Jim Peebles: Co-Winner of the 2019 Nobel Prize in Physics

Jim Peebles in 2010. Credit: Juan Diego Soler via Wikipedia.

Today is one of the most important days of the year in my line of work: the Nobel Prize award ceremony. The Nobel Peace Prize probably gets the most attention (good and bad) of the six prizes from the public, but Physics is probably the next most notable—though maybe I’m biased. I wanted to highlight it, though, because one of the recipients, James Peebles, hails from my own graduate school, Princeton. (See the Nobel Foundation’s write-up here.)

I do feel like the Physics Prize highlights the most fundamental discoveries about the universe compared with the others. This year’s Chemistry Prize was awarded for the invention of the lithium-ion battery, which admittedly is a big deal, but the Nobel Prize in Medicine was awarded “for their discoveries of how cells sense and adapt to oxygen availability.” I’m sure that’s also important, but it’s not an attention-grabbing headline. The Economics Prize was awarded “for their experimental approach to alleviating global poverty.” Also very important. Also one of the least interesting headlines imaginable in our sensation-driven media world. And Literature? I’m sure Peter Handke is worthy, but writing in a particular language (any language, though English is the least disadvantaged) means it isn’t going to resonate with as many people.

So, bottom line, the Nobel Prize in Physics is a big deal. However, I thought the way they awarded it this year was odd. Looking at past laureates, it’s not completely unprecedented, but it’s definitely very unusual.

Here’s how it works. Each Nobel prize may be divided among up to three people (although for the Peace Prize, they can be organizations). Usually, the recipients are awarded it for a single scientific discovery, but sometimes, it can be two independent discoveries if the Nobel Foundation believes they are equally noteworthy. In Physics, this first happened in 1936, when Victor Hess received the prize for the discovery of cosmic rays, and Carl Anderson won it for the discovery of the positron.

But usually (including in the 1936 case), the two discoveries are related to each other: optical (laser) tweezers and ultra-short laser pulses in 2018, fiber optics and CCD sensors in 2009, and so forth. This year, however, the Nobel Committee awarded the Physics Prize for two completely unrelated discoveries—one of which wasn’t even a particular discovery.

One half of this year’s prize prize was awarded to Michel Mayor and Didier Queloz of the University of Geneva for discovering the first extrasolar planet orbiting a Sun-like star, 51 Pegasi b, in 1995. This is a good choice and has been a long time coming in the eyes of many astronomers.

Meanwhile, the other half of the prize was awarded to Jim Peebles of Princeton, which, while deserved, has nothing to with exoplanets because Dr. Peebles is a cosmologist. These things are about as far apart as it is possible to get within the field of astrophysics. You do sometimes see very disparate discoveries being awarded the prize in the same year, but it’s very rare.

Even more unusual, Dr. Peebles was awarded the prize “for theoretical discoveries in physical cosmology.” This wasn’t for a particular discovery like most of the others. This prize was awarded for his total body of work.

I’d never seen this before. I was surprised that the Nobel Foundation would consider a body of work rather than a specific discovery. In fact, I thought going in, that it might be unprecedented, but it turns out that I was wrong. There was one prior year in which the Physics Prize was awarded in a nearly identical way, and that year was 1978.

In 1978, half of the prize went to Arno Penzias and Robert W. Wilson for (more or less accidentally) discovering the cosmic microwave background (CMB), while the other half went to Pytor Kapitsa “for his basic inventions and discoveries in the area of low temperature physics.” Two scientists receiving the prize for a specific discovery, and a third in a completely unrelated field receiving it for his overall body of work. It’s interesting how these decisions are made.

But back to Jim Peebles. I met Dr. Peebles briefly when I was at Princeton, although we didn’t interact much because he was in the Physics Department while I was in Astrophysics. (Whether or not they are separate depends on the school.) I already knew at the time that he was one of a short list of professors even at Princeton whose achievements you read about in popular science books. But what is it about his body of work that makes him stand out from the other cosmologists?

To clarify one point, “physical cosmology” is pretty much the whole science of cosmology (the study of the universe as a whole), not just a branch of it. The qualifier is only there to distinguish it from religious, mythological, and philosophical cosmology, which (to greatly oversimplify) deal with the spiritual organization of the universe as opposed to the physical.

And the answer to my question is that Jim Peebles was a cosmologist before it was cool. He started working in the field way even before the CMB was discovered in 1964, and at the time, there wasn’t much interest in it, in part because we had very little data. We had the CMB, which so far as we could tell was just a uniform radio hiss, and we had a vague map of galaxy clusters and a lot of pretty pictures of galaxies we couldn’t explain. We didn’t even know about dark matter yet (except for Fritz Zwicky).

That’s not very much to base a whole field of astronomy on, but Dr. Peebles kept at it. He was one of several people who predicted the existence of the CMB, and he put a lot of effort into analytic and computer modelling of galaxy and cluster formation, and in doing so, he laid the foundations for the entire field as a rigorous science.

In answer to my biggest question. Dr. Peebles wasn’t awarded the Nobel Prize for a specific discovery because there wasn’t one. As he himself has said, “It was not a single step, some critical discovery that suddenly made cosmology relevant but the field gradually emerged through a number of experimental observations.” It really was his body of work as a whole that built the field.

So congratulations to Dr. Peebles. And congratulations also to Drs. Mayor and Queloz. By rights, their half of the prize should be more relevant to me because I study exoplanets myself, but that’s another story, and one I’ve told before. But keep an eye out for an upcoming post about the humorous side of cosmology.

About Alex R. Howe

I'm a full-time astrophysicist and a part-time science fiction writer.
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1 Response to Jim Peebles: Co-Winner of the 2019 Nobel Prize in Physics

  1. Pingback: Cosmology in the 1980s: The Dark Matter Flowchart | Science Meets Fiction

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