Chino Hills, Calif.
SHERMER REPLIES: Each of these topics (nuclear energy, fossil fuels, and hydroelectric and wind power) involves complex webs of science, technology, economics and politics. The last two are where an “anti” bias can creep in from the far left. People in that camp tend to oppose anything “unnatural” and favor nature over humans if given the choice. Perhaps instead of “antiscience,” it is “antiprogress.” Whatever you call it, both the left and the right have their biases that go into influencing public policy relating to these energy technologies.
MELTING SPACE DUST
In “Secrets of Primitive Meteorites,” Alan E. Rubin mentions the search for a heating process in the early solar system that would partly melt dust to form the layered chondrules found in meteorites. He laments the problems with competing ideas for the cause, such as supernova shock waves. I am curious about the viability of the idea that nonaccreted grains were accelerated and heated by close encounters with protoplanetesimals, thereby generating the variable heating required.
RUBIN REPLIES: Protoplanetesimals may be only a few kilometers in size; dust grains flying by such bodies would not be noticeably heated. There was a suggestion in the 1970s that chondrules may have formed by frictional melting of dust grains in the nascent atmospheres of protoplanets. The problem with this scenario is that many chondrules contain silicate grains that are unrelated to their hosts (that is, they may differ in mineral chemistry and have a different oxygen-isotopic composition). These “relict” grains are not simply unmelted host chondrule material; they were derived from a preexisting earlier generation of chondrules.
It is more straightforward to assume that some early chondrules were broken by collisions with other chondrules in the solar nebula and that their fragments were incorporated into dust balls that were later partly remelted. An energy source capable of melting just the outer part of a chondrule and not an interior relict grain is required. That is why many researchers prefer flash-heating mechanisms such as lightning bolts.
“Brain Cells for Grandmother,” by Rodrigo Quian Quiroga, Itzhak Fried and Christof Koch, describes splendid research suggesting that small sets of neurons code for single concepts in humans. But an important caveat was not mentioned: much of the evidence comes from studies of brains of patients with epilepsy, and it is a leap to assume that epilepsy does not alter neuronal function of these neurons or of other cells and networks in the brain.
Martin J. Steinbach
Distinguished Research Professor Emeritus York University, Toronto
This article was originally published with the title Letters.