Professor C.D. Hoyle
has secured a $117,000 National
Science Foundation grant to
explore the nature of gravity
with his students in HSU's
Gravitational Research Laboratory.

Student Holly Leopardi uses the Department of Physics & Astronomy’s torsion pendulum

Student Holly Leopardi uses the Department of Physics & Astronomy’s torsion pendulum, which is used to measure gravity at infinitesimal distances.

STUDENTS AND PHYSICS Professor C.D. Hoyle hope to capture crucial evidence of what lies behind the origins of the universe, its accelerating expansion, and whether Einstein's famous idea of gravitational force or quantum mechanics is the more accurate model of nature.

In a series of experiments that will continue through 2013, HSU undergraduates will put gravity on trial across distances half the thickness of a human hair—10-20 microns—to see if gravitational force breaks down at extremely short distances. If it does, Einstein's celebrated theory might take second place to more recent string theory, which attempts to meld the theory of relativity and quantum mechanics into a single theoretical model of the universe. Quantum mechanics describes the structure, motion, and interaction of subatomic particles mathematically.

"In a nutshell, the purpose of this research project is to conduct a world-leading test of gravity at extremely short distances and more precisely than has ever been done before," says Hoyle, principal investigator at the Gravitational Research Laboratory. "It may produce evidence that will either confirm or refute certain aspects of string theory."

String theory is a unifying concept of physics which attempts to "explain everything in the universe" based on the extremely minute scales of quantum mechanics—atoms, molecules, magnetism, electricity and so on. (Einstein also strove to interlock all of nature's forces in one holistic explanation.)

What Hoyle and his students are searching for is experimental evidence that might help sort out the mathematical inconsistencies between the theory of relativity and quantum mechanics. It should be possible to integrate the two, synthesize them, in a single consistent model that describes the universe.

To date there is no experimental evidence for string theory that can be measured and reproduced over and over again in the laboratory. And the idea presents complications of its own. In Hoyle's words, "it predicts a whole bunch of weird things like extra dimensions and multiple universes and the fact that gravity should behave differently when particles are very close together."

Working at the cutting edge of laboratory physics, Hoyle's students have built their own highly sensitive torsion pendulum that measures infinitesimal alterations in gravitational pull. A torsion pendulum rotates rather than swings and is akin to hanging a dumbbell from a fiber. The degree of twist in the fiber measures the strength of gravity. Researchers gauge whether the predictions of gravity's behavior are correct or whether new effects are at work.

Although a torsion pendulum is straightforward in concept and function, taking accurate tabletop measurements of gravitational forces is a demanding task. First of all, Hoyle's students will be measuring distances that are almost impossibly small. The pendulum's fiber may twist by an angle of no more than a nano-radian. How small is that?

Hoyle offers this illustration: imagine a lone pea on the ground in San Diego. The angle subtended by that pea all the way from the city to the Gravitational Research Lab in HSU's Science A Building is approximately one nano-radian.

Another thing: you don't go down to the local hardware store to buy a torsion pendulum that functions at the one-micron level. Hoyle's physics students are building their project from scratch. They are putting in a lot of time developing the required hardware and techniques. "You can't even buy the needed optical system to measure nano-radians of deflection," Hoyle says.

So his students are picking up valuable experience in designing and building optical systems of their own. They are making their own electronic circuits to "read" and record physical and environmental parameters in the lab such as temperature, magnetic fields, and seismic activity. They are getting hands-on experience with computer-aided design, software programming suites, software/hardware interfaces, data analysis, and science displays.

"There is so much groundwork to be done," says physics student Holly Leopardi. "You don't just walk into the lab, push the start button and begin analyzing data. You have to build the whole thing first."