"Clearly, [science] can't explain events," said Weinberg, the Josey Regental Chair of Science at the University of Texas at Austin and winner of the Nobel Prize in physics. "Only physics plus other events explain events."
Weinberg made a distinction between explaining events and explaining physics, however, saying, "There's no real a priori distinction between rules and accidents."
"If you say that the meaning of explanation is cause, what you really have to do is trace a series of events, and you see that many other things have to exist for something to happen," Weinberg said.
"[Physics] deals with that which is timeless and not related to accidents," he said. "The rules of physics, we hope, have this character."
Weinberg refuted the suggestions made by philosophers that science describes, but does not explain. "There were philosophers that didn't know how to give a functional meaning to something-just teleological explanations," he said. Defining teleological explanations as the human purpose of an activity, Weinberg suggested that there is no teleology in physics, a fact that leads philosophers to believe science can merely describe. "[This belief] is wrong not just in detail, but procedurally," he said.
"Physicists are not really interested in the explanation of events," he added. Instead, physicists "explain a rule of nature when [they] show it can be deduced from a more fundamental principle."
"Today, you deduce Kepler's laws from Newton's laws because we have a sense that Newton's laws are more fundamental," he said. "But what does fundamental mean?"
Weinberg concluded that he has not succeeded in making one level of explanation more fundamental than another. "But I think we are moving toward a satisfying picture of the world," he said. "We hope there will be an understanding of nature from which all other regularities can be deduced, regularities being things like Newton's and Kepler's laws."
Weinberg pointed out, however, that this theory of understanding the world as deducible from a few, elegant laws of nature, while providing for a "satisfying" world view, seems to "make scientific explanation a matter of taste."
"Why is it that this vision of nature did not exist for our very clever predecessors in ancient Greece?" he asked. When we read about philosophers' grappling with nature, he said, we do not find any sense of dissatisfaction.
"Descartes' explanations of nature are entirely qualitative," Weinberg added. "Why wasn't his explanation a more detailed deduction from more fundamental principles?"
Weinberg said that the answer is similar to what we would find when asking why there was no skiing in the ancient world. "It's not obvious you could enjoy the experience," he said. "They had never seen it done. It's hard to imagine that it could be done."
Weinberg added that because scientists cannot argue that their studies are intrinsically interesting or needed to defend the nation or to improve technology, they often have trouble funding their search for "fundamentalness."
Weinberg conceded that "science explains a lot," but it cannot explain everything. "There are accidents we can never recover," he said.
Often, scientists make the mistake of thinking certain accidents are governed by rules, such as when Kepler tried to create a law predicting the radii of planets.
"We know the distances from the sun are accidents, and we wouldn't try to explain them as mathematical derivations from a fundamental law," Weinberg said.
"I want to emphasize that, although my whole picture of explanation in physics relies upon accidents and rules, the distinction between fundamental laws and others is not clear," he added. "What are accidents and what are laws?"
Weinberg said that there is a limitation in the word "deduce."
"Maybe something is explained by something else without our being able to deduce it," he said, citing chemistry as an example.
"Almost any physicist would say chemistry is explained by physics, but it will never be entirely explained, and indeed chemistry exists as an entirely separate discipline that physics can't replace," Weinberg said. "But we know down deep that that's why the chemicals are the way they are. The explanations are in nature. The laws of physics require chemicals to behave the way they do."
Weinberg concluded by saying that "a final explanation is really impossible. We may be able to show that a final theory is the only logically consistent theory, but it will be at the extreme limits of our power of explanation."
Although students said that they agreed with Weinberg's argument, several wished he had gone into greater depth on some of the issues.
Chad Mills '04 said that he wished Weinberg had addressed the topic of chaos, specifically relating to the theory of multiple big bangs since "multiple big bangs could have provided for different initial conditions."