I was asked the other day whether Alan Guth should expect to win the Nobel Prize for inflation, now that WMAP has found tentative evidence for a slight “tilt” in the primordial perturbations, just as we might expect from inflation. At the moment I’m leaning toward “not yet,” but it started me thinking about which cosmology discoveries have yet to be honored by Nobels but should be at some point. (After the 2004 prize for asymptotic freedom, there aren’t really any completely obvious particle-physics prizes lurking out there, although prizes for color, spontaneous symmetry breaking, and CP violation would be quite warranted.)
There are two discoveries that are obviously Nobel-worthy: the temperature anisotropies in the cosmic microwave background, and the acceleration of the universe. One that is a bit less obvious, but still extremely strong, is dark matter. In each case, however, it is not precisely clear which people should actually get the prize, given the constraints: (1) laureates should be individuals, not collaborations, (2) prizes are giving to living people, not posthumously, and (3) at most three people can share one prize.
The 1992 observation of CMB anisotropies by NASA’s COBE satellite was the first step in a revolution in how cosmology is done, one that has come to dominate a lot of current research. Subsequent measurements by other experiments have obviously led to great improvements in precision, and most importantly extended our understanding of the anisotropies to smaller length scales, but I think the initial finding deserves the Nobel. So to whom should the prize be awarded? On purely scientific grounds, it seems to me that there was an obvious three-way prize that should have been given a while ago, to David Wilkinson, John Mather, and George Smoot. Wilkinson was the grandfather of the project, and was the leading CMB experimentalist for decades. Mather was the Project Manager for the satellite itself (as well as the Principal Investigator for the FIRAS instrument that measured the blackbody spectrum), while Smoot was the PI for the DMR instrument that actually measured the anisotropies. Unfortunately, Wilkinson passed away in 2002. Another complicating factor is that there were various intra-collaboration squabbles, leading to books by both Smoot and Mather that weren’t always completely complimentary toward each other. Still, background noise like that shouldn’t get in the way of great science, and these guys definitely deserve the Nobel.
The first direct evidence for the accelerating universe came from two groups: the Supernova Cosmology Project and the High-Z Supernova Team. The issues of priority are a bit complicated, but both groups certainly deserve substantial credit in discovering this surprising and enormously influential result. The SCP is an easier case: they started first, and were clearly led by Saul Perlmutter, who is a shoo-in for the Nobel. The High-Z team was a bit more democratic, and started second but actually went on record first with the claim that the universe was accelerating. Their PI was Brian Schmidt (full disclosure: my old grad-school officemate); the first author on the discovery paper was Adam Riess; and their spiritual leader was Robert Kirshner (most of the team members were either students or postdocs of Bob’s at one point or another). Hard to construct a sensible prize from that mess, but if I were in charge of the universe I might give 50% of the prize to Perlmutter and 25% each to Schmidt and Riess, and feel really bad about not including Kirshner. But the discovery is clearly worthy of a Nobel, and I likely won’t complain with whatever way they choose to divvy up the award.
Then we get into murkier waters, I think. The idea of dark matter is one of the most influential and important in modern cosmology, and a Nobel would be perfectly appropriate. You might complain that we haven’t actually discovered dark matter yet, which is certainly true and relevant; but one way or another, something is going on with the dynamics of galaxies and clusters that is above and beyond what our current theories predict, and that empirical fact is hugely important. It was first pointed out by the late Fritz Zwicky in the 1930’s, comparing the velocities of galaxies in the Coma cluster to their total mass. But the field matured immensely with Vera Rubin‘s measurements of the rotation curves of spiral galaxies, giving direct evidence that the gravitational force fell off more slowly than the distribution of visible matter could account for. Rubin absolutely deserves the prize, in my opinion. Then there is the more specific cold dark matter idea, which is a specific model for the nature of dark matter and its role in galaxy formation; credit for that is more diffuse (although the paper by Blumenthal, Faber, Primack and Rees was obviously influential), and we’re less sure that the basic idea is right, so I don’t see any need for a prize there quite yet. I think it would be great to give a joint prize to Rubin and someone else, perhaps Wendy Freedman for measuring the Hubble constant, or Jim Peebles for developing physical cosmology.
Then we get to inflation, which is a sticky issue in various ways. There is absolutely no question that inflation has been one of the most, arguably the most, influential idea in cosmology in the last several decades. There is a great deal of discussion about who gets credit for it, since a number of papers discussed very similar-sounding ideas; but it was clearly Alan Guth‘s 1981 paper that put the story together in the right way. However, Guth’s model (“old inflation”) didn’t quite work, and the two follow-up papers by Andrei Linde and by Andreas Albrecht and Paul Steinhardt (“new inflation”) actually showed that the idea was plausible. That’s a total of four people, you’ll notice. Because Andy Albrecht was a graduate student at the time of his inflation paper with Steinhardt, and because both Linde and Steinhardt have gone on to write many more influential papers about inflation, credit is sometimes informally given to “Guth, Linde, Steinhardt and others…”, which is a little unfair.
But more importantly, we don’t know whether inflation is right. There is no question that it has made a number of predictions that have been dramatically verified: the universe is spatially flat, there is a spectrum of adiabatic and Gaussian primordial density perturbations, and that spectrum is nearly scale-free although not necessarily precisely so. And these predictions were by no means guaranteed in advance; models in which the perturbations were generated by cosmic strings, for example, were quite viable in the 1980’s, but have now been ruled out by CMB anisotropy observations.
Still, the idea that some non-inflationary mechanism set the initial conditions for the Big Bang still seems plausible to me, even if I don’t know what that mechanism would be. The predictions from inflation have been sharp, but they have not been the kinds of things that we couldn’t imagine getting from any other model. If we were to find evidence for gravitational-wave perturbations in the polarization of the CMB, of the type inflation could easily explain, then I might be convinced; but it’s quite possible that the gravity wave are really there but at a level too tiny to ever be observed.
So I’m somewhat torn. Inflation is a compelling and ingenious and influential idea, and it should be recognized. But the Nobel committee doesn’t like to give out prizes unless they’re completely sure that the discovery/theory to which they’re being given has no chance of being wrong. I’m not sure how to elevate inflation from the status of “probably on the right track” to the status of “correct beyond a reasonable doubt.” In the meantime, if the Nobel committee decides to take a risk and give Alan Guth the prize, you won’t hear any complaints from me.
I think one of the “problems” with the Nobel is that it is NOT a lifetime acheivement award but given for a particular discovery. The example I am thinking of is Alan Sandage. Also I would think that David Schramm (unfortunately no longer eligible) might be considered for big-bang nucleosynthesis work.
Hawking!?
Alpher, Peebles and Dicke (if he’s still alive; is he?) for the prediction
of the Cosmic Microwave Background. This one should have gone to
Gamow, Alpher and Hermann. If Rubin and Alpher were awarded, Gamow
would at least posthumously have two of his students awarded.
In terms of particle physics prizes, discovery of neutrino oscillations is a slam-dunk prize waiting to happen, but has to wait until MiniBooNE clears up whether LSND has a claim on this prize.
Dicke is dead. Otherwise, he would have deserved it for the invention of the Dicke radiometer alone.
Every year, I root for Peebles and Sunyaev for CMB anisotropies. Or Peebles, Yu and Sunyaev. Of course, Zel’dovich would have richly deserved to be in there, but he is no longer living.
The companion to Penzias and Wilson’s paper was Dicke, Peebles, Roll and Wilkinson. Does anyone know what happened to Roll? (Jer Yu, incidentally, is in administration at a university in Hong Kong.)
Sean, I would think Starobinsky, Kazanas, and Sato
should also be in the running as their papers were earlier than Guth’s paper, though
they never called it “inflation”.
Just a point of curiousity: Is “the expansion of the universe is accelerating” in the incontrovertible, 100%, sure thing category? I’ll admit to being a bit suspicious of discoveries made since I left physics in the mid-1990’s :-), but I thought that there was still room for doubt about the acceleration of the universe…
After all, there are nice pretty pictures of CMB anisotropy, but the evidence for acceleration seems a bit more subtle.
Being less traditional, I would nominate John Carlstrom and the DASI team for their detection of CMB polarization. An awesome feat from the South Pole! Because experimentalists are underweights in the Nobel arena, this nomination would help balance the scale between theorists and experimentalists. Going further out on a limb, I will remark that anyone who can detect the B-mode of polarization should receive an instant Nobel Prize!
Alex, nothing is ever a sure thing. But the acceleration of the universe is now solidly in the beyond-reasonable-doubt category, having been confirmed by multiple independent methods (supernovae, CMB, large-scale structure in different ways).
Sean, not to quibble, but I’ve heard several big-name cosmologists at my university make the statement that while the universe probably is in fact accelerating, the evidence just isn’t irrefutable yet. (One even compared it to the original Hubble diagram and another stated he ‘wouldn’t bet a house on it.’)
Blumenthal, Faber, Primack and Rees?? Uh oh, looks like the southern California bias is already settling in with Sean.
Acting as a daring speculator, I will boldly nominate Bekenstein and Hawking for their black hole-entropy formula. One cannot deny that this formula – with its twist on the second law – has had a profound influence upon our collective view of the cosmos as an information reservoir. In comparison to our fruitful mining operations upon the CMB, we – unfortunately – are still far from being able to mine for empirical data from a black hole horizon.
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Cynthia: Acting as a daring speculator, I will boldly nominate Bekenstein and Hawking for their black hole-entropy formula.
Since we won’t see any empirical evidence for this in their lifetimes (and possibly in the lifetime of anyone currently living), I wouldn’t hold my breath.
Regarding the acceleration of the universe: If this is almost a sure thing, at this point, can anyone give the two- or three-sigma confidence interval for some cosmological quantity that parametrizes acceleration — a-double-dot/a, or Omega_Lambda — based on current measurement, and independent of any theoretical prejudice such as Omega_total = 1? Sean’s 2000 MOG article he pointed to referenced papers that kind of do this, but there must be more accurate data by now…
As for empirical evidence for black-hole entropy: I would settle for evidence for black-hole evaporation. Searches have been done for evaporating cosmological black holes, with no success — but that doesn’t prove anything except there weren’t enough black holes of the right size made in the big bang.
The other near-impossible experiment that brilliant experimenters should think about: observing the cosmic *neutrino* background. We know it’s got to be there, but the neutrinos are so low energy they’re pretty much impossible to detect. The cool thing about the cosmic neutrino background is that it would be a direct window into a much earlier phase of the universe than we can see through the cosmic microwave background.
Alex, it always depends on what assumptions you make, but the dark energy equation-of-state parameter w is as good a place to start as any. According to WMAP, putting together all the experiments gives these parameters:
http://lambda.gsfc.nasa.gov/product/map/dr2/params/ocdm_w_all.cfm
The measured value of w is -1.06 (+.13/-.08). Since “acceleration” requires w less than -1/3, that’s better than a 5-sigma detection. If you assume that the dark energy density is constant, the significance is substantially higher.
People can disbelieve the data all they like, of course.
Alex R: I agree… Detecting a “neutrino-type” background signature of the cosmos would be more realistic than detecting a “entropy-type” signature of a black hole horizon. Despite the obvious restraints imposed by objective reality, it’s rather amusing to fantasize about black holes!
can anyone give the two- or three-sigma confidence interval for some cosmological quantity that parametrizes acceleration — a-double-dot/a, or Omega_Lambda
I did it back in 2003. This is based on the SCP supernovae through about 2001. (Well, not all of them, but the ones from the Perlmutter 99 paper plus an additional HST-observed 11 that were the main topic of that paper.) I did lots of fits, and didn’t always assume Omega_Total=1. I did, in practice, always assume *either* that Omega_Total=1 *or* that dark energy is Vacuum energy (i.e. w=-1), although just for kicks at one point I even relaxed that. (There, there was more probability for Omega_w->0, but it also needed values of w that were way less than -1, and as such are really scary.)
Depending on which fit you want to believe, the probability that Omega_Lambda>0 assuming that w=-1, but *not* assuming that Omega_Total=1, is higher than 0.99. (My two favorite fits have 0.9997 and 0.9974, respectively.) This is based on that dataset, which is a few years old now. If you got to the datasets in the ESSENCE and CFHTLS papers that have come out in the last year, I susepect you’ll get an even higher probability for Omega_Lambda>0.
Of course, lots of people have tried to say that there are systematics in supernovae that are causing this…. It’s always something to worry about, but so far none of those arguments have held up. There have been various complaints about dust reddening– those have by and large gone away (indeed, I sort of think between the Knop 2003 and Sullivan 2003 paper they were slain). There have been “grey dust” models, but you need some pretty wacky modesl of grey dust to get anything to work. Supernova Ia evolution is a big question mark, but even there you have to do a lot of fine-tuning to get things to match with some of the work Adam Riess has done with z>1 supernovae, together with the lower-redshift ones.
I think it’s safe to be pretty sure that either the Universe is accelerating and thus has Dark Energy in it, or we’ve found something like the luminiferous ether that will shortly lead to a deeper understanding of Physics, brought to you by find theoretical minds like those of cosmicvariance.com. (Me, I’m just a data monkey.)
-Rob
Damn — can one of the mods fix the post I just made? I screwed something up in closing a link tag. Feel free to delete this comment if you manage to fix it.
Sorry :/
-Rob
Re: the cosmic neutrino background, it would be really cool if we detected that. We’re quite a ways off from that right now, though. It takes ginormous detectors to make reasonable measurements of neutrinos from the Sun, the atmosphere, and nuclear reactors right now…. And the CMB neutrinos are all *really* low energy, which will make the whole thing a lot harder.
But… damn, that would be cool if we saw that.
-Rob
Rob, I closed the tags, but your link was eaten, if you want to re-post it. Note that stuff beginning with “http://” is automatically turned into a hyperlink, even if you don’t include the html explicitly.
And yeah, detecting the neutrino background would be great, as would finding evidence for Hawking radiation. Neither seems especially promising at the moment.
Here’s the link to the Knop 2003 paper that I cited above:
http://brahms.phy.vanderbilt.edu/~rknop/research/papers/hstpaper/
Rob (of comment 10): Santa Cruz is not southern California.
Some naive comments:)
I do not think anisotropy and acceleration will be worth of Nobel, Because there are too many problem to be resolved. In other words, these discoveries may be not surprising if we pay more attention to our theoretical framework where our so called discoveries have been explained. It is possible that we have not found any new physics from these discoveries. I think it will take us more time to check.
In addition, If Guth could be provided with Nobel, Hawking may be in a better position to win the Nobel.:)
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