Quantifying Quandary
In "The Post-Traumatic Stress Trap," David Dobbs reports on a growing number of experts who believe that post-traumatic stress disorder (PTSD) is being overdiagnosed. In support of this argument, Dobbs cites a 1990s study in which researchers asked veterans "about 19 specific types of potentially traumatic events.... Two years out, 70 percent of the veterans reported at least one traumatic event they had not mentioned a month after returning, and 24 percent reported at least three such events for the first time." These memories are assumed to be "new," but it may be that the subjects simply could not bring themselves to put their experiences into words so soon after those experiences occurred and that after some time they could.
John Dunn
Merrick, N.Y

As a staff psychiatrist at the St. Louis VA Medical Center for many years (I am currently in private practice), I think concerns about diagnosis of, and disability benefits for, PTSD can be extrapolated to mental illness in general. Psychiatric disability is challenging for the Veterans Health Admin­istration and the Social Security Administration because the severity of illness fluctuates with few visible manifestations, and physicians are neither trained nor well situated for disability determination—they are often conflicted between pursuing treatment that could eliminate disability and encouraging chronic disability so that their patients can receive benefits. PTSD is a good place to start developing procedures and protocols for disability assessment.
Mohinder Partap
St. Louis

Dark Energy Alternatives
“Does Dark Energy Really Exist?” by Timothy Clifton and Pedro G. Ferreira, posits that the apparent accelerated expansion of the universe could be a misconception caused by our living in the center of a giant cosmic void (in which the expansion rate would vary with position, thus making dark energy unnecessary).

The evidence for the universe’s accelerated or uneven expansion is that distant supernovae look dimmer than expected. But could this dimming be explained by a sparse but uniform haze of individual particles? The cosmic microwave background could also be caused by measuring the temperature and distribution of such a haze.
Bill Manzke
Dublin, Ohio

Another explanation for the supernovae dimming could be that light decelerates over time. If light traveled faster in the past, then it would have traveled farther than we think, making its intensity less than expected.
Joel Sanet
Miami

THE AUTHORS REPLY: What Manzke calls “haze” is usually called dust by astronomers. Lots of dust between supernovae and us could dim the images that we measure with our telescopes. But this would mean that distant supernovae would consistently look dimmer as we looked farther and farther away. We can use this as a test because if we look sufficiently far back, the universe was not accelerating (or, alternatively, the supernovae were not in the void), so there will not be the systematic dimming that a haze would produce. Further, if there were lots of absorption from dust, this would change the spectrum of the light we receive. Astronomers check to see if this is the case.

Hot dust causing the cosmic microwave background is an interesting thought, but it is unlikely to be true. The microwave background radiation is almost perfectly evenly distributed across the sky, and its properties show it was emitted from something in perfect thermal equilibrium. If it were being emitted from dust, it would have a very different spectrum and would be very unlikely to be so perfectly evenly distributed.

Regarding Sanet’s letter, the speed of light having a constant value is at the heart of relativity and has been built into modern quantum theories of the fundamental forces. Nevertheless, there are some researchers who have been looking into the possibility that the speed of light could change on cosmological time­scales. This would have other implications for cosmological problems and has been used by some to try to explain why the universe looks so smooth on very large scales. But it is very difficult to create a theory in which the speed of light can vary. For now, there is a lot of evidence in support of conventional relativity, and so that is the favored theory.

Balancing Fact?
“Finding Balance,” by Brendan Borrell [News Scan], reports on evidence for the theory, posited by Thomas Stoffregen of the University of Minnesota, that motion sickness is caused by poor posture control. Borrell states that Stoffregen hopes to further test his theory by having subjects float in water, where “the human body becomes passively stable, and postural control is no longer an issue,” making motion sickness “impossible.” I am a frequent scuba diver and have been diving with many who get sick while floating on the surface in rough seas. Less common but still frequent are people who get seasick while underwater in mostly shallow depths of around 25 feet when there is “surge” (back-and-forth water movement).
Chris Albertson
Redondo Beach, Calif.

STOFFREGEN REPLIES: Motion sickness while floating on the water is not surprising, as people will try to hold their head above the water. When the head is held out of the water, it is not passively stable. More interesting is people having motion sickness while fully submerged in shallow water that is moving. Moving water could lead to unstable control of the body, especially if people are trying to maintain visual contact with something. In this case, water motion would tend to push the body around, destabilizing the attempted visual fixation.

My proposal for testing our theory is to place people (fully submerged) at neutral buoyancy in calm and stationary water and to show them visual motion stimuli representing things that are effective at making people sick on land. If people get sick underwater but exhibit instability before becoming sick, we would have a confirmation of the theory, together with the disappointing realization that water immersion cannot permit “hard” theory testing after all.

Note: This article was originally printed with the title, "Letters."