James Peebles

Background

James Peebles’s father worked as a clerk at the Winnipeg Grain Exchange (see Winnipeg Commodity Exchange). From an early age — and influenced by his father — Peebles was interested in all things mechanical and recalls being more of a dreamer than a serious student in high school. “I was never exposed as a kid to any real science,” he recalled in a 1988 interview with the American Institute of Physics. “It wasn’t until I got to college that I began to appreciate what physics is all about.”

He originally planned to study engineering at the University of Manitoba, where many of his friends majored in physics, which prompted him to switch programs during his third year. While the university’s strength was classical physics, Peebles desired to learn more about modern areas of study. In 1958, he entered Princeton University, where he studied various forms of quantum physics and particle theory, and he received his doctorate in 1962.

Among those who influenced Peebles were University of Manitoba professor Ken Standing, who told him he had to go to Princeton University. Once there, he was inspired by professor Robert Henry Dicke for helping him understand how physics could be applied and for urging him not to engage in “sloppy” thinking. “I was very uneasy about going into this subject because the experimental observational basis was so modest,” he recalled in 2019. “I just kept going.”

Peebles remained at Princeton University to pursue his academic career. His positions included assistant professor (1965), associate professor (1968), professor (1972) and professor emeritus (2000).

Peebles expressed his enjoyment and fascination with studying physics and cosmology. He reportedly enjoys the ability to settle arguments and discover whether theoretical concepts make sense. Compared to other branches of science such as biology, Peebles observed in 2019 that in basic physics “you can actually start from the fundamentals and work your way up.” Early on in his career, he contemplated doing only a few projects related to cosmology but discovered “each project led to ideas for others, in a flow that was too interesting to resist.”

Work

James Peebles’s work explores physical cosmology with a mathematical approach (see Mathematics). It has provided the basis for contemporary ideas about the history of the universe.

“Research such as ours is driven by the human imperative to understand where we are,” Peebles observed in his 2019 Nobel Prize speech. “It motivates the study of our positions in family, or in society, or on earth. The results may be termed geology, or sociology, or poetry.”

When he began researching cosmology during the mid-1960s, there was little empirical evidence to support estimates regarding the age of the universe or how to measure cosmological distances. He theorized that it might be possible to detect radio signals created soon after the Big Bang. While designing an experiment to seek out such signals, they were found by Bell Laboratories scientists Arno Penzias and Robert Wilson, who won the Nobel Prize in Physics for their work in 1978.

Peebles’s subsequent work helped formulate the existence of cosmic microwave background radiation throughout the universe, originating from a period around 400,000 years after the Big Bang. Peebles also found that tiny fluctuations in the temperature of that radiation were critical for understanding how matters drew together to form galaxies.

During the early 1980s, Peebles suggested that the universe contained plenty of particles, defined as dark matter, whose gravitational pull was involved in creating galaxies. Building upon Albert Einstein’s theory of the cosmological constant, Peebles felt that the universe contained less mass than was commonly believed and that it was both accelerating and expanding. Peebles’s work has led to the belief that only about five per cent of matter is known in the universe, with the remainder hidden from us.

In an article on modern cosmology that Peebles wrote for Scientific American in 2001, Peebles suggested five pieces of evidence that the universe was expanding and cooling:

1. Light from distant galaxies is shifted to the red spectrum as a result of expanding space and galaxies pulling away from one another.
2. Thermal radiation fills space in areas where it was once denser and hotter.
3. The presence of large amounts of deuterium and helium is evidence that temperatures were previously higher.
4. Visible galaxies from billions of years ago look younger.
5. The curvature of space-time appears related to the universe’s material content, which aligns with the theory of relativity.

Summing up his field of study in a 2017 interview with The Globe and Mail, Peebles observed that “one thing that’s pretty constant is that you never know what’s going to happen next.”

Nobel Prize

Jim Peebles was awarded half of the 2019 Nobel Prize in Physics for “theoretical discoveries in physical cosmology” (the remainder of the prize was awarded to Swiss astronomers Michel Mayor and Didier Queloz for discovering a planet orbiting around a distant star). (See also Nobel Prizes and Canada; Physics). Göran K. Hansson, secretary general of the Royal Swedish Academy of Sciences, noted that Peebles’s work is “the foundation of our modern understanding of the universe’s history, from the Big Bang to the present day.”

Given his half-century-long career, Peebles wasn’t surprised when he received the phone call indicating he had won the prize. “I’m the last man standing, so to speak, from those early days,” he told The New York Times. “It had crossed my mind.”

Legacy

Upon his receipt of the 2019 Nobel Prize, a Toronto Star editorial summed up Jim Peebles’s work as “nothing short of changing cosmology from speculation to science.”

Publications

• Physical Cosmology (1971)
• The Large-Scale Structure of the Universe (1980)
• Quantum Mechanics (1992)
• Principles of Physical Cosmology (1993)
• Finding the Big Bang (2009)
• Cosmology’s Century: An Inside History of Our Modern Understanding of the Universe (2020)
• The Whole Truth (2022)

Awards and Honours

• Eddington Medal, Royal Astronomical Society (1981)
• Dannie Heineman Prize for Astrophysics, American Institute of Physics and American Astronomical Society (1982)
• Fellow, Royal Society (1982)
• Fellow, Royal Society of Canada (1987)
• Catherine Wolfe Bruce Gold Medal, Astronomical Society of the Pacific (1995)
• Oscar Klein Medal, Stockholm University (1997)
• Gold Medal of the Royal Astronomical Society, Royal Astronomical Society (1998)
• Gruber Cosmology Prize, The Gruber Foundation (2000, with Allan Sandage)
• Harvey Prize, Technion-Israel Institute of Technology (2001)
• The Shaw Prize in Astronomy, The Shaw Prize Foundation (2004)
• Crafoord Prize, Royal Swedish Academy of Sciences and The Crafoord Foundation (2005, with James Gunn and Martin Rees)
• Dirac Medal, The Abdus Salam International Centre for Theoretical Physics (2013)
• Member, Order of Manitoba (2017)
• Nobel Prize in Physics, Royal Swedish Academy of Sciences (2019)
• Companion, Order of Canada (2020)