HARVARD GAZETTE ARCHIVES

Ned Hall: 'Philosophical work in quantum mechanics has become so technical that to do cutting-edge work is [similar] to do[ing] research in physics.' (Staff photo Jon Chase/Harvard News Office)

Hall, a newly appointed professor of philosophy, came to Harvard from the Massachusetts Institute of Technology in July. With a focus on the philosophy of science, Hall said he was attracted to Harvard in part because of the opportunity to work across discipline boundaries with scientists.

"Philosophical work in quantum mechanics has become so technical that to do cutting-edge work is [similar] to do[ing] research in physics," Hall said.

The theory of quantum mechanics is one focus for Hall and he's considering writing an introductory text on the subject. He is examining the problems related to measurement in quantum mechanics, one of the least elegant parts of the theory. This theoretical messiness indicates that our understanding is imperfect, he said.

"Philosophers of science have always been bothered by these messy parts of the theory. How do you tidy it up?" Hall said. "It may not make a difference to physicists, because it doesn't affect their results, but the textbook story as it stands is not a very plausible one."

Teachers often gloss over the inconsistencies in the theory, Hall said, but bright students realize something is amiss.

"Bright students always spot the trouble areas. They don't understand how the theory is supposed to work. They ask questions, but they're often told, 'Shut up and calculate,'" Hall said.

Hall has also given considerable thought to the idea of causation, the simple concept that one event causes another. Though grasped intuitively by most, causation as examined by philosophers digs at the roots of what it means to cause an event. A simple illustrative example offered by Hall is the case of two children throwing rocks at a window. The child whose rock hits the glass first breaks the window, allowing an observer to say that the throwing of the rock by that child caused the window to break.

But Hall said the example is not so simple. Usually, if it's reasonable to say that a child throwing a rock caused a window to break, then the opposite should also be true: that if the child hadn't thrown the rock, the window would not have broken. But in this case, the second rock thrown would have broken the window - so the simple idea that causes are whatever is needed for their effects won't work.

Much as the philosophy of quantum mechanics overlaps into physics, the concepts of causation spill into statistics, where numerical correlation has taken the place of direct causal relationships, Hall said. More recent thinking in statistics, however, has revived the idea that statistics can directly link one event to another as a cause.

Today, a study that shows a negative correlation between exercise and heart disease in 60- or 70-year-olds might prompt one to describe it as a causal relationship, in effect, that the exercise done by the 60- or 70-year-olds is the cause of their good heart health. But Hall said the correlation doesn't necessarily prove that. Good heart health could well be a result of good exercise habits the people had when they were younger, while the benefit of exercise done today could be minor.

"Correlations are all well and good, but they don't give us what we want. Correlation is no substitute for causation," Hall said.

It was a dual love of science and philosophy that caused Hall to become a philosopher of science. His mother, a chemist, tutored him to augment his high school chemistry classes in Los Altos, Calif. Hall described his parents as "wonderfully nerdy" and said he loved the "how do we know that life isn't a dream" questions they encouraged in him as he was growing up.

Hall attended Reed College, where he took an upper-level philosophy course in his freshman year that introduced him to the classic texts of philosophy. He was hooked. He still remembers reading Aristotle's Metaphysics.

"I remember being absolutely entranced by it, sitting in the library, poring over it line by line," Hall said. "It had this sense of incredible intellectual power to it."

Hall went on to receive twin bachelor's degrees in chemistry and in philosophy in 1987. After completing his undergraduate studies, he took the GRE exams in chemistry, but wound up applying only to philosophy graduate programs.

"Something deep and subterranean said, 'You don't want to go that way [into chemistry]," Hall said.

He received a doctorate in philosophy from Princeton in 1996.

Hall said he wishes he could live long enough to become expert at several sciences and that one aspect of philosophy he enjoys is its broad scope, which allows him to explore different fields.

"The good thing about philosophy is that you have license to dip into anywhere you want to," Hall said.

alvin_powell@harvard.edu

Related stories: