Letters.

Give it a rest

"Breaking the law" (SN: 10/7/00, p. 234) claims, "After all, even the sacred first law's conservation of energy breaks down in the quantum realm, albeit in a limited way, he notes. That's because Heisenberg's uncertainty principle allows energy momentarily to appear from nothing, although it must be quickly paid back." This claim is heard occasionally, but I am wondering what the justification for it is, and where it can be found. Many authors emphatically deny that quantum mechanics borrows energy from nothing. Thus, is there a derivation from quantum field theory, or is it time to put to rest a myth?

Paul Merriam Santa Cruz, Calif.

Quantum systems don't actually borrow energy from nothing. However, in many cases, their energy values may range widely around a well-defined average. The size of those swings is influenced by Heisenberg's uncertainty principle. When thinking about those variations, scientists often use metaphors of borrowing and paying back that are, "technically speaking, not completely right," says Brian R. Greene of Columbia University. However, he adds, "the uncertainty principle can definitely be used in these rough ways to guide our intuition--and it generally does not lead us astray."

--P. Weiss

Koch coda

The article about tuberculosis ("Know your enemy," SN: 10/21/00, p. 270) states that Robert Koch in 1882 was the first person to link a particular microbe to a disease. References indicate that Armauer Hansen demonstrated in 1868 that Mycobacterium leprae was associated with the tissues of leprosy patients. He may not have had Koch's postulates to prove this linkage, but many credit Hansen as being the first individual to implicate a bacterium as the cause of a human disease.

Valerie Vander Vliet Lewis University Romeoville, Ill.

William R. Jacobs Jr. of the Howard Hughes Medical Institute at the Albert Einstein College of Medicine in New York agrees that Hansen made such a demonstration and is properly credited for the work. He adds, however, that Koch "was the first to prove and publish that a bacterium could cause disease by fulfilling three criteria: 1) isolation of bacilli from a diseased patient, 2) purification of bacilli, and 3) administration of bacilli into an animal reproduced the tuberculosis disease."

--D. Christensen

Unique units?

The article "What's worth saving?" (SN: 10/14/00, p. 250) could leave the impression that the evolutionary significant unit (ESU) is the de facto concept employed for all listing decisions under the Endangered Species Act. In fact, the ESU has not been used in the vast majority of recent listing decisions under the act. Nor should it be. The act allows the National Marine Fisheries Service and the U.S. Fish and Wildlife Service to list distinct vertebrate population segments. What qualifies as "distinct" is the million-dollar question. I would argue that the ESU concept falls short of the goals of the act by ignoring populations that are distinct because of their ecological or cultural significance. Evolutionary significance is critical for preservation of biodiversity, but it isn't the only factor that should be considered.

J. Alan Clark Seattle, Wash.