Riess ’92 wins Nobel in physics

Found Universe’s expansion is accelerating

On Oct. 4, Adam G. Riess ’92 woke up to a 5 a.m. phone call from Sweden. The professor of astronomy and physics at John Hopkins University was told that he had won the 2011 Nobel Prize in physics. Two others shared the prize: Saul Perlmutter of the Lawrence Berkeley National Laboratory, and Brian P. Schmidt of the Australian National University.

Though he didn’t know whether he would win the Nobel Prize this year, Riess knew that if he had earned the prize, he would get a phone call that morning. “It was definitely on my mind when I went to sleep the night before,” said Riess.

An accomplished cosmologist, Riess has won just about every prestigious prize in his field: the Shaw Prize in Astronomy in 2006, the MacArthur “genius” grant in 2008, and the Einstein Medal earlier this year.

Science at universal proportions

Riess began the work that would win him the Nobel Prize in 1998, when he and Schmidt led a team that observed surprising evidence that the expansion of the universe is accelerating.

At the time, the team, as well as the greater scientific community, believed that the universe’s expansion was actually decelerating. Riess and Schmidt used this common assumption and set out to determine the mass of the universe by measuring the luminosity of supernovae and fitting the data to an appropriate cosmological model.

However, their fit yielded a nonsensical negative mass of the universe and a positive acceleration of expansion. To explain these results, the team concluded not only that the universe expansion rate had to be accelerating, but a nonzero cosmological constant in Einstein’s theory of general relativity was also needed. This positive constant means that vacuum must have an intrinsic energy density, which generates a pressure in space that should be the cause of the acceleration.

The inclusion of the cosmological constant has been debated before. Einstein originally used the constant to explain what he thought was a static universe. Later, Edwin Hubble discovered that the galaxy was expanding but believed it to be decelerating. This discovery made the cosmological constant zero, and Einstein called his original use of the constant his “biggest blunder.” Now, because the expansion of the universe is accelerating, a positive cosmological constant is needed again.

These results ignited research in dark energy, a generalized name for the energy source responsible for an accelerating universe. Dark energy is thought to make up about 70 percent of the universe, and is still not well-understood.

Riess says he was responsible for the analysis part of the study, so he was nervous about getting a result that contradicted most of the scientific community’s expectations at the time.

“At first, I thought I just made a mistake. Like the many experiences I had with p-sets at MIT, I thought I had simply made a mathematical error,” said Riess.

Luckily, Perlmutter’s team at Berkeley independently found the same results almost simultaneously — this made it easier for the scientific community to accept the unexpected results so quickly.

Riess’s current research consists of finding new techniques for measuring distances in the universe.

Beginning at MIT

Riess made the discovery at the age of 28, within a few years of getting his PhD at Harvard in 1996. “I was really lucky. Just in the right place at the right time,” said Riess.

Moving from the suburbs of New Jersey, Riess enrolled at MIT as an undergraduate in 1988, majoring in physics and minoring in history. He chose MIT over Brown, Cornell, and UPenn because he thought MIT would be a good place to do physics, was unique, felt more like a community, and was in an urban setting.

Riess says his time at MIT was probably the most difficult part of his life. “There was definitely a wider gap between what I was capable of and what was expected of me during my time at MIT than any other period of my life,” said Riess.

Riess said MIT’s quantitative, hands-on education prepared him for his research career. He loved Junior Lab (8.13/8.14), a lab course still required for physics majors. Most of his research is very much like a huge J-Lab experiment, says Riess.

In fact, Riess’s first research experience began at MIT. He had a UROP in the Center for Space Research (now known as the Kavli Institute for Astrophysics and Space Research) in his junior year. However, the experience did not excite him about research — Riess thought he didn’t have the necessary tools, and the experience wasn’t that productive. Nevertheless, he’s glad that he stuck with research in graduate school.

While at MIT, Riess was a member of the fraternity Phi Delta Theta and enjoyed living there starting his freshman year. He was able to get help from a few brothers who were also physics majors. Today, he says that his experience in Phi Delta Theta and MIT has definitely helped shape who he has become.

Department of Physics Head Edmund Bertschinger was Riess’ 8.05 (Quantum Physics II) professor at MIT. According to Bertschinger, Riess was remarkably diligent, coming frequently to office hours until everything was clear to him. He was impressed by Riess’s passion for learning and his involvement in Phi Delta Theta. “I gained a lot of respect for fraternities after seeing his commitment to them and seeing how the fraternity helped Adam organize his life at MIT,” said Bertschinger.

Outside of cosmology research, Riess enjoys listening to jazz, rock, and classical music. He’s also an avid coin collector and a Baltimore Ravens fan. When he’s not too busy taking care of his two children, Riess also likes to read up on history and keep up with politics.