Questions and answers with Leonard Susskind and George Hrabovsky
DOI: 10.1063/PT.4.2479
Somewhere in Steinbeck country two tired men sit down at the side of the road. Lenny combs his beard with his fingers and says, “Tell me about the laws of physics, George.” George looks down for a moment, then peers at Lenny over the top of his glasses. “Okay, Lenny, but just the minimum.”
The passage above is an adaptation of an exchange found in John Steinbeck’s Of Mice and Men. In that 1937 classic, the main characters are Lennie and George. In this adaptation, the characters are Leonard Susskind and George Hrabovsky, coauthors of The Theoretical Minimum: What You Need to Know to Start Doing Physics (Basic Books, 2013). The new introductory textbook aims to be a mathematical tool kit on the subject for the “ardent amateur.”
Despite what the adapted passage might suggest, it’s primarily Lenny Susskind, the Stanford University theoretical physicist, doing the explaining in The Theoretical Minimum. The book closely follows Susskind’s YouTube lectures of the same name that were originally presented in Stanford’s Continuing Studies program. (The term “theoretical minimum” originated with Russian physicist Lev Landau.) “The lectures, explanations, equations are mine,” he said when Physics Today contacted him and Hrabovsky, a self-taught scientist, to discuss the book. Hrabovsky wrote many of the exercises and applied his expertise using the Mathematica software to lay out the equation- and plot-filled book. “George,” says Susskind, “was really good at [putting] things together.”
Susskind, director of the Stanford Institute for Theoretical Physics, is known for his particle physics, string theory, and cosmology research, particularly on quantum gravity and black holes. He is the 1998 recipient of the American Physical Society’s J. J. Sakurai Prize for Theoretical Particle Physics. Susskind says he also finds satisfaction from teaching. "[It’s] an important part of my thinking process,” he adds. “I find explaining physics the best way to understand it myself.”
Hrabovsky is president of Madison Area Science and Technology (MAST), a Wisconsin-based nonprofit organization for amateurs that has a primary goal of supporting scientific research and education “without regard to credentials.” Despite not having a scientific degree, Hrabovsky has presented papers at scientific conferences. At an American Astronomical Society meeting, he presented on astrophysics research he conducted in the University of Wisconsin’s physics department, and at a World Mathematica Meeting, he presented on using that software to tutor physics students. He is also a member of APS and the American Association of Physics Teachers.
In their responses to the questions posed by Physics Today, Susskind elaborates on his approach to teaching physics to amateurs, and Hrabovsky advocates for a learning and discovery approach recommended by Richard Feynman.
PT: How did you two meet, and what brought you together to write this book?
Susskind: The truth is that I have never met George in person. Sometime about a decade ago, [Stanford] began to put [the “Theoretical Minimum” lectures] on the internet and the response was extraordinary—millions of hits on YouTube. I got tons of email from all over the world asking if I would publish the lectures as books. My response was, “Someday.”
Then one day I got an email from George, who said he loved the lectures, and might I want a collaborator to write them into books? I said OK, let’s try it. You do the formatting, figures, and all that hard stuff. I’ll send you my notes that I had written, and we’ll see how it comes out.
PT: George, what motivated you to become a “professional” amateur scientist? And besides the “Theoretical Minimum” lectures, what resources have you used to learn physics?
Hrabovsky: [NASA’s] Gemini project got me interested in space. After that, I got interested in chemistry and the weather, then I went off on my own to learn more.
I fell in love with physics when I was puzzling my way through a chemistry book and came to the gas laws. That was my first real experience of learning something about physics that was not purely descriptive, like, “This is the structure of the atom,” and so on. From that moment on I devoured everything I could find. I taught myself calculus and then acquired The Feynman Lectures on Physics (by Richard Feynman, Robert Leighton, and Matthew Sands; Addison Wesley Longman, 1970).
I was fascinated by gravity and fluids: By 15 I was reading Gravitation (by Charles Misner, Kip Thorne, and John Wheeler; W. H. Freeman, 1973). And I began to work with some local meteorology professors on tornado physics and numerical modeling of thunderstorms. Becoming a Mathematica consultant has helped a lot, as it provides me with contracts that pay the bills while I pursue my research through MAST.
PT: Describe the pedagogical approach the book takes. How can it be useful to physics majors and physics lecturers?
Susskind: I’m not sure I had what you call a pedagogical approach. I love physics and I love explaining how things work to an appreciative audience. The lectures originally started as very soft popular-level lectures, but the students in the class clearly wanted more. They were tired of the pop-sci experience and were hungry for the real thing. They came to me and said that they were not afraid of the hard stuff with equations; if there was mathematics that they would need to know, then just teach it.
I figured I would try it, but I expected that after two weeks, the 100 or so people in the class would be down to 10. That’s not what happened. People kept coming back for more, and, if anything, it brought more students who heard about the class. I guess I do have a pedagogical approach: Explain things honestly. Don’t fake it with phony analogies and metaphors. There are a lot of people out there who are ready to be challenged. Those are the ones I care about teaching.
I get a lot of mail from physics students all over the world who say that the lectures and the book are very helpful. I think the reason they are popular is because [people] recognize that I am having fun teaching, and that the explanations are my best effort at conveying my own understanding. As for lecturers, I would certainly not say that they should imitate what I do. You have to keep in mind that my lecturing style may not be for every physics student.
PT: For those who prefer but can’t access the traditional classroom experience, what would you suggest as an effective self-study learning strategy?
Hrabovsky: Start with our book. Supplement your reading with a math book covering calculus—I like [Wilfred] Kaplan’s [and Donald J. Lewis’s] two-volume set with linear algebra (Calculus and Linear Algebra; John Wiley and Sons, 1970, 1971; available for free online as part of the University of Michigan library’s Scholarly Monograph Series ). I am currently teaching an online course called Elementary Mathematical Methods for Science—the notes can be found at www.madscitech.org .
To paraphrase Feynman, when you find a problem you like to do, play with it and go really deep into it. Does it suggest new problems to play with? Can you change parameters or expressions and do it in a new form? Can you construct something out of your solution? After a while you will look up and realize that you are blazing a new trail.
PT: What books are you reading at the moment?
Hrabovsky: Robert Bloch’s Bitter Ends (Carol Publishing, 1990); Berthold Schweizer and Abe Sklar’s Probabilistic Metric Spaces (republished by Dover Publications, 2011); andPierre Cartier and Cecile DeWitt-Morette’s Functional Integration (Cambridge University Press, 2006).
Susskind: The majority of my reading is fiction, [but] I just finished reading the four-volume biography of Lyndon Johnson by Robert Caro. [The publisher, Alfred A. Knopf, reprinted and released the entire set earlier this year.] I’ve started reading The Sleepwalkers (by Christopher Clark; HarperCollins, 2013), which is about the causes of WWI.
