Questions and answers with Joseph Conlon

“The apple didn’t fall far from the tree,” says University of Oxford theoretical physicist Joseph Conlon. The author of Why String Theory?, reviewed in this month’s issue of Physics Today , says that from an early age he was good at math—a critical skill for a string theorist—thanks to the influence of his father and uncle, both PhD mathematicians, and his mother, a physics teacher.

By age 18 Conlon had earned a bachelor’s degree in mathematics from the local University of Reading in the UK; he did it part-time, while still in secondary school. Conlon followed that up by obtaining his bachelor’s and PhD degrees in physics at the University of Cambridge. At Oxford, he now focuses on phenomenological applications of string theory to particle physics and cosmology. “One thing I certainly benefited from is that if you [pursue] a physics undergraduate degree, having already done a math undergraduate degree, then you don’t need to concentrate on the math; you can just concentrate on understanding the physics concepts,” says Conlon.

For those who would question string theory’s validity because it can’t be experimentally tested, Conlon “presents a set of compelling arguments for the value of string theory while acknowledging its weaknesses and open challenges,” writes Gary Shiu in his Physics Today review. “Like courtroom juries, readers are encouraged to draw their own logical conclusions.” Conlon is also a cocreator of the public outreach website http://whystringtheory.com , which aims to be “a layman’s journey to the frontiers of physics.”

Physics Today books editor Jermey Matthews and senior editor Steven Blau, a theoretical physicist by training, recently caught up with Conlon to discuss the book.

PT: Why did you write the book?

CONLON: It’s to answer the question I think lots of people are asking: Why are so many people working on string theory if this is something you can’t directly say is the true theory of the universe at the smallest possible scales?

PT: So how would you answer the question “Why string theory?” for a nonexpert?

CONLON: String theory has brought ideas and insights and results to so many different areas beyond its supposedly core area of quantum gravity. The analogy I use in the book is it’s like in a gold rush, you get rich by selling spades, rather than by finding nuggets. String theory has … been able to provide spades to lots of people across mathematics and theoretical physics in so many different topics. And this is why so many people are interested in it.

PT: What inspired you to study string theory?

CONLON: I guess it was a fairly natural thing for me to do, given my interests and inclinations at the time. When I was in Cambridge, I was training in particle theory, and I was trying to learn as much particle theory as I could. You take courses on quantum field theory, you take courses on the standard model, you take a course in string theory.

The reason I wanted to carry on with the PhD in string theory was the feeling that lots of the standard model was carved out and understood in the 1970s and 1980s. String theory seemed more like something where I could get in and feel it wasn’t already done by the generation that came before.

PT: Were you ever tempted by any of the other alternative approaches to quantum gravity like loop quantum gravity or dynamic causal histories?

CONLON: Not really. I was never really exposed to them. As an undergraduate, it wasn’t something I learned or particularly had the option of learning then. And I haven’t been particularly tempted since then. From quite early on in my work on string theory I’ve been more interested in connecting it to experiments and observation. It’s great that people work on the formal problems of quantum gravity, but it’s not really my style of physics.

PT: As you were writing the book, was there something that you were hoping to be able to convey but said, “this is just too tough a nut to crack”? Did you have to leave anything on the table?

CONLON: Yes. There was a series of results around 1995 that were very important, involving D-branes. I ended up covering this less than I thought I would. And it partly was because I felt it was hard to try and convey to a general reader what was important about them without just dropping into buzz words.

PT: And, conversely, is there anything that you were particularly proud you were able to get across in simple language?

CONLON: I guess you have to ask the readers that. There are things I learned about—for example, the monstrous moonshine [a mathematical theory involving symmetries and related to conformal field theories] is a topic which I learned more about in the process of writing the book. I enjoyed writing about that because I learned about it at a slightly more technical level. It was a discovery process for me, too.

PT: According to the Physics Today review, your book also touches on “the sociology of string theory.” Was that your intention?

CONLON: Yes. Science is always more interesting when it’s done by humans, rather than [being] just abstract results. There’s also [a danger] you can get in if you look at someone very big [successful] and you say, “Gosh, they’ve gotten all these fantastic results. I can never possibly be like them. I’ll never be smart enough.”

But people are good at different things. Even though you might not be able to get the results that person did, you’ve got skills that they don’t have. I tried to convey that there are many, many different ways of being a good theoretical physicist. And part of that was by talking about the sociology, the different types of people who do the subject and do it successfully.

PT: Was explaining string theory to the general public a particular itch you wanted to scratch, or are you interested in writing other popular books?

CONLON: A bit of both. I thought string theory was being misrepresented, particularly in the general press, that there was this [notion] that string theory primarily was a theory of quantum gravity. And so string theory would then … compete with other theories of quantum gravity. And this is something I wanted to argue against because most people who work on string theory don’t focus on quantum gravity. That was the itch I wanted to scratch.

The book was also a chance to kind of let go the other side of my brain [used to write research papers] … and just write freely.

PT: What is your next project?

CONLON: In the process of finishing the book, basically I stopped doing research for six to nine months. So for the next two or three years I just want to do research because I enjoy doing research. And then I think I would like to write another book. I don’t know yet what it would be on.

PT: What books are you currently reading?

CONLON: I’ve got two on the go. The longer one, which I’m about halfway through, is [Winston] Churchill’s series The Second World War (Houghton Mifflin, ca. 1948–ca. 1953). And then the sort of more easy reading is one by Apollo astronaut (and physicist) Walter Cunningham, The All-American Boys: An Insider’s Look at the U.S. Space Program (revised edition, iPicturebooks, 2010).