ADVERTISEMENT
latest stories:
See Inside August 2009

Readers Respond on "The Expanding Universe"

Letters to the editor on PTSD, motion sickness, and more...

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.

Rights & Permissions
Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Scientific American Holiday Sale

Give a Gift &
Get a Gift - Free!

Give a 1 year subscription as low as $14.99

Subscribe Now! >

X

Email this Article

X