In “The Exercise Paradox,” Herman Pontzer asserts that greater physical activity does not allow people to control weight. He goes on to describe studies on how the human body burns calories that help to explain why this is so.

But in one of these studies, “couch potatoes” expended an average of around 200 fewer calories a day, compared with moderately active subjects. A difference of 200 fewer calories a day equates to more than 20 fewer pounds a year. Year after year after year, that really adds up.

Tolland, Conn.

Cyclists participating in the Tour de France are said to ingest more than 5,000 calories a day. According to Pontzer's article, this would seem to be way too much. So why do they do it? And why don't they become obese?

via e-mail

PONTZER REPLIES: In response to Azevedo: A 200-calorie-a-day difference could certainly affect weight. What we see across studies, though, is that individuals who burn more energy per day are not any less likely to gain weight than those with lower energy expenditures—our bodies do a remarkably good job in matching intake to output. Yet with daily energy expenditure being so difficult to change, it is much easier to overeat than to underexpend, meaning we should probably focus more on diet to prevent obesity.

Regarding Bräu's question: Events such as the Tour de France, the Ironman Triathlon and various marathons are too short and extreme for the body to adapt to them. Athletes in those events eat prodigious amounts and often still lose weight because their bodies burn more than 5,000 calories a day. These feats fall well outside the requirements of daily life for even the most active populations, and thus they are not truly sustainable over the long term. Racers need significant recovery periods, and the metabolic demands of these events may be one reason that some athletes are drawn to performance-enhancing drugs that support high expenditures.


In “Imagine No Universe” [Skeptic], Michael Shermer explores attempts to answer the question of why there is “something rather than nothing” in the universe and the difficulty in defining “nothing.”

Why do we assume we have the potential brainpower to ever explain such mysteries? Could there not be aspects of the universe our human intelligence is unable to reach at the present time? Consider this: A dog travels in your car. Can it ever understand motor mechanics or geography? Your cat watches television. Has it any knowledge of electronic communications?

Why do we, just one of the species in existence, assume our brains are capable of knowing why we exist and what there is beyond infinity? This should not inhibit us in striving to understand the purpose of life, and so on. But we should accept that it may take a millennium of human development to know everything. Perhaps then we will become gods!

Essex, England

SHERMER REPLIES: I agree that we should not assume we have the cognitive capacity to explain such mysteries, and there are even those who call themselves “mysterians” who believe that hard problems such as consciousness may be inexplicable because of such cognitive limitations, so perhaps “nothingness” and “God” are as well.

As for the coming millennium, in my next book, Heavens on Earth, I suggest that in the far future, civilizations may become sufficiently advanced to colonize entire galaxies, genetically engineer new life-forms, terraform planets, and even trigger the birth of stars and new planetary solar systems through massive engineering projects. Civilizations this advanced would have so much knowledge and power as to be essentially omniscient and omnipotent. What would you call such a sentience? If you didn't know the science and technology behind it, you would call it God, which is why I postulate that any sufficiently advanced extraterrestrial intelligence or far future human is indistinguishable from God.


“Novel Math,” by Mark Fischetti [Graphic Science], discusses studies of works of fiction that found, respectively, limited variations of emotional arcs and fractal patterns in the lengths of sentences.

I am a high school English teacher who has taught the works of Kurt Vonnegut for about the past 20 years. I am certainly not a brilliant math person, but I am fascinated by the mathematical connections with art and the universe. The second I began reading the article, I started laughing and flashed on my man, Kurt.

In the late 1940s he (probably facetiously) proposed a master's thesis at the University of Chicago on the graphing of stories. His proposal was rejected, but the graphs of stories show up in his work Palm Sunday, which is hilarious (though maybe only to English majors). He also discussed the subject in a short lecture segment that can be seen at www.youtube.com/watch?v=oP3c1h8v2ZQ.

Daegu High School
Daegu, South Korea


In “Deep-Space Deal Breaker,” Charles L. Limoli discusses how new studies show that cosmic radiation might damage astronauts' brains more than we had previously thought.

Although I agree that cosmic radiation is a difficult and challenging issue for deep-space travel, it is by no means a “deal breaker.” It is “merely” an engineering problem, albeit a hard one. In the late 1800s some assumed that powered flight for humans would not be possible. Yet given the numerous examples from the natural world, others instead saw human flight as an engineering challenge that could be overcome.

Limoli touches on a couple of strategies in early stages of development for protecting humans in space, but he notes that none of these efforts “has the potential to be a cure-all. The best we can hope is to reduce, rather than eliminate, damage.” I can imagine many methods to better shield astronauts: we could invent nanobots that will quickly repair the damage or magnetic fields that will surround spacecraft to deflect the radiation in a manner similar to how Earth's magnetic field protects us on the surface. We don't know which of these or other potential solutions will eventually prove practical, but there is no doubt that with effort and a dose of logical imagination, engineers can indeed solve the issue.

St. Paul, Minn.

EDITORS' NOTE: In “Pop Goes the Universe,” Anna Ijjas, Paul J. Steinhardt and Abraham Loeb criticize the inflationary theory of the universe. A response to that article by Alan H. Guth and David Kaiser, both at the Massachusetts Institute of Technology, Andrei Linde of Stanford University and Yasunori Nomura of the University of California, Berkeley, is available at www.ScientificAmerican.com/inflation-response.