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Office of News Services
University of Colorado-Boulder
Boulder, Colorado

Contact: 
John Price, (303) 492-2484, john.price{at}colorado.edu 
Joshua Long, (505) 664-0061, josh.long{at}lanl.gov 
Greg Swenson, (303) 492-3113 

Note to Editors: Contents embargoed until 2 p.m. EST,
on Wednesday, Feb. 26.

CU-BOULDER RESEARCHERS CONDUCT MOST SENSITIVE SEARCH FOR NEW FORCES
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University of Colorado at Boulder researchers have conducted the most 
sensitive search to date for gravitational-strength forces between 
masses separated by only twice the diameter of a human hair, but they 
have observed no new forces.

The results rule out a substantial portion of parameter space for new 
forces with a range between one-tenth and one-hundredth of a 
millimeter, where theoretical physicists using string theory have 
proposed that "moduli forces" might be detected, according to the 
researchers.

In string theory, which is considered the most promising approach to 
the long-sought unified description of all known forces and matter, 
everything in the universe is proposed to be composed of tiny loops of 
vibrating strings.

"Our results represent the most sensitive search for new forces at 
this length," said lead author Joshua Long, a former postdoctoral 
researcher in the lab of CU-Boulder physics Professor John Price. Long 
now works at the Los Alamos Neutron Science Center in Los Alamos, N.M.

A paper on the subject by Long, Price, Allison Churnside, Eric Gulbis 
and Michael Varney of CU-Boulder will appear in the Feb. 27 issue of 
the journal Nature.

In order for string theory to work, there must be six extra spatial 
dimensions beyond the three that are observable, and theorists believe 
these extra dimensions are curled up into small spaces. This 
"compactification" creates what are called moduli fields, which 
describe the size and shape of the compact dimensions at each point in 
space-time, according to Price.

Moduli fields generate forces with strengths comparable to gravity, 
and according to recent predictions might be detected on length scales 
of about one-tenth of a millimeter.

"If these forces exist, we now know they have to be at even smaller 
distances than we have measured here," said Price. "However, these 
results don't mean that the theories are wrong. Researchers will just 
have to measure at even shorter distances and with higher
sensitivity." 

The experiment uses two thin tungsten reeds. One of them is moved back 
and forth so that the gap between the two reeds varies at a frequency 
of 1,000 cycles per second, according to Price. 

Motions caused by forces on the second reed are detected with highly 
sensitive electronics. The experiment can detect forces as small as a 
femto-newton, or about one-billionth of the weight of a grain of sand, 
he said.

Price said he will continue conducting experiments to try to measure 
even shorter distances next.

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