GRAVITATIONAL WAVES
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


RUSSIAN REACTORS
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.


AUTISM EXPERIENCE
In “Intensive, Early Therapy Helps Children with Autism Improve Communication Skills,” Nicholas Lange and Christopher J. McDougle refer to autism as a “disorder” to be cured. But what if children with autism don't see it like this? Perhaps, for them, it is a way of going through the world, neither inferior nor superior to any other.

Gideon Forman
Toronto


ILLUSORY OWNERSHIP
In “Adobe’s Software Subscription Model Means You Can’t Own Your Software” [TechnoFiles], David Pogue laments that large software companies such as Adobe and Microsoft are switching to a subscription model for their programs. Let's not pretend that we have ever owned these applications. We merely pay for a license encumbered with restrictions on installations, inspection and manipulation.

Adam Weber
Pittsboro, N.C.


GUNS AND VIOLENCE
In “Why We Should Choose Science over Beliefs” [Skeptic], Michael Shermer asserts that I have practiced “cherry picking and data mining of studies to suit ideological convictions” in my arguments that private gun ownership reduces violent crime. Like Shermer, my views on guns have changed over time. He ignores that, as I have shown in More Guns, Less Crime (third edition, 2010), the large majority of peer-reviewed studies demonstrate right-to-carry laws reduce crime and background checks do not.

John R. Lott, Jr.
President Crime Prevention Research Center

SHERMER REPLIES: The gun-control issue is one of the most complex I have ever encountered. So much data and so many variables affect the outcome of gun-control laws that one can easily make the data come out either in support of or against such measures. From the studies I have read (and cited in my debates with Lott), such proposed measures as background checks, assault weapon bans and magazine size restrictions could help reduce America's death rate from guns (more than 10 per 100,000), which is almost an order of magnitude higher than that of most European nations. I did read Lott's book. But I also read a scholarly analysis of it called “Shooting Down the More Guns, Less Crime Hypothesis,” which is available for free at www.nber.org/papers/w9336.


CLARIFICATIONS
Renewable Energy's Hidden Costs,” by John Matson [Graphic Science], did not specify the low-end estimate for wind energy's greenhouse payback time, which is less than one year and is more reflective of modern wind turbines.

Gravitational-Wave Detectors Get Ready to Hunt for the Big Bang,” by Ross D. Andersen, asserted that gravitational waves are “impervious to the astrophysical giants in their path”; they are nearly impervious. Gravitational waves are much more impervious than light waves are, but they can be affected by massive cosmic structures.


ERRATA
Russia’s Nuclear Reactors Could Take over the World, Safe or Not,” by Eve Conant, stated that TerraPower in Bellevue, Wash., is developing fast mini reactors and that it tests its prototypes in a Russian facility in Dimitrovgrad. TerraPower's fast reactors do not qualify as “mini,” and it is testing nuclear materials, not prototypes, at the Russian facility. Also, the article referred to VVERs as being housed in a containment building. It should have specified recent VVERs. Furthermore, Finland was described as choosing Rosatom for its next reactor in July. Rather a private Finnish consortium had proposed using a Rosatom reactor for an already approved project.

In “Researchers Aim to Level the Playing Field for Patients Awaiting New Livers,” by Dina Fine Maron [Advances], the key to maps indicating wait times for liver transplants had an error in it. The corrected graphic can be seen at ScientificAmerican.com/liver-transplants.

Why Humans Live So Long,” by Heather Pringle, incorrectly describes the causes and effects of the heat and swelling associated with inflammation. It should have said heat and redness come from an increase in the flow of warm blood to damaged tissue and swelling results when increased vascular permeability causes blood cells and plasma to leak into the affected area.