Kosterlitz looks back at it all happily now, especially when considering the perks. He recalls the boisterous Nobel festivities in Sweden where he was feted by the Swedish Embassy and awarded by the King of Sweden. In Washington, he met one of his idols: U.S. President Barack Obama. There were even unexpected honors that happened as an indirect result of the Nobel. One that holds a special place in his heart is being named the 2017 Climbing Ambassador at the so-called “climbing Oscars.” The award recognized his other life: mountain climbing.

“I got into it when I was in my teens,” Kosterlitz said. “I used to quite like walking in mountains and discovered that there were a few which needed some skills beyond scrambling up and down steepish slopes, so I started to experiment with rock climbing and learned how to use a rope… I became quite strong and fit and able to do many of the hardest climbs in the world at the time. Eventually, I had to make a choice between becoming a professional climber or a professional physicist, and I chose the latter because it earned money and would last much longer.”

Another unexpected perk Kosterlitz discovered as a result of the win was a talent he never knew he would need: the ability to dole out words of wisdom. He found it became of great use as a Nobel Laureate, and still does.

“You are asked to pontificate on all sorts of topics,” Kosterlitz said. Where is the field of physics going? What advice does he have for those starting out into the field? He’s even asked to comment on broader subjects outside of physics, like the global education of children. “You’re suddenly expected to become an authority on things you’ve never even really considered.”

With all that in mind, Kosterlitz — who was born in Aberdeen, Scotland, in 1943 and earned his Ph.D. from Oxford University in 1969 — was thankful when things settled down and he gained the freedom to do what he does best: ponder some of biggest problems in physics and try to develop theories to solve them.

“In physics, there’s always new or unsolved problems,” Kosterlitz said. “No matter how much you know, there’s always something fascinating that you won’t understand. You never get bored. There’s always something to sit and think about.”

And Kosterlitz has made a career of exactly that. In fact, it was that open mindset that led to the Nobel in the first place. That and a willingness to “risk complete failure and looking like a fool,” he said.

Pondering unsolved questions

After growing frustrated with experimental physics in the early 1970s while at Birmingham University, Kosterlitz began scouring for something theoretical to sit and think about. He ended up connecting with Thouless, who suggested that he look at the problem of phase transitions in two-dimensional systems.

“He also mumbled some things about topology and vortex excitations, which I half understood at the time,” said Kosterlitz. But he didn’t let that deter him, and he spent the next six months taking a crack at the problem.

The work led to a publication in 1973 where the pair drew on a branch of mathematics called topology to provide a theoretical understanding of phase changes in ultra-thin, two-dimensional systems. Kosterlitz and Thouless’s theory of phase transitions became known as the K-T transition and since then has informed the development of materials that could be helpful in making next-generation electronic devices and quantum computers.

Today, Kosterlitz is taking a similar risk in his research and is attempting to tackle another of the biggest unsolved problems in the field: the dynamics of nonequilibrium physics. These are physical systems that have emerged from thermodynamically stable states and are constantly heading towards some state of rest. The mystery lies in the mechanics of how they get to this state of rest and how random fluctuations, or noise, affects that process. Ultimately, the highly theoretical work looks to predict where and how this all happens.

“It's a huge unsolved problem,” Kosterlitz said. “If you think about the real world and regard it as a big mechanical system, it’s certainly not in equilibrium — it’s disordered and always evolving,” Kosterlitz said. “Almost all real-world systems are affected by some sort of noise… but that noise is important. We found, to my surprise, that there are potentially infinite bands of possible stationary states and that if you apply external noise, a unique stationary state is picked out.”

Kosterlitz and collaborators from China have published two studies on the subject in the Proceedings of the National Academy of Sciences, so far, detailing the how these systems transition to unique stationary states through a series of nonlinear steps. The theory sounds promising, but being able to generalize it to realistic situations has some serious technical difficulties and may never be solved.

“Understanding out-of-equilibrium statistical mechanics is a problem that’s been around for longer than I have,” Kosterlitz said. “It's the sort of thing that if you just start doing it out of interest, you probably won't get anywhere, so not many people are looking at this.”

Outside of this current research, Kosterlitz also takes the time to teach a graduate physics course on mathematics. It marks one of the last courses he will teach at Brown as he thinks about what comes next. Last year, Kosterlitz, who joined the Brown faculty in 1982, made plans to fully retire in 2025. And while he looks forward to it, he’s mindful of everything physics has brought him in life.

“It’s a subject which has always suited me,” Kosterlitz.