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See Inside Scientific American Volume 310, Issue 6

Readers Respond to "The Proton Radius Problem"

Letters to the editor from the February 2014 issue of Scientific American


February 2014
Credit: Scientific American

PERCEPTIVE POULTRY
In “Brainy Bird,” Carolynn “K-lynn” L. Smith and Sarah L. Zielinski discuss evidence that chickens are more intelligent than has been supposed.

Yet the complex behaviors that the authors present as evidence do not support the claim that chickens have advanced cognitive skills. They could just as easily be explained by the blind guidance of genes. For example, the absence of evidence for individual variation in the described chicken actions makes a stronger case for species-specific behavior through natural selection than for mammalian-level cognition.

But each species does deserve its own level of ethical treatment consistent with its cognitive abilities. There is no question that keeping animals cooped up is bad because it induces stress.

James Luce
Peralada, Spain

I would be curious to know if commercial broilers and egg layers would perform as well as the birds used in Smith's behavioral studies. Modern broilers appear to have significantly smaller normalized brain masses than lines that have not undergone such strong selection for meat production.

Carl J. Schmidt
Department of Animal and Food Sciences University of Delaware

Smith and Zielinski claim that the genetics of birds raised for their meat somehow naturally shortens their life span because if they were allowed to continue to live, they would develop a host of age-related diseases. This is false. If Cornish game hens are allowed to grow to maturity, they become healthy, huge chickens.

Russell R. Burton
San Antonio, Tex.

THE AUTHORS REPLY: In response to Luce: Whereas genetic programming or innate responses can explain some animal behaviors, the extent of individual flexibility exhibited by fowl in their calling to raise an alarm or indicate food refutes them. With alarm calls, for example, the behavior changes in response to moment-to-moment variation in the bird's context and audience—who is present, their relationship to the bird, the caller's safety, the individual's status within the group. All these things require mental architecture to take into consideration the aspects of the specific event and to select the appropriate action. An innate response is unlikely to be so versatile. We do, however, agree that higher cognitive function is not a requirement for an animal to deserve compassionate treatment.

Schmidt is absolutely correct about the reduction in brain mass in broilers. Layer hens appear to exhibit many of the same behaviors observed in the chicken strains used in the studies cited in the article. This question remains to be tested, however.

Burton is right about the life spans of Cornish game hens. That strain is, however, much smaller than other kinds of meat chicken, which do suffer major health-related issues as they grow.


PROTON SIZE
In “The Proton Radius Problem,” Jan C. Bernauer and Randolf Pohl state that they have found wildly different values for the proton radius from two different experiments.

Is it possible that the measurements are different because the proton is not perfectly spherical? Perhaps the experiments might have exposed this.

Bob Drwal
South Barrington, Ill.

Could the close interaction of a muon passing the proton in muonic hydrogen cause a tidal wave at the surface of the proton, changing the form of the proton locally so that a lesser radius is measured?

Dirk Kronemeijer
Havixbeck, Germany

Is it possible that the central density of the muon wave function in muonic hydrogen is high enough to probe the quark structure of the proton?

Stanley Friesen
Frederick, Md.

To say that a proton has a clear-cut radius implies that it has a well-defined edge. But clearly, particles are not solid things with discrete edges.

Ed Miller
Oberlin, Ohio

THE AUTHORS REPLY: To first address Drwal's question: The proton does not have to possess spherical symmetry but could be, for example, a “prolate,” a spheroid in which the polar axis is greater than the equatorial one. Both experiments average over all orientations, however, so the proton-charge radius measured in both is not affected by proton deformation.

The muon indeed changes the shape of the proton, as Kronemeijer suggests. This so-called proton polarizability expresses how easy it is to deform the proton. The radius result is corrected for such an effect. The effect's absolute size is still debated, but it seems unlikely that it can explain the discrepancy in our measurements.

Regarding Friesen's query: The muon wave function averages over the entire proton. Even in the scattering experiment, the momentum transfers are so small, and hence the wavelength so large, that one cannot resolve individual quarks.

Miller is correct. The proton is more of a fuzzy ball, with an approximately exponentially decaying charge density. The quantity that is measured in both experiments is the square root of the average of the radius squared, weighted by the charge density. This definition is mathematically well defined and useful in theory. In practice, about two thirds of the proton's charge is contained in that radius.


FEATHERED FEEDING
“Living Claw to Mouth,” by Jason G. Goldman [Advances], reports that a British study found that songbirds scout for food in the morning but do not eat it until the afternoon. American birds must have developed different eating habits than European ones. When we put out food on our deck just before dawn, it is gone within 10 minutes. Then it sits until almost the next dawn.

Herb Stein
Washingtonville, N.Y.

GOLDMAN REPLIES: Most backyards are limited to a single feeder or perhaps a few feeders at a single location. But the study in question instead involved a large array of 101 feeders spaced widely apart across an entire forest, which provides a much more complete picture of bird behavior.

In addition, one of the most important aspects of the study was that it focused on a population of birds relatively free from human interference. Garden songbirds are able to rapidly adapt to changes in their environment caused by humans. If homeowners are providing food every day, then those birds can use a different foraging strategy than they would in a habitat where food sources are less predictable.


SUPERIOR METRICS
You should be ashamed to publish the “Politics of the Metric System,” an excerpt of an 1864 article on then British resistance to the system, in the 50, 100 & 150 Years Ago column, compiled by Daniel C. Schlenoff.

More than two centuries after France introduced the system in 1799, almost the whole world uses it exclusively. That is, except for the U.S., Liberia and Myanmar (Burma)—and Scientific American itself!

Herzel Laor
Boulder, Colo.

This article was originally published with the title "Letters."

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