Hidden Switches in the Mind,” by Eric J. Nestler, discusses epigenetic changes—alterations to how genes behave that do not affect the information they contain. Is it possible that such changes are at least partially responsible for bacteria becoming resistant to various drugs, given that the changes are passed on to daughter cells? If so, the changes would provide yet another way to overcome resistance to various drugs. Instead of looking for an entirely new antibiotic, it might be simpler to find a way to undo the epigenetic changes and restore the bacterial susceptibility to the drugs we already have.
Ted Grinthal
Berkeley Heights, N.J.

Editors’ note: The author, not being a microbiologist, referred this question to Rich­ard Lo­sick, whose laboratory at Har­vard University focuses on bacteria. Losick’s reply follows:

Epigenetics does indeed contribute to antibiotic resistance in bacteria by giving rise to bacteria known as persisters. Indeed, epigenetic mechanisms were initially discovered in bacteria, although the mechanisms are quite different from the histone-based ones described in the article (bacteria do not have histones). Persisters are bacteria that survive antibiotic treatment without having acquired a resistance mutation. Instead they have reversibly entered a state in which they are less susceptible to killing by the antibiotic than other genetically identical cells in the population. Indeed, if we could devise drugs that blocked entry into the persister state, such drugs could contribute to the effectiveness of antibiotic therapy.

Whereas David Weinberger’s speculations about predictive abilities of big data–crunching models in “The Machine That Would Predict the Future” are intriguing, planners and social scientists aren’t about to step aside just yet. As an example of “big data,” IBM’s Watson has impressive computing power when the question is clear, but important societal questions rarely are. For the near future, we don’t see large computing power suc­cessful­ly responding to the simple questions facing modern societies with complex answers: For instance, how do you motivate Asian governments to take action on climate change? How do you reduce poverty? How do you get people out of their cars and onto public transit?

The challenge to prediction today is successfully integrating philosophy and the social and behavioral sciences with the physical sciences and engineering. Just witness the failure of climate scientists to advance the climate change agenda, resulting, in part, from social, behavioral and political scientists being left out of the conversation. With multidisciplinary cooperation as a starter, “big data” might be better equipped to predict the future.
David R. Hardy

I would suggest that there is an insurmountable hurdle to physicist Dirk Hel­bing’s work, described by Weinberger, in trying to make a “computing system that would effectively serve as the world’s crystal ball”: the discrete architecture of the natural world. Helbing’s background is apparently the modeling of highway traffic, which has a basic linear architecture. Road traffic acts like a hydraulic problem, where small particles can flow into one another continuously. My background is railroads, which couldn’t behave more differently. On almost every level, their options and costs are effectively discrete. Railway costs are highly correlated, irregular, stepwise functions. They are dynamically unstable as they interact. That is, these costs are complexly unique lookup tables, not continuous equations, which means that highway and other linear models cannot be used rigorously (although people do try to use them).

So is the mathematical architecture of the world more like a road network or a rail network? If the latter, then it is mathematically impossible to predict the future. It would be a world ruled by discrete events, including black swan events. As a quote attributed to mathematician Benoît Mandelbrot put it, “Even though economics is a very old subject, it has not truly come to grips with the main difficulty, which is the inordinate practical importance of a few extreme events.” God does, in fact, play with dice in the natural world.
Tom Erickson
Wallingford, Pa.

Charles Q. Choi’s reportage of Rouslan Krechetnikov’s study on the physics of keeping coffee from spilling, as reported in “Fluid Dynamics in a Cup” [Advances], is interesting. But Choi should go, at peak dinnertime, to a restaurant known for very good service. Watch the wait staff move quickly across the floor. When they are carrying liquids, the rule is long stride, short stride, long stride, short stride.

You can walk briskly and not spill things if you’re careful to break up your rhythm as you move. I learned that the first day on the job as a waiter in the 1960s.
Rod Roduin
via e-mail

I believe a solution for spilling coffee was already discovered 35 years ago on the University of California, Berkeley, campus. At the time, the student union lacked lids for coffee, and inevitably some of the precious brew would slosh out before I reached my 8 a.m. class. Realizing the problem was a buildup of vibrations until a large “beat” frequency caused the liquid to spill, I tried breaking them up by randomly moving the cup side to side and fore and aft as I walked. Eureka! No constant motion, no beat frequency and no coffee spilt.  
George Cooper
Alameda, Calif.

This Way to Mars,” by Damon Landau and Nathan J. Strange, says that “for a test flight, astronauts steer the vehicle into an orbit that almost always remains above the south pole of the moon.”

As a retired orbit mechanic, I see this statement as impossible unless there is a Lagrangian point above the lunar south pole. A satellite can remain stationary only over the body’s equator.
Richard Bobrow
Westminster, Calif.

Landau replies: I appreciate Bobrow’s observation that the stationary points in the earth-moon system are only in the earth-moon plane.

When writing, however, we were sure to put in “weasel words” where we did not want to open up a can of worms. Here “almost always” is meant to be taken as “not all of the time.” We were alluding to a very elliptical orbit with a low perilune “above” the north pole and apolune “above” the south pole. In our orbit in the earth-moon rotating frame, we are within view of the south polar region 96 percent of the time.