Nobel Prize in Physics Awarded for Studies of Earth’s Place in the Universe

The cosmologist James Peebles split the prize with two astronomers, Michel Mayor and Didier Queloz, for work the Nobel judges said: “transformed our ideas about the cosmos.”

This year’s Nobel Prize in Physics went to an astrophysicist who came up with sweeping ideas to explain how matter in the young universe swirled into galaxies, and to two astronomers who showed that other stars similar to the sun also possess planets.

The other half honored work by Michel Mayor and Didier Queloz, who were the first to discover a planet circling around a distant sun-like star.

James Peebles is a professor of science at Princeton. Michel Mayor is an astrophysicist and professor emeritus of astronomy at the University of Geneva. Didier Queloz is a professor of physics at the Cavendish Laboratory at Cambridge University, and at the University of Geneva.

In the 1960s, when Dr. Peebles began studying the universe, there were few observations to prove or disprove anyone’s conjectures. Cosmological distances were often just rough guesses, and estimates of the age of the universe varied widely.

In 1964, two radio astronomers, Arno Penzias and Robert Wilson, discovered by accident a background hiss of microwaves pervading the universe. Dr. Penzias and Dr. Wilson, who won the Nobel Prize in Physics in 1978, were perplexed until they came across theoretical calculations by other scientists, including Dr. Peebles.

Dr. Peebles and his colleagues had predicted this background radiation, a residue from about 400,000 years after the Big Bang when the universe had cooled enough for hydrogen and helium atoms to form.

The microwave background was almost uniform in all directions, reflecting a temperature of only a few degrees above absolute zero, but it was not perfectly smooth. Dr. Peebles calculated that there should be faint fluctuations and that the fluctuations would reveal regions where the matter had begun to clump together — the structure that would eventually be revealed as stars, galaxies, and clusters of galaxies.

In the early 1980s, Dr. Peebles proposed the idea that the universe was filled with unseen “cold dark matter” — particles that did not interact with the ordinary matter but whose gravitational pull formed galaxies and clusters of galaxies. A couple of years later, he added to his model a term that Albert Einstein had originally proposed but later discarded as his “biggest blunder.”

Einstein had invented this idea, called the cosmological constant, to balance gravity and keep the universe static and unchanging. But astronomers established that the universe is actually expanding. Dr. Peebles utilized the cosmological constant, now known as dark energy, for a different reason: He aimed to show that the universe contained considerably less mass than was thought at the time.

Around 1990, observations of the universe caught up to Dr. Peebles’s theories.

Scientists measured some of the fundamental fluctuations in the microwave background, and a NASA mission, the Cosmic Background Explorer, captured a wealth of confirming data.

In 1998, two teams of astronomers discovered that Dr. Peebles was right and that the universe was not only expanding but accelerating. That research also garnered a Physics Nobel, in 2011.

Dr. Peebles noted that much of the universe remains mysterious. Scientists have yet to identify what makes up dark matter or dark energy.

The other half of this year’s Physics Nobel goes to research that filled in a missing piece of the observable universe.

Astronomers had long presumed there must be planets in orbits around other stars. But until a quarter-century ago, they knew of none. Over the decades, claims of planets evaporated on closer examination.

In 1992, astronomers found the first planets outside the solar system, but those orbited an exploded star, making them an unlikely place for life to exist.

As a graduate student working with Dr. Mayor, Dr. Queloz was setting up the equipment and writing the software to begin a search at the Haute-Provence Observatory in southern France.

If they found a planet, they would not see it directly. Rather, they were looking for a periodic wobble in the colors of light from the star. The gravity of a planet would pull on the star. The motion back and forth would shift the wavelengths of the starlight, much as a whistle of a train or the siren on a police car rises when approaching and falls when receding.

This technique was sensitive enough to detect something the size of Jupiter, but astronomers thought that planets the size of Jupiter would be as far from their stars as Jupiter is from Earth, and take years to pinpoint.

Thus, any discoveries would come long after Dr. Queloz finished his thesis. In 1994, Dr. Mayor went on sabbatical at the University of Hawaii.

“Off he went, and you can imagine my surprise when a couple of weeks later, I started the program and identified that star that had a completely erratic pattern,’” Dr. Queloz recalled.

He had started observing 20 bright stars in our galactic neighborhood. The erratic star was 51 Pegasi, similar to our sun and 51 light-years away.

The planet in the data was as big as Jupiter, but it hugged the star in a tight orbit that took only four days to complete.

 

Almost six months later, Dr. Queloz was convinced his data was real, and he sent a fax to Dr. Mayor saying he thought he might have discovered a planet. “Michel had this very nice answer,” Dr. Queloz said. “He said, ‘Yes, maybe.’”

 

Years later, Dr. Mayor admitted that he did not believe the data. “He just wanted to be nice with me,” Dr. Queloz said. But when they made more observations, the same pattern continued.

 

On Oct. 6, 1995, they announced their discovery.

 

Although this broiling planet was not habitable, it pointed to how astronomers could now study planetary systems that could be similar to our own.

 

“Completely transformative,” Dr. Fischer said of the discovery. “We are the middle of a scientific revolution that people won’t appreciate until a hundred years go by.”

 

More than 4,000 exoplanets have been discovered in our Milky Way galaxy since Dr. Mayor and Dr. Queloz announced their results, including some that may be habitable. More and more are being spotted with space telescopes like TESS, launched by NASA last year.

 

And it turns out that large planets orbiting so close to their stars are not unusual.

 

Source: www.guardian.com, www.nytimes.com

Posted by: MS