symmetry

Q&A with Nobel laureate Barry Barish

Barish explains how LIGO became the high-achieving experiment it is today.

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Illustration: Barry Barish
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. 

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Fermilab’s 11th employee

Fantastical designs elevate physics in works by Fermilab’s first artist.

A pen drawing shows Wilson Hall next to the accelerator complex.

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

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).

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)

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).

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.

Wilson Hall sits among droplets representing the water cycle.

Fermilab
Gonzales designed posters for many events, including colloquia, symposia and workshops.

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.

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.

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.

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

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

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.

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

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.

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.

The Fermilab logo was created in a collaboration between Wilson and Gonzales; the final version has rigorous specifications.

Fermilab
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Something borrowed

SLAC engineer Knut Skarpaas designs some of physics’ most challenging machines, finding inspiration in unexpected places.

Skarpass observes woman weaving

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. 

Skarpass taking apart a loom in messy workshop.
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.

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An international celebration of dark matter

Around the world, scientists and non-scientists alike celebrated the first international Dark Matter Day.

Dark Matter Day recap

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.

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 celebrated Dark Matter Day with Facebook Live broadcasts

Employees at SLAC National Accelerator Laboratory celebrated Dark Matter Day with Facebook Live broadcasts related to two upcoming projects that will study dark matter, the LZ experiment at the Large Synoptic Survey Telescope.

SLAC National Accelerator Laboratory
Bart Bernhardt, co-founder of Nerd Nite SF, donned a Dark Matter Day t-shirt during an October 18 event in San Francisco.

Bart Bernhardt, co-founder of Nerd Nite SF, donned a Dark Matter Day t-shirt during an October 18 event in San Francisco.

Nerd Nite SF
Obi-Wan Kenobi was spotted in a Dark Matter Day t-shirt in the Berkeley Lab Strategic Communications office.

Obi-Wan Kenobi was spotted in a Dark Matter Day t-shirt in the Berkeley Lab Strategic Communications office.

Berkeley Lab
School children made their own dark matter particles during a workshop at STFC’s Rutherford Appleton Laboratory in the UK.

School children made their own dark matter particles during a workshop at STFC’s Rutherford Appleton Laboratory in the UK.

STFC
The auditorium was packed for a special

The auditorium was packed for a special "Talking Science" public lecture at STFC’s Daresbury Laboratory.

STFC
In a Parliamentary showcase at the House of Commons, MPs met with leading UK dark matter experts (L-R): Tommy Sheppard MP, Carol

In a Parliamentary showcase at the House of Commons, 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 Bowsher.

STFC
Dark Matter Day event in Victoria Street, London. (L-R) Sean Paling, Director of the Boulby Underground Laboratory, with Greg

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 Frenk.

STFC
The interest of the public in Karlsruhe, Germany, was so great that the NTI lecture hall on Campus South

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

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.

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.

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.

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.

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”

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 Shanghai

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.

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.

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.

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.

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 principles of dark matter

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

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 Innovation

On Tuesday, October 31, CERN joined the global celebration of Dark Matter Day from the Globe of Science and Innovation

CERN
With Dark Matter Day falling on Halloween, some creative participants came dressed up in costumes related to dark matter

With Dark Matter Day falling on Halloween, some creative participants came dressed up in costumes related to dark matter

CERN
A volunteer demonstrates magnetism at a Dark Matter Day event at Adler Planetarium in Chicago.

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.

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.

Visitors and volunteers talk particle accelerators at the Dark Matter Day event at Adler Planetarium in Chicago.

Leo Bellantoni, Fermilab
Lindsay Forestell

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.”

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How is the Force like dark matter?

For Dark Matter Day, scientist and Star Wars fan Dan McKinsey talks dark matter and the Force.

Photo of scientist Dan McKinsey from the chest up with text that reads

Scientist Dan McKinsey of Berkeley Lab and UC Berkeley shares some thoughts on dark matter.

Ask Symmetry – How is the Force like dark matter?

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McKinsey recently answered questions about dark matter on Reddit Science.

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CERN alumna turned deep-sea explorer

Grace C. Young is fascinated by fundamental questions about realms both quantum and undersea.

Grace Young walking on the ocean floor

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.

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Speak physics: What is a cross section?

Cross sections tell physicists how likely particles are to interact in a given way.

Header: Speak physics: What is a cross section?

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.

Inline 1_ Speak physics What is a cross section_2

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:

Inline 1_ Speak physics What is a cross section
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.”

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Scientists make rare achievement in study of antimatter

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.

Photo of BASE Spokesperson Stefan Ulmer working on the experiment

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.”

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