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Fueling the Controversy Regarding your July story about Geoffrey Ballard and the future of hydrogen-fuel-cell vehicles [Discover Magazine Awards, Energy]: Advances in the real world must be economically justified as well as technologically feasible. The way the U.S. separates hydrogen from water today requires vast amounts of electricity, and with today's energy economics, most of our electricity is generated by fossil fuels. We have the technology to produce electricity from solar and wind sources, but it is limited in its economic feasibility. Furthermore, the existing infrastructure of the gasoline industry cannot be converted to hydrogen, and it is hard to believe it will be economical to generate that [hydrogen] infrastructure as long as gasoline is available at its current price levels.

Jerry Ebersbaker—Hot Springs Village, Arizona

Geoffrey Ballard responds: Geoffrey Ballard responds: Biogenetic forms of hydrogen are believed by some prominent scientists to be the final answer for the generation of hydrogen. But the beauty of a hydrogen economy, made possible by an economical fuel cell, is that all energy forms— wind, solar, biomass, geothermal, nuclear, petroleum, clean coal— lend themselves to being utilized, a condition not possible with a wood, coal, or gasoline economy. My impression is that governments, auto manufacturers, and oil companies are devoting time, talent, and money to produce a hydrogen economy in an economic and logical manner. However, the full cooperation of government, industry, academia, and the public is essential to its successful introduction.

A Woman's Choice Upon reading the article on Steven Goodman [Discover Dialogue, July] and his opinions on mammograms, I wondered why he did not address the mortality rates related to radiation and chemotherapy. Although he does say, "Almost nobody appreciates the surgery part, which changes the equation from 'can't hurt, might help' to 'might hurt, might help,'" what about the risks related to these other therapies? One or both are routinely recommended to treat any form of cancer more advanced than DCIS [ductal carcinoma in situ], which is one of the earliest forms of breast cancer. With early detection, one or both are often avoided. I also wonder, what "form of cancer" is it that "never would have caused any trouble"? I have survived breast cancer twice, and I am not aware of any such form. Both times, my cancer was diagnosed by early detection with mammography and biopsy. With the surgical options I chose, I've avoided both radiation and chemotherapy.

Dory Berke, R.N.—Sacramento, California

Steven Goodman responds: I am delighted that the writer is doing well. Her letter shows why mammography screening is such a difficult issue. The form of possibly nonprogressive cancer is the form she mentions— DCIS. Some of these cancers (30 percent to 70 percent) will not cause health problems if left alone and will not require later chemotherapy or radiation. However, this does not mean that DCIS shouldn't be surgically removed, because we cannot tell if it will progress. But it does mean that not every DCIS found by mammography represents an averted bout of chemotherapy or radiation. The National Breast Cancer Coalition ( and the National Cancer Institute's Physician's Data Query ( Information/pdq) have fact sheets that explain this conundrum well.

Questioning the Answers I am disappointed that you show enthusiasm for the attempts of John Wheeler and others to explain what the physical sciences are by definition incapable of explaining ["Does the Universe Exist if We're Not Looking?" June]. We cannot explain the origin of the universe by means of principles that belong to the universe. If it is true that all aspects of physical reality had their start in the Big Bang, then it will always be impossible to use quantum mechanics or any other science to tell why the Big Bang occurred, to prove that other universes exist, or to explain the existence of this universe in terms of our influence as observers. The speculations of Wheeler can never be empirically tested nor made to fit with modern cosmological theory. In terms of plausibility, they are on a par with most prescientific creation myths.

David Clotfelter—Northridge, California

John Wheeler responds: Science can in fact cope with the mechanism of creation, although not with its purpose. A question I like to ask is, "How come existence?" By this I don't mean to what end are we here. I mean what circumstances of physical law and cosmic history resulted in the world as we know it, including its thinking, questioning beings. To me, that is a scientific question. I believe that once scientists understand more deeply the mysteries of quantum mechanics and its relationship to gravity and space-time, a satisfying scientific answer will emerge.

Erratum The edition of the Odyssey shown in "Homer's Bones" in the July issue should have been credited to Columbia University, Rare Book and Manuscript Library, Plimpton MS 3, vol. 2, f. 16.

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