This is an excellent choice, and (of course) congratulations to the recipients. Their work really did add an extremely significant chunk to our understanding of the universe. And I think it has now been long enough to confirm that their observations really were accurate.
It was also, I think, the first scientific paper I actually read -- I did an assignment on it as a callow young undergraduate, and I still remember sitting in Fisher library poring through the text copy of the journal and trying to figure out what was going on.
Since the page doesn't actually explain the work, I'll have a go. I'm doing this from memory, so someone correct me if I get something wrong. Basically, they set out to study how the distance of a receding galaxy relates to its redshift (ie the speed at which it's receding). Up to this point we could easily measure the redshift of a galaxy, but not its actual distance.
How do you measure the distance to a galaxy? What they did was to look for Type 1a supernovae. This is a particular subclass of supernovae which always have the same luminosity, because they occur when a previously-stable neutron star goes just over the mass limit and becomes unstable. There's a sufficient number of these going off in the universe in any given week that they make a good "standard candle", so by measuring their brightness you can estimate their distance.
What these guys found was extremely surprising: the relationship between distance and speed was not what we would have expected based on a universe which has been evolving only under the influence of gravity since its birth -- there was an extra term which appears to be accelerating the expansion of the universe over time.
And that, right there, is an amazing fact about the universe which nobody knew fifteen years ago.
SNIa are not quite standard candles, not good enough to by themselves make this measurement. However, experimentally it has been observed that their brightness correlates with how fast they brighten and then fade. This relationship, which is not well understood theoretically, makes it possible to measure how fast they brighten and fade and use this to know how bright they are. The difference between an accelerating and a decelerating universe is too small to be seen without this correction.
Second, what these guys did that no one had done before was to figure out how to find the supernovae. Up until then, the way it was generally done was that someone (generally an amateur astronomer) would notice a bright dot in some galaxy and report it. Then the professional astronomers would use large telescopes to observe it in detail and follow it as it brightened and faded. However, this only works for nearby galaxies that amateurs look at.
The problem is that professional telescopes are scheduled months in advance, but you of course can't know that there will be a SN in a few months time so you can apply for telescope time. What they did was sort of the opposite - by surveying a large number of galaxies with a smallish telescope they would be guaranteed to find a number of actual supernovae. They wouldn't know exactly where, of course, but with a large enough number of surveyed galaxies there would always be a few in some galaxies. They managed to convince the time allocation committees on the large telescopes that it was not a waste of telescope time to give them the time just based on the expectation that they would have something to look at. (I think this was the first time where telescope time was awarded to look at something that would happen in the future... ;-) With this method in place, the number of observed high-redshift supernovae skyrocketed.
Robert Kirshner advised both Schmidt and Riess at Harvard and was an integral member of the High-Z Search Team. His book The Extravagant Universe is worth reading if you are interested in the topic. http://www.amazon.com/dp/069111742X/?tag=googhydr-20&hva... Many thought that Kirshner himself would get the Nobel for his work in the field, and I am sure it is a little bitter-sweet (if mostly sweet) for his team members to be among the winners.
Martin Rees just commented on that:
"I think, however, that this is one of the increasingly frequent instances when the Nobel Committee is damagingly constrained by its tradition that a prize can't be shared between more than three individuals. The key papers recognised by this award were authored by two groups, each containing a dozen or so scientists. It would have been fairer, and would send a less distorted message about how this kind of science is actually done, if the award had been made collectively to all members of the two groups."
Yeah, but once you relax that rule you'll wind up devaluing, pretty quickly, the Nobel Prize. If every one of those 24 authors can equally claim to be a Nobel Prize winner on their CVs, then you've just significantly increased the number of living Nobel laureates in physics.
The real problem would arise a few years down the road, though, next time the Nobel gets awarded for some high-energy experimental work (discovery of the Higgs boson?). Those papers can typically have hundreds of authors, listing everyone involved with the project (the most extreme example I've seen has 2512 authors). Now all of a sudden pretty much everyone in high-energy physics is a Nobel laureate, and the proper Nobel laureates are a tiny minority.
I think the constraint that no more than three people can share it is fair. It just means the committee needs to look into it and find out who the real brains behind the operation were.
It just means the committee needs to look into it and find out who the real brains behind the operation were.
But the problem is that this is impossible. Who are the real brains? The person who had the idea, but didn't do anything about it? The person who organized the project and got funding for it but didn't do any real science? The person who build the hardware without which nothing would have been possible? The person who wrote the software, without which nothing would have been possible? The person who wrote the paper that explained the results? The grad student who found a crucial error in the analysis without which the results would have been wrong?
In many (most?) fields of science these days, progress is made by huge projects. Clearly there are wide differences between how crucial different people are to the success of the project, but to cut it down to 1-3 "winners" to the detriment of everyone else hardly seems fair. It seems more reasonable to say that if there are 200 people on the paper that's awarded the prize, everyone is a 0.5% Nobel Laureate....
As science delves deeper and deeper, it has become a more collaborative enterprise. Consider that there were only 3 authors on the paper describing the structure of DNA but ~300 on the paper describing the structure of the human genome.
Adam Riess! One of my friends took "Stars and the Universe" with him last semester here at Hopkins and really enjoyed the class (perhaps corroborating the claim that the most capable researchers tend to also be great educators).
Erm, at the risk of being (equally) trite, one data point doesn't corroborate anything except for the somewhat fluffy claim that some good researchers are also good educators.
"The Nobel Prize in Physics 2011 was awarded "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae" with one half to Saul Perlmutter and the other half jointly to Brian P. Schmidt and Adam G. Riess."
Seems clear to me. Perlmutter gets 50%, Schmidt and Riess each get 25%.
It was also, I think, the first scientific paper I actually read -- I did an assignment on it as a callow young undergraduate, and I still remember sitting in Fisher library poring through the text copy of the journal and trying to figure out what was going on.
Since the page doesn't actually explain the work, I'll have a go. I'm doing this from memory, so someone correct me if I get something wrong. Basically, they set out to study how the distance of a receding galaxy relates to its redshift (ie the speed at which it's receding). Up to this point we could easily measure the redshift of a galaxy, but not its actual distance.
How do you measure the distance to a galaxy? What they did was to look for Type 1a supernovae. This is a particular subclass of supernovae which always have the same luminosity, because they occur when a previously-stable neutron star goes just over the mass limit and becomes unstable. There's a sufficient number of these going off in the universe in any given week that they make a good "standard candle", so by measuring their brightness you can estimate their distance.
What these guys found was extremely surprising: the relationship between distance and speed was not what we would have expected based on a universe which has been evolving only under the influence of gravity since its birth -- there was an extra term which appears to be accelerating the expansion of the universe over time.
And that, right there, is an amazing fact about the universe which nobody knew fifteen years ago.