I was puzzled by one aspect of “The First Monster Black Holes,” Priyamvada Natarajan's article on the oldest supermassive black holes: If there were a substantial number of such black holes in the early universe, observable today at great distances, what happened to them? Would we not see them, and the quasars they produce, nearby in the modern universe?

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Supermassive black holes have been found at the centers of spiral galaxies. Given that they are many times larger than previously thought, is “dark matter” still needed to hold those galaxies together?

Carriere, Miss.

NATARAJAN REPLIES: In response to Ward: We do see monster black holes around us in the nearby universe. Almost every galaxy near us harbors a central black hole, and the brightest ones host the most massive black holes. But these local monsters are no longer feeding on gas, so they do not glow as quasars. Instead they are detected by their impact on the motions of stars in their vicinity, which are sped up. By measuring the speeds, we can infer the presence of the dormant but strong gravitational grip of the black hole and can actually estimate its mass.

To answer Emerick: Indeed, supermassive black holes are found ubiquitously, including at the centers of spiral galaxies. Despite the fact that these central black holes are supermassive, their region of influence is limited: stars eventually overtake them in mass in the inner regions of galaxies and start to dominate gravitationally. Alas, these behemoths are insufficient to hold the rest of the galaxy together—their gravity dominates only a small region. And to explain the rotational speeds of stars in the outer regions of galaxies, we require vast amounts of dark matter.


“Why Fake Operations Are a Good Thing” [The Science of Health], Claudia Wallis's article on sham surgeries used to evaluate operations, omits one of the most significant drivers for physicians to carry out procedures, whether they be surgery or something less invasive, and that is economics. It is not possible for physicians to make nearly as much per hour seeing, counseling or prescribing drugs for patients.

Fort Worth, Tex.


In “The Tribalism of Truth,” Matthew Fisher, Joshua Knobe, Brent Strickland and Frank C. Keil claim that “contemporary political discourse is becoming more combative and focused on winning.” Are we to believe that politics is more combative now than it was during the days of the Whiskey Rebellion, the American Civil War, William Jennings Bryan's “Cross of Gold,” McCarthyism, desegregation, busing, Roe v Wade and the Vietnam War?

Politics have always been combative, and whether it is decided by votes or arrows, the first-place finisher gets the power—with no silver medal for coming in a strong second.

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The authors argue that the world is divided into objectivist and relativist views on answers to moral or political questions and that an objectivist outlook is linked to arguing to win, whereas a relativist one is linked to arguing to learn. It seems to me that a third outlook is possible: that of the objectivist learner. Indeed, the basis of the scientific method is to assume that there is an objective truth or reason behind observable phenomena, which a series of well-designed experiments can elucidate.

An open and frank dialogue about things for which there is no objective truth, such as whether veggie cream cheese is tasty, is another way of learning: opinion learning. The difficulty comes when an objective truth is treated as an opinion, or vice versa. Doing so hampers learning.

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In “[Redacted],” his article on the Food and Drug Administration possibly withholding certain drug trial data, Charles Seife suggests that the FDA may “block evidence of outcome switching and even hide references to a medication's side effects” to protect a pharmaceutical company's competitiveness. But that's not the whole story. For an upper-level director in a government agency, there is also the prospect of a high-paid position, on or before retirement, with the very companies that the agency is mandated to supervise.

Naperville, Ill.


“Are Smartphones Really Destroying the Adolescent Brain?” by Carlin Flora, is a timely and balanced look at research on smartphone usage in adolescents. As the article notes, studies have associated overuse with a number of negative effects in teenagers, but association is not causation.

In addition to the concerns Flora reports, I might note that before the 20th century, the human retina was not exposed to flashes of light as fast as those on any computer screen. It is conceivable that this massive daily exposure to quick flashes could cause interruption of pathways in the growing brain. Studies using advanced brain imaging might provide a convincing mechanism if and how this damage might occur. Further, several years ago Dimitri Christakis of the University of Washington compared groups of newborn mice exposed to simulated TV lights and sound with a control group and found that prolonged exposure diminished the quality of essential survival functions in the exposed group.

Johnstown, Pa.


In “A Universal Flu Vaccine Is Vital” [Forum], Catharine I. Paules and Anthony S. Fauci warn that seasonal vaccines are inadequate protection against a future pandemic flu. But developing a vaccine against all strains is not only vital to reduce the suffering from a pandemic per se. In the U.K., during the winter of 2017–2018, tens of thousands of scheduled operations were postponed because hospitals were being overwhelmed by infections with the current influenza strain (a relatively small number compared with what might be expected from a pandemic). Demography suggests that such problems can only be predicted to increase.

Prestwood, England


David Pogue's article on AI-created art, “The Robotic Artist Problem” [TechnoFiles], seems to miss the value of art altogether. We are interested in the Mona Lisa because of what it tells us about Leonardo da Vinci, about his subject and, more important, about their relationship. A creation by a robot would only be of interest with respect to what we learn about the human engineer who created it because we are social creatures drawn to relationships and the characters in them.

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In “Go Public or Perish” [Science Agenda], the editors decry universities discouraging scientists from speaking to the public. We live in a society that is based on science but is made up of politicians and voters who are largely scientifically illiterate. It is the duty of scientists to help them understand what we know or are learning. We don't need to be salespeople, but we should explain the difference between scientific evidence and sensationalism or denial.

Grass Valley, Calif.