Life, the Multiverse and Everything
In “Looking for Life in the Multiverse,” Alejandro Jenkins and Gilad Perez say that life would be possible in a universe without the weak nuclear force. But they fail to note that the weak force is unique in treating matter and antimatter asymmetrically. Only because of this asymmetry did matter slightly outweigh antimatter before nearly all antimatter annihilated with an equal amount of matter, within the first seconds after the big bang. Everything we see—including stars, which are essential to life—is composed of that slight excess of matter. A universe without the asymmetric weak force would have virtually no normal matter and hence no life in any form we might recognize.
Robert L. Piccioni
The writer is author of Everyone’s Guide to Atoms, Einstein, and the Universe

THE AUTHORS REPLY: By itself, the weak nuclear force cannot distinguish between matter and antimatter, because it preserves what physicists call charge-parity (CP) symmetry, meaning that it treats a particle in the same way as the mirror image of the corresponding antiparticle. As Piccioni points out, however, it is possible to combine the weak force with other interactions in such a way that this CP symmetry is broken.

Today we know that CP asymmetry is way too small to account for the fact that our universe contains as much matter as it does, but no antimatter. Some new physical interactions at high energies, as yet undetected, are needed to resolve this fascinating puzzle. These other interactions could also produce an excess of matter over antimatter in a weakless universe. We did not cover this interesting point in our Scientific American article because of space limitations.

That information about “Life, the Universe, and Everything” could be found on none other than page 42 of this issue was ironic, given that this number had been specified in 1979 as the “Answer to the Ultimate Question” in Douglas Adams’s classic text, The Hitchhiker’s Guide to the Galaxy. For those of us who can barely get around the monoverse we find ourselves living in, it is a comfort to know that Scientific American has provided additional evidence that a convergence of multiverses arises from this locus, 42, as predicted by Adams.
William D. Brown
Seekonk, Mass.

Proceeding, with Care
In “Big Need for a Little Testing” [Perspectives], the editors write that “many companies are hesitant to invest in nanotechnology R&D, fearing the exposure to legal action that could result if one day a technology is deemed dangerous. Procter & Gamble, for example, is not pursuing nanotechnology because of the long-term risk of litigation.”

Contrary to what was stated, P&G is interested in nanotechnology, and we are actively pursuing the benefits it can deliver. We believe it holds great potential to bring exciting new levels of performance to products people use everyday. Nanotechnology opens up many possibilities to boost performance, reduce environmental impact and improve sustainability in virtually every consumer product category. As with any new technology, however, the potential for adverse effects must be understood, and the technology should advance only as fast as our ability to thoroughly evaluate it. We are taking an appropriately cautious approach with nanotechnology. In addition to our own research programs, we are also working together with others in the industry, with university labs and with government scientists to ensure the right tools are in place for the responsible development of this promising technology.
Mark Lafranconi
Section Head, Central Product Safety
Procter & Gamble

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Nuclear Inferno
In “Local Nuclear War, Global Suffering,” Alan Robock and Owen Brian Toon claim that a nuclear exchange of 100 Hiroshima-size weapons between India and Pakistan would cause a global catastrophe from smoke particles lofted into the stratosphere. How do the authors reconcile the massive amount of smoke pumped into the earth’s atmosphere during World War II?

Toward the end of the war, more than 60 Japanese cities were firebombed. Other areas to consider, of course, are the British, German and Russian cities burned and destroyed during the war, as well as particularly “dirty” bombings like the oil refineries at Ploesti, Romania and numerous major battles. In my opinion, the authors have overstated the global damage from a nuclear war of the type they describe, and perhaps they did not consider thoroughly enough the environmental effects incurred during WWII.
Kevin A. Capps
Corona del Mar, Calif.

THE AUTHORS REPLY: There were indeed numerous fires in Japan and Europe during World War II, several of which occurred near the end of the war.

The observational database from WWII is not adequate to tell if smoke from these fires reached the stratosphere. For the scenario discussed by Capps, over a period of four weeks, 155 square kilometers (60 square miles) of cities burned in Japan. Unless each fire was of a sufficient intensity to produce a firestorm, the smoke would not have been pumped into the stratosphere and would have remained in the troposphere, like the smoke from the oil well fires during the Gulf War in 1991. This means the smoke would have a lifetime in the atmosphere of only about a week, with only small, short-term local effects. Even if all the smoke did get into the stratosphere, the optical depth would have been much less than that from the regional nuclear conflict we studied: the burned area we considered was 1,300 km2. The number of large firestorms in WW II was small compared with the 100 in our study.

Our models suggest that the small number of events in WWII would not have produced climate effects that would have been detectable against the background of natural weather and climate variability. We do not know if there was a small effect on climate from the smoke generated in WWII, because nobody has studied it. Thus, WWII does not give any evidence that our results are incorrect. In fact, the unfortunate example of cities burning supports our theory that large firestorms would follow atomic bombing. More recent studies of large forest and brush fires, such as in Australia during January 2003, do show that smoke can be injected into the lower stratosphere and may be lofted by sunlight to higher altitudes.