June 1, 2020

For years, physicists have pondered the existence of gravitons — microscopic particles believed to transmit the gravitational force. Observing gravitons would verify that gravity has a quantum-mechanicalThe mathematical description of the motion and interaction of atomic and subatomic particles. description. Although the existence of gravitons is widely accepted by the scientific community, finding conclusive evidence to demonstrate their existence has proven to be a challenge in fundamental physics. Now, with a recent contribution from three Arizona State University physicists, an answer to this long-standing problem may be within reach.

In their recent essay, “The Noise of Gravitons,” Associate Professor Maulik Parikh, Professor and Nobel Prize laureate Frank Wilczek and Postdoctoral Research Associate George Zahariade theorized that if gravitons exist, objects wouldn’t simply fall down under gravity, but would shake microscopically — producing a small jitter or noise. If this tiny noise could be detected, it could provide experimental evidence for the existence of gravitons.

For this significant work, Parikh, Wilczek and Zahariade were recently recognized with the top prize from the Gravity Research Foundation — one of the highest awards given for research exclusively on gravity. The Gravity Research Foundation has recognized excellence in gravity research for over 70 years, with previous winners including Stephen Hawking and five Nobel laureates. This is Parikh and Wilczek’s second time winning this prestigious award, putting them in a very small group of individuals who have won the top prize twice.

The trio worked on this project for over two years, often from different continents, but said they didn’t initially set out to delve into this complex question.

“This started with something completely different,” Zahariade said. “We were discussing how to treat a particular problem that had to do with subatomic particles called neutrinos. It didn’t have anything to do with gravitational radiation. It turned out that problem that we were looking at originally didn't lead anywhere and wasn't as promising. Then we started thinking about gravitational waves and somehow we started thinking about quantum gravitation waves. One thing led to another. It was a very weird process in some sense, but very organic in its evolution.”

They describe their approach to this issue as one that is not speculative, but instead grounded in previously existing concepts that haven’t been used to their full potential. In their essay, they note that the study of noise has historically played an important role in several major developments in physics, including the discovery of the cosmic microwave background (the afterglow of the Big Bang) and Einstein’s proof of the existence of molecules.

“The usual way that people have expected quantum gravity to manifest itself has always been through studying black holes or maybe the earliest moments of the universe just after the Big Bang,” Parikh said. “This is a very different approach that says that even here on Earth, where gravity isn't super strong, we might expect to see little jitters or a little noise coming from the fact that gravity is actually quantum-mechanical in nature.”

Although their nearly 30-page paper is still being finalized, they have already received positive feedback from the physics community on the award-winning six-page essay they submitted to the Gravity Research Foundation.

“There's a real hunger for work that brings together gravity and quantum mechanics because it's kind of a big outstanding challenge in physics to bring together these two dominant modes of thought that seem almost to exist in different universes of ideas,” Wilczek said. “I feel that this work is really good and really important. We're getting this early recognition and positive feedback that I think will help draw the attention of the physics world to this investigation.”

After receiving this top honor for their work, the group said they feel motivated to continue pursuing this question from new directions and have already begun working on follow-up projects.

Top photo: An artist's impression of gravitational waves generated by binary neutron stars. Credits: R. Hurt/Caltech-JPL/NASA

Emily Balli

Communications Specialist and Lead Writer , The College of Liberal Arts and Sciences