Readers Respond to "Gravitational Waves"

Letters to the editor from the October 2013 issue of Scientific American

Gravitational-Wave Detectors Get Ready to Hunt for the Big Bang,” by Ross D. Andersen, discusses various strategies being studied in the U.S. to develop space-based gravitational-wave observatories but fails to mention the eLISA mission concept, a strong candidate for the European Space Agency's next large mission. eLISA is a descendant of the Laser Interferometer Space Antenna (LISA) mission concept mentioned in the article. Europe has also made a particularly strong investment with the LISA Pathfinder mission, set to launch in 2015, which will demonstrate technological readiness and provide Europe with the opportunity to lead the first space-based gravitational-wave mission. No other competitive concept for such a mission currently exists.

The atom interferometry approach described in the article may be a candidate for future missions, but it is not nearly mature enough to be considered competitive with the eLISA concept.

John Mather
Robin Stebbins
NASA Goddard Space Flight Center

While Andersen's article is entertaining, anyone reading it will come away with a distorted and misinformed view of gravitational-wave astronomy.

To say that LIGO has “limited” ambitions and is a “proof-of-concept mission” for space-based interferometers is simply inaccurate. LIGO and LISA operate in completely different frequency bands and are sensitive to very different classes of astrophysical sources. Each will teach us different things about the universe.

The most serious misrepresentation is the article's portrayal of atom interferometry as a true contender to LISA for a space-based mission. There is no sensible comparison to make between LISA and atom interferometers. LISA-like mission concepts have been studied and peer-reviewed for the past 20 years, with an active and successful program to develop the critical technologies in Europe and the U.S. Atom interferometry is at a much less mature level; conceptual designs are still being investigated and modified. While it is important to pursue these investigations, it is an enormous stretch to go from laboratory practice to a space-based atom-interferometer design with adequate sensitivity to observe even the strongest gravitational-wave sources.

David Reitze
Executive director, LIGO Laboratory California Institute of Technology
Gabriela Gonzalez
Spokesperson, LSC Louisiana State University

In “Russia’s Nuclear Reactors Could Take over the World, Safe or Not,” by Eve Conant, a Westinghouse spokesperson dismisses the need for a core catcher in the company's AP1000 design, noting that aspects of the design preclude a meltdown. This and other quotes from nuclear experts demonstrate an attitude that could well doom nuclear power expansion in the U.S. Nuclear proponents need to understand they can never make a plant 100 percent immune from a catastrophe and must design both to prevent and to mitigate a disaster. Even if a nuclear accident is a low-probability event, it is a high-consequence one.

Neal Friedman
Woodinville, Wash.

This article was originally published with the title "Letters."

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