Deep in the basement of the Varian Physics Lab in the Engineering Quad is an atom interferometer, an experimental apparatus that could hold the key to confirming Einstein’s century-old prediction of ripples in the space-time continuum.
A ripple in water is visible to the naked eye, but a ripple in outer space is more difficult to detect. Einstein predicted the existence of gravitational waves, ripples in the space-time continuum caused when black holes, stars or galaxies interact. These ‘ripples’ have never been directly detected, but a research project by Stanford physicists in collaboration with NASA may soon change that.
Started in 2004, the Stanford Advanced Gravitational Wave Detector Research Program achieved its first breakthroughs in the field in 2008 and attracted the attention of NASA in 2010. In October, it was awarded a joint NASA Innovative Advanced Concepts (NIAC) grant with NASA’s Goddard Space Flight Center and AOSense, Inc. to further develop the atom interferometry technology. If the preliminary designs show success, the technology can be adapted for future spacecraft missions.
The collaboration plays to each of the participants’ strengths.
“Stanford is great for the basic research, AOSense is great for engineering the technology for practical applications and NASA is great for flying the missions,” said physics professor Mark Kasevich Ph.D.’92, who leads the Stanford research group.
When gravitational waves reach earth their impact is minimal, expanding or contracting the planet by the width of an atom only. The atom interferometer, a type of sensor known as a Gravitational Wave Detector (GWD), could potentially capture and measure these waves for the first time, revealing information about the universe such as when a star dies.
Currently, the only use of the atom interferometer is testing two theoretical predictions of general relativity—Einstein’s Equivalence Principle and the detection of gravitational waves. However, the future prospects of atom interferometry are more extensive.
“It’s an extremely disruptive technology,” said postdoctoral fellow Jason Hogan Ph.D. ’10, who works on the project.
Atom interferometric sensors form the basis of inertial navigation systems in submarines and other autonomous systems such as Google Cars, and have promising applications in climate and extraterrestrial modeling and imaging, ore and oil prospecting and earthquake early-warning systems.
The U.S. military has shown interest in the technology’s potential application in submarine and aircraft sensors, and according to the TechNewsDaily, Kasevich’s lab is working on gyroscopes, gravimeters, accelerometers and gravity gradiometers for the U.S. Department of Defense. But Kasevich is quick to point out that his group’s work on campus is in accordance with University policy banning classified research from being conducted on campus.
Currently, preliminary tests, which promise to be the most sensitive ever performed, are being conducted in the basement of Varian in a 33-foot drop tower. Creating a space version of this technology is still a long away.
Even so, there is a nervous optimism that the efforts will soon pay off. According to the several members of the research group, a successful test would fundamentally alter our understanding of space and the universe.
Assuming the tests go according to plan, there are still many challenges ahead.
“Atom interferometry has only been around for 20 years, so it is still a maturing field,” Hogan said. “As with any maturing field, there are growing pains.”
The feasibility of building an atom interferometer sensor that can fit on a satellite is still at least five to 10 years away. Mission costs are also expected to be high, with estimated costs being north of $1 billion.
However, Kasevich is confident that continued investment will be worth the cost.
“I am excited about the possibilities of this technology,” he said. “And even if our current approach turns out to be incorrect, it is fair to assume that a new technology or approach will emerge from our efforts nonetheless.”