A cosmologist who revealed the universe was made mostly of invisible matter and energy and two scientists who detected the first planet orbiting an alien star were jointly awarded the 2019 Nobel Prize in physics Tuesday.
By studying the afterglow of radiation left over from the universe’s birth, James Peebles of Princeton University developed a theoretical framework for the evolution of the cosmos that led to the discovery of dark energy and dark matter — substances that can’t be observed by any scientific instruments but nonetheless make up 95 percent of the universe.
Fellow laureates Michel Mayor and Didier Queloz of the University of Geneva revolutionized astronomy, the Nobel Committee said, when in 1995 they announced the discovery of a large, gaseous world circling a star 50 light-years from our own sun — the first extrasolar planet found around a solar-type star. In the decades since, scientists have detected thousands more of these exoplanets, and astronomers now think our universe contains more planets than stars.
“This year’s Nobel laureates in physics have painted a picture of a universe far stranger and more wonderful than we ever could have imagined,” Ulf Danielsson, a Nobel committee member, said at a news conference Tuesday. “Our view of our place in the universe will never be the same again.”
For almost a century, scientists have theorized that the universe began with a Big Bang, growing from a hot, dense particle soup into the current collection of dust, stars and galaxies flung across a vast and still-expanding space. Fifty years ago, a pair of radio astronomers stumbled upon the signature of those earliest days of expansion: the cosmic microwave background, a faint form of radiation that suffuses the entire sky.
This radiation is a “gold mine” for physicists, the Nobel Committee said. By analyzing tiny variations in this ancient afterglow, scientists can peer back in time to understand how the universe evolved.
Peebles studied the temperature of the cosmic microwave background to understand how much matter was created in the Big Bang and how that matter later condensed to form galaxies and galaxy clusters.
“I was not working alone,” Peebles said via phone interview at the news conference Tuesday, pointing out that researchers in the Soviet Union provided important contributions to scientists’ understanding of the universe’s evolution.
After the detection of the cosmic microwave background in 1964, the field progressed in fits and starts, he said; “I put out lots of wrong ideas, too, you know.”
Eventually Peebles’s theories led to the discovery of dark energy, the invisible force that drives the expansion of the universe, and dark matter, the unobservable material that holds galaxies together.
Everything we can touch or see, everything ever detected by a scientific instrument and everything that has yet to be found, makes up just 5 percent of the universe.
Even in that small slice of the cosmos, there is more than meets the naked eye. The science behind the second half of this year’s physics prize is proof of that.
The first exoplanet observed by Mayor and Queloz wasn’t visible through any telescopes. Instead, the astronomers intuited the world’s existence by observing the way it affected its star.
Their research relied on the fact that planets don’t actually orbit stars; instead, both planets and stars orbit their common center of mass. If a planet is sufficiently large compared to its sun, it will cause the star to wobble just a bit. This wobble produces tiny shifts in the light the star emits, and scientists can analyze these shifts to determine the size and distance of the planet.
The first world that Mayor and Queloz discovered, dubbed 51 Pegasi b, was unlike any in our own solar system. The planet was large and gaseous, like Jupiter, but it was so close to its star that it took just four days to complete an orbit. Its temperature exceeded 1,000 degrees Celsius.
When he first saw the planet’s signature in his data, “I panicked,” recalled Queloz, who was a graduate student working with Mayor at the time of the discovery. “I thought something was wrong with the instrument.”
It took endless reanalysis for the astronomers to convince themselves they were looking at something real. Then they had to convince the rest of the world. The newfound planet was so different from what scientists predicted they’d find, many researchers were initially skeptical of the discovery.
But later observations confirmed the detection, and soon astronomers across the globe were conducting their own exoplanet searches, scanning the skies and looking over reams of historical data to detect the telltale wobble of a planet-hosting sun. Observations from ground- and space-based telescopes have now revealed more than 4,000 confirmed exoplanets and challenged scientists’ notions about how planetary systems evolve.
“We had thought that other solar systems would be similar to our own,” Danielsson said. “We were wrong!”
In a tradition as regular as the prizes themselves, the announcement Tuesday prompted debate over the lack of diversity among recipients. Just three women have ever been awarded the physics prize in its more than 100 year history, and no black scientist has ever been recognized.
The choice to recognize Peebles’ cosmology theories sparked particular anger, because the woman who proved the existence of dark matter, Vera Rubin, was never given the award. The Carnegie Institution astronomer battled sexism and “utterly revolutionized our concept of the universe,” astronomer Emily Levesque once told Astronomy magazine. She had been considered a leading candidate for the physics prize before her death in 2016.
“I think for many women in cosmology,” tweeted theoretical physicist Chanda Prescod-Weinstein, “the treatment of Vera Rubin by the Nobel Prize will always be a collective wound.”
The Royal Swedish Academy of Sciences, which awards the prizes, told Nature last week the organization had implemented measures to address bias against women and scientists of color, including explicitly asking nominators to consider diversity in gender, geography and topic. All six recipients of this year’s prizes for medicine and physics have been white men.
Much as Peebles’ research emphasized Earthlings’ insignificance in the context of the universe, Mayor’s and Queloz’s discovery revealed how rare and unusual we are.
Even so, Danielsson added, somewhere out in the dark and mysterious cosmos, on one of those strange and distant worlds, it’s possible that some other form of life exists. Humanity might not be alone.