Open this photo in gallery Canadian-American cosmologist James Peebles toasts with colleagues during a small reception after he won the 2019 Nobel Prize for Physics, on Oct. 8, 2019. EDUARDO MUNOZ/Reuters

For many science enthusiasts, James Peebles made his most memorable debut while riding his bicycle across their television screens during a 1978 PBS documentary about the Big Bang theory.

Now 84, the Princeton University professor from St. Boniface, Man., is back in the public eye, this time as a recipient of the Nobel Prize in Physics for his many contributions to humanity’s understanding of the universe.

“It was never a plan of great discovery,” the tall, soft-spoken cosmologist said over the phone during a news conference after the prize was announced. “These things just happen.”

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On Tuesday, the Royal Swedish Academy of Sciences in Stockholm named Dr. Peebles a winner of one half of this year’s $1.2-million physics prize. The other half was awarded to Swiss astronomers Michel Mayor and Didier Queloz, who launched a new era in the search for other worlds.

PEERING INTO COSMIC HISTORY The cosmic microwave background, discovered in 1965 and theoretically described by Nobel Prize winner James Peebles, consists of energy emitted when the universe was filled with a white hot plasma, fewer than 400,000 years after the Big Bang. Over time, the signal has shifted in frequency from visible light to the microwave part of the spectrum. Big Bang 0 Cosmic microwave background 0.0004 (400,000 years) Dark age First stars 0.30 AGE OF THE UNIVERSE (billions of years) 0.95 First galaxies Modern universe 13.7 ivan semeniuk and john sopinski/THE GLOBE AND MAIL, SOURCE: spacetelescope.org; nasa; adobe PEERING INTO COSMIC HISTORY The cosmic microwave background, discovered in 1965 and theoretically described by Nobel Prize winner James Peebles, consists of energy emitted when the universe was filled with a white hot plasma, fewer than 400,000 years after the Big Bang. Over time, the signal has shifted in frequency from visible light to the microwave part of the spectrum. Dark age Cosmic microwave background Big Bang First stars First galaxies Modern universe 0 0.0004 (400,000 years) 0.30 0.95 13.7 AGE OF THE UNIVERSE (billions of years) ivan semeniuk and john sopinski/THE GLOBE AND MAIL SOURCE: spacetelescope.org; nasa; adobe PEERING INTO COSMIC HISTORY The cosmic microwave background, discovered in 1965 and theoretically described by Nobel Prize winner James Peebles, consists of energy emitted when the universe was filled with a white hot plasma, fewer than 400,000 years after the Big Bang. Over time, the signal has shifted in frequency from visible light to the microwave part of the spectrum. Dark age Cosmic microwave background Big Bang First stars First galaxies Modern universe 0 0.0004 (400,000 years) 0.30 0.95 13.7 AGE OF THE UNIVERSE (billions of years) ivan semeniuk and john sopinski/THE GLOBE AND MAIL SOURCE: spacetelescope.org; nasa; adobe

Dr. Peebles spent his childhood in small towns orbiting Second World War-era Winnipeg. Always curious about how things worked, he recalled that as a youngster he once threw a tantrum, "because I wasn’t allowed to put together the coffee percolator.”

His interest in science led him to the University of Manitoba where a physics professor, Ken Standing, steered him toward graduate studies at Princeton. (Dr. Standing died earlier this year at the age of 93).

“It was not advice,” Dr. Peebles said of Dr. Standing’s influence. “It was: You will go to Princeton."

Dr. Peebles earned his PhD in 1962 working with another key mentor, Robert Dicke who encouraged him to pursue cosmology – a “chancy subject,” Dr. Peebles said, with few people working in the field at the time. That proved to be a good thing. “I discovered that I could do interesting things and be pretty sure no one else was doing them," he said.

By 1964, he was working on the possibility of detecting a radio signal emanating from the early universe. Such a signal should have been emitted when the universe was filled with a hot uniform plasma, shortly after the Big Bang. Dr. Peebles and his team designed an experiment to look for the emission, but to their surprise, it was detected serendipitously the following year by Arno Penzias and Robert Wilson of Bell Laboratories who won a Nobel Prize for their find in 1978.

Dick Bond, a professor at the Canadian Institute for Theoretical Astrophysics in Toronto, said that Tuesday’s Nobel Prize decision “makes up” for the fact that Dr. Peebles was left out back then, despite having anticipated and explained what is now called the cosmic microwave background.

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Later, Dr. Peebles went on to study the origin of matter and the large-scale structure of the universe. In the 1980s, he was central to the development of the standard mathematical view of cosmology. It includes the understanding that the evolution and fate of the universe are governed not by stars and galaxies, but by two mysterious entities – dark matter and dark energy – which have since been confirmed observationally.

“The subject has changed so much,” Dr. Peebles told The Globe and Mail in a 2017 interview. “But one thing that’s pretty constant is that you never know what’s going to happen next.”

Dr. Peebles has maintained his ties to Canada over the years. He was instrumental in the founding of a cosmology and gravity program supported by the Canadian Institute for Advanced Research and also has a research chair named after him at the Perimeter Institute for Theoretical Physics in Waterloo, Ont. Rob Myers, the institute’s director, who did his graduate work at Princeton during the 1980s, said that as a student he was inspired by Dr. Peebles’s “impressive lectures and good-natured manner” in addition to his research achievements.

Scott Tremaine, a Canadian astrophysicist at the Institute for Advanced Study, also located in Princeton, New Jersey, praised Dr. Peebles’s penchant for never being satisfied with the answers that his theories provided and for pressing for a deeper understanding of nature at the grandest scale.

“The Russian physicist Lev Landau once cynically described cosmologists as ‘often wrong, but never in doubt,’ ” Dr. Tremaine said. “Peebles is rarely wrong, but always in doubt, and he has inspired several generations of cosmologists to attempt to follow in his footsteps.”

Meanwhile, Dr. Peebles’s Nobel co-winners are best known for celestial discoveries that are closer to home.

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In 1995, Dr. Mayor and Dr. Queloz detected a slight wobble in a nearby star, known as 51 Pegasi. The wobble is caused by the gravitational pull of a massive planet in a close orbit around the star. The find was a technical tour de force that ushered in the study of planets beyond our solar systems, or exoplanets. Since then, astronomers have identified several thousand such worlds using a variety of methods and are increasingly aiming to detect planets similar to Earth.

Sara Seager, a Canadian exoplanet researcher at the Massachusetts Institute of Technology, remembers being a graduate student at Harvard University when the astronomers’ stunning discovery was first announced. Within a year, she switched from cosmology to working on exoplanets herself.

“In exoplanets, the line between what is considered completely crazy and what is considered mainstream science is constantly shifting,” Dr. Seager said. “The Nobel award is a cataclysmic shift in the right direction.”

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