Wednesday, October 9, 2013

The Nobel Prize for Physics: 2013 and Looking Ahead

It’s Nobel Prize week and early yesterday the winners of the physics prize were announced. Congratulations go to Peter Higgs and Francois Englert for "the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider” according to an official statement. Another scientist, Robert Brout was co-author of a key paper with Englert in 1964, but he died in 2011 so he couldn’t be given the prize, according to the Nobel rules.

Francois Englert (left) and Peter Higgs at CERN on July 4th, 2012, when the discovery of the Higgs boson was announced. Credit: Maximilien Brice/CERN 
Many media pundits predicted that scientists associated with the Higgs would win, but there was uncertainty about who would be given the award, since the Nobel can be given to a maximum of three recipients. One problem was that Gerald Guralnik, Carl Hagen and Tom Kibble performed very similar work and published it only a few weeks after the others. Here’s a reaction to the Nobel decision from Tom Kibble and one from Gerald Guralnik. I can certainly understand this stinging a little.

The Nobel Prize in physics has always been awarded to individuals, but some suggested that a share of the prize might be awarded to scientists at CERN’s Large Hadron Collider. That didn’t happen, but maybe it will in the future, since they certainly deserve it. For now they have a consolation prize with the official mention of their crucial confirmation.

One interesting feature of this year’s prize was the slight delay in the announcement yesterday morning. This article from the Associated Press gives some fascinating insight into the secretive Nobel process, while failing to actually explain the delay. The deliberations of the Nobel Committee are supposed to be kept secret for 50 years, which doesn’t say a lot for their openness and transparency. However, some details of the process are made available and I was surprised to learn that the decision on the Nobel isn’t made until the day of the announcement, using a majority vote by the full academy. With all of the media speculation that occurs in the build-up to the announcement, especially this year for the Higgs, I wonder if the academy imposes any sort of media blackout in an attempt to avoid bias. Unconscious bias is especially hard to avoid.

Many articles about the physics prize have already been written and more will be published over the next few days. They can easily be found with Google News. For detailed background on the science that does not mention the unfortunate nickname for the Higgs boson, I recommend this blog post by physicist Matt Strassler. For well-argued critiques of the Nobel Prize's rules and tradition, I recommend these articles by Sean Carroll at his blog and in the New York Times (I have some thoughts on this topic, but I'll save them for another blog post).

Looking ahead

I’ll now discuss who might be having a sleepless night one year from now, when the physics field will presumably be more open. My discussion will be limited to astrophysics (*), where my background lies.

Thomson Reuters suggested that the astronomers who did key work on exoplanets had a chance for the 2013 prize, namely Geoff Marcy, Michel Mayor and Didier Queloz (another strong candidate is William Borucki, the Principal Investigator for the very successful Kepler mission). When I saw this prediction I wondered if the relative lack of new physics that has come from exoplanet work might be a handicap. For example, in this article by Kate Becker, 2011 Laureate Adam Riess discusses the type of work that tends to win the Nobel: "I think the key is its importance must be fundamental, generally involving new physics."

A screenshot from paperscape.org. Credit: paperscape.org
Here’s a graphical way to look at this issue, using a great new visualization of the ArXiv called paperscape. The dots in this figure represent papers, where astrophysics papers are colored dull pink and papers in other fields of physics have different colors, such as green and blue. The points representing papers are located near other papers that they reference, using an N-body algorithm. As an example, in this close-up view you can see that papers involving dark energy and the cosmic microwave background show close links between astrophysics and other areas of physics. There’s a lot of color mixing going on. It’s notable that three different Nobels have been awarded for work in these areas.

A close-up of a screenshot from paperscape.org. Go to the web-site for a much clearer picture. Credit: paperscape.org
The field of “extrasolar planets” – now commonly called exoplanets – is located in the lower right, in a region that is clearly separate from other areas of physics, implying that there is a lack of contact between exoplanet work and other areas of physics. Despite this apparent weakness I still think that exoplanet workers should win the physics prize sometime in the future, as the field is remarkable in so many other ways. Astronomers have found evidence for a class of object that is more common than stars and that has incredibly diverse properties. They are beginning to answer one of the longest-standing questions in science: how common are earth-sized and earth-like planets? They have taken a crucial step towards understanding how common life might be in our galaxy. Currently I’m reading a terrific book by Lee Billings about this great adventure, called “Five Billion Years of Solitude”.

I can give a personal reason for supporting an exoplanet-related Nobel Prize: if Marcy or Mayor are given the award, I can boast that I was a co-author with a Nobel prize winner. The problem with this boast is that I've never met either of them and many other scientists can make a similar claim, in this era of author-inflation.

I'll note, at risk of revealing my earlier concern to be a strawman, that there is a precedent for awarding the Nobel for astrophysics work that is more applied physics than fundamental physics. For example, Nobel prizes were awarded to Sir Martin Hyle for developing aperture synthesis in radio astronomy and to Riccardo Giacconi for the discovery of X-ray sources

The map from paperscape can be used to discuss hints about other potential future Nobels involving astrophysics. The area of the circle for each paper is proportional to the number of citations a paper has received, and it’s easy to spot the two key papers by Adam Riess and Saul Perlmutter that led to the 2011 prize (go to paperscape.org, zoom in and click on the two largest circles near “dark energy”, using my figure as a guide). So, assuming that citations are a good reflection of scientific importance, the large circles near “cosmic microwave background” may hint that Charles Bennett, David Spergel and others involved with NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) will attract interest from the Nobel Committee in the future.

Glancing at this area of the map is a good reminder than no Nobel has yet been awarded for the discovery of dark matter. Here, Vera Rubin is an outstanding candidate for her work on galaxy rotation, as others have noted. It’s interesting to me that evidence of dark matter was found well before evidence for dark energy, and yet a Nobel has been awarded only for the latter. Another subject area that might receive attention is inflation, where Alan Guth, Andrei Linde and others have done critical work. However, extra observational evidence, from projects like Planck, the Atacama Cosmology Telescope and the South Pole Telescope, might be needed to convince the Nobel committee. 

Vera Rubin at the Kitt Peak 84-inch telescope in 1970. Credit: Carnegie Institution, Department of Terrestrial Magnetism and Vera Rubin.
Since the arXiv is only about 20 years old, the crucial papers by the new Nobel winners, and by others like Vera Rubin and Alan Guth do not appear in paperscape. A similar comment applies to the highly influential papers by Rashid Sunyaev on the Sunyaev Zeldovich effect and the Shakura-Sunyaev model for material in a disk around a compact object, such as a black hole. For some extra background, here's an interview I did with Sunyaev last year. I think he would be an excellent choice as a Nobel Laureate.

Rashid Sunyaev. Credit: Rashid Sunyaev.
I've already mentioned dark matter and dark energy. Another crucial part of observational cosmology is the Hubble constant, giving the expansion rate of the universe. Here, Wendy Freedman and others have done very important work, including this highly-cited paper. It should be noted that Freedman has already won the prestigious Gruber prize in cosmology, along with Charles Bennett and the WMAP team, the winners of the 2011 Nobel prize (Perlmutter, Riess and Schmidt), John Mather (co-winner of the 2006 Nobel prize) and the COBE team, along with Guth, Linde, Rubin and Sunyaev. No wonder it’s sometimes referred to as the Nobel Prize of astronomy.

This list of possibilities is not meant to be complete, and I'm sure there are better judges than me. What important and potentially Nobel-worthy work in astrophysics have I missed?



(*) Here are some quick Nobel statistics to give perspective. Of the 107 Nobel prizes in physics I count ten that clearly involve astrophysics (I won’t count Einstein because the award didn’t explicitly mention general relativity). Eight out of ten of these have been awarded since the 1960s and 3 since 2002, showing a possible rise in prominence of astrophysics compared to other areas of physics. Has astrophysics been pulling its weight compared to other areas? I didn’t find historical statistics on numbers of paper in different areas of physics, but I see that about 24% of physics papers on the arXiv in 2012 are in astrophysics. This isn’t too different from the recent fraction of astrophysics-related Nobels, although we're obviously dealing with small number statistics.

Other statistics: only one Nobel has been awarded for work involving optical astronomy: the 2011 prize. One notable omission, besides the discovery of dark matter, is the discovery that the universe is expanding. Edwin Hubble, Georges Lemaitre and Vesto Slipher, among others, did important work here, but died years ago.

I'll end with a disappointing statistic. Over the 196 Nobel Laureates in all areas of physics, only 2 have been women, none of them involved in astrophysics. It's time that changed.


2 comments:

  1. Great post Peter! It's nice to see Paperscape being used to get a big picture of physics. Note that you can easily specify a location on the map by quoting the arXiv ID at that point. One can then easily search for the arXiv ID in the search box to go straight to that location. Even easier is to give a direct link, such as http://paperscape.org/?s=astro-ph/9812133

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    1. Thanks very much. It may not be obvious, but I was using the Nobel as a news hook because I wanted to draw attention to paperscape, which I think is great. I'll add some direct URLs later: that was just what I needed.

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