The winners of 2011 Nobel prize in Physics have been announced. “For the discovery of the accelerating expansion of the Universe through observations of distant supernovae” one half does to Saul Perlmutter of the Supernova Cosmology Project and the other half jointly to Brian P. Schmidt and Adam G. Riess of the High-Z Supernova Search.
I remember when both groups announced their results in 1998. I was a grad student at the time, and assumed (since I’d been basically told as much by inflationary theory) that the universe had to be flat, and had to be filled entirely with dark matter. I thought I was sooooo smart for being skeptical. The universe is accelerating? Ridiculous!
But here we are 13 years later, and the results from supernova searches, combined with the results from WMAP and other microwave mapping programs lead us to an essentially inescapable conclusion: the universe is accelerating and geometrically flat. It contains about 75% Dark Energy (or quintessence, or cosmological constant), and about 25% Matter (a combination of dark and otherwise). It’s rather unusual to award the Nobel prize after only 13 years, but in this case, there is ample evidence that the basic result, the acceleration of the universe, will stand up to future scrutiny.
To give an indication of how well independent experiments agree, consider this, from the Supernova Cosmology project:
This whole thing got me thinking about how exciting it is when an “Astronomy” prize is awarded. Generally, the prize is given to a discovery which is in some way materially connected to technology, rather than to one that merely explains how the universe works and further elucidates our place in it. In the history of the Nobel prize, it’s only gone to astronomical or cosmological discoveries a few times:
- 1967 – Hans Bethe “for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars”.
- 1974 – To Sir Martin Ryle and Antony Hewish “for their pioneering research in radio astrophysics: Ryle for his observations and inventions, in particular of the aperture synthesis technique, and Hewish for his decisive role in the discovery of pulsars.” Most astronomers, including me, think that the 1974 award was a grave injustice. Jocelyn Bell built the array that discovered the pulsars, identified and explained the signals. In a real sense, she should have won the prize solo or shared it with Ryle. Instead, as she was a grad student at the time (and a female one at that) Hewish put her name downlist on the paper announcing the result (rather than 1st author, as would have been justified in this case).
- 1978 – One half awarded to Pyotr Leonidovich Kapitsa “for his basic inventions and discoveries in the area of low-temperature physics”,the other half jointly to Arno Allan Penzias and Robert Woodrow Wilson “for their discovery of cosmic microwave background radiation,” an unusual award that was split between discoveries. The 1978 prize also comes with a list of people who were very close to discovering the microwave background independently — notably Dicke and Peebles.
- 1983 – Subramanyan Chandrasekhar “for his theoretical studies of the physical processes of importance to the structure and evolution of the stars” and William Alfred Fowler “for his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe”.
- 1993 – Russell A. Hulse and Joseph H. Taylor Jr. “for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation.” As a sidenote, Taylor (the supervising professor of Hulse, who was then a grad student) recognized the significant of what they’d discovered, and the probability that it was likely to lead to a Nobel prize. Out of a sense of justice and historical perspective (based on the Hewish and Bell case), Hulse was listed first on the paper announcing the result.
- 2002 – One half went jointly to Raymond Davis Jr. and Masatoshi Koshiba “for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos” and the other half to Riccardo Giacconi “for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources”.
- 2006 – John C. Mather and George F. Smoot “for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation” This award was the next logical step after Penzias and Wilson’s prize in 1978. Penzias and Wilson discovered the microwave background. Mather, Smoot, and the COBE team showed that the background had bumps and wiggles in it, the seeds of cosmological structure.
- 2011 – To Permutter, Riess, and Schmidt, for discovery of the accelerating universe.
Hubble (who determined conclusively that there were other galaxies in the universe and that the universe was expanding) is notably absent from the list, though I’m sure that we could all think of other major omissions if we tried.
Congratulations to Perlmutter, Riess, and Schmidt, the Supernova Cosmology Project team and the High-Z Supernova Search team!