Brain Trauma in Iraq
Emily Singer’s article on brain trauma suffered by U.S. military personnel in Iraq underscores the fact that even with recent advances in functional neuro­imaging techniques, brain injuries are difficult to diagnose, owing to the complexity of the brain and of the cognitive functions it enables the healthy adult to perform (“Brain Trauma in Iraq,” May/June 2008). The affected veterans deserve help, all the more so because they are returning to a workforce in which cognitive ability is increasingly valued. Neurology appeals to medical students and other health professionals in search of a monumental challenge, since it demands multidisciplinary expertise while seldom yielding simple solutions. Singer’s article suggests that we need to encourage more health professionals to choose this specialty in the hopes that they will help develop better diagnostics and therapies.
William E. Cooper
Midlothian, VA

On April 17, the California State Senate unanimously passed a bill that will ensure screening of veterans for traumatic brain injury; it is to be hoped that the bill will serve as a model for other states. For too long, the U.S. Department of Veterans Affairs has taken a reactive stance to the problem of TBI. Imaginative research such as that described in Singer’s piece, coupled with proactive screening such as that now legislated by California, will be crucial in mitigating the awful effects of TBI.
Jerome V. Blum
Los Altos Hills, CA

The Wonder of Physics
When I was a boy, I read almost everything I could find about the prospects of atomic energy. Not long after I entered MIT in 1936, Hiroshima became an enduring emotional moment of my life.

Throughout that life, and especially after retirement, I have been reading about the advances in knowledge of subatomic physics. Now, at almost 89 years old, I simply must live long enough to learn what the Large Hadron Collider, which was depicted in the photo essay of your May/June 2008 issue, first reveals.
Martin Antman
Jacksonville, FL

Extraterrestrial Life?
Though entertainingly written, Nick Bostrom’s essay on the search for extraterrestrial life (“Where Are They?” May/June 2008) suffered from lax logic. From the fact that “humans have, to date, seen no sign of any extraterrestrial civilization,” Bostrom concludes that we must be alone in the galaxy. But the absence of evidence is not evidence of absence. There are many potential explanations for our failure to detect extraterrestrials, the leading candidate being that we have only been listening for about 50 years. This means Earth’s “light cone”–the volume of space from which any signal could have reached us–is only 100 light-years across, or a mere 0.1 percent of the diameter of our galaxy.
Wade Roush
Boston, MA

As director of the Future of Humanity Institute, Bostrom does well to whistle in a cosmic graveyard and place all his hopes in one Great Filter–one “probability barrier,” as he puts it, that determines whether a civilization will become advanced enough to colonize space. If that Great Filter is safely behind us, he argues, then the future looks bright. But the filter that does a civilization in may not have to be great. If there can be, instead, many potholes and a few landslides along the road from the collapse of a protostar to the rise of a galactic empire, then chances are that at least a few of them lie ahead of us. Peak oil and global warming come to mind.
Michael J. Sloboda
Hong Kong

Bostrom points to the “vast expense” of the International Space Station as evidence that advanced civilizations are keen to explore space. But if the ISS is expensive, consider the cost of building something able to escape from our star with an excess velocity of (even) 1 percent of the speed of light. And to build it so that it can operate without resupply for a long time. Perhaps the resources of a planet small enough to have inhabitable gravity are insufficient for such a project, neglecting the number of times it would have to be replicated for colonization of a nearby system. Perhaps the propulsion science to reduce this cost does not exist outside of science fiction.
David Korenstein
Wayne, PA

Dubious Recommendations
I enjoyed Michael Schrage’s review of the recommendation engines in use on sites such as Amazon (“Recommendation Nation,” May/June 2008). You may be interested to know that financial trading sites such as OptionsXpress employ similar engines. When I buy puts on Caterpillar and calls on Pepsi, up pops the “Customers Who Bought This Item Also Bought …” window. Other traders can follow my lead and make the same mistakes I do. The thing is, the recommendations don’t distinguish the plays of sly traders from those of dolts.

Since the financial world began imploding last summer and the market has gone completely haywire, these recommendations have only gotten wilder. Together we do not generate the wisdom of crowds. More like major-league bozosity.
James Wish
Medway, MA

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