Researchers propose a new way to detect the elusive graviton


March 3, 2014

Among the four fundamental forces of nature, only gravity has not had a basic unit, or quanta, detected. Physicists expect that gravitational force is transmitted by an elementary particle called a graviton, just as the electromagnetic force is carried by the photon.

While there are deep theoretical reasons why gravitons should exist, detecting them may be physically impossible on Earth. Download Full Image

For example, the conventional way of measuring gravitational forces – by bouncing light off a set of mirrors to measure tiny shifts in their separation – would be impossible in the case of gravitons. According to physicist Freeman Dyson, the sensitivity required to detect such a miniscule distance change caused by a graviton requires the mirrors to be so massive and heavy that they’d collapse and form a black hole.

Because of this, some have claimed that measuring a single graviton is hopeless. But what if you used the largest entity you know of – in this case the universe – to search for the telltale effects of gravitons. That is what two physicists are proposing.

In the paper, “Using cosmology to establish the quantization of gravity,” published in Physical Review D (Feb. 20, 2014), Lawrence Krauss, a cosmologist at Arizona State University, and Frank Wilczek, a Nobel-prize winning physicist with MIT and ASU, have proposed that measuring minute changes in the cosmic background radiation of the universe could be a pathway of detecting the telltale effects of gravitons.

Krauss and Wilczek suggest that the existence of gravitons, and the quantum nature of gravity, could be proved through some yet-to-be-detected feature of the early universe.

“This may provide, if Freeman Dyson is correct about the fact that terrestrial detectors cannot detect gravitons, the only direct empirical verification of the existence of gravitons,” Krauss said. “Moreover, what we find most remarkable is that the universe acts like a detector that is precisely the type that is impossible or impractical to build on Earth.”

It is generally believed that in the first fraction of a second after the Big Bang, the universe underwent rapid and dramatic growth during a period called “inflation.” If gravitons exist, they would be generated as "quantum fluctuations" during inflation.

Ultimately, these would evolve, as the universe expanded, into classically observable gravitational waves, which stretch space-time along one direction while contracting it along the other direction. This would affect how electromagnetic radiation in the cosmic microwave background (CMB) radiation left behind by the Big Bang is produced, causing it to become polarized. Researchers analyzing results from the European Space Agency’s Planck satellite are searching for this “imprint” of inflation in the polarization of the CMB.

Krauss said his and Wilczek’s paper combines what already is known with some new wrinkles.

“While the realization that gravitational waves are produced by inflation is not new, and the fact that we can calculate their intensity and that this background might be measured in future polarization measurements of the microwave background is not new, an explicit argument that such a measurement will provide, in principle, an unambiguous and direct confirmation that the gravitational field is quantized is new,” he said. “Indeed, it is perhaps the only empirical verification of this very important assumption that we might get in the foreseeable future.”

Using a standard analytical tool called dimensional analysis, Wilczek and Krauss show how the generation of gravitational waves during inflation is proportional to the square of Planck’s constant, a numerical factor that only arises in quantum theory. That means that the gravitational process that results in the production of these waves is an inherently quantum-mechanical phenomenon.

This implies that finding the fingerprint of gravitational waves in the polarization of CMB will provide evidence that gravitons exist, and it is just a matter of time (and instrument sensitivity) to finding their imprint.

“I’m delighted that dimensional analysis, a simple but profound technique whose virtues I preach to students, supplies clear, clean insight into a subject notorious for its difficulty and obscurity,” said Wilczek.

“It is quite possible that the next generation of experiments, in the coming decade or maybe even the Planck satellite, may see this background,” Krauss added.

The Department of Physics is academic unit in ASU's College of Liberal Arts and Sciences.

Director, Media Relations and Strategic Communications

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ASU Cronkite School establishes engagement hub


March 3, 2014

New Cronkite bureau to help news organizations connect with audiences

Arizona State University’s Walter Cronkite School of Journalism and Mass Communication will establish an engagement and education hub for American Public Media’s Public Insight Network, a community of tens of thousands of citizen sources who help journalists create deeper stories by sharing their experiences. The expansion is funded by $250,000 from the John S. and James L. Knight Foundation and additional support from the Corporation for Public Broadcasting and American Public Media. ASU Cronkite School building Download Full Image

The Public Insight Network, or PIN, is an active online network of more than 215,000 people across the country who have signed up to share their knowledge, experience and insights with journalists, helping them improve the quality, diversity and relevance of their reporting. Journalists in more than 80 newsrooms use the network to uncover stories, ask questions, test hunches, unearth angles and provide important context to stories.

The PIN bureau will occupy a digital newsroom in the Cronkite School’s state-of-the-art facility on ASU’s Downtown Phoenix campus. Media professionals and faculty will train students to interact with PIN sources in innovative ways and help create services, such as localization of national stories or idea mining; they also will devise ideas to attract clients and grow revenue sources. Students will hold paid positions or earn academic credit for their participation.

“This project provides students with the research, analytical and entrepreneurial skills that they need to meaningfully interact with sources and audiences – preparing them for the journalism jobs of tomorrow,” said Michael Maness, Knight Foundation vice president of journalism and media innovation. “At the same time, it will expand Public Insight Network services to newsrooms across the country, helping ensure its sustainability into the future.”

ASU President Michael M. Crow said, “At ASU we ask all of our colleges for a deep and engaged role in improving the success of our communities. This effort at the Cronkite School, with our partners, is a great example of what we think a modern university is all about.”

David Kansas, American Public Media’s senior vice president and chief operating officer, welcomed the PIN bureau as an exciting development in the evolution of PIN and the future of journalism education. “It will provide an important service to the industry and a rich educational experience and career pipeline for students while helping to position PIN and the networked journalism it fosters for long-term sustainability,” he said.

The new bureau will be led by Rebecca Blatt, a former senior editor for special projects at WAMU 88.5, the award-winning public radio station that serves the Washington, D.C., metropolitan area. Blatt has worked as an editor and producer at the station since 2008. Since 2011, she has managed PIN projects and community outreach and engagement efforts for the station, utilizing the network to produce special projects and cover breaking news. She previously worked as an associate editor in the NPR newscast unit and started in radio, producing interviews for North Carolina Public Radio’s “The Story.”

Blatt is the recipient of numerous awards for projects she has edited and produced, including the Casey Medal for Meritorious Journalism, the Education Writers Association Award for Education Reporting and the New York Festivals’ Radio Broadcasting Gold World Medal. She holds a bachelor’s degree from the University of Pennsylvania and a master’s degree from the University of North Carolina at Chapel Hill. She will join the Cronkite School in mid-March.

“I am thrilled to be joining the tremendous faculty and students at the Cronkite School – as well as partners at APM and Knight Foundation – as we embark on this new endeavor,” she said. “The PIN bureau will provide a powerful learning experience for students, a valuable service for partner newsrooms and an incredible opportunity to explore new models for collaboration and innovation throughout the news industry.”

This semester, Cronkite students are working with radio, television, print and digital media outlets in Arizona, Colorado, Connecticut, Kentucky, Oklahoma, Minnesota, North Carolina, North Dakota, Texas and Utah to help expand the Public Insight Network and integrate it into the newsrooms’ reporting. Beginning in the fall, they will offer PIN services to an expanded portfolio of media clients.

Christopher Callahan, dean of the Cronkite School, said the PIN bureau is one of a growing number of professional immersion programs available to Cronkite students. The others include Carnegie-Knight News21, an investigative multimedia reporting initiative that sends students around the country to report on topics of national significance; Cronkite NewsWatch, a live, four-day-a-week, student-produced news broadcast that reaches 1.4 million households in Arizona; Cronkite News Service in Phoenix and Washington, D.C., where students cover stories of concern to Arizona audiences; the New Media Innovation Lab, where students from various disciplines create cutting-edge digital media products; and the Cronkite Public Relations Lab, where students develop PR strategies and campaigns for real clients. Cronkite is also launching immersive sports reporting programs in Phoenix and Santa Monica, Calif., as part of its new sports journalism program.

“The Public Insight Network is a great example of how journalists today are engaging with their audiences in new and important ways,” Callahan said.

Lisa Robbins

editor/publisher, Media Relations and Strategic Communications

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