KICP in the News

Cosmic convergence
AAAS, Science, August 3, 2015
This lab at the South Pole gathers signals from the massive IceCube detector 1.5 kilometers below.  <i>PHOTO: FELIPE PEDREROS, ICECUBE/NSF</i>
This lab at the South Pole gathers signals from the massive IceCube detector 1.5 kilometers below.

by Adrian Cho, AAAS, Science

A year and half ago, physicists working with one of the world's odder scientific instruments scored a bittersweet breakthrough. The massive IceCube particle detector - a 3D array of 5160 light sensors buried kilometers deep in ice at the South Pole - spotted ghostly subatomic particles called neutrinos from beyond our galaxy (Science, 22 November 2013, p. 920). Researchers had previously detected lower energy neutrinos gushing from the sun and raining down from particle interactions in the atmosphere. But - except for a burp from a nearby supernova explosion in 1987 - neutrinos from the far reaches of the cosmos had eluded capture.

The discovery is Nobel-caliber stuff, some physicists say, but it also sounded a cautionary note. IceCube saw only about a dozen cosmic neutrinos per year. At that meager rate, the $279 million detector might never spot enough of them to work as advertised: as a neutrino telescope that could open up a whole new view of the heavens.

But as the data continue to come in, researchers are optimistic. After all, the fact that cosmic neutrinos have been spotted means that a big enough detector should be able to harvest enough of them to study the sky, says Francis Halzen, a theoretical physicist at the University of Wisconsin, Madison, and the driving force behind IceCube. "We see the flux, and now we have to figure out what it takes to do astronomy with it," he says. Halzen and his team are pushing to expand IceCube, which already fills a volume of a cubic kilometer. Meanwhile, other researchers have developed approaches that they say could be cheaper and more efficient.

More important, cosmic neutrinos are already telling a story, especially when combined with other particles from space: highly energetic photons called gamma rays, and ultrahigh-energy cosmic rays - protons and heavier atomic nuclei that reach energies a million times higher than humans have achieved with particle accelerators. Physicists have long wondered where in the universe the most energetic neutrinos, gamma rays, and cosmic rays are born. Now, in a tantalizing convergence, all three questions appear to share the same answer, says Olga Botner, a physicist and IceCube team member from Uppsala University in Sweden. "We believe that the engines that generate the cosmic rays also generate the gamma rays and neutrinos," she says.

If so, physicists have only one mystery to solve. The convergence also suggests the solution won't require exotic new particle physics: The conventional astrophysics of stars and galaxies should suffice.

AS TRACERS of the heavens, neutrinos offer many advantages over other particles from space. Electrically charged cosmic rays swirl in galactic magnetic fields; gamma rays tangle with radiation lingering from the big bang - the cosmic microwave background (CMB). Uncharged neutrinos, by contrast, zoom straight from their sources through almost everything the universe throws at them. "Neutrinos are the ultimate high-energy messenger," says Abigail Vieregg, a physicist at the University of Chicago in Illinois. "They're perfect - if you can see them."


Related Links:
KICP Members: Abigail G. Vieregg
The Fabric of the Universe
UChicago Arts, July 15, 2015
The Fabric of the Universe
UChicago Arts

Benedikt Diemer (Ph.D candidate, Astronomy & Astrophysics, UChicago); Isaac Facio (MFA candidate, Fiber & Material Studies, SAIC)

Faculty Advisors: Andrey Kravtsov (Astronomy & Astrophysics, UChicago); Helen Maria Nugent (Designed Objects (AIADO), SAIC)

The Fabric of the Universe is an investigation into a novel way of visualizing the structure of the universe: using 3-dimensional textiles. Isaac Facio and Benedikt Diemer will transform the shapes formed by the dark matter in large computer simulations into fabric using digital textile manufacturing technologies. The properties of the fabric, such as its opacity, will represent the properties of dark matter structures, such as their density. Ultimately, the textile will take shape in a large-scale sculpture of the dark matter filaments and nodes in the universe, known as the "cosmic web".

Funded by the Graduate Division, School of the Art Institute of Chicago (SAIC).


Related Links:
KICP Members: Andrey V. Kravtsov
KICP Students: Benedikt Diemer
Kavli Roundtable Discussion: "Dwarf Galaxies Loom Large in the Quest for Dark Matter"
The Kavli Foundation, June 24, 2015
Side-by-side images from the Dark Energy Survey indicate the difficulty of identifying a dwarf galaxy. The right image shows approximately 300 stars thought to belong to a newly discovered dwarf satellite galaxy of the Milky Way. These stars are farther away than foreground stars within the Milky Way, but much closer than background galaxies, both of which appear in the left image but are blacked out in the right image. (Credit: Fermilab/Dark Energy Survey)
Side-by-side images from the Dark Energy Survey indicate the difficulty of identifying a dwarf galaxy. The right image shows approximately 300 stars thought to belong to a newly discovered dwarf satellite galaxy of the Milky Way. These stars are farther away than foreground stars within the Milky Way, but much closer than background galaxies, both of which appear in the left image but are blacked out in the right image. (Credit: Fermilab/Dark Energy Survey)
by Adam Hadhazy, The Kavli Foundation

A batch of newly discovered satellite dwarf galaxies orbiting the Milky Way should help scientists better grasp the evolution of the universe while also honing in on dark matter's identity.

IN ITS INAUGURAL YEAR OF OBSERVATIONS, the Dark Energy Survey has already turned up at least eight objects that look to be new satellite dwarf galaxies of the Milky Way. These miniature galaxies - the first discovered in a decade - shine with a mere billionth of our galaxy's brightness and each contains a million times less mass. Astronomers believe the vast majority of material in dwarf galaxies is dark matter, a mysterious substance composing about 80 percent of all matter in the universe. Dwarf galaxies have therefore emerged as prime targets for gathering potential clues about dark matter's composition.

Some theories suggest dark matter particles and antiparticles should produce telltale gamma rays when they collide with each other. Accordingly, scientists used the Fermi Gamma-Ray Space Telescope to study the newfound dwarf galaxy candidates, as well as a group of dwarf galaxies already on the books.

The telescope detected no significant gamma-ray signals from either set of dwarf galaxies, however, leaving scientists still in the hunt for dark matter. Four studies earlier this spring from the Dark Energy Survey and Fermi announced this flurry of results.

On May 18, 2015, The Kavli Foundation spoke with three astrophysicists about the continuing search for dark matter data in space and how dwarf galaxies can help us understand the evolution of our universe.

The participants were:

  • JOSH FRIEMAN is the Director of the Dark Energy Survey at the Department of Energy's Fermilab Center for Particle Astrophysics, a Professor of Astronomy and Astrophysics at the University of Chicago, and a member of the Kavli Institute for Cosmological Physics (KICP).
  • ALEX DRLICA-WAGNER - is the Schramm Experimental Fellow at the Fermilab Center for Particle Astrophysics and a KICP Associate fellow.
  • ANDREA ALBERT - is a Research Associate at the SLAC National Accelerator Laboratory and the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University.

The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

THE KAVLI FOUNDATION: What were your first thoughts when you saw the signs of these dwarf galaxies in Dark Energy Survey data?

ALEX DRLICA-WAGNER: It was very exciting and definitely not something you get to experience every day. It was obvious from the start that some of the objects in the data were real stellar systems and very probable that they were new dwarf galaxies.

JOSH FRIEMAN: We released the first year of Dark Energy Survey data internally to our international collaboration of scientists in late December. Within a week or two, Alex and his co-lead author, Keith Bechtol, who is a postdoctoral research fellow at the Kavli Institute for Cosmological Physics, helped to lead the group of Dark Energy Survey scientists who identified these objects. Alex and Keith had spent a long time developing methods for detecting dwarf galaxies in this data, so when it became available they were instantly able to jump on it.

DRLICA-WAGNER: When you see something like this emerge from your data analysis for the first time, that's very special. You've invested so much time going through all of the data, you can feel a little lost down there in all the details.

ANDREA ALBERT: Yeah, I know how that feels!

TKF: How did the Dark Energy Survey enable the discovery of these dwarf galaxies?

FRIEMAN: We didn't actually build the Dark Energy Survey to do this. These nearby dwarf galaxies are foreground objects to what we're really trying to study, which are hundreds of millions of distant galaxies. We are measuring those distant galaxies' properties and their distribution to figure out why the expansion of the universe is speeding up due to dark energy. We realized that those same data would be very useful not only for studying the distant universe, but also for identifying very faint dwarf satellite galaxies of our own Milky Way.

DRLICA-WAGNER: With the Dark Energy Camera, the principal instrument for the Dark Energy Survey, this is the first time we've had a super-sensitive, large-field digital camera in the southern hemisphere. The explosion of dwarf discoveries about a decade ago in the northern hemisphere was made possible because of the state-of-the-art technology involved in the Sloan Digital Sky Survey [SDSS]. With the Dark Energy Camera, we have an even better camera than SDSS and we have a whole new region of sky.

FRIEMAN: This is one of those examples where you build something with one goal in mind, but if it's properly designed it turns out to be quite useful for a variety of other scientific studies as well.

DRLICA-WAGNER: As Josh just said, the Dark Energy Survey was not intended for this kind of science, but it really presented an amazing opportunity. We were able to find this abundance of new stellar systems by combining two models of what we expect dwarf galaxies to look like. In general, dwarf galaxies have more stars near their centers and fewer stars near their peripheries. Additionally, the stars in dwarf galaxies tend to follow a very distinct pattern of color and brightness. By combining these two models, we had a much better chance of finding dwarf galaxies.

TKF: Why are dwarf galaxies so notoriously difficult to spot?

DRLICA-WAGNER: Dwarf galaxies are hard to find because they contain very few bright stars. Also, dwarf galaxies are mostly made of dark matter. If we figured out a way to see dark matter, then dwarf galaxies would be easy to see.

ALBERT: We're awesome at seeing stars because we are awesome at seeing light. Unfortunately, dark matter does not directly make light. So we call it "dark." Physicists are not that creative when we come up with names!

FRIEMAN: One thing astronomers like to do when they're presenting at conferences is to show an image of what a dwarf galaxy looks like. The presenter will show an image and it looks like nothing is there, like a random field of stars. And then on the next slide, the astronomer will circle all the objects that are members of that dwarf galaxy, and then it pops out at you.

What you really need to find these dwarf galaxies are very sensitive observations that allow you to detect faint stars and determine their colors. All that is critical for being able to distinguish a grouping of stars that together form a dwarf galaxy from the light of background galaxies and from foreground stars in the Milky Way.

ALBERT: I'd also mention that many of the reasons why dwarf galaxies are very, very challenging to detect are also the reasons why they are one of the best targets we have today for dark matter searches.

TKF: That comment segues into why dwarf satellite galaxies of the Milky Way are so scientifically valuable. Alex, you've said before that their dark matter content makes them important for both astronomy and physics. Can you elaborate?

DRLICA-WAGNER: This long-standing problem of the identity of dark matter is a topic where you historically have seen a lot of interplay between astronomy and physics. Dark matter was first a purely astronomical problem. It was originally discovered by observations showing that the force of gravity is not strong enough to prevent galaxies and clusters of galaxies from flying apart. So astronomy at the very start was sort of telling physics, "Hey, there's something here that we don't understand." In parallel physicists, were coming up with their own ideas for new fundamental particles. Eventually, people started to assemble the idea that missing "dark" matter particles could be holding galaxies together.

FRIEMAN: This notion of dark matter particles goes back 35 years or so and it's very compelling. Assume you have an unseen particle that weighs, say, 10 to 100 times the mass of a proton. Say it only rarely interacts with particles of normal matter through a force similar to the "weak force," one of the four known forces of nature. Particles with these properties would very naturally be around in the right amounts in the universe to be the dark matter that we infer in galaxies and clusters of galaxies. The particles would also possess the right properties to explain the formation of galaxies and larger structures.

DRLICA-WAGNER: This melding of ideas from astronomy and physics has really come together to make a cosmic frontier of physics. We're trying to push our fundamental understanding of physics through a better understanding of the cosmos with observations like those from the Dark Energy Survey.

TKF: Dwarf galaxies and the search for dark matter particles are a prime example of the intersection of astronomy and physics. Andrea, your specialty is looking for the signatures of dark matter particles that hypothetically self-annihilate, rather like how normal matter particles and antimatter particles annihilate each other. This annihilation should generate telltale gamma rays. Yet the Fermi Gamma-Ray Space Telescope hasn't glimpsed gamma-ray signatures from dwarf galaxies, including the newly discovered dwarfs, that are suggestive of dark matter. What is your reaction to this?

ALBERT: It is disappointing. I think anyone who says that it's exciting that we haven't discovered particles of dark matter is a liar. [Laughter] So yes, we have not seen dark matter yet. However, we are just starting to scratch the surface. We have calculated a rate at which we expect annihilations to occur, according to various models, and determined what the gamma-ray signature of these annihilations should be. This annihilation rate and its gamma-ray signals are tied to the mass of the dark matter particles. At this point, we have just started to test for the most promising dark matter candidates across a small range of masses. There are models for more massive dark matter particles than we can now detect with Fermi, and which are just as viable. So I think that if dark matter is hiding, we are narrowing in on it, and that's exciting.

FRIEMAN: There's a real synergy between the Dark Energy Survey, which is an optical survey of the sky, and the Fermi experiment, which is searching over the whole sky for gamma rays. It has been very exciting putting these two projects together to make progress in constraining dark matter. I agree with Andrea that even though the latest studies report a non-detection of signature gamma rays, it's nevertheless important progress in constraining what the dark matter could be. And I think it's pushing us closer to either detecting dark matter particles or having to go in a different direction to explain dark matter.

ALBERT: The search for dark matter reminds me of the history of the search for the Higgs boson, which we finally discovered in 2012 at the Large Hadron Collider [LHC] at CERN. A couple of years before then, we were looking for the Higgs boson in the less powerful Tevatron particle accelerator at Fermilab. An experiment there was one of the first to rule out certain masses of the Higgs boson. That told us we needed to go and build a better accelerator before we would actually find the thing. Fermi's been running for over six years now, but there is a new gamma-ray experiment in the making called the Cherenkov Telescope Array. It is going to be able to test for much heavier dark matter particle masses inaccessible to Fermi.
"Many of the reasons why dwarf galaxies are very, very challenging to detect are also the reasons why they are one of the best targets we have today for dark matter searches." - Andrea Albert

TKF: How else can dwarf galaxies help us pin down the properties of dark matter?

DRLICA-WAGNER: It's worth noting that there are multiple targets in the sky where you'd expect to see a gamma-ray signal from dark matter. One of the most tantalizing is the center of the Milky Way galaxy itself. Unfortunately, the center of our Galaxy is a very active region, and there are loads of gamma rays coming from there. The issue is that when you see these gamma rays, it could just be that you don't fully understand how our Galaxy's center is producing them astrophysically. Or, on the other hand, there could be a dark matter component to the gamma-ray emissions. Dwarf galaxies are extremely important because you can use them as a cross-check on any interesting signals you see from the Galactic center.

ALBERT: Interpreting this excess of gamma rays from the Milky Way's center as possibly coming from dark matter annihilations highlights how important it is to have a large sample of these dwarf galaxies. The Galactic center is close to us and it's really bright in gamma rays, whereas these dwarf galaxies are like little, dim candles. So how are we ever going to compare dwarf galaxies to the big, bright Galactic center? If we have enough dwarf galaxies, we can stack up them up statistically for a comparison, so we can then start to test and rule out models that don't fit the data.

DRLICA-WAGNER: That's right. While we will likely have a smaller gamma-ray signal from dwarf galaxies, the signal is much cleaner and easier to study than from the very active center of the Milky Way galaxy.
"We're trying to push our fundamental understanding of physics through a better understanding of the cosmos with observations like those from the Dark Energy Survey." - Alex Drlica-Wagner

TKF: By finding these new satellite dwarf galaxies of the Milky Way, do you think we're closer to solving the so-called missing satellite problem? According to the leading theory of Big Bang cosmology, known as the cold dark matter model, there should be hundreds of satellite dwarf galaxies orbiting the Milky Way. Yet we've only found a few dozen. Are we now starting to plug this gap?

FRIEMAN: This has been an interesting problem and it gets into the cosmological issue of the formation of structure in the universe, of how galaxies and galaxy clusters came to be. One of the exciting things about dwarf galaxies is that they are likely some of the first large structures that formed in the universe. In the cold dark matter model, structure forms hierarchically. That means that smaller structures formed first and then merged together to form larger structures, made of both dark matter and galaxies.

DRLICA-WAGNER: The population of dwarf galaxies tells us something about how galaxies form. They address larger astrophysical questions about how our galaxy came to be and how other large galaxies form from gathering up the small, original galaxies in the universe.

FRIEMAN: There is this issue, though, when you run a computer simulation of how structure forms in the cold dark matter model. A galaxy with a similar size as the Milky Way ends up with a halo of dark matter surrounding it. But this halo should have lots of clumps within it that have masses comparable to those of dwarf galaxies. The assumption is that since dark matter and normal matter clump together due to gravity, you would naively expect those dark matter clumps to be where dwarf galaxies form. In other words, the dark matter halo around our galaxy should be teeming with hundreds of dwarf galaxies or more, but we see only a few. The missing satellite problem is that there's a mismatch between the number of dwarf galaxies found and the number predicted from theory.

As we've drilled down deeper, further and fainter with the SDSS and now with the Dark Energy Survey, we are finding more dwarf galaxies. But that's only one piece of the puzzle. You also have to understand the detailed physics of galaxy formation to say whether those clumps of dark and normal matter in the Milky Way halo would actually have formed stars that we can see. There are some scenarios in which you don't expect all of those clumps to have lit up and formed dwarf galaxies. So I would say this finding of the eight new dwarf galaxies helps inform the missing satellite problem, but it also wasn't the problem that was keeping theorists up at night the last few years.

ALBERT: An astrophysical problem that I'm hearing people talk more about these days is the "too big to fail" problem. The problem is, why don't we see larger dwarf galaxies? Why isn't matter clumping on a larger scale than the dwarf galaxies, but on a smaller scale than the Milky Way galaxy?

FRIEMAN: To date, we've had roughly 25 dwarf galaxies to study with regard to the sizes they attain in the dark matter around the Milky Way. In the next few years, as we get more information on the new dwarf galaxies we've found, plus other new ones, that number will increase. That should help us quantify the "too big to fail" problem and decide how much of a problem it is.

TKF: Do you think the Dark Energy Survey will turn up more dwarf galaxies?

FRIEMAN: We found these dwarf galaxies in the Dark Energy Survey's first six-month season of observations. We'll have five of these observing seasons over five years. During the first season, we observed about 40 percent of the area of the sky we will eventually cover. In the second season, which ended in February, we observed most of the remainder of the sky area, so we are hoping for a good harvest of new dwarfs. In the subsequent seasons, we won't cover new areas, but we will take deeper observations of the previously covered area. In principle, that can enable us to find dwarf galaxies we haven't spotted yet that have fainter or fewer stars in them.

DRLICA-WAGNER: Over these later seasons, we will also gain a better understanding of the dwarf galaxies we have already found. As for the number of new dwarfs we'll find, we'd expect to find maybe 10 more based on the area of the survey we have covered and the additional area we are adding. But there are important caveats, such as whether dwarf galaxies are distributed evenly across the sky. It's an open scientific question that we hope to address with future years of the Dark Energy Survey.
"These new dwarf galaxies are perhaps some of the earliest structures that formed in the universe and are the building blocks of the large-scale structure we see today." - Josh Frieman

TKF: Josh, you've said that cosmology is like archeology on a grand scale. Just as an archaeologist might look at ruins or pottery shards to piece together an ancient society, we can see how galaxies are distributed in space to learn what the universe looked like in the past. Can these new dwarf galaxies help us trace back the history of the Milky Way and the universe?

FRIEMAN: You can think of these dwarf galaxies as pottery shards left over from an earlier period of cosmic evolution. These new dwarf galaxies are perhaps some of the earliest structures that formed in the universe and are the building blocks of the large-scale structure we see today. They're much smaller than the mass of the Milky Way, and some of these dwarfs appear to have stars in them that are quite old. So these dwarf galaxies are potentially an indicator of what happened in the early phases of structure formation.

The first two major results from the Dark Energy Survey are kind of poetic when viewed in juxtaposition. One major result is these dwarf galaxies. The other is a large-scale dark matter map we released in April, which shows superclusters of galaxies and dark matter - some of the largest structures in the universe that have ever been seen. So surveys like the Dark Energy Survey are giving us information over this very broad range of scales, from dwarf galaxies to superclusters, that add to our picture about how structure has formed and evolved over time. And that's important also for the main thing that we want to do with the Dark Energy Survey, which is understand why the expansion of the universe is speeding up due to dark energy. There's a grand competition taking place on the largest scales of the universe between gravity trying to pull things together and dark energy trying to push things apart. Understanding how structure formed and evolved over time is one of the tools that we will use to figure out the nature of dark energy.

TKF: Alex and Andrea, do you guys also feel like cosmic archeologists? Or maybe more like cosmic bounty hunters trying to capture dwarf galaxies and their signals of dark matter annihilation?

ALBERT: I feel like a cosmic Sherlock Holmes. All of the dark matter analyses I've been involved in have not seen anything, so it feels like dark matter is just out of my grasp. Dark matter is kind of like my Moriarty.

DRLICA-WAGNER: My thesis was similar to Andrea's work searching for dark matter annihilation in gamma rays. One thing that I've learned from the recent discoveries in DES is that it is really, really fun to find things. I can only imagine how extraordinarily exciting it will be if and when we find definitive evidence of dark matter.

ALBERT: It would be a bigger finding than the Higgs boson. It would be evidence for physics beyond the Standard Model of particle physics that is a great description of the 20 percent of normal matter in the universe which actually only makes up five percent of the grand total of the total mass and energy in the universe.

FRIEMAN: Yes, we can say we have a really, really good understanding of five percent of the universe.

ALBERT: There's a quote that resonates with me and my feelings toward finding dark matter that people attribute to Confucius: "The hardest thing of all to find is a black cat in a dark room, especially if there is no cat." Fortunately, at this point, I don't think we've searched the entire room!

- Adam Hadhazy, Summer 2015


Related Links:
KICP Members: Alex Drlica-Wagner; Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES); Sloan Digital Sky Survey (SDSS)
Chicago blues and the science in sound
The University of Chicago News Office, June 19, 2015
Bradford Benson, KICP senior member
Bradford Benson, KICP senior member
by Greg Borzo, The University of Chicago News Office

'Science and Sound' Preview Video

Everyone knows about visualizing data, but few have heard of sonifying data. Nevertheless, sound has great potential for organizing, interpreting and sharing scientific knowledge. Sound can also be a powerful tool to learn more about culture and the natural world.

Citing microbial bebop, Chicago blues, cosmic sound and a string quartet inspired by DNA's double helix, panelists at a program called "Science and Sound" on June 3 made a strong case for exploring and exploiting sound as a tool in scientific endeavors.

The occasion was the 11th in a series of joint speaker events for faculty at the University of Chicago as well as scientists, researchers and engineers at Argonne National Laboratory and Fermi National Accelerator Laboratory. It was held at Buddy Guy's Legends, the "cathedral" of Chicago blues and the "perfect place to discuss how sound serves science, pervades our lives and influences our emotions," said Donald Levy, vice president for Research and for National Laboratories at the University of Chicago.

Panelist Peter Larsen, assistant computational biologist at Argonne, explained how an algorithm he calls microbial bebop generates data into music by normalizing the data to a dynamic range of integer values and mapping those values to notes and chords. "I doubt that I'll ever come up with a composition that will change my understanding of microbial ecology, but the very exercise of doing this has already accomplished that," he said. "My job is to think of interesting ways to analyze big data... and microbial bebop has helped me find and understand better approaches to understanding data."

Another panelist, however, decided not to transcribe data directly into music, realizing that such an approach would not create an effective, cohesive composition. In composing "Helix Spirals" for string quartet, Grammy-winning composer Augusta Read Thomas, University Professor of Composition, approached the project metaphorically. She found inspiration in science and showed how well music can present an abstract and intellectual expression of nature.

"Helix Spirals" celebrates the Meselson-Stahl DNA replication experiment of 1958. The first movement, Thomas explained, portrays loci, that is, specific but "flickering" locations of genes or DNA sequences on a chromosome. The second movement portrays DNA replication with different instruments representing different strands. And the third conveys the beauty, richness and force of life.

"Nature is a great teacher of transformation, connections and, for me, music composition," said Thomas, who is now working on a piece about protein folding.

Indeed, music and sound is a "metaphor for the regularity of nature and even the movement of the heavens," said moderator Sidney Nagel, the Stein-Freiler Distinguished Service Professor in Physics.

Listening to learn
Instead of using science to generate or inspire music, panelist Michael Dietler, professor in anthropology, works the other way around. He listens to music to better understand cultures. "Music is a socially patterned, cultural phenomenon, and the blues has a lot to teach us about Chicago's African American culture," he said. Noting that many students spend four years on campus without exploring what Chicago has to offer, Dietler created a course on the history of the blues, which he called an enormously influential form of music.

"It's one thing to listen to the blues and quite another to understand how it evolved, impacts people, influences culture and continues to develop today," Dietler said. The difference is akin, he added, to the difference between enjoying the sound of French and actually understanding what is being said, idiomatically, historically and culturally.

Meanwhile, one of the best ways to learn about the universe is to listen to it. "Just like you can learn a lot about an instrument by studying the frequency of the sound it makes, you can learn a lot about the content of the universe by studying the Cosmic Microwave Background," said Bradford Benson, associate scientist and Wilson fellow at Fermilab and assistant professor in astronomy and astrophysics at the University of Chicago.

Cosmic Microwave Background is radiation left over from the Big Bang. "As we map the sky, we can detect sound waves from the early history of the universe, more than 13 billion years ago," Benson said. "When we measure the Cosmic Microwave Background's power spectrum - analogous to what you might do with a stereo amplifier - we find a remarkable harmonic structure," Benson said.

Overall, the panelists agreed that sound and science go well together, whether it is to listen to the cosmos - and each other - or to utilize sound as a tool to understand data and present knowledge, directly or indirectly. For instance, although microbial bebop is not an effective way to share data, it is a great way to engage students in science, Larsen has found. But the day may come when sonified data and audible pie charts are as commonplace as visual maps.

"We have to learn how to create and interpret charts, Venn diagrams, and other visual presentations of data," Dietler said. "Likewise, we could learn how to utilize sound and music more in science. We're used to conducting many things visually, but there's no reason why we couldn't handle more things audibly."

"Some of what we learn is communicated through sound, but there's a big potential to tap sound in new ways to achieve much more," Nagel concluded.


Related Links:
KICP Members: Bradford A. Benson
MIRA and marathons
Argonne, June 18, 2015
Katrin Heitmann, Salman Habib and Steve Rangel will be supporting HOPES and the Chicago Area Runners Association when they run The Chicago Marathon October 11.
Katrin Heitmann, Salman Habib and Steve Rangel will be supporting HOPES and the Chicago Area Runners Association when they run The Chicago Marathon October 11.
by Sarah Schlieder, Argonne

For three Argonne employees it's all about speed - both in and out of the lab.

Katrin Heitmann, a joint staff member in the High Energy Physics and Math and Computer Sciences Divisions; Salman Habib, senior physicist in the High Energy Physics and Math and Computer Sciences Divisions and Steve Rangel, lab appointee and Ph.D. student at Northwestern University have run the largest cosmological simulation on MIRA - one of the world's fastest supercomputers. Their aim was to create high-resolution simulations what would allow scientists to connect numerous surveys of the universe that measure the distribution of galaxies.

"Dealing with data is a big challenge in and of itself. What a large computer like MIRA enables is a lot of statistics." - Katrin Heitmann, Staff Member HEP and MCS

MIRA is capable of 10 quadrillion calculations per second. Located at the Argonne Leadership Computing Facility, it can do in one day what it would take the average personal computer 20 years to complete.

MIRA is also what brought Heitmann and Habib to Argonne from Los Alamos National Laboratory in Los Alamos, New Mexico.

Rangel joined the team soon after their move to Argonne. He said he first became interested in data science and data analysis when he was pursuing his master's degree. Later, his interest evolved into a passion for high performance computing.

"It was sort of a natural fit to come here and work with Salman and Katrin's group." - Steve Rangel, Ph.D. student at Northwestern University

The team has now begun to analyze the simulations, measuring galaxy distribution from a theory standpoint and comparing that data to observations of the universe. The team worked together to transform data from the MIRA simulation into an image that closely resembles the actual universe. Argonne joint staff member Nan Li and University of Chicago Professor Mike Gladders constructed the final visualization.

But besides performing the world's biggest simulation on MIRA, the team will put their own speed to the test later this year when they run the Bank of America Chicago Marathon.

The team ran together for the first time in this year's Bank of America Shamrock Shuffle, held March 29 in downtown Chicago. Rangel then suggested they run a marathon.

"At first I said, 'No way!'" Heitmann said. "Then, I got to thinking about it and thought it would be kind of cool if our group did it together. But I said we should at least do it for something more meaningful than just suffering for 26 miles."

With that idea in mind, Heitmann said she searched for charities listed on the Chicago Marathon website for which people can run. There, she found Chicago HOPES for Kids.

HOPES began in 2006 as an initiative of the Chicago Public Schools Department of Education Support for Students in Temporary Living Situations, or STLS. The organization collaborates with schools and shelters to establish after-school tutoring programs and provides students with additional support outside the classroom despite the challenges of homelessness, according to their website.

Heitmann and Habib will be running the marathon as part of the organization's team Hustle for Hopes. The money raised is used to purchase educational materials for the students.

"I like to support something local, that I can actually go see the students and meet with these people," Heitmann said.

Rangel will be running with the Chicago Area Runners Association (CARA) Road Scholars - a mentorship-based running program for at-risk Chicago area high school students. Mentors train students to successfully complete a half-marathon. The program also uses running to teach at-risk youth lessons in commitment, dedication and discipline, according to the CARA website. Funds raised by the marathon participants will be used to provide teens in the program with running shoes, transportation to training sites and cover race entry fees.

"I was lucky enough to start running when I was a kid," Rangel said. "For me, it really hits home."

The 26.2-mile marathon is scheduled to be held October 11 in downtown Chicago.


Related Links:
KICP Members: Michael D. Gladders; Salman Habib; Katrin Heitmann
John Carlstrom to receive Gruber Cosmology Prize for experimental explorations of universe
The University of Chicago News, June 11, 2015
Prof. John Carlstrom, Deputy Director of the PFC and the KICP
Prof. John Carlstrom, Deputy Director of the PFC and the KICP
The University of Chicago News

The 2015 Gruber Foundation Cosmology Prize has honored the University of Chicago's John E. Carlstrom, alumnus Jeremiah P. Ostriker, PhD'64, and Princeton University's Lyman Page for their individual and collective contributions to the study of the universe on the largest scales.

The 2015 prize is divided into two parts: half to a distinguished theorist, and the other half to two exceptional experimentalists. The theorist is Ostriker, a professor emeritus at Princeton University, now teaching at Columbia University. Ostriker, whose graduate school mentor was UChicago Nobel laureate Subrahmanyan Chandrasekhar, is being honored for his groundbreaking body of work over a five-decade career.

Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics, and Page, the Henry De Wolf Smyth Professor of Physics, have each overseen ground-based experiments that have provided a wealth of information about the origins and evolution of the universe. Carlstrom has worked extensively to study the cosmic microwave background, the relic radiation from the infancy of the universe, using the South Pole Telescope and other instruments.

"Together, the theoretical and experimental work of these three scientists has contributed to, clarified and advanced today's standard cosmological model," the Gruber Foundation wrote in announcing this year's prize.

Ostriker will receive half of the $500,000 award, while Carlstrom and Page will divide the other half. All three also will receive a gold medal Aug. 3 at the XXIX General Assembly of the International Astronomical Union in Honolulu, Hawaii.

Previous recipients of the Gruber Prize include Wendy Freedman, the University Professor in Astronomy & Astrophysics, who received the 2009 prize "for the definitive measurement of the rate of expansion of the universe, Hubble's Constant." One of the foremost awards in the field of cosmology, the prize honors "a leading cosmologist, astronomer, astrophysicist or scientific philosopher for theoretical, analytical, conceptual or observational discoveries leading to fundamental advances in our understanding of the universe," according to the Gruber Foundation.

Stephan Meyer, professor in astronomy & astrophysics, received a share of the prize in 2006 as a member of the Cosmic Background Explorer Team "for studies confirming that our universe was born in a hot Big Bang." He repeated the feat in 2012 as a member of the Wilkinson Microwave Anistropy Probe, which was honored for "exquisite measurements of anisotropies in the relic radiation from the Big Bang - the Cosmic Microwave Background."


Related Links:
KICP Members: John E. Carlstrom; Stephan S. Meyer
Scientific projects: South Pole Telescope (SPT)
2015 Gruber Prize in Cosmology: John E. Carlstrom
The Gruber Foundation, June 9, 2015
2015 Gruber Prize in Cosmology: John E. Carlstrom
The Gruber Foundation

The 2015 Gruber Prize in Cosmology honors theorist Jeremiah P. Ostriker for his lifetime of achievements and the experimentalists John E. Carlstrom and Lyman A. Page, Jr., for their pioneering observations of the cosmic microwave background (CMB), the relic radiation from the infancy of the universe's existence. Individually and collectively the works of these three scientists has helped to establish and advance the standard cosmological model: a universe that arose out of an inconceivably dense state of matter and energy, and has been expanding and cooling ever since, eventually coalescing into today's familiar skyscape of planets, stars, and galaxies.

During a five-decade career at Princeton University, Jeremiah Ostriker has made significant contributions to the studies of galaxy formation, the interstellar medium, and the intergalactic medium. He has also repeatedly challenged assumptions about how the universe works and proposed radical alternative interpretations. In 1972 he and Princeton colleague P. James E. Peebles created computer simulations that indicated either Newton's law of gravitation is wrong or some sort of invisible mass must be present to stabilize rotating spiral galaxies such as our own Milky Way. A year later, in collaboration with a postdoctoral fellow, Ostriker and Peebles surveyed existing data from a wide array of observations of individual galaxies and clusters of galaxies and concluded, in the opening sentence of a now-classic paper: "There are reasons, increasing in number and quality, to believe that the mass of ordinary galaxies may have been underestimated by a factor of 10 or more."

In 1995, Ostriker and another Princeton colleague, Paul J. Steinhardt, argued that the total amount of matter in the universe, dark or otherwise, is at odds with some key theoretical implications of the Big Bang interpretation of the universe. Ostriker and Steinhardt invoked yet another mysterious missing component that they said should be permeating the universe.

Today we call the missing components that Ostriker proposed in the 1970s and 1990s dark matter and dark energy, respectively -- abstract ideas that have been borne out by innumerable observations. In fact, while other theorists were making arguments similar to that of Ostriker and Steinhardt in the mid-1990s, what distinguishes their paper is the suggestion that this component should contribute about 70 percent to the total mass and energy of the universe --a figure validated by many later observations, including those made by the instruments overseen by Carlstrom and Page.

While both Page and Carlstrom have worked extensively in the study of the CMB, they lead two projects in particular. Carlstrom, who has been at the University of Chicago since 1995, is the principal investigator on the South Pole Telescope, which was constructed at the U. S. science station at the Pole in late 2006 and early 2007. Page, who has been at Princeton since 1990, serves in the same capacity for the Atacama Cosmology Telescope, which was constructed on Cerro Toco in the mountainous Atacama Desert in Chile in 2007.

Those instruments, both still active, probe the CMB, the relic radiation dating to the infancy of the cosmos. When the universe was 380,000 years old it had cooled enough for hydrogen atoms and photons to decouple and go their separate ways. That "flashbulb" moment has survived as a sort of snapshot -- a "baby picture" of the universe-- though over the past 13.7 billion years the expansion of space has stretched the light from the image all the way into the microwave end of the electromagnetic spectrum. Look closely enough and finely enough at the CMB, though, and you should be able to see extraordinarily subtle shadings in temperature: the DNA for the galaxies, clusters of galaxies, and super-clusters of galaxies that populate the universe as we know it.

Among the many contributions to cosmology that the South Pole Telescope and the Atacama Cosmology Telescope have made are: the discovery of hundreds of clusters of galaxies going back to when the universe was about one-third its present age, providing a history of the growth of the large-scale structure of the universe; independent verification that the universe consists of approximately 25 percent dark matter, 70 percent dark energy, and 5 percent atoms; and strong evidence that the structure in the CMB is a remnant of quantum fluctuations. This latter data is in excellent agreement with the model of inflation, a theoretical primordial hyper-expansion of space that would have determined the distribution of all that energy and matter.

What is dark matter? What is dark energy? How to explain a quantum universe? In honoring Carlstrom, Ostriker, and Page, the 2015 Gruber Cosmology Prize recognizes science doing what science does best: answering fundamental questions while opening new frontiers for observers and theorists alike and raising new fundamental questions to puzzle us.


Related Links:
KICP Members: John E. Carlstrom
Scientific projects: South Pole Telescope (SPT)
Prof. Daniel Holz receives Quantrell Award
The University of Chicago News Office, June 1, 2015
Daniel Holz, KICP senior member
Daniel Holz, KICP senior member
The University of Chicago News Office

The Llewellyn John and Harriet Manchester Quantrell Awards are believed to be the nation's oldest prize for undergraduate teaching. Presented annually, the awards reflect the College's commitment to honoring inspiring teachers. UChicago faculty often count the Quantrell among their most treasured honors.

"Ernest Quantrell, who first established the Quantrell Awards in 1937, wanted to honor faculty members who were great scholar-teachers and who inspired our students to become more enlightened thinkers and more effective citizens of their communities and of our nation," says John W. Boyer, dean of the College. "As teachers and as scholars and as citizens of the University at large, this year's Quantrell winners exemplify the very best about the College and the University."

Daniel Holz, Associate Professor, Physics
Soon after Daniel Holz learned of his Quantrell Award, he looked up the list of previous recipients.

"I was actually a graduate student here at UChicago, and I've had some of the previous recipients as professors. They're truly outstanding," says Holz, PhD'98, an associate professor in physics. "It's really an honor to be on the same list."


Related Links:
KICP Members: Daniel E. Holz
Honoring graduate teachers and mentors: Prof. Angela Olinto
The University of Chicago News Office, June 1, 2015
Angela V. Olinto, KICP senior member Homer J. Livingston Professor, Astronomy & Astrophysics
Angela V. Olinto, KICP senior member
Homer J. Livingston Professor, Astronomy & Astrophysics
The University of Chicago News Office

The 2015 Faculty Award for Excellence in Graduate Teaching and Mentoring

Angela V. Olinto
Homer J. Livingston Professor, Astronomy & Astrophysics
When Angela Olinto entered graduate school in physics at the Massachusetts Institute of Technology in 1982, there were two women and 60 men in her class. But over her 21 years at the University of Chicago, Olinto has welcomed 10 women and five men as graduate students into her research group, which specializes in particle astrophysics and cosmology.

"It's thrilling to look back and realize I've had about 70 percent women in my group, which is not something I planned," Olinto says. "It's been a colorful and brilliant group, lots of different nationalities and personalities, lots of different points of view. I've always learned as much from them as I taught them."

Olinto's students now have dispersed across the country and around the world. But many of them came together via email to nominate Olinto for the Faculty Award for Excellence in Graduate Teaching and Mentoring. Coordinating the effort was Olinto's current graduate student, Ke Fang, who graduates this summer.

"Independent of actually receiving the award, just the nomination itself was a great honor to me," Olinto says.


Related Links:
KICP Members: Angela V. Olinto
KICP Students: Ke Fang
Students in arts and sciences influence, benefit each other
The University of Chicago News Office, May 29, 2015
Benedikt Diemer (left), PhD candidate in astrophysics, and Isaac Facio, master of fine arts candidate at SAIC, collaborated on
Benedikt Diemer (left), PhD candidate in astrophysics, and Isaac Facio, master of fine arts candidate at SAIC, collaborated on "The Fabric of the Universe," a project that translated computer simulations of dark matter into 3-D textiles.
by Ryan Manzuk, The University of Chicago News Office

This year, in a new partnership with the School of the Art Institute of Chicago, the Arts, Science & Culture Initiative awarded grants to five teams composed of nine UChicago and three SAIC graduate students.

The goal of providing these collaborative grants is "to test the idea that different domains of knowing and knowledge -- arts, science and culture -- can enrich and influence each discipline's particular questions, tools, methodologies and specific curiosities," said Julie Marie Lemon, the program's director and curator.

The collaborative efforts between the students of arts, science and culture resulted in creative projects that were presented in early May.

One of the projects was "The Fabric of the Universe," created by Isaac Facio, a master of fine arts candidate in fiber and material studies at SAIC, and Benedikt Diemer, a UChicago PhD candidate in astrophysics. This project used computer simulations of dark matter and translated them into a more tangible form using three-dimensional textiles, resulting in a novel way of visualizing the structure of the universe.

Diemer said that the project has offered a new perspective for his research in astrophysics.

"Our project has caused me to look at my data in 3-D where I previously only made 2-D visualizations. This has definitely improved my understanding of the dark matter structures in my simulations," he said.

As a testament to the novel insights offered by this project, "'The Fabric of the Universe' was awarded a grant from the renowned TextielLab, part of the TextielMuseum, in Tilburg, the Netherlands, to produce the fabric," said Lemon, the program director.

And each year, Lemon noted, "the collaborations and the projects have become more and more sophisticated, and more students become interested in the initiative."


Related Links:
KICP Students: Benedikt Diemer
UChicago celebrates the promise of Chicago youth
The University of Chicago News Office, May 25, 2015
Daweed Abdiel, a KICP Space Explorer
Daweed Abdiel, a KICP Space Explorer
by Maureen Kelleher, The University of Chicago News Office

Though Daweed Abdiel always has been intellectually curious and a good student, college wasn't always on his radar. Most of his older family members had started college but never finished. In his first two years of high school, "I wasn't thinking about college too much," he said. "I was a good student, but I had no direction."

That changed after Abdiel joined the Upward Bound program offered through the Office of Special Programs-College Prep. Staff members who lead the program encouraged him to apply to colleges. "This program helped me determine I wanted a small liberal arts college." With Upward Bound showing the way, he got what he wanted. In August, Abdiel will attend Denison University with the support of two prestigious awards: a Gates-Millennium Scholarship and a Posse Scholarship.

"We have young people who develop a real sense of confidence and self-awareness about who they are and their ability to meet challenges and be successful," said Dovetta McKee, director of the Office of Special Programs-College Prep. "It changes their mindset about the leadership role they can play in their communities, and makes them models for young people who follow behind them," she said.

Abdiel was one of about 60 Chicago high school seniors honored at the 2015 Student Recognition Night, sponsored by the Office of Civic Engagement. The seniors took part in one of two programs: Upward Bound or the Collegiate Scholars Program, which prepares talented Chicago Public Schools students to succeed in the nation's top colleges and universities.

In addition, University students who have served with the Neighborhood Schools Program received recognition for their work in local public schools and community programs. All three efforts are part of UChicago Promise, the University's multi-pronged effort to increase college access and success for Chicago youth.

Increasing college access and success starts young. The Neighborhood Schools Program connects 375 UChicago students with 3,000 students in the surrounding neighborhoods. Many are still grade-schoolers, and tutoring can make a real impact on their future prospects.

"We leaned on NSP quite a lot and they came through," said Ed Kajor in a video shown at the event. Kajor, a learning behavior specialist at Burke Elementary in Washington Park, credits tutoring from volunteers like Amanda Weisler, a third-year sociology major, for boosting the school's scores on standardized tests.

"Our program is one of a few that is truly receptive to local school needs, said Shaz Rasul, director of community programs in the Office of Civic Engagement. "If a principal tells us she needs help with third grade, we will find tutors for the third grade who can be available during the school day. This is important because schools are often judged by what happens in the classroom, not enrichment time after school."

University students benefit, too. Real-world experience has led more than one NSP volunteer into a career in education, from Sara Stoelinga, who was honored at the event with the Don York Faculty Initiative Award, to keynote speaker Geoffrey Aladro AB'06, who is currently Miami-Dade's Teacher of the Year.

When Aladro discovered his long-held dream of corporate work wasn't all he thought it would be, he changed gears and chose teaching because of his NSP experiences. "I haven't really worked since I became a teacher," he told the crowd, "because I love my work."

Fourth-year Jonathan Fifer, who volunteered with NSP throughout his College career, intends to follow in their footsteps. His next goal will be to earn a master's degree from Teachers College, Columbia University, where he'll study early childhood education. "I've always been interested in the little kids," he said. "Even when they're crying or being bad, you can see their thought process. I can't be mad at them."

While teaching high school students about the college application process gets them started on their higher education journey, the Upward Bound and Collegiate Scholars programs also support young people's intellectual growth. Ivelise Colon, a Collegiate Scholar, has chosen Whittier College's alternative liberal arts program, where she will design her own major, incorporating elements of psychology, sociology and early childhood education. "I want to do my own thing," she said.

"The hallmark of Collegiate Scholars is the interaction with faculty. We are one of very few institutions in the country where there is intentional engagement between University faculty and public school students from across the city," said Abel Ochoa, interim director of the Collegiate Scholars Program. "It really elevates a student's frame of thinking to be taught by a professor who has written a textbook, done concrete research, or is considered a world-renowned expert in his field."

Like Colon, Abdiel has seen his intellectual interests shift over time, from physics to chemistry with a generous side helping of economics and African-American Studies. He credits his Upward Bound mentors for exposing him to the Kavli Institute of Cosmological Physics and for staying the course with him as his interests evolved. "They won't tell you what to do, but they'll ask you questions," he said. "They'll help you find your passions."


Related Links:
KICP Members: Randall H. Landsberg; Donald G. York
The Particle That Broke a Cosmic Speed Limit
Quanta Magazine, May 17, 2015
The Particle That Broke a Cosmic Speed Limit
by Natalie Wolchover, Quanta Magazine

Physicists are beginning to unravel the mysteries of ultrahigh-energy cosmic rays, particles accelerated by the most powerful forces in the universe.

In the night of October 15, 1991, the "Oh-My-God" particle streaked across the Utah sky.

A cosmic ray from space, it possessed 320 exa-electron volts (EeV) of energy, millions of times more than particles attain at the Large Hadron Collider, the most powerful accelerator ever built by humans. The particle was going so fast that in a yearlong race with light, it would have lost by mere thousandths of a hair. Its energy equaled that of a bowling ball dropped on a toe. But bowling balls contain as many atoms as there are stars. "Nobody ever thought you could concentrate so much energy into a single particle before," said David Kieda, an astrophysicist at the University of Utah.

Five or so miles from where it fell, a researcher worked his shift inside an old, rat-infested trailer parked atop a desert mountain. Earlier, at dusk, Mengzhi "Steven" Luo had switched on the computers for the Fly's Eye detector, an array of dozens of spherical mirrors that dotted the barren ground outside. Each of the mirrors was bolted inside a rotating "can" fashioned from a section of culvert, which faced downward during the day to keep the sun from blowing out its sensors. As darkness fell on a clear and moonless night, Luo rolled the cans up toward the sky.

"It was a pretty crude experiment," said Kieda, who operated the Fly's Eye with Luo and several others. "But it worked - that was the thing."

The faintly glowing contrail of the Oh-My-God particle (as the computer programmer and Autodesk founder John Walker dubbed it in an early Web article) was spotted in the Fly's Eye data the following summer and reported after the group spent an extra year convincing themselves the signal was real. The particle had broken a cosmic speed limit worked out decades earlier by Kenneth Greisen, Georgiy Zatsepin and Vadim Kuzmin, who argued that any particle energized beyond approximately 60 EeV will interact with background radiation that pervades space, thereby quickly shedding energy and slowing down. This "GZK cutoff" suggested that the Oh-My-God particle must have originated recently and nearby - probably within the local supercluster of galaxies. But an astrophysical accelerator of unimagined size and power would be required to produce such a particle. When scientists looked in the direction from which the particle had come, they could see nothing of the kind.

"It's like you've got a gorilla in your backyard throwing bowling balls at you, but he's invisible," Kieda said.

Where had the Oh-My-God particle come from? How could it possibly exist? Did it really? The questions motivated astrophysicists to build bigger, more sophisticated detectors that have since recorded hundreds of thousands more "ultrahigh-energy cosmic rays" with energies above 1 EeV, including a few hundred "trans-GZK" events above the 60 EeV cutoff (though none reaching 320 EeV). In breaking the GZK speed limit, these particles challenged one of the farthest-reaching predictions ever made. It seemed possible that they could offer a window into the laws of physics at otherwise unreachable scales - maybe even connecting particle physics with the evolution of the cosmos as a whole. At the very least, they promised to reveal the workings of extraordinary astrophysical objects that had only ever been twinkles in telescope lenses. But over the years, as the particles swept brushstrokes of light across sensors in every direction, instead of painting a telltale pattern that could be matched to, say, the locations of supermassive black holes or colliding galaxies, they created confusion. "It's hard to explain the cosmic-ray data with any particular theory," said Paul Sommers, a semiretired astrophysicist at Pennsylvania State University who specializes in ultrahigh-energy cosmic rays. "There are problems with anything you propose."

Only recently, with the discovery of a cosmic ray "hotspot" in the sky, the detection of related high-energy cosmic particles, and a better understanding of physics at more familiar energies, have researchers secured the first footholds in the quest to understand ultrahigh-energy cosmic rays. "We're learning things very rapidly," said Tim Linden, a theoretical astrophysicist at the University of Chicago.


Related Links:
KICP Members: Toshihiro Fujii; Tim Linden; Angela V. Olinto; Paolo Privitera
KICP Students: Ke Fang
Scientific projects: Pierre Auger Observatory (AUGER)
Historic AAAS Kavli Competition Expands to Honor Excellence in Science Journalism Worldwide
The American Association for the Advancement of Science, May 5, 2015
Historic AAAS Kavli Competition Expands to Honor Excellence in Science Journalism Worldwide
by Ginger Pinholster, The American Association for the Advancement of Science

The American Association for the Advancement of Science (AAAS) today announced a global expansion of its historic science journalism awards program, thanks to an additional generous endowment from The Kavli Foundation.

For the first time in its 70-year history, the AAAS Kavli Science Journalism Awards program will this year accept entries from reporters working worldwide. Endowed by The Kavli Foundation in 2009, this year's doubling of the program endowment will further allow AAAS to bestow 16 instead of eight prizes annually. The value of top (Gold) awards will be increased from $3,500 to $5,000, and a $3,500 Silver prize has been added to each of the eight reporting categories.

A premier competition of its type, the AAAS Kavli Science Journalism Awards program is widely recognized as an apex achievement for reporters covering the sciences, engineering and mathematics for a general audience. The contest is administered by AAAS, but independent panels of journalists select the winners. With the decision to accept international entries across all categories beginning with the 2014-15 competition cycle, the program is now believed to be the only truly general-interest, reporter-juried science journalism contest open to reporters from around the world.

"Like scientific discovery, excellent science journalism can happen anywhere in the world," said AAAS CEO Rush Holt, executive publisher of the Science family of journals. "By recognizing the world's best science news-reporting, AAAS and The Kavli Foundation are working to build a culture of respect for the value of science journalism to society, while promoting public understanding of science more broadly."

"The Kavli Foundation is committed to science journalism, and to public understanding and support of science. We are delighted to support the expansion of the AAAS Kavli Science Journalism Awards and to making them international in scope. Our commitment reaffirms all that the AAAS-Kavli partnership has come to reflect: no-strings-attached support for the highest possible standards in science journalism," said Robert W. Conn, President and CEO, The Kavli Foundation. "We are also pleased this expansion is happening now. In the United States and worldwide today, there is an unprecedented need for excellence in science journalism, which is essential to help the public understand and trust scientific results, and how science is shaping our lives."

To date, the awards have been given to more than 330 professional journalists for distinguished science news-reporting. The awards program was established in 1945 by the Westinghouse Educational Foundation through the initiative of Robert D. Potter, the president of the National Association of Science Writers. AAAS was asked to administer the program, which was meant to encourage good science journalism at a time when very few news outlets had full-time science writers. Westinghouse continued its support of the program until 1993. The Whitaker Foundation funded the awards from 1994 to 2003. From 2004 to 2008, Johnson & Johnson Pharmaceutical Research and Development, L.L.C. sponsored the awards, including the establishment in 2005 of the first category open to journalists from around the world: reporting on science news for children.

In February 2009, The Kavli Foundation, based in Oxnard, California, provided an initial $2 million endowment to AAAS, ensuring the future of the awards program. The Kavli Foundation endowment also made it possible for AAAS to establish two prizes in the television category, for spot news/feature reporting as well as in-depth reporting.

Now in 2015, an additional $2 million expansion of the original Kavli Foundation endowment will make it possible for AAAS to open up each prize category to journalists worldwide.

Entries for this year's competition are being accepted today through 1 August 2015 in eight categories: large newspaper, small newspaper, magazine, television spot news/feature reporting, television in-depth reporting, radio, online, and children's science news. Independent screening and judging committees evaluate submissions based on scientific accuracy, initiative, originality, clarity of interpretation, and value in fostering a better public understanding of science and its impact. Decisions made by the committees of reporters and editors will be final.

Recent winners of the AAAS Kavli Science Journalism Awards have reported on the complexities of human biology, the enduring challenge of understanding cancer, a massive dam-removal project, issues raised by the era of personal genomics, climate-change impacts, endangered species, and many science-based topics with broad implications for society.

About AAAS
The American Association for the Advancement of Science (AAAS) is the world's largest general scientific society and publisher of the journal Science as well as Science Translational Medicine, Science Signaling, and a new digital, open-access journal, Science Advances. AAAS was founded in 1848 and includes nearly 250 affiliated societies and academies of science, serving 10 million individuals. Science has the largest paid circulation of any peer-reviewed general science journal in the world. The non-profit AAAS is open to all and fulfills its mission to "advance science and serve society" through initiatives in science policy, international programs, science education, public engagement, and more. For the latest research news, log onto EurekAlert!, the premier science-news Web site, a service of AAAS.

About The Kavli Foundation
The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research, and supporting scientists and their work. The Foundation's mission is implemented through an international program of research institutes and scientific meetings in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics, and through the support of conferences, symposia, endowed professorships and other activities. The Foundation also supports initiatives aimed at strengthening science journalism and also the communication of science, including the AAAS Kavli Science Journalism Awards, the Kavli Science Journalism Workshops at MIT and the Alda Kavli Leadership Program at Stony Brook University. The Foundation is a founding partner of the biennial Kavli Prizes, which recognize scientists for their seminal advances in three research areas: astrophysics, nanoscience, and neuroscience.

Live Session with Michael Turner, May 1, 2015
Live Session with Michael Turner

World Science U Master Class with Michael Turner
Tue Mar, 10 2015 2PM - 3PM (CDT)

Michael Turner, theoretical cosmologist and Director of the Kavli Institute for Cosmological Physics at the University of Chicago, leads a free Master Class focusing on dark energy. The class is part of World Science U's Master Class offering - giving you the opportunity to learn directly from the world's greatest thinkers. Professor Turner hosted a live online session on March 10th, 2015 to answer your questions and delve deeper into the material.


Related Links:
KICP Members: Michael S. Turner
Absence of gravitational-wave signal extends limit on knowable universe
Fermilab, April 27, 2015
The Holometer is sensitive to high-frequency gravitational waves, allowing it to look for events such as cosmic strings.   <i>Photo: Reidar Hahn</i>
The Holometer is sensitive to high-frequency gravitational waves, allowing it to look for events such as cosmic strings.

Photo: Reidar Hahn
by Diana Kwon, Fermilab

Imagine an instrument that can measure motions a billion times smaller than an atom that last a millionth of a second. Fermilab's Holometer is currently the only machine with the ability to take these very precise measurements of space and time, and recently collected data has improved the limits on theories about exotic objects from the early universe.

Our universe is as mysterious as it is vast. According to Albert Einstein's theory of general relativity, anything that accelerates creates gravitational waves, which are disturbances in the fabric of space and time that travel at the speed of light and continue infinitely into space. Scientists are trying to measure these possible sources all the way to the beginning of the universe.

The Holometer experiment, based at the Department of Energy's Fermilab, is sensitive to gravitational waves at frequencies in the range of a million cycles per second. Thus it addresses a spectrum not covered by experiments such as the Laser Interferometer Gravitational-Wave Observatory, which searches for lower-frequency waves to detect massive cosmic events such as colliding black holes and merging neutron stars.

"It's a huge advance in sensitivity compared to what anyone had done before," said Craig Hogan, director of the Center for Particle Astrophysics at Fermilab.

This unique sensitivity allows the Holometer to look for exotic sources that could not otherwise be found. These include tiny black holes and cosmic strings, both possible phenomena from the early universe that scientists expect to produce high-frequency gravitational waves. Tiny black holes could be less than a meter across and orbit each other a million times per second; cosmic strings are loops in space-time that vibrate at the speed of light.

The Holometer is composed of two Michelson interferometers that each split a laser beam down two 40-meter arms. The beams reflect off the mirrors at the ends of the arms and travel back to reunite. Passing gravitational waves alter the lengths of the beams' paths, causing fluctuations in the laser light's brightness, which physicists can detect.

The Holometer team spent five years building the apparatus and minimizing noise sources to prepare for experimentation. Now the Holometer is taking data continuously, and with an hour's worth of data, physicists were able to confirm that there are no high-frequency gravitational waves at the magnitude where they were searching.

The absence of a signal provides valuable information about our universe. Although this result does not prove whether the exotic objects exist, it has eliminated the region of the universe where they could be present.

"It means that if there are primordial cosmic string loops or tiny black hole binaries, they have to be far away," Hogan said. "It puts a limit on how much of that stuff can be out there."

Detecting these high-frequency gravitational waves is a secondary goal of the Holometer. Its main purpose is to determine whether our universe acts like a 2-D hologram, where information is coded into two-dimensional bits at the Planck scale, a length around ten trillion trillion times smaller than an atom. That investigation is still in progress.

"For me, it's gratifying to be able to contribute something new to science," said researcher Bobby Lanza, who recently earned his Ph.D. conducting research on the Holometer. He is the lead author on an upcoming paper about the result. "It's part of chipping away at the whole picture of the universe."


Related Links:
KICP Members: Craig J. Hogan; Stephan S. Meyer
Earth-sized telescope expands to the South Pole to see black holes in detail
The University of Chicago News Office, April 21, 2015
The 10-meter South Pole Telescope, at the National Science Foundation's Amundsen-Scott South Pole Station, joined the global Event Horizon Telescope array in January 2015.   <i>Courtesy of Dan Marrone, University of Arizona</i>
The 10-meter South Pole Telescope, at the National Science Foundation's Amundsen-Scott South Pole Station, joined the global Event Horizon Telescope array in January 2015.

Courtesy of Dan Marrone, University of Arizona
The University of Chicago News Office

Astronomers building an Earth-sized virtual telescope capable of photographing the event horizon of the black hole at the center of our Milky Way have extended their instrument to include the University of Chicago-built South Pole Telescope.

The South Pole Telescope, situated at the National Science Foundation's Amendsen-Scott South Pole Station, now is part of the largest virtual telescope ever built - the Event Horizon Telescope. By combining telescopes across the Earth, the Event Horizon Telescope will take the first detailed pictures of black holes.

"We are thrilled that the South Pole Telescope is part of the EHT. The science, which addresses fundamental questions of space and time, is as exciting to us as peering back to the beginning of the universe," said UChicago Prof. John Carlstrom, who leads the SPT collaboration.

The Event Horizon Telescope is an array of radio telescopes connected using a technique known as Very Long Baseline Interferometry. Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation, or "baseline," between them.

Now that the technique has been extended to the South Pole Telescope, the Event Horizon Telescope spans the entire Earth, from the Submillimeter Telescope on Mount Graham in Arizona, to California, Hawaii, Chile, Mexico, Spain and the South Pole.


Related Links:
KICP Members: John E. Carlstrom
Scientific projects: South Pole Telescope (SPT)
Virtual Telescope Expands to See Black Holes
University of Arizona News, April 21, 2015
The South Pole Telescope and the Atacama Pathfinder Experiment joined together in a
The South Pole Telescope and the Atacama Pathfinder Experiment joined together in a "Very Long Baseline Interferometry" experiment for the first time in January. The two telescopes simultaneously observed two sources - the black hole at the center of the Milky Way galaxy, Sagittarius A*, and the black hole at the center of the distant galaxy Centaurus A - and combined their signals to synthesize a telescope 5,000 miles across. (Image: Dan Marrone/UA)
by Daniel Stolte, University of Arizona News

Astronomers building an Earth-size virtual telescope capable of photographing the event horizon of the black hole at the center of our Milky Way have extended their instrument to the bottom of the Earth - the South Pole - thanks to recent efforts by a team led by Dan Marrone of the University of Arizona.

Marrone, an assistant professor in the UA's Department of Astronomy and Steward Observatory, and several colleagues flew to the National Science Foundation's Amundsen-Scott South Pole Station in December to bring the South Pole Telescope, or SPT, into the largest virtual telescope ever built - the Event Horizon Telescope, or EHT. By combining telescopes across the Earth, the EHT will take the first detailed pictures of black holes.

The EHT is an array of radio telescopes connected using a technique known as Very Long Baseline Interferometry, or VLBI. Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation - or "baseline" - between them.

"Now that we've done VLBI with the SPT, the Event Horizon Telescope really does span the whole Earth, from the Submillimeter Telescope on Mount Graham in Arizona, to California, Hawaii, Chile, Mexico, Spain and the South Pole," Marrone said. "The baselines to SPT give us two to three times more resolution than our past arrays, which is absolutely crucial to the goals of the EHT. To verify the existence of an event horizon, the 'edge' of a black hole, and more generally to test Einstein's theory of general relativity, we need a very detailed picture of a black hole. With the full EHT, we should be able to do this."

The prime EHT target is the Milky Way's black hole, known as Sagittarius A* (pronounced "A-star"). Even though it is 4 million times more massive than the sun, it is tiny to the eyes of astronomers. Because it is smaller than Mercury's orbit around the sun, yet almost 26,000 light-years away, studying its event horizon in detail is equivalent to standing in California and reading the date on a penny in New York.

With its unprecedented resolution, more than 1,000 times better than the Hubble Space Telescope, the EHT will see swirling gas on its final plunge over the event horizon, never to regain contact with the rest of the universe. If the theory of general relativity is correct, the black hole itself will be invisible because not even light can escape its immense gravity.

First postulated by Albert Einstein's general theory of relativity, the existence of black holes has since been supported by decades' worth of astronomical observations. Most if not all galaxies are now believed to harbor a supermassive black hole at their center, and smaller ones formed from dying stars should be scattered among their stars. The Milky Way is known to be home to about 25 smallish black holes ranging from five to 10 times the sun's mass. But never has it been possible to directly observe and image one of these cosmic oddities.

Weighing 280 tons and standing 75 feet tall, the SPT sits at an elevation of 9,300 feet on the polar plateau at Amundsen-Scott, which is located at the geographic South Pole. The University of Chicago built SPT with funding and logistical support from the NSF's Division of Polar Programs. The division manages the U.S. Antarctic Program, which coordinates all U.S. research on the southernmost continent.

The 10-meter SPT operates at millimeter wavelengths to make high-resolution images of cosmic microwave background radiation, the light left over from the Big Bang. Because of its location at the Earth's axis and at high elevation where the polar air is largely free of water vapor, it can conduct long-term observations to explore some of the biggest questions in cosmology, such as the nature of dark energy and the process of inflation that is believed to have stretched the universe exponentially in a tiny fraction of the first second after the Big Bang.

"We are thrilled that the SPT is part of the EHT," said John Carlstrom, who leads the SPT collaboration. "The science, which addresses fundamental questions of space and time, is as exciting to us as peering back to the beginning of the universe."

To incorporate the SPT into the EHT, Marrone's team constructed a special, single-pixel camera that can sense the microwaves hitting the telescope. The Academia Sinica Institute for Astronomy and Astrophysics in Taiwan provided the atomic clock needed to precisely track the arrival time of the light. Comparing recordings made at telescopes all over the world allows the astronomers to synthesize the immense telescope. The Smithsonian Astrophysical Observatory and Haystack Observatory of the Massachusetts Institute of Technology provided equipment to record the microwaves at incredibly high speeds, generating nearly 200 terabytes per day.

"To extend the EHT to the South Pole required improving our data capture systems to record data much more quickly than ever before," said Laura Vertatschitsch of the Smithsonian Astrophysical Observatory. A new "digital back end," developed by Vertatschitsch and colleagues, can process data four times faster than its predecessor, which doubles the sensitivity of each telescope.

For their preliminary observations, Marrone's team trained its instrument on two known black holes, Sagittarius A* in our galaxy, and another, located 10 million light-years away in a galaxy named Centaurus A. For this experiment, the SPT and the Atacama Pathfinder Experiment, or APEX, telescope in Chile observed together, despite being nearly 5,000 miles apart. These data constitute the highest- resolution observations ever made of Centaurus A (though the information from a single pair of telescopes cannot easily be converted to a picture).

"VLBI is very technically challenging, and a whole system of components had to work perfectly at both SPT and APEX for us to detect our targets," said Junhan Kim, a doctoral student at the UA who helped build and install the SPT EHT receiver. "Now that we know how to incorporate SPT, I cannot wait to see what we can learn from a telescope 10,000 miles across."

The next step will be to include the SPT in the annual EHT experiments that combine telescopes all over the world. Several new telescopes are prepared to join the EHT in the next year, meaning that the next experiment will be the largest both geographically and with regard to the number of telescopes involved. The expansion of the array is supported by the National Science Foundation Division of Astronomical Sciences through its new Mid-Scale Innovations Program, or MSIP.

Shep Doeleman, who leads the EHT and the MSIP award, noted that "the supermassive black hole at the Milky Way's center is always visible from the South Pole, so adding that station to the EHT is a major leap toward bringing an event horizon into focus."

This work was funded through NSF grants AST-1207752 to Marrone; AST-1207704 to Doeleman at MIT's Haystack Observatory; and AST-1207730 to Carlstrom at the University of Chicago.

An international research collaboration led by the University of Chicago manages the SPT. The NSF-funded Physics Frontier Center of the Kavli Institute for Cosmological Physics, the Kavli Foundation, and the Gordon and Betty Moore Foundation provide partial support.

The APEX telescope, located in Chile's Atacama Desert, is a collaboration of the European Southern Observatory, the Max Planck Institute for Radioastronomy and the Onsala Space Observatory in Sweden.


Related Links:
KICP Members: John E. Carlstrom
Scientific projects: South Pole Telescope (SPT)
Scientists Release Largest Map Yet Of Dark Matter In The Cosmos
NPR, April 15, 2015
Scientists Release Largest Map Yet Of Dark Matter In The Cosmos

Researchers from the Dark Energy Survey used data captured by the Dark Energy Camera, a 570-megapixel imaging device they say is one of the world's most powerful digital cameras, to put together the largest contiguous map of dark matter created. They presented their findings Monday at a meeting of the American Physical Society in Baltimore.

The scientists say the map covers only about 3 percent of the area of sky. They hope it will improve understanding of the role dark matter plays in the creation of galaxies - and to investigate dark energy.

"We measured the barely perceptible distortions in the shapes of about 2 million galaxies to construct these new maps," Vinu Vikram of Argonne National Laboratory, one of the lead scientists on the study, said in a statement Monday. "They are a testament not only to the sensitivity of the Dark Energy Camera, but also to the rigorous work by our lensing team to understand its sensitivity so well that we can get exacting results from it."

The Fermi National Accelerator Laboratory built and tested the camera, which is mounted on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. The National Center for Supercomputing Applications at the University of Illinois in Urbana-Champaign processed the data that went into the map.

Here's more from the statement:
"As scientists expand their search, they will be able to better test current cosmological theories by comparing the amounts of dark and visible matter.

"Those theories suggest that, since there is much more dark matter in the universe than visible matter, galaxies will form where large concentrations of dark matter (and hence stronger gravity) are present. So far, the DES analysis backs this up: The maps show large filaments of matter along which visible galaxies and galaxy clusters lie and cosmic voids where very few galaxies reside. Follow-up studies of some of the enormous filaments and voids, and the enormous volume of data, collected throughout the survey will reveal more about this interplay of mass and light."

"Our analysis so far is in line with what the current picture of the universe predicts," said Chihway Chang, another of the lead scientists who is with ETH Zurich. "Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models."

The Dark Energy Survey is on the second year of a five-year study.


Related Links:
KICP Members: Joshua A. Frieman; Vinu Vikram
Scientific projects: Dark Energy Survey (DES)
Mapping dark matter may help solve a cosmic mystery
PBS, April 15, 2015
Mapping dark matter may help solve a cosmic mystery

Scientists have announced the creation of the largest map yet of the invisible material that helps make up the universe, what's known as dark matter.

Jeffrey Brown explores some of the very cosmic questions around this story.

JEFFREY BROWN: That's worth saying again: We can't see it, but we can apparently map it. What's called dark matter is, in fact, everywhere, and it's believed to play a crucial role in forming and holding together galaxies with its gravitational pull.

In findings announced Monday, researchers used a dark energy camera and a large telescope in Northern Chile to create this color-coded map, showing a small piece of the visible sky. Orange and red areas represent denser concentrations of dark matter. Blue areas are less dense.


Related Links:
KICP Members: Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES)
Horizon 2015 : Dancing in the Dark - The End of Physics?
BBC, March 30, 2015
Horizon 2015 : Dancing in the Dark - The End of Physics?

Scientists genuinely don't know what most of our universe is made of. The atoms we're made from only make up four per cent. The rest is dark matter and dark energy (for 'dark', read 'don't know'). The Large Hadron Collider at CERN has been upgraded. When it's switched on in March 2015, its collisions will have twice the energy they did before. The hope is that scientists will discover the identity of dark matter in the debris.

The stakes are high - because if dark matter fails to show itself, it might mean that physics itself needs a rethink.


Related Links:
KICP Members: Juan I. Collar; Daniel Hooper
Understanding the Dark Side of Physics
Science Friday, March 27, 2015
Astronomers using NASA's Hubble Space Telescope discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two massive galaxy clusters. The ring's discovery is among the strongest evidence yet that dark matter exists. Image by NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)
Astronomers using NASA's Hubble Space Telescope discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two massive galaxy clusters. The ring's discovery is among the strongest evidence yet that dark matter exists. Image by NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)
Science Friday

Neutrons, protons, and electrons - these are the basic building blocks of matter. But this kind of matter is only a tiny fraction of the entire universe. The rest, about 95 percent, in fact, is divided between dark matter and dark energy. Understanding what makes up dark matter and dark energy could help answer some of the biggest questions in physics. Physicists Jodi Cooley, Dan Hooper, and Nobel Prize winner Steven Weinberg join Ira Flatow to discuss what we do and don't know about this "darker" side of physics, and what we hope to learn.


Steven Weinberg
Author, "To Explain the World: The Discovery of Modern Science" (HarperCollins, 2015)
Nobel Prize Winner, 1979, Physics
University of Texas at Austin
Austin, Texas

Dan Hooper
Staff Scientist, Fermilab
Associate Professor, Astronomy and Astrophysics
University of Chicago
Chicago, Illinois

Jodi Cooley
Associate Professor, Physics
Southern Methodist University
Dallas, Texas

John E. Carlstrom, Thomas M. Crawford and Lloyd Knox, "Particle physics and the cosmic microwave background"
Physics Today, March 13, 2015
This honeycomb-like array of feedhorns at the 10-m South Pole Telescope directs radiation to superconducting detectors used to measure the polarization of the cosmic microwave background. The seven hexagonal cells in the center, about 5.8 cm across, are sensitive to radiation at frequencies of about 150 GHz. The larger feedhorns surrounding them are used for frequencies near 95 GHz. Progress in detector development is so rapid that within a year arrays should have sensitivities an order of magnitude greater than that of the state-of-the-art detector shown here. (Courtesy of the South Pole Telescope.)
This honeycomb-like array of feedhorns at the 10-m South Pole Telescope directs radiation to superconducting detectors used to measure the polarization of the cosmic microwave background. The seven hexagonal cells in the center, about 5.8 cm across, are sensitive to radiation at frequencies of about 150 GHz. The larger feedhorns surrounding them are used for frequencies near 95 GHz. Progress in detector development is so rapid that within a year arrays should have sensitivities an order of magnitude greater than that of the state-of-the-art detector shown here. (Courtesy of the South Pole Telescope.)
Physics Today

Temperature and polarization variations across the microwave sky include the fingerprints of quantum fluctuations in the early universe. They may soon reveal physics at unprecedented energy scales.

The detection of the CMB and the consensus that the universe had a hot and dense early phase led to a fertile relationship between cosmology and particle physics. The hot early universe was a natural particle accelerator that could reach energies well beyond what laboratories on Earth will attain in the foreseeable future. Precise measurements of both the spectrum of the CMB and its tiny variations in brightness from one point to another on the sky reflect the influences of high-energy processes in the early cosmos.

For instance, the gravitational effects of neutrinos have been detected at high significance; such measurements imply that the sum of the neutrino masses is no more than a few tenths of an eV. The CMB data also show the influence of helium produced in the early universe and thus constrain the primordial helium fraction. Moreover, the data are nearly impossible to fit without dark energy and dark matter - two ingredients missing from the standard model of particle physics.


Related Links:
KICP Members: John E. Carlstrom; Thomas M. Crawford
Scientific projects: South Pole Telescope (SPT)
Scientists find rare dwarf satellite galaxy candidates in Dark Energy Survey data
Fermilab, March 11, 2015
The image is a snapshot of DES J0335.6-5403, a celestial object found with the Dark Energy Camera. It is the most likely of the newly discovered candidates to be a galaxy, according to DES scientists. This object sits roughly 100,000 light-years from Earth, and contains very few stars - only about 300 could be detected with DES data. <i>Image credit: Image: Fermilab/Dark Energy Survey.</i>
The image is a snapshot of DES J0335.6-5403, a celestial object found with the Dark Energy Camera. It is the most likely of the newly discovered candidates to be a galaxy, according to DES scientists. This object sits roughly 100,000 light-years from Earth, and contains very few stars - only about 300 could be detected with DES data.
Image credit: Image: Fermilab/Dark Energy Survey.

Scientists on two continents have independently discovered a set of celestial objects that seem to belong to the rare category of dwarf satellite galaxies orbiting our home galaxy, the Milky Way.

Dwarf galaxies are the smallest known galaxies, and they could hold the key to understanding dark matter and the process by which larger galaxies form.

A team of researchers with the Dark Energy Survey, headquartered at the U.S. Department of Energy's Fermi National Accelerator Laboratory, and an independent group from the University of Cambridge jointly announced their findings today. Both teams used data taken during the first year of the Dark Energy Survey, all of which is publicly available, to carry out their analysis.

"The large dark matter content of Milky Way satellite galaxies makes this a significant result for both astronomy and physics," said Alex Drlica-Wagner of Fermilab, one of the leaders of the Dark Energy Survey analysis.

Satellite galaxies are small celestial objects that orbit larger galaxies, such as our own Milky Way. Dwarf galaxies can be found with fewer than 100 stars and are remarkably faint and difficult to spot. (By contrast, the Milky Way, an average-sized galaxy, contains billions of stars.)

These newly discovered objects are a billion times dimmer than the Milky Way and a million times less massive. The closest of them is about 100,000 light-years away.

"The discovery of so many satellites in such a small area of the sky was completely unexpected," said Cambridge's Institute of Astronomy's Sergey Koposov, the Cambridge study's lead author. "I could not believe my eyes."

Scientists have previously found more than two dozen of these satellite galaxies around our Milky Way. About half of them were discovered in 2005 and 2006 by the Sloan Digital Sky Survey, the precursor to the Dark Energy Survey. After that initial explosion of discoveries, the rate fell to a trickle and dropped off entirely over the past five years.

The Dark Energy Survey is looking at a new portion of the southern hemisphere, covering a different area of sky than the Sloan Digital Sky Survey. The galaxies announced today were discovered in a search of only the first of the planned five years of Dark Energy Survey data, covering roughly one-third of the portion of sky that DES will study. Scientists expect that the full Dark Energy Survey will find up to 30 of these satellite galaxies within its area of study.

Atlas image obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

While more analysis is required to confirm any of the observed celestial objects as satellite galaxies, researchers note their size, low surface brightness and significant distance from the center of the Milky Way as evidence that they are excellent candidates. Further tests are ongoing, and data collected during the second year of the Dark Energy Survey could yield more of these potential dwarf galaxies to study.

Newly discovered galaxies would also present scientists with more opportunities to search for signatures of dark matter. Dwarf satellite galaxies are dark matter-dominated, meaning they have much more mass in unseen matter than in stars. The nature of this dark matter remains unknown but might consist of particles that annihilate each other and release gamma rays. Because dwarf galaxies do not host other gamma ray sources, they make ideal laboratories to search for signs of dark matter annihilation. Scientists are confident that further study of these objects will lead to even more sensitive searches for dark matter.

In a separate result also announced today, the Large Area Telescope Collaboration for NASA's Fermi Gamma-Ray Telescope mission reported that they did not see any significant excess of gamma ray emission associated with the new Dark Energy Survey objects. This result demonstrates that new discoveries from optical telescopes can be quickly translated into tests of fundamental physics.

"We did not detect significant emission with the LAT, but the dwarf galaxies that DES has and will discover are extremely important targets for the dark matter search," said Peter Michelson, spokesperson for the LAT collaboration. "If not leading to an identification of particle dark matter, they will certainly be useful to constrain its properties."

The Dark Energy Survey is a five-year effort to photograph a large portion of the southern sky in unprecedented detail. Its primary instrument is the Dark Energy Camera, which - at 570 megapixels - is the most powerful digital camera in the world, able to see galaxies up to 8 billion light-years from Earth. Built and tested at Fermilab, the camera is now mounted on the 4-meter Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory in the Andes Mountains in Chile.

The survey's five-year mission is to discover clues about the nature of dark energy, the mysterious force that makes up about 70 percent of all matter and energy in the universe. Scientists believe that dark energy may be the key to understanding why the expansion of the universe is accelerating.

"The Dark Energy Camera is a perfect instrument for discovering small satellite galaxies," said Keith Bechtol of the Kavli Institute for Cosmological Physics at the University of Chicago, who helped lead the Dark Energy Survey analysis. "It has a very large field of view to quickly map the sky and great sensitivity, enabling us to look at very faint stars. These results show just how powerful the camera is and how significant the data it collects will be for many years to come."

The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries.


Related Links:
KICP Members: Keith Bechtol; Alex Drlica-Wagner; Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES)
One Hundred Years of General Relativity
Science Friday, March 6, 2015
A two-dimensional projection of a three-dimensional analogy of spacetime curvature described in general relativity.  <i>Image by Johnstone/CC BY-SA 3.0</i>
A two-dimensional projection of a three-dimensional analogy of spacetime curvature described in general relativity.
Image by Johnstone/CC BY-SA 3.0
Science Friday

Albert Einstein published his theory of general relativity 100 years ago. The theory has shaped the idea of black holes, pulsars, and modern cosmology. Science historian David Kaiser guides us through the history of Einstein's insight, and physicists Michael Turner and Alex Filippenko discuss where the theory might take us in the future.

  • David Kaiser
    Germeshausen Professor of the History of Science
    Senior Lecturer, Department of Physics
    Massachusetts Institute of Technology
    Boston, Massachusetts
  • Michael Turner
    Director and Rauner Distinguished Service Professor
    Kavli Institute for Cosmological Physics
    The University of Chicago
    Chicago, Illinois
  • Alex Filippenko
    Professor, Astronomy
    University Of Berkeley
    Berkeley California


Related Links:
KICP Members: Michael S. Turner
Mystery of the Universe's Gamma-Ray Glow Solved, February 5, 2015
Fermi LAT five-year exposure of a 20-degree-wide region in the constellation Virgo. Brighter colors indicate brighter gamma-ray sources.
Fermi LAT five-year exposure of a 20-degree-wide region in the constellation Virgo. Brighter colors indicate brighter gamma-ray sources.
by Calla Cofield,

The steady glow of high-energy gamma-ray light that spreads across the cosmos has puzzled astronomers for decades. One team of researchers thinks it has the best explanation yet for the source of this strange emission.

After observing the universe with NASA's Fermi Gamma-ray Space Telescope for six years, scientists with the mission say the majority of the gamma-ray glow they have seen can be explained by objects already known to science. If there are any as-yet unknown sources out there, their contribution to the glow would be very small, scientists say.

"We have a very plausible story. We're not 100 percent confident that this is the final answer, but it really constrains what other exotic possibilities could be out there," said Keith Bechtol, a postdoctoral researcher at the University of Chicago and a member of the Fermi collaboration who worked on the analysis.


Related Links:
KICP Members: Keith Bechtol
Scientific projects: Fermi Gamma-ray Space Telescope (Fermi)
Neutrino astronomy: Balloon with a view
The Economist, January 20, 2015
Up, up and away!
Up, up and away!
The Economist

An experiment in Antarctica may solve the mystery of cosmic rays

MEET ANITA. Strictly, ANITA III--for she is the third iteration of the Antarctic Impulsive Transient Antenna. Her job, when she is launched sometime in the next few days, will be to float, suspended from a giant balloon, over Antarctica's ice, in order to record radio waves which that ice is giving off. These radio waves are generated by neutrinos passing through the ice, making Antarctica the biggest neutrino-detection laboratory in the world.

The particular neutrinos that ANITA seeks are of extremely high energy. Where they come from, no one knows--nor, strictly speaking, is it actually known that they exist, for ANITAs I and II, which were smaller devices, failed to find them. But theory says they should be there, generated in whatever giant explosions also create cosmic rays.

Cosmic rays are high-velocity protons, sprinkled with a smattering of heavier atomic nuclei, that fly through space until they hit something such as Earth's atmosphere, when they disintegrate into a shower of other particles. They have been known for a century, but their origin remains mysterious because, being electrically charged, their paths are bent by the galaxy's magnetic field. That means the directions they come from do not point to whatever created them.

Neutrinos, however, are electrically neutral, as their name suggests. Their paths should thus point back towards their origins. Neutrinos do not interact much with other sorts of matter, but when one of ultra-high energy does so, the result is a shower of particles travelling at speeds which exceed that of light in ice. An object travelling faster than light's speed in the medium through which it is passing will generate electromagnetic waves. These are known, after their discoverer, as Cherenkov radiation. And it is pulses of radio-frequency Cherenkov radiation, the electromagnetic equivalent of a sonic boom, which ANITA is looking for.

Once airborne under her balloon--an object made of cling-film-like plastic that, when fully inflated, will be a fifth of the size of a football stadium--ANITA will take advantage of the polar vortex, a wind in constant revolution around the pole. She will fly at an altitude of 35-40km, which will mean her antennae can see 1.5m km2 of ice. Ultra-high-energy neutrinos travelling through the ice are thought to interact with it and produce Cherenkov radiation about once per century per km^2, so an area of this size would be expected to yield about 40 bursts a day. ANITA will complete several laps of the continent, each lasting about 15 days. Then the balloon will be cut loose, and she will deploy a parachute and be guided back to the surface for re-use.

Astrophysicists are not the only people rubbing their mittens together in expectation of the results of this experiment. The neutrinos ANITA is looking for are far more energetic than anything produced by the Large Hadron Collider, the world's most powerful particle accelerator. That means they may obey hitherto unperceived extensions of the laws of physics. One possibility is that, among the Cherenkov-radiation-generating particles produced when a neutrino collides with the ice, there may be an occasional miniature black hole.

That would be particularly exciting, because such black holes might themselves disintegrate in a characteristic puff of radiation named after another physicist, Stephen Hawking. If Hawking radiation exists, it means black holes are not truly black--a discovery which would almost certainly win Dr Hawking a Nobel prize.

Though it is not designed to search for Hawking radiation, ANITA would probably see it if it were there. And, since Hawking radiation is created, quite literally, out of nothing (the particles it is made from emerge from the vacuum of space and then steal the energy needed to become real from the black hole itself), that would assist understanding of a very strange piece of physics indeed.


Related Links:
KICP Members: Keith Bechtol; Abigail G. Vieregg
Scientific projects: Antarctic Impulsive Transient Antenna (ANITA)
Is Quantum Entanglement Real?
The New York Times, November 17, 2014
KICP Associate Fellow Jason Gallicchio and collaborators propose to investigate Quantum Entanglement using the oldest light in the Universe
KICP Associate Fellow Jason Gallicchio and collaborators propose to investigate Quantum Entanglement using the oldest light in the Universe
by David Kaiser, The New York Times

FIFTY years ago this month, the Irish physicist John Stewart Bell submitted a short, quirky article to a fly-by-night journal titled Physics, Physique, Fizika. He had been too shy to ask his American hosts, whom he was visiting during a sabbatical, to cover the steep page charges at a mainstream journal, the Physical Review. Though the journal he selected folded a few years later, his paper became a blockbuster. Today it is among the most frequently cited physics articles of all time.

Bell's paper made important claims about quantum entanglement, one of those captivating features of quantum theory that depart strongly from our common sense. Entanglement concerns the behavior of tiny particles, such as electrons, that have interacted in the past and then moved apart. Tickle one particle here, by measuring one of its properties - its position, momentum or "spin" - and its partner should dance, instantaneously, no matter how far away the second particle has traveled.

The key word is "instantaneously." The entangled particles could be separated across the galaxy, and somehow, according to quantum theory, measurements on one particle should affect the behavior of the far-off twin faster than light could have traveled between them.

Entanglement insults our intuitions about how the world could possibly work. Albert Einstein sneered that if the equations of quantum theory predicted such nonsense, so much the worse for quantum theory. "Spooky actions at a distance," he huffed to a colleague in 1948.

In his article, Bell demonstrated that quantum theory requires entanglement; the strange connectedness is an inescapable feature of the equations. But Bell's proof didn't show that nature behaved that way, only that physicists' equations did. The question remained: Does quantum entanglement occur in the world?

Starting in the early 1970s, a few intrepid physicists - in the face of critics who felt such "philosophical" research was fit only for crackpots - found that the answer appeared to be yes.

John F. Clauser, then a young postdoctoral researcher at the Lawrence Berkeley National Laboratory, was the first. Using duct tape and spare parts, he fashioned a contraption to measure quantum entanglement. Together with a graduate student named Stuart Freedman, he fired thousands of pairs of little particles of light known as photons in opposite directions, from the middle of the device, toward each of its two ends. At each end was a detector that measured a property of the photon known as polarization.

As Bell had shown, quantum theory predicted certain strange correlations between the measurements of polarization as you changed the angle between the detectors - correlations that could not be explained if the two photons behaved independently of each other. Dr. Clauser and Mr. Freedman found precisely these correlations.

Other successful experiments followed. One, led by the French physicist Alain Aspect, tested the instantaneousness of entanglement. Another, led by the Austrian physicist Anton Zeilinger, considered entanglement among three or more particles.

Even with these great successes, work remains to be done. Every experimental test of entanglement has been subject to one or more loopholes, which hold out the possibility, however slim, that some alternative theory, distinct from quantum theory and more in line with Einstein's intuitions, may still be salvageable. For example, one potential loophole - addressed by Dr. Aspect's experiment - was that the measurement device itself was somehow transmitting information about one particle to the other particle, which would explain the coordination between them.

The most stubborn remaining loophole is known as "setting independence." Dr. Zeilinger and I, working with several colleagues - including the physicists Alan H. Guth, Andrew S. Friedman and Jason Gallicchio - aim to close this loophole, a project that several of us described in an article in Physical Review Letters.

HERE'S the problem. In any test of entanglement, the researcher must select the settings on each of the detectors of the experimental apparatus (choosing to measure, for example, a particle's spin along one direction or another). The setting-independence loophole suggests that, though the researcher appears to be free to select any setting for the detectors, it is possible that he is not completely free: Some unnoticed causal mechanism in the past may have fixed the detectors' settings in advance, or nudged the likelihood that one setting would be chosen over another.

Bizarre as it may sound, even a minuscule amount of such coordination of the detectors' settings would enable certain alternative theories to mimic the famous predictions from quantum theory. In such a case, entanglement would be merely a chimera.

How to close this loophole? Well, obviously, we aren't going to try to prove that humans have free will. But we can try something else. In our proposed experiment, the detector setting that is selected (say, measuring a particle's spin along this direction rather than that one) would be determined not by us - but by an observed property of some of the oldest light in the universe (say, whether light from distant quasars arrives at Earth at an even- or odd-numbered microsecond). These sources of light are so far away from us and from one another that they would not have been able to receive a single light signal from one another, or from the position of the Earth, before the moment, billions of years ago, when they emitted the light that we detect here on Earth today.

That is, we would guarantee that any strange "nudging" or conspiracy among the detector settings - if it does exist - would have to have occurred all the way back at the Hot Big Bang itself, nearly 14 billion years ago.

If, as we expect, the usual predictions from quantum theory are borne out in this experiment, we will have constrained various alternative theories as much as physically possible in our universe. If not, that would point toward a profoundly new physics.

Either way, the experiment promises to be exciting - a fitting way, we hope, to mark Bell's paper's 50th anniversary.


Related Links:
KICP Members: Jason Gallicchio
Follow Wired Twitter Facebook RSS Mysterious Missing Pulsars May Have Gotten Wrapped in Dark Matter and Turned Into Black Holes
Wired, November 13, 2014
The core of the Milky Way at a distance of some 26,000 light years from Earth.  <i>Image credit:</i> NASA/CXC/UMass/D. Wang et al./STScI/JPL-Caltech/SSC/S.Stolovy
The core of the Milky Way at a distance of some 26,000 light years from Earth.
Image credit: NASA/CXC/UMass/D. Wang et al./STScI/JPL-Caltech/SSC/S.Stolovy
by Marcus Woo, Wired

The center of the galaxy should be chock-full of rapidly spinning, dense stellar corpses known as pulsars. The problem is, astronomers can't seem to find them.

The galactic center is a bustling place. Lots of gas, dust, and stars zip about, orbiting a supermassive black hole about three million times more massive than the sun. With so many stars, astronomers estimate that there should be hundreds of dead ones, says astrophysicist Joseph Bramante of Notre Dame University. Scientists have found only a single young pulsar at the galactic center, where there should be as many as 50 such youngsters.

Bramante and astrophysicist Tim Linden of the University of Chicago have a possible solution to this missing-pulsar problem, which they describe in a paper accepted for publication in the journal Physical Review Letters. Maybe those pulsars are absent because dark matter, which is plentiful in the galactic center, gloms onto the pulsars, accumulating until the pulsars become so dense they collapse into a black hole. Poof. No more pulsars.


Related Links:
KICP Members: Tim Linden
Cosmic-Ray Telescope Flies High
Scientific American, November 4, 2014
Important Test for JEM-EUSO in Canada Angela Olinto, US PI
Important Test for JEM-EUSO in Canada
Angela Olinto, US PI
by Debra Weiner, Scientific American

Cosmic rays, traveling nearly at the speed of light, bombard Earth from all directions. The electrically charged particles are the most energetic component of cosmic radiation -- yet no one knows where they come from.

Astrophysicists speculate that high-energy cosmic rays may have emerged from supermassive black holes in faraway galaxies or possibly from decaying particles from the big bang.

Whatever their origin, these rays crash into Earth's atmosphere about once per square kilometer per century. The impact produces an air shower of tens of billions of secondary, lower-energy particles that in turn excite nitrogen molecules in the atmosphere. The interactions produce ultraviolet fluorescence that lights up the air shower's path. Scientists are trying to use such paths to measure the direction and energy of cosmic rays and reconstruct their trajectories back millions of light-years into space to pinpoint their source.

Seeing these extreme events is rare. Earth-based observatories can spot cosmic- ray collisions only if they occur directly above the detectors. The Pierre Auger Observatory in Argentina, which houses the world's largest cosmic-ray detector and covers an area roughly the size of Rhode Island, records about 20 extreme-energy particle showers a year.

Hoping to improve the odds of observing the rays, a team of scientists from 15 nations came together more than a decade ago and designed a cosmic- ray telescope for the International Space Station (ISS). On the Japanese Experimental Module, the Extreme Universe Space Observatory (JEM- EUSO) will record ultraviolet emissions with a wide-angle, high-speed video camera that points toward Earth. With such a large observation area, the camera will see more air showers. The team originally hoped to launch EUSO in 2006. But troubles on Earth -- first the space shuttle Columbia disaster in 2003, then the Fukushima nuclear meltdown in 2011 and now the turmoil in Ukraine -- have delayed its deployment until at least 2018.

The science, however, marches onward. In August the team launched a prototype of the telescope 38 kilometers into the stratosphere onboard a helium filled balloon. For two hours, researchers followed below in a helicopter, shooting a pulsed UV laser and LED into the telescope's field of view. The test was a success: the prototype detected the UV traces, which are similar to the fluorescence generated by extreme energy cosmic-ray air showers. In 2016 astronauts will transport a shoebox-size prototype called Mini-EUSO to the ISS and see how it fares at the altitude of the full mission.


Related Links:
KICP Members: Angela V. Olinto
Finding Dark Energy in the Details
Quanta Magazine, September 23, 2014
Finding Dark Energy in the Details
by Natalie Wolchover, Quanta Magazine

The astrophysicist Joshua Frieman seeks to pinpoint the mysterious substance driving the accelerating expansion of the universe.

Like most theoretical cosmologists, Joshua Frieman was thrilled when astronomers announced in 1998 that the expansion of the universe appeared to be speeding up, driven by an invisible agent that they called "dark energy."

Frieman and his fellow theorists imagined two possible causes for the cosmic acceleration: Dark energy could be the quantum jitter of empty space, a "cosmological constant" that continues to accrue as space expands, pushing outward ever more forcefully. Alternately, a yet-undetected force field could pervade the cosmos, one akin to the field that scientists believe powered the exponential expansion of the universe during the Big Bang.

But the scientists also realized that the two options would have nearly identical observational consequences, and either theory could fit the crude measurements to date.

To distinguish between them, Frieman, a professor of astronomy and astrophysics at the University of Chicago and a senior staff scientist at the Fermi National Accelerator Laboratory (Fermilab) in nearby Batavia, Ill., co-founded the Dark Energy Survey (DES), a $50 million, 300-person experiment. The centerpiece of the project is the Dark Energy Camera, or DECam, a 570-megapixel, optical and near-infrared CCD detector built at Fermilab and installed on the four-meter Blanco Telescope in Chile two years ago. By observing 300 million galaxies spanning 10 billion light-years, DES aims to track the cosmic acceleration more precisely than ever before in hopes of favoring one hypothesis over the other. Frieman and his team are now reporting their first results.

Quanta Magazine caught up with Frieman in late August during COSMO 2014, a conference he helped organize. With his closely clipped gray beard, tortoiseshell glasses and organic cotton shirt, the scientist fit right in with the other gourmands lunching at Eataly Chicago down the street. Between bites of tagliatelle, he explained just what is and isn't known about dark energy, and how DES will help impel theorists toward one of the two disparate descriptions of its nature. An edited and condensed version of the interview follows.

QUANTA MAGAZINE: Why did you start the Dark Energy Survey?

JOSHUA FRIEMAN: As a theorist in the 1990s working on theoretical ideas for what could be causing the universe to speed up, I came to the conclusion that we could make different models and do a lot of theoretical speculation, but that we wouldn't know which of those paths to go down until we had much better data.

So a handful of us in Illinois started discussing possibilities for getting that data. And it just so happened that, around that time, the National Optical Astronomy Observatory announced an opportunity, saying, more or less, "If someone can build a really cool instrument for the telescope we operate in Chile, we'll give you a bunch of telescope time." That's when we formed the Dark Energy Survey collaboration and came up with the design for our camera.

Isn't it unusual for a theorist to lead a major astrophysics experiment?

It's somewhat unusual, but the boundaries between theory and observation in cosmology are getting blurred, which I think is a healthy development. It used to be that theorists like me would work with a pen and paper, and then observers would go out and take the data and analyze it. But we now have a new model in which teams are trained to analyze and interpret large data sets, and that isn't purely theory or purely observational work; it combines the two.

How do you picture an invisible unknown like dark energy?

One way to think about dark energy is as a fluid, in the sense that it can be described by its density and its pressure. Those two properties tell you its effects on the expansion of the universe. The more dark energy there is - that is, the greater its density - the stronger its effects are. But the thing that's really crucial about dark energy is that unlike anything else we know about, it has negative pressure, and that's what makes it gravitationally repulsive.

Why does negative pressure make it repulsive?

Einstein's theory says the force of gravity is proportional to the energy density plus three times the pressure, so pressure itself actually gravitates. That's something we're not familiar with, because for ordinary matter, the pressure is just a tiny fraction of the density. But if something has a pressure that's a sizable fraction of the energy density, and if that pressure is negative, then I can flip the sign of gravity. Gravity's no longer attractive - it's repulsive.

By far the leading candidate for dark energy is the "cosmological constant." What's that?

Albert Einstein introduced the cosmological constant in 1917 as an additional term in the equation of gravity. In Einstein's theory, gravity is the curvature of space-time: You have some source of energy and pressure that curves space-time, and then other matter moves within this curved space. Einstein's equations relate the curvature of space-time to the energy and pressure of whatever's in space.

Einstein originally put the cosmological constant on the curvature side of the equation because he wanted to get a certain solution, which turned out to be wrong. But soon after that, the Belgian physicist Georges Lemaitre realized that the cosmological constant naturally lives with the pressures and energy densities, and that it could be interpreted as the energy density and pressure of something. Already on the energy density and pressure side of the equation was everything in the universe: dark matter, atoms, whatever. If I remove all that stuff, then the cosmological constant must be the energy density and pressure of empty space.

How could empty space possess energy and pressure?

In classical physics, empty space would have no energy or pressure. But quantum effects can create energy and pressure even if there are no real particles there. In quantum theory, you can imagine virtual particles zipping in and out of the vacuum, and those virtual particles - which are always being produced and then annihilating - have energy. So if dark energy is the cosmological constant, then it could be the energy associated with these virtual particles.

How do you measure dark energy?

There are two things we're trying to do that can give us constraints on dark energy: One is to measure distances, which tells us the history of cosmic expansion. The second is to measure the growth of structure in the universe.
Gravitational lensing.

The galaxy cluster Abell 1689, imaged by the Hubble Space Telescope, bends light around its center, distorting the shapes of more distant galaxies in an effect known as gravitational lensing.

For the latter, we're using a technique called "weak gravitational lensing," which involves measuring, very precisely, the shapes of hundreds of millions of galaxies, and then inferring how those shapes have been distorted because the light rays from those galaxies get bent by gravity as they travel to us. This lensing effect is really tiny, so in 99 cases out of 100, you can't tell just by looking at a galaxy if it has been lensed. So we have to tease out the signal statistically.

If we look at the shapes of galaxies that are not so far versus ones that are farther, part of the difference in the shapes will be due to the fact that the light has passed through different amounts of clumpy structure. Measuring the lensing signal will give us a measure of how the clumpiness of the universe has evolved over cosmic time, and that clumpiness is impacted by dark energy. Gravity pulls stuff in, making the universe become more and more clumpy over time, but dark energy does the opposite. It makes things push away from each other. So if we can measure how the clumpiness of the universe has changed over cosmic time, we can infer something about dark energy: how much of it there was, and what its properties were at different points in time.

DES will try to calculate the dark energy "equation of state" parameter, w. What does w represent?

The parameter w tells us the ratio of the pressure of the dark energy to its density. If dark energy is the cosmological constant, then you can show that the only w that's consistent for empty space is the one where the pressure is exactly equal to minus the energy density. So w has a very specific value: minus one.

If dark energy isn't the cosmological constant, what else might it be?

The simplest alternatives, and the ones that I worked on in the 1990s, are inspired by "inflation." Before we knew that the expansion of the universe is currently speeding up, we had this idea that the universe was speeding up in the very earliest fraction of a second after the Big Bang. That idea of very early cosmic acceleration is called inflation. So the simplest thing to do was to borrow the theory that explains this other epoch of sped-up expansion, and that involves scalar fields.

A scalar field is an entity that has a value everywhere in space. As the field evolves, it can act like dark energy: If it evolves really slowly, it will have negative pressure, which will cause the universe to accelerate. The simplest models of primordial inflation say that, for some period, the universe was dominated by one of these scalar fields, and it eventually decayed and disappeared. And if that's our best idea for what happened when the universe was speeding up almost 14 billion years ago, we should consider that maybe we have something like that going on now.

If you look at these models, they tend to predict that w, the ratio of the pressure to energy density, would be slightly different from minus one. We would like to test that idea.


Related Links:
KICP Members: Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES)
Keith Bechtol races to victories in Chicago Half Marathon
Chicago Sun-Times, September 8, 2014
Keith Bechtol races to victories in Chicago Half Marathon
by Dale Bowman, Chicago Sun-Times

You didn't have to be an astrophysicist to tell conditions were nearly perfect Sunday morning for the start of the 18th Chicago Half Marathon on the South Side.

But apparently it helped, at least for Keith Bechtol. The astrophysicist at the University of Chicago won the men's side in 1 hour, 6 minutes, 52 seconds. Jeff Jonatis was second, 50 seconds back.

Kristen Heckert, a Plainfield South math teacher and coach from Bolingbrook, won the women's race in 1:17:35. Pamela Staton was second (1:20:45).

"Fantastic: Not much wind and right around 60 degrees," Bechtol said.


Related Links:
KICP Members: Keith Bechtol