KICP in the News
UChicago celebrates the promise of Chicago youth
The University of Chicago News Office, May 25, 2015
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."
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KICP Members: Randall H. Landsberg; Donald G. York
The Particle That Broke a Cosmic Speed Limit
Quanta Magazine, May 17, 2015
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.
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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
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.
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.
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Live Session with Michael Turner
Livestream.com, May 1, 2015
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.
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KICP Members: Michael S. Turner
Absence of gravitational-wave signal extends limit on knowable universe
Fermilab, April 27, 2015
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."
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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
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.
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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
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.
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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
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.
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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
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.
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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
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.
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KICP Members: Juan I. Collar; Daniel Hooper
Understanding the Dark Side of Physics
Science Friday, March 27, 2015
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.
Author, "To Explain the World: The Discovery of Modern Science" (HarperCollins, 2015)
Nobel Prize Winner, 1979, Physics
University of Texas at Austin
Staff Scientist, Fermilab
Associate Professor, Astronomy and Astrophysics
University of Chicago
Associate Professor, Physics
Southern Methodist University
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John E. Carlstrom, Thomas M. Crawford and Lloyd Knox, "Particle physics and the cosmic microwave background"
Physics Today, March 13, 2015
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.
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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
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.
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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
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.
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KICP Members: Michael S. Turner
Mystery of the Universe's Gamma-Ray Glow Solved
Space.com, February 5, 2015
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.
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KICP Members: Keith Bechtol
Scientific projects: Fermi Gamma-ray Space Telescope (Fermi)
Neutrino astronomy: Balloon with a view
The Economist, January 20, 2015
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.
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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
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.
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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.
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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 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.
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KICP Members: Tim Linden
Cosmic-Ray Telescope Flies High
Scientific American, November 4, 2014
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.
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KICP Members: Angela V. Olinto
Finding Dark Energy in the Details
Quanta Magazine, September 23, 2014
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.
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.
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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
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.
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KICP Members: Keith Bechtol
Do we live in a 2-D hologram?
The University of Chicago News Office, August 28, 2014
A unique experiment at the U.S. Department of Energy's Fermi National Accelerator Laboratory called the Holometer has started collecting data that will answer some mind-bending questions about our universe - including whether we live in a hologram.
Much like characters on a television show would not know that their seemingly 3-D world exists only on a 2-D screen, we could be clueless that our 3-D space is just an illusion. The information about everything in our universe could actually be encoded in tiny packets in two dimensions.
Get close enough to your TV screen and you'll see pixels, small points of data that make a seamless image if you stand back. Scientists think that the universe's information may be contained in the same way, and that the natural "pixel size" of space is roughly 10 trillion trillion times smaller than an atom, a distance that physicists refer to as the Planck scale.
"We want to find out whether spacetime is a quantum system just like matter is," said Craig Hogan, director of Fermilab's Center for Particle Astrophysics and the developer of the holographic noise theory. "If we see something, it will completely change ideas about space we've used for thousands of years."
The Holometer team comprises 21 scientists and students from Fermilab, Massachusetts Institute of Technology, University of Chicago and University of Michigan. The science team includes Hogan and Stephan Meyer, who are both professors in astronomy & astrophysics at UChicago.
Quantum theory suggests that it is impossible to know both the exact location and the exact speed of subatomic particles. If space comes in 2-D bits with limited information about the precise location of objects, then space itself would fall under the same theory of uncertainty. The same way that matter continues to jiggle, as quantum waves, even when cooled to absolute zero, this digitized space should have built-in vibrations even in its lowest energy state.
Essentially, the experiment probes the limits of the universe's ability to store information. If there are a set number of bits that tell you where something is, it eventually becomes impossible to find more specific information about the location - even in principle. The instrument testing these limits is Fermilab's Holometer, or holographic interferometer, the most sensitive device ever created to measure the quantum jitter of space itself.
Now operating at full power, the Holometer uses a pair of interferometers placed close to one another. Each one sends a one-kilowatt laser beam, the equivalent of 200,000 laser pointers, at a beam splitter and down two perpendicular 40-meter arms. The light is then reflected back to the beam splitter where the two beams recombine, creating fluctuations in brightness if there is motion. Researchers analyze these fluctuations in the returning light to see if the beam splitter is moving in a certain way - being carried along on a jitter of space itself.
"Holographic noise" is expected to be present at all frequencies, but the scientists' challenge is not to be fooled by other sources of vibrations. The Holometer is testing a frequency so high - millions of cycles per second - that motions of normal matter are not likely to cause problems. Rather, the dominant background noise is more often due to radio waves emitted by nearby electronics. The Holometer experiment is designed to identify and eliminate noise from such conventional sources.
"If we find a noise we can't get rid of, we might be detecting something fundamental about nature - a noise that is intrinsic to spacetime," said Fermilab physicist Aaron Chou, lead scientist and project manager for the Holometer. "It's an exciting moment for physics. A positive result will open a whole new avenue of questioning about how space works."
The Holometer experiment, funded by the U.S. Department of Energy and other sources, is expected to gather data over the coming year. For more information about the experiment, visit http://holometer.fnal.gov/.
Fermilab is America's premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance, LLC - a partnership of Universities Research Association and the University of Chicago. Visit Fermilab's website at www.fnal.gov.
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KICP Members: Craig J. Hogan; Stephan S. Meyer
Merging galaxies and droplets of starbirth: Hubble snaps a violent galactic merger and chain of star formation
Spacetelescope.org News, July 10, 2014
The Universe is filled with objects springing to life, evolving and dying explosive deaths. This new image from the NASA/ESA Hubble Space Telescope captures a snapshot of some of this cosmic movement. Embedded within the egg-shaped blue ring at the centre of the frame are two galaxies. These galaxies have been found to be merging into one and a "chain" of young stellar superclusters are seen winding around the galaxies' nuclei.
At the centre of this image lie two elliptical galaxies, part of a galaxy cluster known as[HGO2008]SDSS J1531+3414, which have strayed into each other's paths. While this region has been observed before, this new Hubble picture shows clearly for the first time that the pair are two separate objects. However, they will not be able to hold on to their separate identities much longer, as they are in the process of merging into one. 
Finding two elliptical galaxies merging is rare, but it is even rarer to find a merger between ellipticals rich enough in gas to induce star formation. Galaxies in clusters are generally thought to have been deprived of their gaseous contents; a process that Hubble has recently seen in action. Yet, in this image, not only have two elliptical galaxies been caught merging but their newborn stellar population is also a rare breed.
The stellar infants - thought to be a result of the merger - are part of what is known as "beads on a string" star formation. This type of formation appears as a knotted rope of gaseous filaments with bright patches of new stars and the process stems from the same fundamental physics which causes rain to fall in droplets, rather than as a continuous column. 
Nineteen compact clumps of young stars make up the length of this "string", woven together with narrow filaments of hydrogen gas. The star formation spans 100,000 light years, which is about the size of our galaxy, the Milky Way. The strand is dwarfed, however, by the ancient, giant merging galaxies that it inhabits. They are about 330,000 light years across, nearly three times larger than our own galaxy. This is typical for galaxies at the centre of massive clusters, as they tend to be the largest galaxies in the Universe.
The electric blue arcs making up the spectacular egg-like shape framing these objects are a result of the galaxy cluster's immense gravity. The gravity warps the space around it and creates bizarre patterns using light from more distant galaxies.
Astronomers have ruled out the possibility that the blue strand is also just a lensed mirage from distant galaxies and now their challenge is to understand the origin of the cold gas that is fuelling the growth of the stellar superclusters. Was the gas already in the merging galaxies? Did it condense like rain from the rapidly cooling X-ray plasma surrounding the two galaxies? Or, did it cool out of a shock in the X-ray gas as the ten-million-degree gaseous halos surrounding the galaxies collided together? Future observations with both space- and ground-based observatories are needed to unravel this mystery.
 Mergers occur when two or more galaxies stray too close to one another, causing them to coalesce into one large body (heic0912). The violent process strips gas, dust and stars away from the galaxies involved and can alter their appearances dramatically, forming large gaseous tails, glowing rings, and warped galactic discs (heic0810).
 The merging system is forming stellar superclusters in equally spaced beads just like evenly spaced drops from a tap. The only real difference is that surface tension in the falling water is analogous to gravity in the context of the star-forming chain. This is a wonderful demonstration that the fundamental laws of physics really are scale-invariant - we see the same physics in rain drops that we do on 100 000 light-year scales.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Image credit: NASA, ESA/Hubble and G. Tremblay (European Southern Observatory)
Acknowledgement: M. Gladders & M. Florian (University of Chicago, USA), S. Baum, C. O'Dea & K. Cooke (Rochester Institute of Technology, USA), M. Bayliss (Harvard-Smithsonian Center for Astrophysics, USA), H. Dahle (University of Oslo, Norway), T. Davis (European SouthernObservatory), J. Rigby (NASA Goddard Space Flight Center, USA), K. Sharon (University of Michigan, USA), E. Soto (The Catholic University of America, USA) and E. Wuyts (Max-Planck-Institute for Extraterrestrial Physics, Germany).
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KICP Members: Michael D. Gladders
Chuan He and Wayne Hu receive named professorships
The University of Chicago News Office, June 12, 2014
The Division of Physical Sciences is pleased to announce that Professors Chuan He and Wayne Hu have received named and distinguished service professorships in recognition of their outstanding contribution to scholarship, teaching and the intellectual community of the University of Chicago.
Wayne Hu, Professor in Astronomy and Astrophysics and the Enrico Fermi Institute will receive the Horace B. Horton Professorship on November 1, 2014.
Hu's research focuses on the theory and phenomenology of structure formation in the Universe as revealed in Cosmic Microwave Background anisotropies, gravitational lensing, galaxy clustering and galaxy clusters. His work has been published in Physics Review D, The Journal of Cosmology and Astroparticle Physics, The New Journal of Physics, and other publications.
Dr. Hu has received a number of awards, including the American Astronomical Society Warner Prize, an Alfred P. Sloan Fellowship, and Packard Fellowship. He joined the University of Chicago faculty in 2000.
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KICP Members: Wayne Hu
Fermi Institute announces recipients of Nathan Sugarman research awards
The University of Chicago News Office, June 5, 2014
by Steve Koppes, The University of Chicago News Office
Two fourth-year students in the College and two graduate students have received the 23rd annual Nathan Sugarman Awards for Excellence in Undergraduate and Graduate Research.
The undergraduate recipients are Jane Huang, a fourth-year in chemistry and 2013 Goldwater Scholar; and Samantha Dixon, a fourth-year in physics and mathematics.
The graduate recipients are Vinicius Miranda, a doctoral student in astronomy and astrophysics; and Eric Oberla, a doctoral student in physics.
Huang was cited "for her in-depth analysis of λ5797, the Rosetta Stone of diffuse interstellar bands." She was nominated by Takeshi Oka, professor emeritus of chemistry and astronomy and astrophysics; and Donald York, the Horace B. Horton Professor of Astronomy and Astrophysics.
Dixon was cited "for her outstanding work in the calibration set-up for the DAMIC dark matter experiment, and in the measurement of radioactive contamination of the CCD detectors." Dixon was nominated by Paolo Privitera, professor of astronomy and astrophysics.
Miranda was cited "for his thorough and careful work in elucidating the effect of inflationary features on cosmic microwave background anisotropy and non-Gaussianity." Miranda was nominated by Wayne Hu, professor of astronomy and astrophysics.
Nathan Sugarman, SB'37, PhD'41, was a charter member of the Enrico Fermi Institute and a longtime professor in chemistry.
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KICP Members: Wayne Hu; Paolo Privitera; Donald G. York
KICP Students: Samantha Dixon; Vinicius Miranda