LIGO Team Finds Important Constraint to Gravity Waves

By Patricia Daukantas

Scientists associated with the Laser Interferometer Gravitational-Wave Observatory (LIGO) and a separate project called Virgo have refined the upper limit to the background residue of gravity waves that could have been generated billions of years ago in the wake of the Big Bang.

It’s important to note that nobody has actually found gravity waves yet. Researchers have been looking for the “stochastic background” of gravity waves left over from the first few seconds of the existence of the universe. If these waves exist, they could offer a glimpse of physical processes that took place when the very young universe was still opaque to electromagnetic radiation. The non-detection (so far) places constraints on cosmological models and on string theory. LIGO and Virgo researchers reported their finding in the August 20 issue of Nature.

The LIGO project has been featured in plenary talks at a couple of OSA conferences. At CLEO/QELS 2008, David Reitze of the University of Florida (U.S.A.) recounted that Albert Einstein predicted gravity waves in 1916, only to change his mind two decades later. (The audio track and slides from his talk are still available online.) At Frontiers in Optics 2005, OSA’s 89^th annual meeting, LIGO deputy director Stan Whitcomb described how the observatory’s Michelson interferometers could measure length changes no bigger than 10^–18 m.

Likewise, the Italian-French Virgo interferometer is an incredibly sensitive instrument using ultrastable lasers and the most reflective mirror ever built. Both LIGO and Virgo teams are working on second-generation interferometers at least an order of magnitude more sensitive than the current versions.