A quarter of a century into academic retirement, physics Nobel laureate P. J. E. Peebles is still looking for answers. This Monday, on the heels of the publication of his book, “The Physicist’s Way: A Philosophical Guide to the Practice of Physics,” Peebles spoke to a packed crowd at the Hazeltine Commons in the Engineering Research Center.
Hosted by the Brown Center for Theoretical Physics and Innovation, the lecture aimed to provide the audience with a preview of Peebles’ new book.
Peebles, a professor emeritus of science at Princeton, received half of the 2019 Nobel Prize in Physics for his pioneering discoveries in physical cosmology, which is the study of the universe’s origins, evolution and structure. His research on the radiation left over from the Big Bang, known as the cosmic microwave background, and dark matter, an invisible form of matter hypothesized to play a key role in galaxy formation, helped establish the framework physicists still use today to study cosmology.
“For more than 60 years, Jim Peebles has been known among physicists as the originator of a tremendous number of techniques, ideas and discoveries,” Professor of Physics Ian Dell’Antonio said in his introduction to the lecture. “There is no current area of research (in cosmology) … that doesn’t owe a tremendous amount to Jim.”
Peebles’ probing into the nature of the universe led to “billion-dollar experiments” and new innovations, Professor of Physics Stephon Alexander told The Herald.
Published by Princeton University Press in October, Peebles’s new book explores the fundamental assumptions underlying physics. Although he has previously authored scientific textbooks, his latest work studies the philosophy and sociology of physics, including what structures and preconceived beliefs allow the field to exist as a discipline at all.
“The starting assumption (that physicists make) is that there is a physical reality,” Peebles said during the lecture.
He explained that philosophers could spend hours arguing this premise, but bringing up philosophy in a group of physicists would likely lead to “awkward silence.” In his book, Peebles argues that there is a way to bridge these two conventionally incompatible fields.
“Physicists have a philosophy,” he told The Herald in an interview. “And it must be recorded.”
During his lecture, Peebles said that one of the major challenges facing modern physics is the lack of unification between quantum mechanics, which describes phenomena at the subatomic scale, and general relativity, which describes how gravity affects the structure of spacetime.
He also outlined the development of modern cosmology, drawing on how he first began investigating gaps in the Big Bang Theory early in his career. As technology advanced, physicists were able to come to an increasingly precise understanding of the universe.
But Peebles underscored the importance of recognizing the limitations of scientific knowledge, emphasizing that even widely accepted theories are in a constant state of refinement.
“There’s no such thing as a final theory,” Peebles told The Herald. “We only get approximations.”
Throughout the lecture, Peebles engaged the audience through humorous anecdotes, joking that Canadian scientists were often too polite to compete with their American counterparts and drawing attention to an Icelandic sweater he wore in a photograph of his lab from the 1960s.
During technical difficulties that delayed the start of the event, a four-person jazz ensemble performed a jazz interpretation inspired by the cosmic microwave background.
Peebles discovered the frequencies of the “cosmic sound waves in the early universe,” Alexander told the Herald, “and so we identified the notes associated with each of those waves, and magically it turned out to be one of the most celebrated chords or scales in jazz music.”
Attendee Nahum Linhart ’30 said that he was told to attend the lecture by Dell’Antonio, from whom he is taking a class this semester, but he “would have come anyway because (Peebles is) like, a superhero in physics.”
Leaving the lecture, Linhart’s main takeaway was that “we don’t really know that much stuff about the world,” he said. “But that’s not a bad thing.”
Nishita Malhan is a senior staff writer covering science and research.
