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.

Associate Director, Media Relations & Strategic Communications


ASU Art Museum to present concurrent exhibitions by artist Pablo Helguera

March 3, 2014

The ASU Art Museum is presenting two concurrent solo exhibitions of work by artist Pablo Helguera, both of which will open March 21. “Pablo Helguera: Librería Donceles” and “Pablo Helguera: Chrestomathy,” curated by Julio César Morales, will be the first presentation outside of the East Coast of this new work by Helguera, a world-renowned visual and performance artist whose work weaves together personal and historical narratives in the context of socially engaged art and language.

“Pablo Helguera: Librería Donceles” is an itinerant, functional Spanish-language bookstore of 12,000 used books on every subject – including literature, poetry, art, history, biology, medicine, anthropology and politics, as well as children’s books. To create the installation, Helguera assembled donations of books from individuals and groups in Mexico City and elsewhere, offering prints of his previous artworks in exchange for boxes of books. “Librería Donceles” will be on view through June 28 in downtown Phoenix at Combine Studios Gallery, home of the ASU Art Museum International Artist Residency Program. art installation Download Full Image

The project’s title is inspired by the old bookstores that line Donceles Street in Mexico City’s historic center, says Morales, and it will foster the open-ended and unhurried environment that draws people to used-book stores, where customers enter without a particular title in mind, and instead roam the shelves with the hope of spontaneously discovering a book that beckons them.

“The first iteration of ‘Librería Donceles’ was in September 2013 at Kent Fine Art in New York, when it became the only Spanish-language used-book store in the city – the same will be true in Phoenix,” says Morales. “By rendering visibility to the Spanish language in Phoenix, the installation recreates the unique, intellectually and culturally rich environment of a secondhand bookstore and questions how Spanish is integrated into the broader cultural life of Arizona.

“Pablo Helguera is a leader, if not a pioneer, in the social practice genre,” Morales explains. “’Librería Donceles’ is a tipping point within his practice that places socially-engaged art to the test in Arizona’s current social climate by offering the only Spanish language book store in Phoenix as a functional art project.”

“Although this project was originally slated for our new Brickyard location, Helguera visited in early February to look at the space before installation,” explains Gordon Knox, ASU Art Museum director. “After those conversations, we decided at the artist’s request to move the 'Libreria Donceles' exhibition to the gallery in downtown Phoenix. Our space in Phoenix is better suited for the store-front nature of his installation, and affords several new opportunities for community interaction that could be lost if the project were presented in a more traditional museum setting.”

Visitors to “Librería Donceles” – Spanish-speakers and non-Spanish-speakers alike – will be welcomed in this spirit of community interaction, and invited to a brief consultation with the artist or an associate. Once their interests and “bibliological profile” (as Helguera has described it) have been assessed, visitors will be given suggestions on where to look to choose their book. Only one book per customer will be allowed, in exchange for a pay-what-you-wish donation. All proceeds from these transactions will be donated in turn to the Phoenix Public Library Foundation in support of early literacy programs.

“Pablo Helguera: Chrestomathy” will be on view through June 21, in the Brickyard Gallery at the new ASU Art Museum Brickyard location. It is the inaugural exhibition in the new museum facility located at 7th Street and Mill Avenue, which houses the ASU Art Museum Ceramics Center & Brickyard Gallery.

“’Chrestomathy’ is a bridge across Helguera’s many fine art projects that explores issues of translation, cultural memory and the origins of recorded music as a form of cultural dialogue,” says Morales.

One landmark work that will be included in “Chrestomathy” is Helguera’s 2012 “Rogaland,” a project “made through a process of mistranslation.” The project is based upon the 1936 book “Gamle gardsanlegg i Rogaland,” by Norwegian archaeologist Jan Petersen, which is an account of the excavations of several medieval farms in the Rogaland region of Norway. Helguera, who neither speaks nor reads Norwegian, mistranslated the explanatory captions for the book’s 63 plates into English by conjuring phrases and statements suggested by the images and the imagined sound of the printed words.

“Having Helguera’s work presented in our two locations outside of the main museum highlights the museum’s geographical spread, its community embeddedness and the diverse range of facilities we operate,” says Knox. “This diversity of venue and these very different shows also display the extraordinary breadth of Helguera’s artistic practice.”

Pablo Helguera is a visual and performance artist, whose projects have included a school that traveled from Anchorage to Tierra del Fuego, complete with a portable schoolhouse; the recording of dying languages on wax cylinders; a memory theater; and the founding of the Instituto de la Telenovela. His work has been seen most recently at CIFO in Miami, the 2012 Havana Biennial and the Centro de Arte Reina Sofía in Madrid.

An opening reception for “Pablo Helguera: Librería Donceles” will be held on March 21, with a members, alumni and press preview from 5:30-6:30 p.m., and a public reception from 6:30-8:30 p.m. The artist and the curator will be present.

An opening reception for “Pablo Helguera: Chrestomathy” will be held in conjunction with the Grand Opening for the new ASU Art Museum Brickyard on April 11, with a members, alumni and press preview from 5:30-6:30 p.m., and a public reception from 6:30-8:30 p.m.

Additional programming in conjunction with the exhibitions is being developed in partnership with Performance in the Borderlands, the Puente Movement, Radio Campesina Network, Roosevelt Row, Teach for America and Culture is Life: Women of Color Media Arts and Collective.

“Pablo Helguera: Librería Donceles” and “Pablo Helguera: Chrestomathy” are supported by the Diane and Bruce Halle Foundation, Kent Fine Arts, the Helme Prinzen Endowment and an ASU Diversity Grant, and are organized by the ASU Art Museum, part of the Herberger Institute for Design and the Arts at Arizona State University. To learn more about the museum, call 480.965.2787 or visit

Location/Parking: The museum has three locations across the metro Phoenix area: the original museum on 10th Street and Mill Avenue on ASU’s Tempe campus, the ASU Art Museum Brickyard in downtown Tempe and the ASU Art Museum International Artist Residency Program in downtown Phoenix at Combine Studios. Designated parking is available at all three locations.

Admission: Free at all three locations.

Hours: The ASU Art Museum and ASU Art Museum Brickyard are open 11 a.m.-8 p.m. on Tuesdays (during the academic year), 11 a.m.-5 p.m., Wednesday through Saturday. The museum is closed on Sundays and Mondays.

The ASU Art Museum International Artist Residency Program in downtown Phoenix at Combine Studios is open from 2-7 p.m., Wednesday through Saturday and by appointment for the duration of Helguera’s installation.

Juno Schaser

Event coordinator, Biodesign Institute