auditorium for a special ‘Talking Science’ public lecture at STFC’s Daresbury Laboratory.STFC
Parliamentary showcase at the House of Commons, where MPs met with leading UK dark matter experts (L-R): Tommy Sheppard MP, Carol Monaghan MP, Prof Carlos Frenk, Patrick Grady MP, Prof Alex Murphy, Prof Sean Paling, Prof Martin Hendry and Dr Brian BowsherSTFC
Dark Matter Day event in Victoria Street, London. (L-R) Sean Paling, Director of the Boulby Underground Laboratory, with Greg Clark MP ( Secretary of State for Business, Energy & Industrial Strategy), Dr Laura Manenti, and Prof Carlos FrenkSTFC
The interest of the public in Karlsruhe, Germany, was so great that the NTI lecture hall on Campus South was filled to the last seat and no standing room was available.KIT
Two Karlsruhe Institute of Technology researchers summarized scientists' current understanding of dark matter and talked about new experiments seeking to uncover its mystery.KIT
The German laboratory DESY turned into an art gallery for Dark Matter Day.Helge Mundt, DESY
Fifteen artists took part, showing works they created after an intense period of exchange with DESY scientists.Helge Mundt, DESY
The artwork at DESY included a sound installation in the HERA accelerator tunnel.Helge Mundt, DESY
The dark matter artwork at DESY was displayed in test halls, accelerator shafts and office corridors.Helge Mundt, DESY
On Dark Matter Day, the other works were topped off with a program of short films called “Dark Matters” and a live link to the CMS experiment at CERN.Helge Mundt, DESY
The Institute of High Energy Physics, Chinese Academy of Sciences and Shanghai Jiao Tong University organized an event in Shanghai.IHEP
Visitors line up outside the Dark Matter Day event in Shanghai.IHEP
The event in Shanghai began with public lectures followed by free discussion between the public and the scientists.IHEP
Attendees at the Shanghai event also watched Phantom of the Universe – The Hunt for Dark Matter.IHEP
Dark Matter Day at CERN included a dark matter cake.CERN
Katharine Leney, Researcher on the ATLAS experiment at CERN, introduced the evening by presenting the basic principles of dark matter using her bespoke dark matter cake. Later in the evening Wessel Valkenburg, Research Fellow at the Theory Department at CERN explained the how and why research is carried out on dark matter.CERN
More than 270 attendees onsite as well as on the live webcast learned from CERN experts about the experiments and theories that seek to provide us with a deeper understanding of this strange and unknown matter.CERN
On Tuesday, October 31, CERN joined the global celebration of Dark Matter Day from the Globe of Science and InnovationCERN
With Dark Matter Day falling on Halloween, some creative participants came dressed up in costumes related to dark matterCERN
A volunteer demonstrates magnetism at a Dark Matter Day event at Adler Planetarium in Chicago.Leo Bellantoni, Fermilab
A jar of jellybeans at the Adler Planetarium event represents the make-up of the universe, mostly dark energy and dark matter.Leo Bellantoni, Fermilab
Visitors and volunteers talk particle accelerators at the Dark Matter Day event at Adler Planetarium in Chicago.Leo Bellantoni, Fermilab
When asked, “What’s the most interesting thing about dark matter that you wish people knew more about?” Lindsay Forestell, TRIUMF PhD scientist, replied: “You could name me every element in the periodic table, show me how all of the proteins and molecules and proteins in your body work, or build me a rocket ship and fly me to the moon. At most you would still only understand less than 5 percent of what’s out there in the Universe.”TRIUMF Previous Next Download the poster Artwork by Ana Kova
For Dark Matter Day, scientist and Star Wars fan Dan McKinsey talks dark matter and the Force.
Scientist Dan McKinsey of Berkeley Lab and UC Berkeley shares some thoughts on dark matter.Ask Symmetry – How is the Force like dark matter? Video of Ask Symmetry – How is the Force like dark matter?
McKinsey recently answered questions about dark matter on Reddit Science.
Grace C. Young is fascinated by fundamental questions about realms both quantum and undersea.
Each summer, the international research laboratory CERN, home to the Large Hadron Collider, welcomes dozens of students to work alongside seasoned scientists on cutting-edge particle physics research. Many of these students will pursue physics research in graduate school, but some find themselves applying the lessons they learned at CERN to new domains.
In 2011, MIT undergraduate Grace Young was one of these CERN summer students.
Like many young adults, Young didn’t know what career path she wanted to pursue. “I tried all the majors,” Young says. “Physics, engineering, architecture, math, computer science. Separately, I always loved both the ocean and building things; it wasn’t until I learned about ocean engineering that I knew I had found my calling.”
Today, Young is completing her PhD in ocean engineering at the University of Oxford and is chief scientist for the deep-sea submarine Pisces VI. She develops technology for ocean research and in 2014 lived underwater for 15 days. During a recent visit to CERN, Young spoke with Symmetry writer Sarah Charley about the journey that led her from fundamental physics back to her first love, the ocean.As a junior in high school you competed in Intel’s International Science Fair and won a trip to CERN. What was your project? GY:
A classmate and I worked in a quantum physics lab at University of Maryland. We designed and built several devices, called particle traps, that had potential applications for quantum computing. We soldered wires onto the mirror inside a flashlight to create a bowl-shaped electric field and then applied alternating current to repeatedly flip the field, which made tiny charged particles hover in mid-air.
We were really jumping into the deep end on quantum physics; it was kind of amazing that it worked! Winning a trip to CERN was a dream come true. It was a transformative experience that had a huge impact on my career path.You then came back to CERN as a freshman at MIT. What is it about CERN and particle physics that made you want to return? GY:
My peek inside CERN the previous year sparked an interest that drove me to apply for the Openlab internship [a technology development collaboration between CERN scientists and members of companies or research institutes].
Although I learned a lot from my assignment, my interest and affinity for CERN derives from the community of researchers from diverse backgrounds and disciplines from all over the world. It was CERN's high-powered global community of scientists congregated in one beautiful place to solve big problems that was a magnet for me.You say you’ve always loved the ocean. What is it about the ocean that inspires you? GY:
I’ve loved being by the water since I was born. I find it very humbling, standing on the shore and having the waves breaking at my feet.
This huge body of water differentiates our planet from other rocks in space, yet so little is known about it. The more time I spent on or in the water, either sailing or diving, the more I began taking a deeper interest in marine life and the essential role the ocean plays in sustaining life as we know it on Earth.What does an ocean engineer actually do? GY:
One big reason that we’ve only explored 5 percent of the ocean is because the deep sea is so forbidding for humans. We simply don't have the biology to see or communicate underwater, much less exist for more than a few minutes just below surface.
But all this is changing with better underwater imaging, sensors and robotic technologies. As an ocean engineer, I design and build things such as robotic submersibles, which can monitor the health of fisheries in marine sanctuaries, track endangered species and create 3-D maps of underwater ice shelves. These tools, combined with data collected during field research, enable me and my colleagues to explore the ocean and monitor the human impact on its fragile ecosystems.
I also design new eco-seawalls and artificial coral reefs to protect coastlines from rising sea levels and storm surges while reviving essential marine ecosystems.What questions are you hoping to answer during your career as an ocean engineer and researcher? GY:
How does the ocean support so much biodiversity? More than 70 percent of our planet is covered by water, producing more than half the oxygen we breathe, storing more carbon dioxide than all terrestrial plant life and feeding billions of humans. And yet 95 percent of our ocean remains unexplored and essentially unknown.
The problem we are facing today is that we are destroying so many of the ocean’s ecosystems before we even know they exist. We can learn a lot about how to stay alive and thrive by studying the oceanic habitats, leading to unforeseeable discoveries and scientific advancements.What are some of your big goals with this work? GY:
We face big existential ocean-related problems, and I'd like to help develop solutions for them. Overfishing, acidification, pollution and warming temperatures are destroying the ocean’s ecosystems and affecting humans by diminishing a vital food supply, shifting weather patterns and accelerating sea-level rise. Quite simply, if we don't know or understand the problems, we can't fix them.Have you found any unexpected overlaps between the research at CERN and the research on a submarine? GY:
Vision isn’t a good way to see the underwater world. The ocean is pitch black in most of its volume, and the creatures don’t rely on vision. They feel currents with their skin, use sound and can read the chemicals in the water to smell food. It would make sense for humans to use sensors that do that same thing.
Physicists faced this same challenge and found other ways to characterize subatomic particles and the celestial bodies without relying on vision. Ocean sciences are moving in this same direction.What do you think ocean researchers and particle physicists can learn from each other? GY:
I think we already know it: That is, we can only solve big problems by working together. I'm convinced that only by working together across disciplines, ethnicities and nationalities can we survive as a species.
Of course, the physical sciences are integral to everything related to ocean engineering, but it's really CERN's problem-solving methodology that's most inspiring and applicable. CERN was created to solve big problems by combining the best of human learning irrespective of nationality, ethnicity or discipline. Our Pisces VI deep sea submarine team is multidisciplinary, multinational and—just like CERN—it's focused on exploring the unknown that's essential to life as we know it.
Cross sections tell physicists how likely particles are to interact in a given way.
Imagine two billiard balls rolling toward one another. The likelihood of a collision depends on easy-to-grasp concepts: How big are they? How precisely are they aimed?
When you start talking about the likelihood of particles colliding, things get trickier. That’s why physicists use the term “cross section.”
Unlike solid objects, elementary particles themselves behave as tiny waves of probability.
And their interactions are not limited to a physical bump. Particles can interact at a distance, for example, through the electromagnetic force or gravity. Some particles, such as neutrinos, interact only rarely through the weak force. You might imagine them as holograms of billiard balls that occasionally flit into a solid state.
In physics, a cross section describes the likelihood of two particles interacting under certain conditions. Those conditions include, for example, the number of particles in the beam, the angle at which they hit the target, and what the target is made of.
“Cross sections link theory with reality,” says Gerardo Herrera, a researcher at the Center for Research and Advanced Studies of the National Polytechnic Institute in Mexico City and a collaborator on the ALICE experiment at the Large Hadron Collider. “They provide a picture of the fundamental properties of particles. That’s their greatest utility.”
Cross sections come in many varieties. They can help describe what happens when a particle hits a nucleus. In elastic reactions, particles bounce off one another but maintain their identities, like two ricocheting billiard balls. In inelastic reactions, one or more particle shatters apart, like a billiard ball struck by a bullet. In a resonance state, short-lived virtual particles appear.
These measurements of one or more aspects of the interaction are called differential cross sections, while summaries of all of these reactions put together are called total cross sections.
Physicists represent cross sections in equations with the Greek letter sigma (σ). But once they have been measured in actual collisions, their data can be visualized in figures like this:Jorge G. Morf´ın , Juan Nievesb , Jan T. Sobczyka
This plot comes from a paper on interactions between neutrinos and atomic nuclei. The vertical axis represents the chances of the different reactions (measured in square centimeters over giga-electronvolts), and the horizontal axis represents the energy of the incoming neutrinos (measured in giga-electronvolts). An electronvolt is a measure of energy based on the amount of energy an electron gains after being accelerated by 1 volt of electricity.
The above image is telling us, for instance, that at an energy of 10 giga-electronvolts the most probable result would be a deep inelastic scattering (green line), followed by a resonance state (red line), and lastly by a quasi-elastic event (blue line). The black curve represents the total cross section. The error bars (thin lines that go sideways and upside-down) indicate the estimated accuracy of each measurement.
“What you see in this figure are attempts to find a common way to display complex experimental results. This plot is showing how we divide up events that we find in our detectors,” says Jorge Morfín, a senior scientist at Fermilab and one of the main authors of the paper.
Cross sections are used to communicate results among researchers with common interests, Morfín says. The previous cross section serves, then, as a way to compare data obtained from labs that use different measurement techniques and nuclear targets, such as NOMAD (CERN), SciBooNE (Fermilab) and T2K (Japan).
Scientists studying astrophysics, quantum chromodynamics, physical chemistry and even nanoscience use these kinds of plots in order to understand how particles decay, absorb energy and interact with one another.
“They make so many connections with different scientific fields and current research that’s going on,” says Tom Abel, a computational cosmologist at SLAC National Accelerator Laboratory and Stanford University.
In the hunt for dark matter, for example, researchers investigate whether particles interact in the way theorists predict.
“We are looking for interactions between dark matter particles and heavy nuclei, or dark matter particles interacting with one another,” Abel says. “All of this is expressed in cross-sections.”
If they see different interactions than they expect, it could be a sign of the influence of something unseen—like dark matter.
In a world where probability and uncertainty reign, Herrera notes that concepts in quantum mechanics can be difficult to grasp. “But cross sections are a very tangible element,” he says, “and one of the most important measurements in high-energy physics.”
Through hard work, ingenuity and a little cooperation from nature, scientists on the BASE experiment vastly improved their measurement of a property of protons and antiprotons.
Scientists at CERN are celebrating a recent, rare achievement in precision physics: Collaborators on the BASE experiment measured a property of antimatter 350 times as precisely as it had ever been measured before.
The BASE experiment looks for undiscovered differences between protons and their antimatter counterparts, antiprotons. The result, published in the journal Nature, uncovered no such difference, but BASE scientists say they are hopeful the leap in the effectiveness of their measurement has potentially brought them closer to a discovery.
“According to our understanding of the Standard Model [of particle physics], the Big Bang should have created exactly the same amount of matter and antimatter, but [for the most part] only matter remains,” says BASE Spokesperson Stefan Ulmer. This is strange because when matter and antimatter meet, they annihilate one another. Scientists want to know how matter came to dominate our universe.
“One strategy to try to get hints to understand the mechanisms behind this matter-antimatter symmetry is to compare the fundamental properties of matter and antimatter particles with ultra-high precision,” Ulmer says.
Scientists on the BASE experiment study a property called the magnetic moment. The magnetic moment is an intrinsic value of particles such as protons and antiprotons that determines how they will orient in a magnetic field, like a compass. Protons and antiprotons should behave exactly the same, other than their charge and direction of orientation; any differences in how they respond to the laws of physics could help explain why our universe is made mostly of matter.
This is a challenging measurement to make with a proton. Measuring the magnetic moment of an antiproton is an even bigger task. To prevent antiprotons from coming into contact with matter and annihilating, scientists need to house them in special electromagnetic traps.
While antiprotons generally last less than a second, the ones used in this study were placed in a unique reservoir trap in 2015 and used one by one, as needed, for experiments. The trapped antimatter survived for more than 400 days.
During the last year, Ulmer and his team worked to improve the precision of the most sophisticated technqiues developed for this measurement in the last decade.
They did this by improving thier cooling methods. Antiprotons at temperatures close to absolute zero move less than room-temperature ones, making them easier to measure.
Previously, BASE scientists had cooled each individual antiproton before measuring it and moving on to the next. With the improved trap, the antiprotons stayed cool long enough for the scientists to swap an antiproton for a new one as soon as it became too hot.
“Developing an instrument stable enough to keep the antiproton close to absolute zero for 4-5 days was the major goal,” says Christian Smorra, the first author of the study.
This allowed them to collect data more rapidly than ever before. Combining this instrument with a new technique that measures two particles simultaneously allowed them to break their own record from last year’s measurement by a longshot.
“This is very rare in precision physics, where experimental efforts report on factors of greater than 100 magnitude in improvement,” Ulmer says.
The results confirm that the two particles behave exactly the same, as the laws of physics would predict. So the mystery of the imbalance between matter and antimatter remains.
Ulmer says that the group will continue to improve the precision of their work. He says that, in five to 10 years, they should be able to make a measurement at least twice as precise as this latest one. It could be within this range that they will be able to detect subtle differences between protons and antiprotons.
“Antimatter is a very unique probe,” Ulmer says. “It kind of watches the universe through very different glasses than any matter experiments. With antimatter research, we may be the only ones to uncover physics treasures that would help explain why we don’t have antimatter anymore.”
For the first time, experiments have seen both light and gravitational waves released by a single celestial crash.
Today scientists announced the first verified observation of a neutron star collision. LIGO detected gravitational waves radiating from two neutron stars as they circled and merged, triggering 50 additional observational groups to jump into action and find the glimmer of this ancient explosion.
This observation represents the first time experiments have seen both light and gravitational waves from a single celestial crash, unlocking a new era of multi-messenger astronomy.
On August 17 at 7:41 a.m. Eastern Time, NASA astronomer Julie McEnery had just returned from an early morning row on the Anacostia River when her experiment, the Fermi Gamma Ray Space Telescope, sent out an automatic alert that it had just recorded a burst of gamma rays coming from the southern constellation Hydra. By itself, this wasn’t novel; the Gamma-ray Burst Monitor instrument on Fermi has seen approximately 2 gamma-ray outbursts per day since its launch in 2008.
“Forty minutes later, I got an email from a colleague at LIGO saying that our trigger has a friend and that we should buckle up,” McEnery says.
Most astronomy experiments, including the Fermi Gamma Ray Space Telescope, watch for light or other particles emanating from distant stars and galaxies. The LIGO experiment, on the other hand, listens for gravitational waves. Gravitational waves are the equivalent of cosmic tremors, but instead of rippling through layers of rock and dirt, they stretch and compress space-time itself.
Exactly 1.7 seconds before Fermi noticed the gamma ray burst, a set of extremely loud gravitational waves had shaken LIGO’s dual detectors.
“The sky positions overlapped, strongly suggesting the two signals were coming from the same astronomical event,” says Daniel Holz, a professor at the University of Chicago and member of LIGO collaboration and the Dark Energy Survey Gravitational Wave group.
LIGO reconstructed the location and distance of the event and sent an alert to their allied astronomers. About 12 hours later, right after sunset, multiple astronomical surveys found a glowing blue dot just above the horizon in the area LIGO predicted.
“It lasted for two weeks, and we observed it for about an hour every night,” says Jim Annis, a researcher at the US Department of Energy’s Fermi National Accelerator Laboratory, the lead institution on the Dark Energy Survey. “We used telescopes that could see everything from low-energy radio waves all the way to high-energy X-rays, giving us a detailed image of what happened immediately after the initial collision.”
Neutron stars are roughly the size of the island of Nantucket but have more mass than the sun. They have such a strong gravitational pull that all their matter has been squeezed and transformed into a single, giant atomic nucleus consisting entirely of neutrons.
“Right before two neutron stars collide, they circle each other about 100 times a second,” Annis says. “As they collide, huge electromagnetic tornados erupt at the poles and material is sprayed out in all directions at close to the speed of light.”
As they merge, neutron stars release a quick burst of gamma radiation and then a spray of decompressing neutron star matter. Exotic heavy elements form and decay, dumping enough energy that the surface reaches temperatures of 20,000 degrees Kelvin. That's almost four times hotter than the surface of the sun and much brighter. Scientists theorize that a good portion of the heavy elements in our universe, such as gold, originated in neutron star collisions and other massively energetic events.
Since coming online in September 2015, the US-based LIGO collaboration and their Italy-based partners, the Virgo collaboration, have reported detecting five bursts of gravitational waves. Up until now, each of these observations has come from a collision of black holes.
“When two black holes collide, they emit gravitational waves but no light,” Holz says. “But this event released an enormous amount of light and numerous astronomical surveys saw it. Hearing and seeing the event provides a goldmine of information, and we will be mining the data for years to come.”
This is a Rosetta Stone-type discovery, Holz says. “We’ve learned about the processes that neutron stars are undergoing as they fling out matter and how this matter synthesizes into some of the elements we find on Earth, such as gold and platinum,” he says. “In addition to teaching us about mysterious gamma-ray bursts, we can use this event to calculate the expansion rate of the universe. We will be able to estimate the age and composition of the universe in an entirely new way.”
For McEnery, the discovery ushers in a new age of cooperation between gravitational-wave experiments and experiments like her own.
“The light and gravitational waves from this collision raced each other across the cosmos for 130 million years and hit earth 1.7 seconds apart,” she says. “This shows that both are moving at the speed of light, as predicted by Einstein. This is what we’ve been hoping to see.”
For the first time, the Large Hadron Collider is accelerating xenon nuclei for experiments.
Most of the year, the Large Hadron Collider at CERN collides protons. LHC scientists have also accelerated lead nuclei stripped of their electrons. Today, for just about eight hours, they are experimenting with a different kind of nucleus: xenon.
Xenon is a heavy noble gas that exists in trace quantities in the air. Xenon nuclei are about 40 percent lighter than lead nuclei, so xenon-xenon collisions have a different geometry and energy distribution than lead-lead collisions.
“When two high-energy nuclei collide, they can momentarily form a droplet of quark gluon plasma, the primordial matter that filled our universe just after the big bang,” says Peter Steinberg, a physicist at the US Department of Energy’s Brookhaven National Laboratory and a heavy-ion coordinator for the ATLAS experiment at CERN. “The shape of the colliding nuclei influences the initial shape of this droplet, which in turn influences how the plasma flows and finally shows up in the angles of the particles we measure. We’re hoping that these smaller droplets from xenon-xenon collisions give us deeper insight into how this still-mysterious process works at truly subatomic length scales.”
Not all particles that travel through CERN’s long chain of interconnected accelerators wind up in the LHC. Earlier this year, scientists were loading xenon ions into the accelerator and firing them at a fixed-target experiment instead.
“We can have particles from two different sources feeding into CERN’s accelerator complex,” says Michaela Schaumann, a physicist in LHC operation working on the heavy-ion program. “The LHC’s injectors are so flexible that, once everything is set up properly, they can alternate between accelerating protons and accelerating ions a few times a minute.”
Having the xenon beam already available provided an opportunity to send xenon into the LHC for first (and potentially only) time. It took some serious additional work to bring the beam quality up to collider levels, Schaumann says, but today it was ready to go.
“We are keeping the intensities very low in order to fulfil machine protection requirements and be able to use the same accelerator configuration we apply during the proton-proton runs with xenon beams,” Schaumann says. “We needed to adjust the frequency of the accelerator cavities [because more massive xenon ions circulate more slowly than protons], but many of the other machine settings stayed roughly the same.”
This novel run tests scientists’ knowledge of beam physics and shows the flexibility of the LHC. Scientists say they are hopeful it could reveal something new.
“We can learn a lot about the properties of the hot, dense matter from smaller collision systems,” Steinberg says. “They are a valuable bridge to connect what we observe in lead-lead collisions to strikingly similar observations in proton-proton interactions.”
Constellations illustrates the many-worlds interpretation of quantum mechanics—with a love story.
The play Constellations begins with two people, Roland and Marianne, meeting for the first time. It’s a short scene, and it doesn’t go well. Then the lights go down, come back up, and it’s as if the scene has reset itself. The characters meet for the first time, again, but with slightly different (still unfortunate) results.
The entire play progresses this way, showing multiple versions of different scenes between Roland, a beekeeper, and Marianne, an astrophysicist.
In the script, each scene is divided from the next by an indented line. As the stage notes explain: “An indented rule indicates a change in universe.”
To scientist Richard Partridge, who recently served as a consultant for a production of Constellations at TheatreWorks Silicon Valley, it’s a play about quantum mechanics.
“Quantum mechanics is about everything happening at once,” he says.
We don’t experience our lives this way, but atoms and particles do.
In 1927, physicists Niels Bohr and Werner Heisenberg wrote that, on the scale of atoms and smaller, the properties of physical systems remain undefined until they are measured. Light, for example, can behave as a particle or a wave. But until someone observes it to be one or the other, it exists in a state of quantum superposition: It is both a particle and a wave at the same time. When a scientist takes a measurement, the two possibilities collapse into a single truth.
Physicist Erwin Schrodinger illustrated this with a cat. He created a thought experiment in which the decay of an atom—an event ruled by quantum mechanics—would trigger toxic gas to be released in a steel chamber with a cat inside. By the rules of quantum mechanics, until someone opened the chamber, the cat existed in a state of superposition: simultaneously alive and dead.
Some interpretations of quantum mechanics dispute the idea that observing a system can determine its true state. In the many-worlds interpretation, every possibility exists in a giant collection of parallel realities. In some, the cat lives. In others, it does not.
In some Constellations universes, the astrophysicist and the beekeeper fall in love. In others, they do not. “So it’s not really about physics,” Partridge says.
Constellations director Robert Kelley, who founded TheatreWorks in 1970, agrees. He says he was intimidated by the physics concepts in the play at first but that he was eventually drawn to the relationship at its core.
“With all of these things swirling around in the play, what really counts is the relationship between two people and the love that grows between them,” he says. “I found that a very charming message for Silicon Valley. We’re surrounded by a whole lot of technology, but probably for most people what counts is when you get home and you’re on the couch and your one-and-a-half-year-old shows up.”
TheatreWorks in Silicon Valley production of Constellations
Cosmologist Marianne (Carie Kawa) and beekeeper Roland (Robert Gilbert) explore the ever-changing mystery of “what ifs” in the regional premiere of Constellations presented by TheatreWorks Silicon Valley, August 23-September 17, at the Mountain View Center for the Performing Arts.Photo by Kevin Berne
Cosmologist Marianne (Carie Kawa) and beekeeper Roland (Robert Gilbert) explore the ever-changing mystery of “what ifs” in the regional premiere of Constellations presented by TheatreWorks Silicon Valley, August 23-September 17, at the Mountain View Center for the Performing Arts.Photo by Kevin Berne
Cosmologist Marianne (Carie Kawa) and beekeeper Roland (Robert Gilbert) explore the ever-changing mystery of “what ifs” in the regional premiere of Constellations presented by TheatreWorks Silicon Valley, August 23-September 17, at the Mountain View Center for the Performing Arts.Photo by Kevin Berne
Kelley says that he found something familiar in the many timelines of the play. “It’s really kind of fun to see all that happen because it’s common ground for us as human beings: You hang up the phone and think, ‘If only I’d said that or hadn’t said that.’ It’s a fascinating thought that every single thing that happens will then determine every single other thing that happens.”
Constantly resetting and replaying the same scenes “was very acrobatic,” says Los Angeles-based actress Carie Kawa, who played Marianne in the TheatreWorks production, which concluded in September. “And there were emotional acrobatics—just jumping into different emotional states. Usually you get a little longer arc; this play is just all middles, almost like shooting a film.”
To her, the repeats and jumps were familiar in a different way: They were an encapsulation of the experience of acting.
“We do the play over and over again,” she says. “It’s the same scene, but it’s different every single time. And if we’re doing it right, we’re not thinking about the scene that just happened or the scene that’s to come, we’re in the moment.”
The play will mean different things to different people, Kawa says.
“A teacher once told me a story about theater and a perspective that he had,” she says. “At first he said, ‘Theater is important because everybody can come together and feel the same feeling at the same time and know that we’re all okay.’
“But as he progressed in this artistry he realized that, no, what’s happening is everybody is feeling a slightly different feeling at the same time. And that’s OK. That’s what helps us experience our humanity and the humanity of the other people around us. We’re all alone in this together.”
Instead of searching for dark matter particles, a new device will search for dark matter waves.
Researchers are testing a prototype “radio” that could let them listen to the tune of mysterious dark matter particles.
Dark matter is an invisible substance thought to be five times more prevalent in the universe than regular matter. According to theory, billions of dark matter particles pass through the Earth each second. We don’t notice them because they interact with regular matter only very weakly, through gravity.
So far, researchers have mostly been looking for dark matter particles. But with the dark matter radio, they want to look for dark matter waves.
Direct detection experiments for dark matter particles use large underground detectors. Researchers hope to see signals from dark matter particles colliding with the detector material. However, this only works if dark matter particles are heavy enough to deposit a detectable amount energy in the collision.
“If dark matter particles were very light, we might have a better chance of detecting them as waves rather than particles,” says Peter Graham, a theoretical physicist at the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. “Our device will take the search in that direction.”
The dark matter radio makes use of a bizarre concept of quantum mechanics known as wave-particle duality: Every particle can also behave like a wave.
Take, for example, the photon: the massless fundamental particle that carries the electromagnetic force. Streams of them make up electromagnetic radiation, or light, which we typically describe as waves—including radio waves.
The dark matter radio will search for dark matter waves associated with two particular dark matter candidates. It could find hidden photons—hypothetical cousins of photons with a small mass. Or it could find axions, which scientists think can be produced out of light and transform back into it in the presence of a magnetic field.
“The search for hidden photons will be completely unexplored territory,” says Saptarshi Chaudhuri, a Stanford graduate student on the project. “As for axions, the dark matter radio will close gaps in the searches of existing experiments.”Intercepting dark matter vibes
A regular radio intercepts radio waves with an antenna and converts them into sound. What sound depends on the station. A listener chooses a station by adjusting an electric circuit, in which electricity can oscillate with a certain resonant frequency. If the circuit’s resonant frequency matches the station’s frequency, the radio is tuned in and the listener can hear the broadcast.
The dark matter radio works the same way. At its heart is an electric circuit with an adjustable resonant frequency. If the device were tuned to a frequency that matched the frequency of a dark matter particle wave, the circuit would resonate. Scientists could measure the frequency of the resonance, which would reveal the mass of the dark matter particle.
The idea is to do a frequency sweep by slowly moving through the different frequencies, as if tuning a radio from one end of the dial to the other.
The electric signal from dark matter waves is expected to be very weak. Therefore, Graham has partnered with a team led by another KIPAC researcher, Kent Irwin. Irwin’s group is developing highly sensitive magnetometers known as superconducting quantum interference devices, or SQUIDs, which they’ll pair with extremely low-noise amplifiers to hunt for potential signals.
In its final design, the dark matter radio will search for particles in a mass range of trillionths to millionths of an electronvolt. (One electronvolt is about a billionth of the mass of a proton.) This is somewhat problematic because this range includes kilohertz to gigahertz frequencies—frequencies used for over-the-air broadcasting.
“Shielding the radio from unwanted radiation is very important and also quite challenging,” Irwin says. “In fact, we would need a several-yards-thick layer of copper to do so. Fortunately we can achieve the same effect with a thin layer of superconducting metal.”
One advantage of the dark matter radio is that it does not need to be shielded from cosmic rays. Whereas direct detection searches for dark matter particles must operate deep underground to block out particles falling from space, the dark matter radio can operate in a university basement.
The researchers are now testing a small-scale prototype at Stanford that will scan a relatively narrow frequency range. They plan on eventually operating two independent, full-size instruments at Stanford and SLAC.
“This is exciting new science,” says Arran Phipps, a KIPAC postdoc on the project. “It’s great that we get to try out a new detection concept with a device that is relatively low-budget and low-risk.”
The dark matter disc jockeys are taking the first steps now and plan to conduct their dark matter searches over the next few years. Stay tuned for future results.
The dark matter radio disc jockeys. Front row, from left: Carl Dawson, Hsiao-Mei “Sherry” Cho and Saptarshi Chaudhuri. Back row, from left: Arran Phipps, Stephen Kuenstner and Kent Irwin. Not pictured: Dale Li and Peter Graham.Dawn Harmer/SLAC
The dark matter radio is placed inside a 2-millimeter-thick superconducting niobium shield. When lowered into the blue dewar and cooled by liquid helium, the shield blocks interference from outside sources, such as radio stations, but is easily penetrated by dark matter.Dawn Harmer/SLAC
Layers of thermal barriers (top) are used to block heat from the laboratory and keep the radio cold. A cable inside the center rod brings signals from inside the shield to the outside world.Dawn Harmer/SLAC
Dark matter waves should oscillate at a specific frequency corresponding to the mass of the dark matter particle. A spike in power will occur if the radio is tuned to match that frequency.Dawn Harmer/SLAC
It takes about one day to cool the probe from room temperature to the operating temperature of negative 450 degrees Fahrenheit.Dawn Harmer/SLAC Previous Next
Scientists Rainer Weiss, Kip Thorne and Barry Barish won the 2017 Nobel Prize in Physics for their roles creating the LIGO experiment.
After being passed up for the honor last year, three scientists who made essential contributions to the LIGO collaboration have been awarded the 2017 Nobel Prize in Physics.
Rainer Weiss will share the prize with Kip Thorne and Barry Barish for their roles in the discovery of gravitational waves, ripples in space-time predicted by Albert Einstein. Weiss and Thorne conceived of the experiment, and project manager Barish is credited with reviving the struggling experiment and making it happen.
“I view this more as a thing that recognizes the work of about 1000 people,” Weiss said during a Q&A after the announcement this morning. “It’s really a dedicated effort that has been going on, I hate to tell you, for as long as 40 years, people trying to make a detection in the early days and then slowly but surely getting the technology together to do it.”
A third founder of LIGO, scientist Ronald Drever, died in March. Nobel Prizes are not awarded posthumously.
According to Einstein’s general theory of relativity, powerful cosmic events release energy in the form of waves traveling through the fabric of existence at the speed of light. LIGO detects these disturbances when they disrupt the symmetry between the passages of identical laser beams traveling identical distances.
The setup for the LIGO experiment looks like a giant L, with each side stretching about 2.5 miles long. Scientists split a laser beam and shine the two halves down the two sides of the L. When each half of the beam reaches the end, it reflects off a mirror and heads back to the place where its journey began.
Normally, the two halves of the beam return at the same time. When there’s a mismatch, scientists know something is going on. Gravitational waves compress space-time in one direction and stretch it in another, giving one half of the beam a shortcut and sending the other on a longer trip. LIGO is sensitive enough to notice a difference between the arms as small as 1000th the diameter of an atomic nucleus.
Scientists on LIGO and their partner collaboration, called Virgo, reported the first detection of gravitational waves in February 2016. The waves were generated in the collision of two black holes with 29 and 36 times the mass of the sun 1.3 billion years ago. They reached the LIGO experiment as scientists were conducting an engineering test.
“It took us a long time, something like two months, to convince ourselves that we had seen something from outside that was truly a gravitational wave,” Weiss said.
LIGO, which stands for Laser Interferometer Gravitational-Wave Observatory, consists of two of these pieces of equipment, one located in Louisiana and another in Washington state. The experiment is operated jointly by MIT, Weiss’s home institution, and Caltech, home institution for Barish and Thorne. The experiment has collaborators from more than 80 institutions from more than 20 countries. A third interferometer, operated by Virgo, recently joined LIGO to make the first joint observation of gravitational waves.