Cosmic background: 51 years ago, an accidental discovery sparked a big bang in astrophysics


The balloon-borne spacecraft, SPIDER, prior to launch. PHOTO BY ZIGMUND KERMISH

ON NEW YEAR’S DAY 2015, A BALLOON-BORNE SPACECRAFT ascended above Antarctica and snapped crisp photos of space, unobscured by the humidity of Earth’s atmosphere. Meanwhile, a telescope located 4,000 miles to the north, in the desolate Chilean desert, scanned roughly half of the visible sky.

By air and by land, physicists have staked out the best vantage points on the globe, not for stargazing, but for peering between the stars at the thermal traces of the Big Bang.

Spread nearly evenly across the universe is a sea of invisible radiation called the Cosmic Microwave Background (CMB) that keeps space a chilly 2.7 degrees above absolute zero. The now-cold CMB, however, is a remnant of a much hotter, more violent cosmic epoch. About 13.8 billion years ago, immediately after the Big Bang, the universe was filled with a hot gas of ionized particles and radiation. As space expanded, the waves of radiation were stretched and diluted into their current low-energy state. The boiling plasma has since cooled and clumped into galaxies, stars, planets and human beings, all drifting through the faint afterimage of the first flash.

The prediction, discovery and study of the CMB 50 years ago comprise a story that is deeply intertwined with several generations of faculty at the Princeton physics department. The story continues today as University researchers probe the microwave background with the goal of understanding the past and future of our cosmos.

The discovery of the background radiation was a serendipitous one. In 1964, Bell Laboratories technicians Robert Wilson and Arno Penzias racked their brains for an explanation of the noisy signal recorded by their radio antenna. When it turned out that the “noise” was actually radiation from the CMB, the two engineers found themselves unexpectedly pulled into the growing field of modern cosmology. The detection of the CMB earned them the Nobel Prize.

Yet the discovery wouldn’t have been possible without the work of physicists at Princeton, 40 miles down the road from Bell Labs. Back then, the branch of science known as cosmology was ignored by most serious researchers. The physics community viewed the origin and development of the universe as dead-end topics, yet a few at Princeton had dared to tackle it.

At the time, P. James Peebles was a physics postdoctoral researcher at Princeton. “When I started working in this field, everyone was saying, ‘There’s no evidence. Why are you studying this?’” said Peebles, who today is the Albert Einstein Professor of Science, Emeritus. Instead, the mainstream focus was particle physics, which studies the subatomic particles that make up the universe.

Guyot Hall

David Wilkinson and Peter Roll used this experimental setup on the roof of Guyot Hall, which housed the Department of Geology (now Geosciences), to search for the CMB, at Bob Dicke’s suggestion. Wilkinson is holding a screwdriver, and Roll is almost obscured by the instrument. Photo by Robert Matthews circa 1964-65

Two Princeton professors, John Wheeler and Peebles’ mentor, Robert Dicke, decided that research on the cosmic scale should not be neglected. Since 1915, when Einstein developed the theory of general relativity to explain the behavior of large objects in space, hardly any further research had been done on gravity or the structure of the universe. This was due in part to respect for Einstein’s picture of the cosmos, and in part to the difficulty of devising fruitful experiments. “In the mid-1950s, Bob started a serious program of laboratory and extraterrestrial tests for general relativity,” said Peebles. “John started a school for the theoretical study of the subject. These changes marked a renaissance.”

While everyone else was thinking small, Dicke and Wheeler were thinking big. More specifically, Dicke was thinking about the Big Bang, a concept that dated back to the 1920s, when it was first observed that the universe is expanding. Yet extrapolating the current expansion back in time to a tiny, hot, dense state from which it all began was not a widely accepted leap. Peebles said: “Until the ’60s, the evidence that this is what happened was minimal. It was still just an idea, popular in some circles, detested in others.”

Dicke took the Big Bang theory from guesswork firmly into the realm of empirical physics when he proposed the CMB as evidence for a hot, dense beginning. Peebles recalls how Dicke almost casually set the course for his career and that of his peers: “He persuaded Dave Wilkinson and Peter Roll [Princeton physics faculty members] to build a device called a Dicke radiometer to look for this radiation, and he told me with a wave of his hand, ‘Why don’t you go think about the theory.’ And I’ve been doing it ever since.”

By 1970, the scientific community had accepted that the CMB had the properties that made it undeniable evidence for the Big Bang. Physicists then shifted their attention to more detailed scrutiny of the remnant radiation as a way of deepening our understanding of the birth of the universe, its expansion and its fate.

One area of scrutiny is whether the universe went through a period of rapid expansion, or inflation, after the Big Bang. To look for signs of inflation and to map the CMB in our region of space, NASA in partnership with Princeton and other universities launched the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, named postmortem in honor of Wilkinson’s contribution to experimental cosmology.

The inflationary model predicts a particular pattern to the fluctuations of the CMB. When WMAP released its first set of results in 2003, they neatly matched the predictions of inflation. Among the many Princeton researchers who played significant roles in WMAP were Lyman Page, the James S. McDonnell Distinguished University Professor in Physics; Norman Jarosik, senior research physicist; and David Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation. Thanks to WMAP, Spergel said, “We have a coherent cosmological model that fits all the data.”

Since then, several other projects, including most recently the European Space Agency’s Planck space telescope, have mapped the CMB and provided evidence for inflation. But scientists are looking for additional evidence in the form of long undulations — called gravitational waves — stretching across the fabric of space. The remnants of these waves could be detected as a faint pattern in the CMB known as B-mode polarization. A reported detection of gravitational waves earlier this year from another project, BICEP2, created a stir in the astrophysics community but turned out to be an artifact of interstellar dust.

Detecting the remnants of gravitational waves is one of the goals of the Atacama Cosmology Telescope (ACT), an international project funded by the National Science Foundation and led by Princeton’s Suzanne Staggs, the Henry DeWolf Smyth Professor of Physics. The team includes Lyman Page, the James S. McDonnell Distinguished University Professor of Physics; Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation; and many colleagues at collaborating institutions.

The data collected during the flight of the balloon-borne SPIDER mission in Antarctica — funded by NASA, the National Science Foundation, the David and Lucile Packard Foundation, and the Natural Sciences and Engineering Research Council of Canada; and led by Assistant Professor of Physics William Jones — could also reveal evidence of these waves in the CMB.

The search for gravitational waves is just one of the ways in which the CMB provides opportunities for studying the early universe. The ACT collaboration is also looking for evidence of dark energy, a mysterious force that is speeding up the expansion of the universe, and answers to even bigger questions about the cosmological model. It is clear that the CMB is an important tool for the foreseeable future of cosmology. However faint, it illuminates the distant past, which in turn illuminates the future.

–By Takim Williams

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The Hub: A new center opens its doors … to student entrepreneurship

The Hub


THE SOCIAL CAMPUS NETWORKING startup Friendsy began with a single campus network at Princeton and has since expanded to 230 campuses nationwide.

This June, Friendsy was one of the first startups to move into the University’s Entrepreneurial Hub, a new incubator space for faculty, students and alumni. Located in downtown Princeton, the Hub houses the Keller Center’s annual eLab Summer Accelerator Program — a launch pad for student startups — as well as an eLab Incubator program that enables students to pursue their entrepreneurial ambitions during the academic year. The Hub also offers shared working space for startups founded by faculty, students and alumni, and serves as the center for Princeton’s entrepreneurship education programs.

“eLab has been tremendously helpful for our growth as a startup company,” said Michael Pinsky, one of Friendsy’s founders, who graduated from Princeton this year with a degree in psychology. “The ability to work with mentors in the field and use the working space at the Hub with what became a very large Friendsy team was incredibly valuable, and it is undoubtedly a major reason for our success.”

Now in its fourth year, the eLab program runs for 10 weeks in the summer and culminates in Demo Days, held in New York City and Princeton, at which the teams present their work to entrepreneurs, investors and innovators. The program has become an integral part of the University’s effort to assist students and faculty with pursuing new ventures.

The Hub was established in response to recommendations made by a committee set up to explore ways to expand entrepreneurship education and help University students, faculty and alumni advance their creative ideas and make important contributions to society.

Elab Summer Accelerator Program

Seven teams of students participated in the eLab Summer Accelerator Program at Princeton’s Entrepreneurial Hub this summer. From left to right: Kehinde Ope, a student at the University of Delaware, and Achille Tenkiang, a member of the Class of 2017 at Princeton University, have formed a startup called BLOC with Saidah Bishop, a student at Dartmouth College (fourth from left). Third from left is Diogo Adrados, Princeton Class of 2015, from the startup Rodeo. On the far right, Michael Pinsky, Princeton Class of 2015, is a co-founder of Friendsy.  PHOTO BY JILL FELDMAN

Mung Chiang, who chaired the committee, said the new space provides “an essential anchor” for a wide range of entrepreneurial activities at Princeton. The 10,000-squarefoot facility offers meeting rooms, offices and information technology support for startups sharing the co-working space. The Hub is also the home of the Princeton Entrepreneurship Council, led by Chiang and established in July 2015 to coordinate entrepreneurship programs on campus.

“The University has taken an important initiative in creating space for entrepreneurs and entrepreneurship education,” said Chiang, the Arthur LeGrand Doty Professor of Electrical Engineering and director of the Keller Center.

Celebrating its 10th anniversary in 2015, the Keller Center’s mission is to educate students as leaders in a technology-driven society by innovating education and fostering entrepreneurship, creativity and design. The center bridges disciplines to ensure that all students are prepared to put science and technology to use in solving critical societal challenges.–By John Sullivan

This year’s eLab teams include:
BLOC logoBLOC An online professional network for black collegians on the rise

clickstick Logo 6ClickStick Innovative dispensing technology with accurate dosage control for personal care, cosmetic and pharmaceutical products

Bodhi TreeBodhi Tree Systems An enterprise software system that facilitates the design and management of pharmaceutical trials

Friendsy LogoFriendsy A college-based social networking service that promotes friendships and relationships among members

KLOSKLOS Guitars A durable, affordable and comfortable carbon-fiber travel guitar

RodeoRodeo A mobile platform for users to browse and discover live events in their community

TeachMe_logoTeachMe A platform that connects college students to share knowledge, skills and experience with others in their community

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Wild birds: A trip to the market reveals species imperiled

Wild Birds

“Wild birds are being vacuumed out of the forests, gardens and fields of Indonesia, and we have to quickly figure out which species are in danger of extinction.” –David Wilcove, professor of ecology and evolutionary biology and public affairs in the Woodrow Wilson School

THE SIGHT OF A SOUTHEAST ASIAN BIRD market rivals the din of one for being overwhelming. Thousands of wild-caught birds are packed into cages that hang from eaves and fill market stalls to the ceiling, lining the paths trod by prospective buyers like a living wall. Taken from fields and forests, these birds are prized for their song, their colors, their spiritual significance or their long-time association with status and wealth. For the people who come to these markets, the birds — young and old, endangered and common — have meaning and value.

But to scientists, conservationists and governments, the wild-pet trade is a destructive yet unmonitored and elusive force on wildlife populations.

Princeton University researchers went deep into the wild-bird markets and trapping operations on the Indonesian island of Sumatra to document the draining of species by the pet trade. They found there a new and interesting weapon in the struggle to gauge — and halt — the devastation of the wildlife trade on animal populations: the very markets where the animals are bought and sold.

Species that are disappearing as a result of the pet trade can be identified by changes in their market prices and trade volumes, a study led by the Princeton researchers found. The researchers studied open-air pet markets on Sumatra from 1987 to 2013 and found that bird species that increased in price but decreased in availability exhibited plummeting populations in the wild.

The researchers concluded in the journal Biological Conservation in July 2015 that a prolonged rise in price coupled with a slide in availability could indicate that a species is being wiped out by its popularity in the pet trade. Through regular pet-market monitoring, conservationists and governments could use this information as an early indicator that a particular species is in trouble, the researchers reported.

Lead author Bert Harris, who was a postdoctoral fellow in the Program in Science, Technology and Environmental Policy in Princeton’s Woodrow Wilson School of Public and International Affairs when the work was conducted, said that market monitoring can be done far more quickly and cheaply than field-based monitoring of wild populations.


Birds such as the Oriental white-eye (top photo ) are packed into tight cages where they are at risk of disease. Many Asian and African countries host a startling number of species yet have lax-to-nonexistent monitoring and conservation programs. The Princeton researchers’ market-monitoring method can be done far more quickly and cheaply than field-based monitoring of wild populations. PHOTO COURTESY OF DAVID WILCOVE

One important function of the study is to highlight the pet trade as an emerging threat facing many birds and other wildlife, one that can act independently from other drivers of extinction such as habitat loss, said senior author David Wilcove, a professor of ecology and evolutionary biology and public affairs in the Wilson School.

He and Harris worked with co-authors Jonathan Green, who was a Princeton postdoctoral researcher in the Wilson School and is now at the University of Cambridge; Xingli Giam, who earned his Ph.D. at Princeton in 2014 and is now at the University of Washington; and researchers from the Wildlife Conservation Society and the Indonesian Institute of Sciences.

“Wild birds are being vacuumed out of the forests, gardens and fields of Indonesia and we have to quickly figure out which species are in danger of extinction,” Wilcove said. “We’ve got to change how we tackle this problem.”

Carter Roberts, president and CEO of the World Wildlife Fund, said that the researchers’ use of wildlife-trade market data to identify endangered species is a “potentially breakthrough idea.”

“What I think makes this paper so exciting is that it suggests a two-pronged approach to addressing the threat to biodiversity posed by the wildlife trade: using market data to identify the species that are likely being severely overexploited, and then targeted research and conservation efforts at those species,” Roberts said.

The researchers found that 14 birds popular in Sumatran pet markets were identified by local experts as declining or severely declining — yet, only two are officially recognized as imperiled. In addition, only two species are restricted to old growth forests, meaning that deforestation alone could not explain the declines. The pet trade was clearly a culprit, too. Furthermore, the researchers found that six species that are not popular as pets exhibited population increases. The researchers confirmed their method by studying the cases of two birds that are critically endangered by the pet trade — the yellow-crested cockatoo and the Bali myna.

Existing studies have explored wildlife markets, but only documented a species’ market volume, or availability, Harris said. The Princeton-led study, which was supported by the High Meadows Foundation, is the first to consider price and market volume. Market availability alone can fluctuate for reasons unrelated to a species’ wild population, such as a decrease in popularity, he said.

During the course of the research, Harris visited bird markets to gather price and availability data. They are chaotic places where Westerners asking about prices are viewed with suspicion.

“The markets are the dirty part of conservation,” Harris said. “They’re noisy and smelly. And after someone who looks like me asks about prices two or three weeks in a row, sellers just stop responding.”

Wilcove was inspired to conduct the current research after a trip to Sumatra when he noticed a prevalence of wild-caught pet birds. Research has found that 22 percent of Indonesian households own birds.

One bird the researchers identified as declining in the wild, the white-rumped shama, which is prized for its song, can be raised in captivity. Yet people seem to prefer the wild individuals, Wilcove said. He and Harris want to explore how governments and conservation groups can convince people to keep captive-raised birds.

“It’s time for some new approaches,” Wilcove said.

–By Morgan Kelly

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The Princeton Plasma Physics Laboratory: The quest for clean energy continues


After a three-year, $94 million overhaul, the Princeton Plasma Physics Laboratory’s primary fusion reactor has resumed the quest for clean energy. The fusion of parts of the atom inside the reactor could release a near limitless amount of energy and reduce our dependence on fossil fuels, while generating minimal hazardous waste. The upgrade included replacing the center of the apple-shaped reactor with a new 29,000-pound magnetic core. PHOTO BY JAMES CHRZANOWSKI

FUSION — the energy-making process that powers the sun — could provide us with a near limitless source of energy, ending our dependence on fossil fuels for making electricity.

This summer, after a nearly three-year overhaul, the world-leading fusion research facility at the Princeton Plasma Physics Laboratory (PPPL) switched on its newly outfitted flagship reactor, the National Spherical Torus Experiment-Upgrade (NSTX-U). The reactor uses electrical current and heat to create a hot, charged state called a plasma, which is encased by powerful magnets so that parts of the atoms can collide and fuse, releasing massive quantities of energy in the process.

The $94 million upgrade has made the NSTX-U the world’s most powerful spherical tokamak — the name given to donut-shaped fusion reactors — while doubling its heating power and magnetic fields, and making it the first major addition to the U.S. fusion program in the 21st century.

“The upgrade boosts NSTX-U operating conditions closer to those to be found in a commercial fusion power plant,” said Stewart Prager, director of PPPL, which is managed by Princeton University for the U.S. Department of Energy and is located some three miles from the campus. “Experiments will push into new physics regimes and assess how well the spherical design can advance research along the path to magnetic fusion energy.”

Fusion reactor

The upgrade included bringing in a 70-ton machine (above) that produces beams that heat the plasma. PHOTO BY MICHAEL VIOLA

The key feature of the design is its compact, cored apple-like shape, as compared with the bulkier, donut-like form of conventional tokamaks. The compact shape enables spherical tokamaks to confine highly pressurized plasma gas — the hot, charged fuel for fusion reactions — within comparatively low magnetic fields. This capability makes spherical tokamaks a cost-effective alternative to conventional tokamaks, which require stronger and thus more expensive magnetic fields.

Building the NSTX-U posed novel challenges for engineers and technicians throughout PPPL. Tasks ranged from flying a 70-ton neutral beam machine over a 22-foot wall to building a 29,000-pound center stack. These huge components fit alongside and inside an existing facility — the original NSTX — with hair-thin precision, requiring an effort that one engineer likened to rebuilding a ship in a bottle.

Researchers now plan to test whether the NSTX-U can continue to produce high-pressure plasmas under the hotter and more powerful conditions that the upgrade allows. Also on the research agenda are tests of how effectively the NSTX-U can keep temperatures approaching 100 million degrees centigrade from dissipating, and whether its spherical design can be a strong candidate for a major next step in the U.S. fusion program.

–By John Greenwald

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