Keep on Truckin'?
I very much enjoyed Eric Haseltine's article, "Twenty Things That Will Be Obsolete in 20 Years" [October]. I must disagree, though, with number 18, the internal-combustion engine. I would like to see internal-combustion fade into antiquity, but what would replace it? The problem with electric vehicles has always been that of energy density. Batteries just don't have the energy/volume ratio or the energy/weight ratio to compete with diesel fuel and gasoline. My judgment is that they never will, although an electricity-producing fuel cell might eventually come close. In particular, I find it hard to imagine fuel cells as a viable energy source for commercial trucks. Long-haul trucking may have dwindled in Europe, but it is not likely to do so in the United States in the next 20 years. Europe does not have the vast distances of the American Midwest and West; its rail system actually runs on time for freight service; and water freight is available to many of the continent's population centers. Trucks hauled 70 percent of all freight shipped in the United States in 1998; the reason is cost and on-time delivery. America's railways have effectively given up where wide coverage and timely delivery are concerned they are buying trucking companies. And water freight is not available to most of the United States.
When some new technology allows 80,000-pound trucks to move without internal combustion, I will cheer along with everyone else. But trucks will remain, unless we plan to build a railway, runway, or canal down every street in the country.
Eric Haseltine responds: I didn't intend to suggest that internal-combustion engines would completely go away, only that fully electric or hybrid internal-combustion engines would dominate. My guess is that hybrid fuel-cell/internal combustion will be the norm. Fuel cells and possibly super-capacitors, not batteries will be the enabling technology. As for trucking well, when diesel fuel costs $4 to $5 per gallon, the economic incentives to reenergize our rail system will be substantial. And last time I looked, Europe wasn't all that small. The distance overland from Lisbon to Oslo is more than 3,600 miles.
Neptune in the Sky With Diamonds
I love reading the latest discoveries about the solar system, and your article on Neptune is no exception ["Neptune Rising," September]. One aspect of the article, though, leaves me confused. You state that "a spherical shell of water sloshes around [Neptune's] solid core." How can liquid water possibly exist in an environment so hot and so pressurized that hydrogen acts like a metal and raw diamonds might be formed? Wouldn't the water have vaporized long before it reached the center of the planet?
Heidi Hammel, senior research scientist with the Space Science Institute in Boulder, Colorado, responds: The water is not at the core but is thought to be in a shell that encircles the core. Neptune's visible atmosphere has pressures similar to those near Earth's surface (about 1 bar), although temperatures are bone-chillingly colder, roughly 60 Kelvin (-351 degrees Fahrenheit). But if one were to go deep enough to reach, say, a crushing 50 bars, the temperature would rise to a balmy 275 K (35 F). At even greater depths the water would eventually become liquid, thus forming the "sloshy" ocean that is thought to drive Neptune's magnetic field.
Mark Sincell, in his article "Neurocomputers" [Future Tech, October], says that individual synaptic connections "can have as many as 200,000 channels." That description is correct, but Sincell's claim that "every channel carries information about a different aspect of cell life, a bit like the way your television simultaneously receives cable programming on different channels" is not. A single synapse may possess several different types of ion channels, each of which is functionally distinct. But even these types of receptors, if thought of as separate "channels" for the transmission of information, do not carry signals that are as distinct as the signals from different cable TV stations. They are rather intimately related to one another and, as a consequence, their information is partially redundant. A conservative estimate of the complexity of signaling at a synapse would place it well below even a single channel of cable TV.
Center for Neuroscience and Institute of Theoretical Dynamics University of California at Davis
Mark Sincell responds: I wasn't trying to say that ion channels are as complex as television channels, or even that they transmit information in the same way. They obviously do not. I was simply using a familiar object (cable TV) as a metaphor to make the complexity of microscopic intercellular communications more comprehensible.
Liver Free or Die
"Gut Instincts" by Meredith F. Small [The Biology of . . . Morning Sickness, September] postulates that it is advantageous for women early in pregnancy to avoid animal food, because during this time the embryo's organs are developing and susceptible to malformation. The article suggests that meat was most likely to expose the embryo to parasites and pathogens. There was, however, a more compelling biological reason for our pregnant ancestors to avoid meat.
While vitamin A is beneficial to almost everyone, it has the potential to be a potent teratogen that can cause major malformations in exposed embryos. In a single meal containing liver, a pregnant woman could possibly consume a teratogenic dose of vitamin A. Neither spices nor cooking would offer much protection against this risk. Evolution selects for survival strategies that work, some of which may not be highly targeted, so a pregnant woman's aversion to meat may exist simply because it encompasses an aversion to liver.
Kenneth J. Rothman
Lynn L. Moore
Assistant Professor, Preventive Medicine Boston University
Corey Powell's article, "Twenty Ways the World Could End Suddenly" [October], is not good science. Several of the risks would cause some deaths but certainly not end the world. Rather than simply playing on people's fears, risks should be placed in context. An asteroid impact that destroys humanity is likely to happen within the next 65 million years. Risk per year: under one millionth of one percent. What presents the greatest risk of extinction? From your list, I believe it's global warming. Please shed more light than heat.
Corey S. Powell responds: I used "end of the world" metaphorically, to mean the end of human society or our species. That level of disaster struck me as sufficiently apocalyptic to justify the title of the article. In many cases it is difficult or impossible to quantify the risk, but where there were relevant data I tried to include them. For instance, a civilization-disrupting asteroid impact arrives every 250,000 years. Averaged over time, deaths as a result of asteroid impacts are more likely than from airplane crashes. The probability that all of humanity would be wiped out by an asteroid in the next 20 years is about a million to one. Many people play the lottery thinking they can beat those kinds of odds.
In our October 2000 article "Twenty of the Greatest Blunders in Science in the Last 20 Years," the estimated number of deaths attributable to the Chernobyl disaster varies far more widely than the figures we cited would indicate. The disaster was not the result of a "runaway chain reaction" but of a runaway nuclear reactor. And although, according to NASA, the cause of death of the Challenger astronauts cannot be positively determined, they were not "incinerated." The announcement of the Clinton Administration MTBE ban was March 2000, not March 1999.