In “Burning Rings of Fire,” Joseph Polchinski explains that according to Stephen Hawking's theory of black holes, when a matter-antimatter pair of particles comes into existence just outside a black hole, one of those particles could go into the hole and the other could be radiated out, which would eventually deplete the hole's entire mass.

Wouldn't it be random whether the antimatter particle or the matter particle of the pair fell into the black hole? If so, then over time, the amount of matter in the black hole annihilated by infalling antimatter particles from spontaneously generated matter-antimatter pairs should be balanced by an equal number of infalling matter particles from such pairs. Therefore, matter-antimatter particle pair formation just outside the horizon of a black hole should have no effect on the hole's mass.

via e-mail

POLCHINSKI REPLIES: Bowman is correct that black holes produce particles and antiparticles in equal numbers. This led Hawking to predict that if a black hole formed from a star made of matter, it would end up converting half of that matter to antimatter. But antimatter still has positive mass and energy, so that part of the story does not change.


Keren Elazari's prescriptions for cybersecurity in “How to Survive Cyberwar” emphasize individual users taking steps to protect themselves. But if the goal is to ensure that each person is a cybersecurity expert, we've already lost the war.

Individuals do not have the market power to “demand that companies make their products more secure,” as Elazari suggests. Large companies must be regulated to ensure that private data are not stored unencrypted and easy to access. Each corporate security breach should be followed up by large punitive damages. Every time Microsoft allows malware to hijack my browser, I should be able to file for, and receive, a token payment of a few dollars.

Redwood City, Calif.


In his article on self-control, “Conquer Yourself, Conquer the World,” Roy F. Baumeister makes a statement about a study on addiction that indicates to me that he has had little experience with what people typically refer to as physical dependence: “The frequently recurring nature of these urges is what makes quitting a challenge. But the addict is not beset by the mythically insurmountable difficulty of resisting an overwhelming desire.”

I hope that he is not referring to the situation addicts are in when withdrawal symptoms crescendo. Nicotine in particular will drive the dependent's executive processes into retreat. Eventually there comes a crisis point. The “grab a smoke” and the “make this stop” situations are completely different. Try not eating for a few days; it's in the same ballpark.

Cary, N.C.


In arguing for a darpa-like approach toward funding educational efforts in “The Case for Education Moon Shots” [Forum], Russell Shilling of the U.S. Department of Education cites a study in which “97 percent of the CEOs of major American companies identified a lack of science, technology, engineering and math (STEM) skills among the national workforce as a problem for their businesses.”

As a lifelong educator (now involved in human resources consultancy within the field), I am sick and tired of business organizations advocating for higher-quality outputs from the education sector but wanting someone else (that is, the government) to make the investment. Even though many of these organizations will continually argue for less government intervention on a range of issues, they turn into a socialist collective when it comes to education and training.

No sustainable business model will deliver a dividend without investment. If businesses want to the change the equation in relation to STEM education, then their investment is part of that equation.

Bentley, Western Australia


Each time I read about the progress of driverless cars in articles in your magazine such as “Driverless Tech Inches Ahead,” by Corinne Iozzio [Advances], I wish I could take the design teams on a tour of the roads around where I live in southeastern Pennsylvania. Some of the roads are so poorly maintained that there are no lane markings anymore.

During the past two winters, there have been huge potholes, with drivers weaving to avoid the worst ones. Are the new driverless cars going to have real-time pothole evaluation and avoidance? And when plows pile snow up at the edge of roads, it is often not clear where the curb is.

Maybe these cars will be sold only in states that meet a certain level of infrastructure maintenance, but if the design teams want to work in real-world, worst-case conditions, they need to pack up their tent and move their cozy operations away from the West Coast and join us here in the Northeast!

Blue Bell, Pa.


I agree with Steve Mirsky's conclusion in his Anti Gravity column on antivaccine sentiments among parents and politicians [“Immune Reaction”]: it is important for children to be immunized against disease.

It is interesting to look at the developing world, where parents are begging for this opportunity and willing to walk miles to make sure their children get vaccinated. Fortunately, Gavi, the Vaccine Alliance, was recently fully funded to immunize 300 million children in the developing world by 2020, which will save five million to six million lives. Of course, donors such as the U.S. must keep their pledges to ensure this happens.

Snohomish, Wash.


Atom Smasher Amps Up,” by Clara Moskowitz [Advances], includes a photograph of a resistive sextuple magnet as part of an article about the Large Hadron Collider at CERN near Geneva. The device, which was being tested at CERN, is not part of the LHC.


A Flare for Cancer,” by Joshua A. Krisch [Future of Medicine 2015], incorrectly states that spheres have more surface area than other shapes.