Readers Respond to the July/August 2023 Issue

Letters to the editors for the July/August 2023 issue of Scientific American


Scientific American, July/August 2023


Phil Plait’s article “Our Sun Was Born Far, Far from Here” [The Universe] was informative as to how our nascent Sol might have formed, and its anthropomorphic analogy of the sun having far-distant and widespread “siblings” was quaint. But to use this analogy, young stars do not spontaneously go wandering off like runaway adolescents. It would have been helpful for the article to include some discussion of how these sibling stars might have become so widely dispersed in our galaxy.


PLAIT REPLIES: Stellar clusters are held together by the combined gravity of all the stars in them. Over time, as the stars move around and interact gravitationally, more massive stars fall to the center while lower-mass ones move outward. As they move farther out, these lower-mass stars are held less tightly by the cluster. The overall gravity of the galaxy can then pull them out. Also, stars in a cluster are packed rather tightly together. So it’s common for there to be gravitational interactions among stars, with lower-mass stars like our sun getting flung out after a close encounter.


“Dangerous Discomfort,” by Terri Adams-Fuller, discusses extreme warming in urban areas caused by the “heat island” effect. There was a relatively reflective surface on the paved street where I live until someone decided the entire neighborhood needed to be retarred. Now it’s all black and hot. The question is how to get policy makers to prioritize strategies to make cities cool.

Dark roofs compound the problem. I’ve reroofed my house with light-colored, highly reflective shingles, and the reduction in air-conditioning is considerable.



I was fascinated to read “Synchronized Minds,” Lydia Denworth’s article about how humans’ brain waves synchronize when we interact. The article focuses on positive effects of this brain synchrony, but I wonder whether it also comes into play in things such as groupthink and mob behavior. If everyone’s brain is working the same way, does that limit what the group sees as possible options?


DENWORTH REPLIES: This letter raises an interesting question that researchers are beginning to address. One 2021 study in the Proceedings of the National Academy of Sciences USA found that shared political ideology led to increased neural synchrony when participants viewed partisan debates. But the effect was moderated by a willingness to tolerate uncertainty. And in another study of perceived in-groups and out-groups in NeuroImage that year, more synchrony was seen among members of the same group (in this case, among Israelis or among Palestinians) than across groups.


“Parrot Invasions,” by Ryan F. Mandelbaum, couldn’t be more timely here in San Francisco. The city just picked our local “wild” parrot as its official animal, giving the bird a narrow win over the sea lion. The article describes such birds as “innovators, problem solvers, socializers and survivors,” which is also a very apt description of San Franciscans.



“Seeing Numbers,” by Nora Bradford [Advances], includes an illustration that presents two groups of dots. The caption poses the question “Which has 50 dots, and which has 51?” You left us to guess the answer or count the tiny dots for ourselves. Readers of Scientific American, like insects, are far more cognitively complex than previously thought and can feel frustration and pain. Henceforth, please treat us with greater consideration.



Thank you for “Star Power” [June], Philip Ball’s fascinating, hype-free article about the future of nuclear fusion power. One question remains: How do engineers get the heat out of the tokamak, the most popular fusion-reactor design? A conventional power plant does this by pumping high-pressure water through a heat exchanger, which turns it into steam, which drives a turbine. This key step in the power-generating process—generating the power—is not addressed in the article.

Ball notes that ITER will be the first fusion reactor that will demonstrate continuous energy output at a power plant’s scale. How will it boil enough water to drive a 200-megawatt turbine when the exhaust from its fire is 150 million kelvins?


Ball describes underway fusion-reactor projects that are, overall, big and expensive, such as ITER in France, which has a 23,000-metric-ton research reactor and will likely cost more than $20 billion.

Lockheed Martin’s Skunk Works division is developing compact fusion reactors small enough to power jet flights and other aircraft, ships and small cities. Enormous fusion projects often are abandoned because of unanticipated delays and cost overruns spiraling out of control. The compact fusion model is likely to be cheaper and faster to develop because such test reactors can be built in months. Smaller approaches to fusion may be more likely to succeed in the long run and to result in a workable device much sooner than the gargantuan projects.


BALL REPLIES: Regarding Wilson’s question: For tokamaks, heat exchange is most likely to be done via water cooling. That is the plan for ITER. It is true that the challenge of drawing off heat from a plasma at many millions of kelvins to heat water to perhaps a couple of hundred degrees Celsius is significant. But the principles of this engineering problem have been figured out. For EUROfusion’s DEMOnstration Power Plant (DEMO) prototype, the current plan seems to be to use a lead-lithium alloy surrounding the fusion chamber as an intermediate heat-exchange blanket. The lithium will also absorb the neutrons emitted by fusion and be converted into tritium fuel—it is a so-called breeding blanket.

To answer Brenner: I don’t think the development of larger versus smaller reactors is generally regarded as either/or. As I say in my article, ITER is not intended as a commercial reactor or even a prototype for one; it is being developed to solve engineering challenges. Smaller reactors such as DEMO and the U.K.’s Spherical Tokamak for Energy Production (STEP) will serve as prototypes for actual plant-scale devices. Even smaller ones like those being developed by some private companies might also become viable: some of them have discussed devices of around 100 megawatts, small and compact enough to be used for container ships.


In “The Most Boring Number,” by Manon Bischoff [June], the chart in the box “A Gap of Judgment” depicted incorrect numbers in the y axis. The corrected illustration can be seen at

“A Stratospheric Gamble,” by Douglas Fox [October], should have described the contemplation of a “scenario in which individual countries … begin injecting aerosols unilaterally” as separate from comments made by Katharine Ricke.


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