Unexpected discovery gets an unexpected Nobel prize

Last week, the 2011 Nobel prize in Physics was awarded to three US physicists, Saul Perlmutter, Brian Schmidt and and Adam Riess "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae". I was really surprised when I heard the news. Not only was I not expecting the Nobel committee to honor such a recent discovery but a prediction by Thomson Reuters led me to believe that the Nobel prize in physics would go to people in the field of Quantum Entanglement. I shall get back to the reason why, I think, this prize was unexpected, but let me first talk about this unexpected discovery.

Ever since Edwin Hubble discovered in 1929 that the universe is expanding, astronomers have been trying to measure the rate of this expansion. To do this, astronomers measure how far any distant galaxy is from earth and then monitor this distance over time. So how is the distance measured? The method used is fairly simple. Let us consider a 100 watt bulb, a source of light, is at a certain distance from an observer. From the amount of light received by the observer, it is possible to calculate the distance between the bulb and the observer because the amount of light that the bulb emits is known (from its wattage) and it is a standard quantity. Therefore if such standard light sources, which are called standard candles, can be identified in the distant galaxies, it is possible to calculate the distance. Instead of a 100 watt bulb, astronomers use Type Ia supernovae, the biggest explosions in the universe since the the Big Bang, as standard candles. As these explosions are well understood, astronomers know the precise amount of light emitted by them.

Though this method for measuring distances is straight forward, there is one big hurdle - finding standard candles. Type Ia supernovae are rare events which typically occur once in a century per galaxy. It is not possible to know when one of them will go off in any galaxy. Luckily there are billions of galaxies in the universe. If the entire sky is monitored continuously, there is a chance of seeing at least a few of these supernovae in a decade. Hence the search for standard candles is difficult and extremely time consuming. This is exactly the kind of research that two teams set out to perform at the beginning of the last decade of the twentieth century. One of the teams was headed by Saul Perlmutter and the other by Brian Schmidt. Adam Reiss was a member of Schmidt's group. Both the groups were interested in identifying the standard candles, calculate their distances from earth and ultimately calculate the rate of expansion of the universe.

When the two teams started working, it was a widely accepted fact amongst the astronomy community that the the rate of expansion of the universe is decreasing. It was believed that the expansion of the universe was an aftermath of the Big Bang and gravity would slow it down with time. Both the teams were interested in measuring this decreasing rate of expansion of the universe. But as they started identifying the standard candles and measured their distance from earth, both the teams identified an anomaly - the expansion of the universe was not slowing down, but speeding up!!! Initially they could not believe their results but with more data their confidence increased. Finally in 1998, both the teams announced their results to the world.

It was definitely an amazing discovery and had a big impact in the physics community. The experimenters had discovered something totally unexpected and it was up to the theoreticians to explain the results. The results implied that there is a new form of energy in the universe which is not only counteracting the effects of gravity but is also accelerating the expansion of universe. The physicists had never seen this form of energy and calculated that this energy makes up 70% of the universe! This exotic new form of energy was named Dark Energy (Shouldn't be confused with Dark Matter. An excellent source for learning more about Dark Energy - Dark Energy FAQ by Sean Carroll. There are two interesting lectures on the same subject by Sean Carroll and Lawrence Krauss).

Though physicists have been trying to understand Dark Energy for over a decade now, it is still a mystery. This is why I think that it was a premature decision by the Nobel committee to award the Nobel prize for this discovery. I believe that experimental observations have to be backed up by theory before they become complete. This observation has definitely had a profound impact on cosmology and on physics in general. But there have been a number of beautiful theories in the past which were not recognized by the committee because of the lack of experimental evidence. If this year's Nobel prize was awarded based on the impact of the observation on the scientific community then arguably the theory that had the most powerful impact on physics, the General Theory of Relativity by Albert Einstein, was not awarded the Nobel Prize. Subrahmanyan Chandrasekhar was awarded the Nobel prize almost half a century after his theoretical studies on the evolution of stars while this year's prize comes only 13 years after the paper was published. What's the hurry? This bias against theoretical sciences worries me. I definitely do not undermine the importance of this experimental observation, but in my opinion, the Nobel committee could have waited till the theory of Dark Energy was understood. My opinion is further strengthened by the rise of a new theory based on Dark flow (another exotic phenomenon) which claims that the observed acceleration of the expansion of the universe could just be an illusion.

But the physics community doesn't share my opinion. It believes that the work deserves a Nobel prize and scientists have been expecting the award ever since the paper was published in 1998. Here are the views of Sean Carroll and the other physicists. In spite of what the physics community thinks, I still believe that the observation of the accelerating universe could have been awarded the Nobel prize once the theory behind Dark Energy is understood.

P.S. Here is an excellent nontechnical blog post about the 2011 Nobel prize in Physics by Jennifer Ouellette of Cocktail Party Physics