Science’s Most Prestigious Prize Awarded For Biggest Questions


The 2019 Nobel Prize in physics was awarded for progress toward two of the grandest and oldest mysteries known to humanity: the nature of the cosmos itself and whether we are alone in the universe.

James Peebles of Princeton University was awarded half of the Prize “for theoretical discoveries in physical cosmology,” while the other half was split between Michel Mayor of the University of Geneva and Didier Queloz of both the University of Geneva and Cambridge University “for the discovery of an exoplanet orbiting a solar-type star.” Both scientific advances are being acknowledged for how they gave us new perspectives on our place in the universe.

Peebles award is for a lifetime of work. After receiving his bachelor’s degree at the University of Manitoba, he moved to Princeton for graduate study under Robert Dicke and received his Ph.D. in 1962. He has been at Princeton ever since.

Early in his career, he was interested in understanding experimental signatures of the beginning of the universe, also called the Big Bang. The Big Bang postulates that the universe was once much smaller and hotter, and it has been expanding since the beginning. As the universe expanded, it cooled off, going from a white-hot plasma, to a dull red glow, and finally to an invisible whisper of radio waves. The exact wavelength that this residual glow depends on the expansion of the universe.  Seeing those radio waves would give scientists great confidence in the theory of the Big Bang.

In 1964, Arno Penzias and Robert Wilson were at Bell Labs and they were attempting to make a measurement of radio sources in the Milky Way. Because they were hoping to study these sources with considerable precision, it was important to understand the signal their antenna would see when it was receiving no signal. So, they turned the antenna to a location in space with no radio sources. However, instead of a silent radio receiver, they heard a faint hiss.

After considerable effort to get rid of the unwanted signal (including, most famously, cleaning the antenna of bird droppings), they concluded that the signal was real. They contacted Robert Dicke’s group at Princeton. The Princeton group realized that Penzias and Wilson had observed the radio signal of the Big Bang, what is now called the cosmic microwave background or CMB. Penzias and Wilson published their observation in the July 1965 issue of Astrophysical Journal, accompanied by a paper by Dicke, Peebles, and other collaborators, which interpreted the radio hiss as the radio remnant of the Big Bang. Penzias and Wilson shared the 1978 Nobel Prize in physics and today’s announcement acknowledges the contribution from the Princeton group.

The discovery and characterization of the CMB was merely the start of an illustrious career. Peebles went on to develop theoretical tools and calculations that made it possible to understand the entire history of the universe. In collaboration with others, his calculations made possible other discoveries, like observations which led to the conclusion that our universe is filled with a repulsive form of gravity, called dark energy.

Mayor and Queloz were recognized not for grand thoughts about the structure of the cosmos, but for the observation of a planet around a sun-like star. In October, 1995, they announced the discovery of an exoplanet called, 51 Pegasi b, a planet comparable to our own Jupiter. It was discovered by looking at the motion of its parent star, 51 Pegasi.

51 Pegasi is slightly larger than our Sun and the planet 51 Pegasi b is slightly bigger than Jupiter. However, where Jupiter takes 12 years to go around our Sun, 51 Pegasi b orbits in just four days. It’s really close to its parent star.

This mass and proximity means that when the planet orbits the star, the star wobbles, kind of like how an adult would wobble if they grabbed a small child’s hands and spun them around quickly. 

Mayor and Queloz could see the wobble using the Doppler effect. Just as the pitch of a train whistle changes as it goes by you, light from moving objects also apparently changes. If object is moving towards you, it looks somewhat bluer and if it is moving away, it looks red. By monitoring the color of 51 Pegasi, the astronomers knew there was a massive body orbiting it.

Since this first discovery of an exoplanet around a sun-like star, there have been more 4,000 exoplanets discovered using the motion method and others. We went from not knowing whether there were any other planets in the universe, to knowing that planets are common.

We don’t yet know if life exists, but we now have the instrumentation to start looking for Earth-like planets around Sun-like stars. It’s only a matter of time before we find our cosmic twin. And, when that happens, there will be a huge conversation about whether we should go there. I hope that we will.

The Nobel Prize is an award for excellence in science and for making discoveries that ennoble humanity. Today’s recipients are deserving new members of that most exclusive of clubs.

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